science and technology

With the widespread forest destruction in Central Kalimantan, a group of environmental activists is engaged in the training of primary school teachers in Katingan regency, in which environment education textbooks meant for local students are being tried out.

This program is facilitated by the Katingan regency administration in cooperation with WWF-Indonesia and relevant agencies, like the local education office, environment office and the national park management.

The training takes place in Mendawai village, Mendawai district, and Petak Bahandang village, Tasik Payawan district — both situated on the Katingan River plain bordering Sebangau National Park. Illegal logging and wildfire-causing forest damage have remained rife in the two villages. Sixty primary school teachers and principals in both districts have joined the program, which comprises class presentations, group discussions and field practice,” said Novita, 25, an activist from Lampung.

According to Novita, who graduated from Lampung University with a degree in agricultural engineering, the subjects taught concern an introduction to environmental education and various topical environmental issues such as global warming.

Nancy made it clear that the activities were designed to arouse children’s concern for and love of nature through environment education.

“This training is expected to deepen teachers’ knowledge of environment matters, which will be imparted to their students for further application in daily life,” said the WWF-Indonesia/Sebangau conservation project communication officer.

A day’s training is followed by subject presentations before class, among others in the state primary school of Tewang Kampung, which is only over a dozen meters away from the Katingan riverbank in Mendawai district. It is accessible by speedboat from the terminal of Kereng Bangkirai, Palangkaraya. The trip takes eight hours. A simple wooden stilted building, the school has about 20 students per class, mostly the children of farmers, fishermen and sawmill workers.

The new lessons given by the trainees to their first to sixth graders include water and air pollution and the importance of forests as the world’s lungs. Students are also taken to observe water springs and soil types as well as to plant trees in school yards. Dedy Mardianto, a Mekar Tani state primary school teacher, has instructed third graders to grow Galam trees to suit the generally peat covered marshy land around Katingan river.

Novita noted that this replanting practice was intended to make local children familiar with the greening activity in view of the considerable forest damage in Katingan regency due to illegal logging and wildfire. “It’s part of environment education to make them strive for improvement as soon as they notice disruption in natural conditions,” added Novi.

Local student Yanti Nurhidayanti, 12, could not help but express her delight at taking environmental studies. “I’m very happy to be taking subjects that were previously never taught in school. Outdoor instruction makes us better understand through direct observations and field trials,” said the fifth grader.

The textbook tryout and teachers’ training are also meant to improve the environment books earlier compiled by local teachers, besides gathering addition information to enrich future text content. As planned, the environment subjects will be made mandatory for the primary school curriculum in Katingan regency, Central Kalimantan.

By: Bambang Parlupi

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HSDPA improves on W-CDMA by using different techniques for modulation & coding. It creates a new channel within W-CDMA called HS-DSCH, or high-speed downlink shared channel. That channel performs differently than other channels & allows for faster downlink speeds. it is important to note that the channel is only used for downlink. That means that data is sent from the source to the phone. It isn't possible to send data from the phone to a source using HSDPA. The channel is shared between all users which lets the radio signals to be used most effectively for the fastest downloads.

HSDPA, short for High-Speed Downlink Packet Access, is a new protocol for mobile telephone data transmission. it is known as a 3.5G (G stands for generation) technology. Essentially, the standard will provide download speeds on a mobile phone equivalent to an ADSL (Asymmetric Digital Subscriber Line) line in a home, removing any limitations placed on the use of your phone by a slow connection. it is an evolution & improvement on W-CDMA, or Wideband Code Division Multiple Access, a 3G protocol. HSDPA improves the data transfer rate by a factor of at least three over W-CDMA. HSDPA can achieve theoretical data transmission speeds of 8-10 Mbps (megabits per second). Though any data can be transmitted, applications with high data demands such as video & streaming music are the focus of HSDPA.

The long-term acceptance & success of HSDPA is unclear, because it is not the only alternative for high speed data transmission. Standards like CDMA2000 1xEV-DO & WiMax are other potential high speed standards. Since HSDPA is an extension of W-CDMA, it is unlikely to succeed in locations where W-CDMA has not been deployed. Therefore, the eventual success of HSDPA as a 3.5G standard will first depend upon the success of W-CDMA as a 3G standard.

The widespread availability of HSDPA may take a while to be realized, or it may never be achieved. Most countries did not have a widespread 3G network in place as of the end of 2005. lots of mobile telecommunications providers are working quickly to deploy 3G networks which can be upgraded to 3.5G when the market demand exists. Other providers tested HSDPA through 2005 & are rolling out the service in mid to late 2006. Early deployments of the service will be at speeds much lower than the theoretically possible rates. Early service will be at 1.8 Mbps, with upgrades to 3.6Mbps as devices are made accessible that can handle that increased speed. Read more...

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate, as opposed to a nuclear bomb, in which the chain reaction occurs in a fraction of a second and is uncontrolled causing an explosion.

The most significant use of nuclear reactors is as an energy source for the generation of electrical power (see Nuclear power) and for the power in some ships (see Nuclear marine propulsion). This is usually accomplished by methods that involve using heat from the nuclear reaction to power steam turbines. There are also other less common uses as discussed below.

Nuclear Reactor Firsts

The first artificial nuclear reactor, Chicago Pile-1, was constructed at the University of Chicago by a team led by Enrico Fermi in 1942. (Fermi and Leo Szilard have patented the nuclear reactor.) It achieved criticality on December 2, 1942 at 3:25 PM. The reactor support structure was made of wood, which supported a pile of graphite blocks, embedded in which was natural Uranium-oxide 'pseudospheres' or 'briquettes'. Inspiration for such a reactor was provided by the discovery of Lise Meitner, Fritz Strassman and Otto Hahn in 1938 that bombardment of Uranium with neutrons provided by an Alpha-on-Beryllium fusion reaction (a neutron howitzer) produced a Barium residue, which they reasoned was created by the fissioning of the Uranium nuclei. Subsequent studies revealed that several neutrons were also released during the fissioning, making available the opportunity for a chain reaction. Shortly after the discovery of fission, Hitler's Germany invaded Poland in 1939, starting World War II in Europe, and all such research became militarily classified. On August 2, 1939 Albert Einstein wrote a letter to President Franklin D. Roosevelt suggesting that the discovery of Uranium's fission could lead to the development of "extremely powerful bombs of a new type", giving impetus to the study of reactors and fission.

Soon after the Chicago Pile, the U.S. military developed nuclear reactors for the Manhattan Project starting in 1943. The primary purpose for these reactors was the mass production of plutonium (primarily at the Hanford Site) for nuclear weapons. After World War II, the U.S. military sought other uses for nuclear reactor technology. Research by the Army and the Air Force never came to fruition; however, the U.S. Navy succeeded when they steamed the USS Nautilus (SSN-571) on nuclear power January 17, 1955.

Besides the military uses of nuclear reactors, there were political reasons to pursue civilian use of atomic energy. U.S. President Dwight Eisenhower made his famous Atoms for Peace speech to the UN General Assembly on December 8, 1953. This diplomacy led to the dissemination of reactor technology to U.S. institutions and worldwide.

"World's first nuclear power plant" is the claim made by signs at the site of the EBR-I, which is now a museum near Arco, Idaho. This experimental LMFBR operated by the U.S. Atomic Energy Commission produced 0.8 kW in a test on December 20, 1951 and 100 kW (electrical) the following day, having a design output of 200 kW (electrical). The first nuclear power plant built for civil purposes was the AM-1 Obninsk Nuclear Power Plant, launched on June 27, 1954 in the Soviet Union. It produced around 5 MW (electrical).


How it works

The key components common to most types of nuclear power plants are:

* Neutron moderator
* Coolant
* Control rods
* Pressure vessel
* Emergency Core Cooling Systems (ECCS)
* Reactor Protective System (RPS)
* Steam generators (not in BWRs)
* Containment building
* Boiler feedwater pump
* Steam turbine
* Electrical generator
* Condenser

Conventional electrical power plants all have a fuel source to provide heat. Examples are natural gas, coal, and fuel oil. For a nuclear power plant, this heat is provided by nuclear fission inside the nuclear reactor. When a relatively large fissile atomic nucleus (usually uranium-235 or plutonium-239) is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission. The neutrons then trigger further fission. When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity. It should be noted that a nuclear explosion involves an uncontrolled chain reaction, and the rate of fission in a reactor is not capable of reaching sufficient levels to trigger a nuclear explosion (even if the fission reactions increased to a point of being out of control, it would melt the reactor assembly rather than form a nuclear explosion). Enriched uranium is uranium in which the percent composition of uranium-235 has been increased from that of uranium found in nature. Natural uranium is only 0.72% uranium-235; the rest is mostly uranium-238 (99.2745%) and a tiny fraction is uranium-234 (0.0055%).


Reactor types

Classifications
Nuclear Reactors are classified by several methods; a brief outline of these classification schemes is provided.

Classification by type of nuclear reaction
* Nuclear fission. Most reactors, and all commercial ones, are based on nuclear fission. They generally use uranium as fuel, but research on using thorium is ongoing (an example is the Liquid fluoride reactor). This article assumes that the technology is nuclear fission unless otherwise stated. Fission reactors can be divided roughly into two classes, depending on the energy of the neutrons that are used to sustain the fission chain reaction:
o Thermal reactors use slow or thermal neutrons. Most power reactors are of this type. These are characterized by neutron moderator materials that slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, until they are thermalized. Thermal neutrons have a far higher probability of fissioning uranium-235, and a lower probability of capture by uranium-238 than the faster neutrons that result from fission. As well as the moderator, thermal reactors have fuel (fissionable material), containments, pressure vessels, shielding, and instrumentation to monitor and control the reactor's systems.
o Neutrons of intermediate energies are less useful because plutonium-239 has a high ratio of capture cross section vs. fission cross section at these energies, impairing neutron economy. Uranium-233 has low capture/fission ratios across the neutron energy spectrum, so the thorium cycle can use intermediate neutron energies.
o Fast neutron reactors use fast neutrons to sustain the fission chain reaction. They are characterized by an absence of moderating material. Initiating the chain reaction requires enriched uranium (and/or enrichment with plutonium 239), due to the lower probability of fissioning U-235, and a higher probability of capture by U-238 (as compared to a moderated, thermal neutron). Fast reactors have the potential to produce less transuranic waste because all actinides are fissionable with fast neutrons, but they are more difficult to build and more expensive to operate. Overall, fast reactors are less common than thermal reactors in most applications. Some early power stations were fast reactors, as are some Russian naval propulsion units. Construction of prototypes is continuing (see fast breeder or generation IV reactors).
* Nuclear fusion. Fusion power is an experimental technology, generally with hydrogen as fuel. While not currently suitable for power production, Farnsworth-Hirsch fusors are used to produce neutron radiation.
* Radioactive decay. Examples include radioisotope thermoelectric generators and atomic batteries, which generate heat and power by exploiting passive radioactive decay.

Classification by moderator material
Used by thermal reactors:
* Graphite moderated reactors
* Water moderated reactors
o Heavy water reactors
o Light water moderated reactors (LWRs). Light water reactors use ordinary water to moderate and cool the reactors. When at operating temperatures if the temperature of the water increases, its density drops, and fewer neutrons passing through it are slowed enough to trigger further reactions. That negative feedback stabilizes the reaction rate. Graphite and heavy water reactors tend to be more thoroughly thermalised than light water reactors. Due to the extra thermalization, these types can use natural uranium/unenriched fuel.
* Light element moderated reactors. These reactors are moderated by lithium or beryllium.
o Molten salt reactors (MSRs) are moderated by a light elements such as lithium or beryllium, which are constituents of the coolant/fuel matrix salts LiF and BeF2.
o Liquid metal cooled reactors, such as one whose coolant in a mixture of Lead and Bismuth, may use BeO as a moderator.
* Organically moderated reactors (OMR) use biphenyl and terphenyl as moderator and coolant.

Classification by coolant
* Water cooled reactor
o Pressurized water reactor (PWR)
+ A primary characteristic of PWRs is a pressurizer, a specialized pressure vessel. Most commercial PWRs and naval reactors use pressurizers. During normal operation, a pressurizer is partially filled with water, and a steam bubble is maintained above it by heating the water with submerged heaters. During normal operation, the pressurizer is connected to the primary reactor pressure vessel (RPV) and the pressurizer "bubble" provides an expansion space for changes in water volume in the reactor. This arrangement also provides a means of pressure control for the reactor by increasing or decreasing the steam pressure in the pressurizer using the pressurizer heaters.
+ Pressurised channels. Channel-type reactors can be refueled under load.
o Boiling water reactor (BWR)
+ BWRs are characterized by boiling water around the fuel rods in the lower portion of primary reactor pressure vessel. During normal operation, pressure control is accomplished by controlling the amount of steam flowing from the reactor pressure vessel to the turbine.
o Pool-type reactor
* Liquid metal cooled reactor. Since water is a moderator, it cannot be used as a coolant in a fast reactor. Liquid metal coolants have included sodium, NaK, lead, lead-bismuth eutectic, and in early reactors, mercury.
o Sodium-cooled fast reactor
o Lead-cooled fast reactor
* Gas cooled reactors are cooled by a circulating inert gas, usually helium. Nitrogen and carbon dioxide have also been used. Utilization of the heat varies, depending on the reactor. Some reactors run hot enough that the gas can directly power a gas turbine. Older designs usually run the gas through a heat exchanger to make steam for a steam turbine.
* Molten Salt Reactors (MSRs) are cooled by circulating a molten salt, typically a eutectic mixture of fluoride salts, such as LiF and BeF2. In a typical MSR, the coolant is also used a matrix in which the fissile material is dissolved.

Classification by use
* Electricity
o Power plants
* Propulsion, see nuclear propulsion
o Nuclear marine propulsion
o Various proposed forms of rocket propulsion
* Other uses of heat
o Desalination
o Heat for domestic and industrial heating
o Hydrogen production for use in a hydrogen economy
* Production reactors for transmutation of elements
o Breeder reactors. Fast breeder reactors are capable of enriching Uranium during the fission chain reaction (by converting fertile U-238 to Pu-239) which allows an operational fast reactor to generate more fissile material than it consumes. Thus, a breeder reactor, once running, can be re-fueled with natural or even depleted uranium.
o Creating various radioactive isotopes, such as americium for use in smoke detectors, and cobalt-60, molybdenum-99 and others, used for imaging and medical treatment.
o Production of materials for nuclear weapons such as weapons-grade plutonium
* Providing a source of neutron radiation (for example with the pulsed Godiva device) and positron radiation[clarify]) (e.g. Neutron activation analysis and Potassium-argon dating[clarify])
* Research reactors : Typically reactors used for research and training, materials testing, or the production of radioisotopes for medicine and industry. These are much smaller than power reactors or those propelling ships, and many are on university campuses. There are about 280 such reactors operating, in 56 countries. Some operate with high-enriched uranium fuel, and international efforts are underway to substitute low-enriched fuel.

Advanced reactors
More than a dozen advanced reactor designs are in various stages of development.[6] Some are evolutionary from the PWR, BWR and PHWR designs above, some are more radical departures. The former include the Advanced Boiling Water Reactor (ABWR), two of which are now operating with others under construction, and the planned passively safe ESBWR and AP1000 units (see Nuclear Power 2010 Program).

* The Integral Fast Reactor was built, tested and evaluated during the 1980s and then retired under the Clinton administration in the 1990s due to nuclear non-proliferation policies of the administration. Recycling spent fuel is the core of its design and it therefore produces only a fraction of the waste of current reactors.[7]
* The Pebble Bed Reactor, a High Temperature Gas Cooled Reactor (HTGCR), is designed so high temperatures reduce power output by doppler broadening of the fuel's neutron cross-section. It uses ceramic fuels so its safe operating temperatures exceed the power-reduction temperature range. Most designs are cooled by inert helium. Helium is not subject to steam explosions, resists neutron absorption leading to radioactivity, and does not dissolve contaminants that can become radioactive. Typical designs have more layers (up to 7) of passive containment than light water reactors (usually 3). A unique feature that may aid safety is that the fuel-balls actually form the core's mechanism, and are replaced one-by-one as they age. The design of the fuel makes fuel reprocessing expensive.
* SSTAR, Small, Sealed, Transportable, Autonomous Reactor is being primarily researched and developed in the US, intended as a fast breeder reactor that is passively safe and could be remotely shut down in case the suspicion arises that it is being tampered with.
* The Clean And Environmentally Safe Advanced Reactor (CAESAR) is a nuclear reactor concept that uses steam as a moderator - this design is still in development.
* Subcritical reactors are designed to be safer and more stable, but pose a number of engineering and economic difficulties. One example is the Energy amplifier.
* Thorium based reactors. It is possible to convert Thorium-232 into U-233 in reactors specially designed for the purpose. In this way, Thorium, which is more plentiful than uranium, can be used to breed U-233 nuclear fuel. U-233 is also believed to have favourable nuclear properties as compared to traditionally used U-235, including better neutron economy and lower production of long lived transuranic waste.
o Advanced Heavy Water Reactor — A proposed heavy water moderated nuclear power reactor that will be the next generation design of the PHWR type. Under development in the Bhabha Atomic Research Centre (BARC).
o KAMINI — A unique reactor using Uranium-233 isotope for fuel. Built by BARC and IGCAR Uses thorium.
o India is also building a bigger scale FBTR or fast breeder thorium reactor to harness the power with the use of thorium.
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Neptune is the eighth planet from the Sun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus.

orbit: 4,504,000,000 km (30.06 AU) from Sun
diameter: 49,532 km (equatorial)
mass: 1.0247e26 kg

In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea.

After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton's laws. It was therefore predicted that another more distant planet must be perturbing Uranus' orbit. Neptune was first observed by Galle and d'Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. An international dispute arose between the English and French (though not, apparently between Adams and Le Verrier personally) over priority and the right to name the new planet; they are now jointly credited with Neptune's discovery. Subsequent observations have shown that the orbits calculated by Adams and Le Verrier diverge from Neptune's actual orbit fairly quickly. Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location.

More than two centuries earlier, in 1613, Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. On two successive nights he actually noticed that it moved slightly with respect to another nearby star. But on the subsequent nights it was out of his field of view. Had he seen it on the previous few nights Neptune's motion would have been obvious to him. But, alas, cloudy skies prevented obsevations on those few critical days.

Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. Much of we know about Neptune comes from this single encounter. But fortunately, recent ground-based and HST observations have added a great deal, too.

Because Pluto's orbit is so eccentric, it sometimes crosses the orbit of Neptune making Neptune the most distant planet from the Sun for a few years.

Neptune's composition is probably similar to Uranus': various "ices" and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it may not have a distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core (about the mass of the Earth) of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane.

Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint.

Like a typical gas planet, Neptune has rapid winds confined to bands of latitude and large storms or vortices. Neptune's winds are the fastest in the solar system, reaching 2000 km/hour.

Like Jupiter and Saturn, Neptune has an internal heat source -- it radiates more than twice as much energy as it receives from the Sun.

At the time of the Voyager encounter, Neptune's most prominent feature was the Great Dark Spot (left) in the southern hemisphere. It was about half the size as Jupiter's Great Red Spot (about the same diameter as Earth). Neptune's winds blew the Great Dark Spot westward at 300 meters/second (700 mph). Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune every 16 hours or so now known as "The Scooter" (right). It may be a plume rising from lower in the atmosphere but its true nature remains a mystery.

However, HST observations of Neptune (left) in 1994 show that the Great Dark Spot has disappeared! It has either simply dissipated or is currently being masked by other aspects of the atmosphere. A few months later HST discovered a new dark spot in Neptune's northern hemisphere. This indicates that Neptune's atmosphere changes rapidly, perhaps due to slight changes in the temperature differences between the tops and bottoms of the clouds.

Neptune also has rings. Earth-based observations showed only faint arcs instead of complete rings, but Voyager 2's images showed them to be complete rings with bright clumps. One of the rings appears to have a curious twisted structure (right).

Like Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown.

Neptune's rings have been given names: the outermost is Adams (which contains three prominent arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago), and finally the faint but broad Galle.

Neptune's magnetic field is, like Uranus', oddly oriented and probably generated by motions of conductive material (probably water) in its middle layers.

Neptune can be seen with binoculars (if you know exactly where to look) but a large telescope is needed to see anything other than a tiny disk. There are several Web sites that show the current position of Neptune (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program.
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Uranus is the seventh planet from the Sun and the third largest (by diameter). Uranus is larger in diameter but smaller in mass than Neptune.

orbit: 2,870,990,000 km (19.218 AU) from Sun
diameter: 51,118 km (equatorial)
mass: 8.683e25 kg

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus (Saturn) and of the Cyclopes and Titans (predecessors of the Olympian gods).

Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781. It had actually been seen many times before but ignored as simply another star (the earliest recorded sighting was in 1690 when John Flamsteed cataloged it as 34 Tauri). Herschel named it "the Georgium Sidus" (the Georgian Planet) in honor of his patron, the infamous (to Americans) King George III of England; others called it "Herschel". The name "Uranus" was first proposed by Bode in conformity with the other planetary names from classical mythology but didn't come into common use until 1850.

Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.

Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to the ecliptic. At the time of Voyager 2's passage, Uranus' south pole was pointed almost directly at the Sun. This results in the odd fact that Uranus' polar regions receive more energy input from the Sun than do its equatorial regions. Uranus is nevertheless hotter at its equator than at its poles. The mechanism underlying this is unknown.

Actually, there's an ongoing battle over which of Uranus' poles is its north pole! Either its axial inclination is a bit over 90 degrees and its rotation is direct, or it's a bit less than 90 degrees and the rotation is retrograde. The problem is that you need to draw a dividing line *somewhere*, because in a case like Venus there is little dispute that the rotation is indeed retrograde (not a direct rotation with an inclination of nearly 180).

Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Uranus (and Neptune) are in many ways similar to the cores of Jupiter and Saturn minus the massive liquid metallic hydrogen envelope. It appears that Uranus does not have a rocky core like Jupiter and Saturn but rather that its material is more or less uniformly distributed.

Uranus' atmosphere is about 83% hydrogen, 15% helium and 2% methane.

Like the other gas planets, Uranus has bands of clouds that blow around rapidly. But they are extremely faint, visible only with radical image enhancement of the Voyager 2 pictures (right). Recent observations with HST (left) show larger and more pronounced streaks. Further HST observations show even more activity. Uranus is no longer the bland boring planet that Voyager saw! It now seems clear that the differences are due to seasonal effects since the Sun is now at a lower Uranian latitude which may cause more pronounced day/night weather effects. By 2007 the Sun will be directly over Uranus's equator.

Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere. There may be colored bands like Jupiter's but they are hidden from view by the overlaying methane layer.

Like the other gas planets, Uranus has rings. Like Jupiter's, they are very dark but like Saturn's they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 11 known rings, all very faint; the brightest is known as the Epsilon ring. The Uranian rings were the first after Saturn's to be discovered. This was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone.

Voyager 2 discovered 10 small moons in addition to the 5 large ones already known. It is likely that there are several more tiny satellites within the rings.

Uranus' magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60 degrees with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus.

Uranus is sometimes just barely visible with the unaided eye on a very clear night; it is fairly easy to spot with binoculars (if you know exactly where to look). A small astronomical telescope will show a small disk. There are several Web sites that show the current position of Uranus (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program.
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Mercury is the closest planet to the Sun and the eighth largest. Mercury is slightly smaller in diameter than the moons Ganymede and Titan but more than twice as massive.

orbit: 57,910,000 km (0.38 AU) from Sun
diameter: 4,880 km
mass: 3.30e23 kg

In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Mercury has been known since at least the time of the Sumerians (3rd millennium BC). It was sometimes given separate names for its apparitions as a morning star and as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus even believed that Mercury and Venus orbit the Sun, not the Earth.

Since it is closer to the Sun than the Earth, the illumination of Mercury's disk varies when viewed with a telescope from our perspective. Galileo's telescope was too small to see Mercury's phases but he did see the phases of Venus.

Mercury has been now been visited by two spacecraft, Mariner 10 and MESSENGER. Marriner 10 flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys. Its first flyby in Jan 2008 provided new high quality images of some of the terrain not seen by Marriner 10.

Mercury's orbit is highly eccentric; at perihelion it is only 46 million km from the Sun but at aphelion it is 70 million. The position of the perihelion precesses around the Sun at a very slow rate. 19th century astronomers made very careful observations of Mercury's orbital parameters but could not adequately explain them using Newtonian mechanics. The tiny differences between the observed and predicted values were a minor but nagging problem for many decades. It was thought that another planet (sometimes called Vulcan) slightly closer to the Sun than Mercury might account for the discrepancy. But despite much effort, no such planet was found. The real answer turned out to be much more dramatic: Einstein's General Theory of Relativity! Its correct prediction of the motions of Mercury was an important factor in the early acceptance of the theory.

Until 1962 it was thought that Mercury's "day" was the same length as its "year" so as to keep that same face to the Sun much as the Moon does to the Earth. But this was shown to be false in 1965 by doppler radar observations. It is now known that Mercury rotates three times in two of its years. Mercury is the only body in the solar system known to have an orbital/rotational resonance with a ratio other than 1:1 (though many have no resonances at all).

This fact and the high eccentricity of Mercury's orbit would produce very strange effects for an observer on Mercury's surface. At some longitudes the observer would see the Sun rise and then gradually increase in apparent size as it slowly moved toward the zenith. At that point the Sun would stop, briefly reverse course, and stop again before resuming its path toward the horizon and decreasing in apparent size. All the while the stars would be moving three times faster across the sky. Observers at other points on Mercury's surface would see different but equally bizarre motions.

Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K. The temperature on Venus is slightly hotter but very stable.

Mercury craters Mercury craters
Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it has no plate tectonics. On the other hand, Mercury is much denser than the Moon (5.43 gm/cm3 vs 3.34). Mercury is the second densest major body in the solar system, after Earth. Actually Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. This indicates that Mercury's dense iron core is relatively larger than Earth's, probably comprising the majority of the planet. Mercury therefore has only a relatively thin silicate mantle and crust.

Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km. The silicate outer shell (analogous to Earth's mantle and crust) is only 500 to 600 km thick. At least some of the core is probably molten.

Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. Thus in contrast to the Earth and Venus whose atmospheres are stable, Mercury's atmosphere is constantly being replenished.

wide angle view Southwest Mercury
The surface of Mercury exhibits enormous escarpments, some up to hundreds of kilometers in length and as much as three kilometers high. Some cut thru the rings of craters and other features in such a way as to indicate that they were formed by compression. It is estimated that the surface area of Mercury shrank by about 0.1% (or a decrease of about 1 km in the planet's radius).

Caloris Basin on Mercury Caloris Basin
One of the largest features on Mercury's surface is the Caloris Basin (right); it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Like the lunar basins, it was probably caused by a very large impact early in the history of the solar system.
wierd Mercury terrain Weird terrain opposite Caloris Basin
That impact was probably also responsible for the odd terrain on the exact opposite side of the planet (left).

In addition to the heavily cratered terrain, Mercury also has regions of relatively smooth plains. Some may be the result of ancient volcanic activity but some may be the result of the deposition of ejecta from cratering impacts.

A reanalysis of the Mariner data provides some preliminary evidence of recent volcanism on Mercury. But more data will be needed for confirmation.

Amazingly, radar observations of Mercury's north pole (a region not mapped by Mariner 10) show evidence of water ice in the protected shadows of some craters.

Mercury has a small magnetic field whose strength is about 1% of Earth's.

Mercury has no known satellites.

Mercury is often visible with binoculars or even the unaided eye, but it is always very near the Sun and difficult to see in the twilight sky. There are several Web sites that show the current position of Mercury (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program. Read more...

Mars is the fourth planet from the Sun and the seventh largest:

orbit: 227,940,000 km (1.52 AU) from Sun
diameter: 6,794 km
mass: 6.4219e23 kg

Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color; Mars is sometimes referred to as the Red Planet. (An interesting side note: the Roman god Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing and terraforming Mars may prefer this symbolism.) The name of the month March derives from Mars.



Mars has been known since prehistoric times. Of course, it has been extensively studied with ground-based observatories. But even very large telescopes find Mars a difficult target, it's just too small. It is still a favorite of science fiction writers as the most favorable place in the Solar System (other than Earth!) for human habitation. But the famous "canals" "seen" by Lowell and others were, unfortunately, just as imaginary as Barsoomian princesses.

The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 1997 July 4. In 2004 the Mars Expedition Rovers "Spirit" and "Opportunity" landed on Mars sending back geologic data and many pictures; they are still operating after more than three years on Mars. In 2008, Phoenix landed in the northern plains to search for water. Three Mars orbiters (Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Express) are also currently in operation.



Mars' orbit is significantly elliptical. One result of this is a temperature variation of about 30 C at the subsolar point between aphelion and perihelion. This has a major influence on Mars' climate. While the average temperature on Mars is about 218 K (-55 C, -67 F), Martian surface temperatures range widely from as little as 140 K (-133 C, -207 F) at the winter pole to almost 300 K (27 C, 80 F) on the day side during summer.

Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.

Mars has some of the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular:

* Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.
* Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.
* Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep (top of page);
* Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.

Much of the Martian surface is very old and cratered, but there are also much younger rift valleys, ridges, hills and plains. (None of this is visible in any detail with a telescope, even the Hubble Space Telescope; all this information comes from the spacecraft that we've sent to Mars.)

The southern hemisphere of Mars is predominantly ancient cratered highlands somewhat similar to the Moon. In contrast, most of the northern hemisphere consists of plains which are much younger, lower in elevation and have a much more complex history. An abrupt elevation change of several kilometers seems to occur at the boundary. The reasons for this global dichotomy and abrupt boundary are unknown (some speculate that they are due to a very large impact shortly after Mars' accretion). Mars Global Surveyor has produced a nice 3D map of Mars that clearly shows these features.

The interior of Mars is known only by inference from data about the surface and the bulk statistics of the planet. The most likely scenario is a dense core about 1700 km in radius, a molten rocky mantle somewhat denser than the Earth's and a thin crust. Data from Mars Global Surveyor indicates that Mars' crust is about 80 km thick in the southern hemisphere but only about 35 km thick in the north. Mars' relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (iron and iron sulfide).

Like Mercury and the Moon, Mars appears to lack active plate tectonics at present; there is no evidence of recent horizontal motion of the surface such as the folded mountains so common on Earth. With no lateral plate motion, hot-spots under the crust stay in a fixed position relative to the surface. This, along with the lower surface gravity, may account for the Tharis bulge and its enormous volcanoes. There is no evidence of current volcanic activity. However, data from Mars Global Surveyor indicates that Mars very likely did have tectonic activity sometime in the past.

There is very clear evidence of erosion in many places on Mars including large floods and small river systems. At some time in the past there was clearly some sort of fluid on the surface. Liquid water is the obvious fluid but other possibilities exist. There may have been large lakes or even oceans; the evidence for which was strenghtened by some very nice images of layered terrain taken by Mars Global Surveyor and the mineralology results from MER Opportunity. Most of these point to wet episodes that occurred only briefly and very long ago; the age of the erosion channels is estimated at about nearly 4 billion years. However, images from Mars Express released in early 2005 show what appears to be a frozen sea that was liquid very recently (maybe 5 million years ago). Confirmation of this interpretation would be a very big deal indeed! (Valles Marineris was NOT created by running water. It was formed by the stretching and cracking of the crust associated with the creation of the Tharsis bulge.)

Early in its history, Mars was much more like Earth. As with Earth almost all of its carbon dioxide was used up to form carbonate rocks. But lacking the Earth's plate tectonics, Mars is unable to recycle any of this carbon dioxide back into its atmosphere and so cannot sustain a significant greenhouse effect. The surface of Mars is therefore much colder than the Earth would be at that distance from the Sun.

Mars has a very thin atmosphere composed mostly of the tiny amount of remaining carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%). The average pressure on the surface of Mars is only about 7 millibars (less than 1% of Earth's), but it varies greatly with altitude from almost 9 millibars in the deepest basins to about 1 millibar at the top of Olympus Mons. But it is thick enough to support very strong winds and vast dust storms that on occasion engulf the entire planet for months. Mars' thin atmosphere produces a greenhouse effect but it is only enough to raise the surface temperature by 5 degrees (K); much less than what we see on Venus and Earth.

Early telescopic observations revealed that Mars has permanent ice caps at both poles; they're visible even with a small telescope. We now know that they're composed of water ice and solid carbon dioxide ("dry ice"). The ice caps exhibit a layered structure with alternating layers of ice with varying concentrations of dark dust. In the northern summer the carbon dioxide completely sublimes, leaving a residual layer of water ice. ESA's Mars Express has shown that a similar layer of water ice exists below the southern cap as well. The mechanism responsible for the layering is unknown but may be due to climatic changes related to long-term changes in the inclination of Mars' equator to the plane of its orbit. There may also be water ice hidden below the surface at lower latitudes. The seasonal changes in the extent of the polar caps changes the global atmospheric pressure by about 25% (as measured at the Viking lander sites).

Recent observations with the Hubble Space Telescope have revealed that the conditions during the Viking missions may not have been typical. Mars' atmosphere now seems to be both colder and dryer than measured by the Viking landers (more details from STScI).

The Viking landers performed experiments to determine the existence of life on Mars. The results were somewhat ambiguous but most scientists now believe that they show no evidence for life on Mars (there is still some controversy, however). Optimists point out that only two tiny samples were measured and not from the most favorable locations. More experiments will be done by future missions to Mars.

A small number of meteorites (the SNC meteorites) are believed to have originated on Mars.

On 1996 Aug 6, David McKay et al announced what they thought might be evidence of ancient Martian microorganisms in the meteorite ALH84001. Though there is still some controversy, the majority of the scientific community has not accepted this conclusion. If there is or was life on Mars, we still haven't found it.

Large, but not global, weak magnetic fields exist in various regions of Mars. This unexpected finding was made by Mars Global Surveyor just days after it entered Mars orbit. They are probably remnants of an earlier global field that has since disappeared. This may have important implications for the structure of Mars' interior and for the past history of its atmosphere and hence for the possibility of ancient life.

When it is in the nighttime sky, Mars is easily visible with the unaided eye. Mars is a difficult but rewarding target for an amateur telescope though only for the three or four months each martian year when it is closest to Earth. Its apparent size and brightness varies greatly according to its relative position to the Earth. There are several Web sites that show the current position of Mars (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.
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Jupiter is the fifth planet from the Sun and by far the largest within our solar system; some have described the solar system as consisting of the Sun, Jupiter, and assorted debris. It and the other gas giants Saturn, Uranus, and Neptune are sometimes referred to as "Jovian planets." The Romans named the planet after the Roman god Jupiter. The astronomical symbol for the planet is a stylized representation of the god's lightning bolt. The Chinese, Korean, and Japanese cultures refer to the planet as the Wood Star, based on the Five Elements.

Overview

Jupiter has been known since ancient times and is visible to the naked eye in the night sky. In 1610, Galileo Galilei discovered the four largest moons of Jupiter using a telescope, the first observation of moons other than Earth's.

Jupiter is 2.5 times more massive than all the other planets combined, so massive that its barycenter with the Sun actually lies above the Sun's surface (1.068 solar radii from the Sun's center). It is 318 times more massive than Earth, with a diameter 11 times that of Earth, and with a volume 1300 times that of Earth. It has been termed by many a "failed star", even though the comparison would be akin to calling an asteroid "a failed Earth". As impressive as it is, extrasolar planets have been discovered with much greater masses. However, it is thought to have about as large a diameter as a planet of its composition can, as adding extra mass would only result in further gravitational compression (until ignition occurs). There is no clear-cut definition of what distinguishes a large and massive planet such as Jupiter from a brown dwarf, although the latter possesses rather specific spectral lines, but in any case Jupiter would need to be about seventy times as massive if it were to become a star.

Jupiter also has the fastest rotation rate of any planet within the solar system, making a complete revolution on its axis in slightly less than ten hours, which results in a flattening easily seen through an Earth-based amateur telescope. Its best known feature is probably the Great Red Spot, a storm larger than Earth. The planet is perpetually covered with a layer of clouds.

Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon and Venus; however at times Mars appears brighter than Jupiter, while at others Jupiter appears brighter than Venus). It has been known since ancient times. Galileo Galilei's discovery, in 1610, of Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) was the first discovery of a celestial motion not apparently centered on the Earth. It was a major point in favor of Copernicus' heliocentric theory of the motions of the planets; Galileo's outspoken support of the Copernican theory got him in trouble with the Inquisition.

Physical Characteristics

Jupiter is composed of a relatively small rocky core, surrounded by metallic hydrogen, surrounded by liquid hydrogen, which is surrounded by gaseous hydrogen. There is no clear boundary or surface between these different phases of hydrogen; the conditions blend smoothly from gas to liquid as one descends.

The atmosphere contains trace amounts of methane, water vapour, ammonia, and "rock". There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. The outermost layer of the atmosphere contains crystals of frozen ammonia.This atmospheric composition is very close to the composition of the solar nebula. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.

Jupiter's upper atmosphere undergoes differential rotation, an effect first noticed by Giovanni Cassini (1690). The rotation of Jupiter's polar atmosphere is ~5 minutes longer than that of the equatorial atmosphere. In addition, bands of clouds of different latitudes flow in opposing directions on the prevailing winds. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 600 km/h are not uncommon. A particularly violent storm, about three times Earth's diameter, is known as the Great Red Spot.



The Great Red Spot is an anticyclonic storm on the planet Jupiter, 22° south of the equator; which has lasted at least 300 years. The storm is large enough to be visible through Earth-based telescopes. It was first observed either by Cassini or Hooke around 1665.
This dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979, when the spacecraft was 5.7 million miles (9.2 million kilometers) from Jupiter. Cloud details as small as 100 miles (160 kilometers) across can be seen here. The colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex and variable wave motion. To give a sense of Jupiter's scale, the white oval storm directly below the Great Red Spot is approximately the same diameter as Earth.

Storms such as this are not uncommon within the atmospheres of gas giants. Jupiter also has white ovals and brown ovals, which are lesser unnamed storms. White ovals tend to consist of relatively cool clouds within the upper atmosphere. Brown ovals are warmer and located within the "normal cloud layer". Such storms can last hours or centuries.

It is not known exactly what causes the Great Red Spot's reddish color. Theories supported by laboratory experiments suppose that the colour may be caused by any of "complex organic molecules, red phosphorus, or yet another sulfur compound", but a consensus has yet to be reached.

The Great Red Spot is remarkably stable, having first been spotted over 300 years ago. Several factors may be responsible for its longevity, such as the fact that it never encounters solid surfaces over which to dissipate its energy and that its motion is driven by Jupiter's internal heat. Simulations suggest that the Spot tends to absorb smaller atmospheric disturbances.

At the start of 2004, the Great Red Spot is approximately half as large as it was 100 years ago. It is not known how long the Great Red Spot will last, or whether this is a result of normal fluctuations.

The Great Red Spot should not be confused with the Great Dark Spot, famously seen in the atmosphere of Neptune by Voyager 2 in 1989. The Great Dark Spot was an atmospheric hole, not a storm, and was no longer present as of 1994 (although another, similar spot had appeared farther to the north).

On October 19, 2003 a black spot was photographed on Jupiter by Belgian astronomer Olivier Meeckers. Although not an unusual occurrence, this one caught the fantasy of some science fiction fans and conspiracy theorists, who went as far as speculating that the spot was evidence of nuclear activity on Jupiter, caused by Galileo's crash into the planet a month prior. Galileo carried about 15.6 kg of plutonium-238 as its power source, in the form of 144 pellets of plutonium dioxide, a ceramic. The individual pellets (which would be expected to separate during entry) initially contained about 108 grams of 238Pu each (about 10% would have decayed away by the time Galileo entered Jupiter), and are short of the required critical mass by a factor of about 100.

Planetary Rings

Jupiter has a faint planetary ring system composed of smoke-like dust particles knocked from its moons by meteor impacts. The main ring is made of dust from the satellites Adrastea and Metis. Two wide gossamer rings encircle the main ring, originating from Thebe and Amalthea. There is also an extremely tenuous and distant outer ring that circles Jupiter backwards. Its origin is uncertain, but this outer ring might be made of captured interplanetary dust.

Magnetosphere

Jupiter has a very large and powerful magnetosphere. In fact, if you could see Jupiter's magnetic field from Earth, it would appear five times as large as the full moon in the sky despite being so much farther away. This magnetic field collects a large flux of particle radiation in Jupiter's radiation belts, as well as producing a dramatic gas torus and flux tube associated with Io. Jupiter's magnetosphere is the largest planetary structure in the solar system.

The Pioneer probes confirmed the existence that Jupiter's enormous magnetic field is 10 times stronger than Earth's and contains 20,000 times as much energy. The sensitive instruments aboard found that the Jovian magnetic field's "north" magnetic pole is at the planet¹s geographic south pole, with the axis of the magnetic field tilted 11 degrees from the Jovian rotation axis and offset from the center of Jupiter in a manner similar to the axis of the Earth's field. The Pioneers measured the bow shock of the Jovian magnetosphere to the width of 26 million kilometres (16 million miles), with the magnetic tail extending beyond Saturn¹s orbit.

The data showed that the magnetic field fluctuates rapidly in size on the sunward side of Jupiter because of pressure variations in the solar wind, an effect studied in further detail by the two Voyager spacecraft. It was also discovered that streams of high-energy atomic particles are ejected from the Jovian magnetosphere and travel as far as the orbit of the Earth. Energetic protons were found and measured in the Jovian radiation belt and electric currents were detected flowing between Jupiter and some of its moons, particularly Io.

Exploration of Jupiter

Pioneer 10 flew past Jupiter in December of 1973, followed by Pioneer 11 exactly one year later. They provided important new data about Jupiter's magnetosphere, and took some low resolution photographs of the planet.

Voyager 1 flew by in March 1979 followed by Voyager 2 in July of the same year. The Voyagers vastly improved our understanding of the Galilean moons and discovered Jupiter's rings. They also took the first close up images of the planet's atmosphere.

In February 1992, Ulysses solar probe performed a flyby of Jupiter at a distance of 900,000 km (6.3 Jovian radii). The flyby was required to attain a polar orbit around the Sun. The probe conducted studies on Jupiter's magnetosphere. Since there are no cameras onboard the probe, no images were taken. In February 2004, the probe came again in the vicinity of Jupiter. This time distance was much greater, about 240 million km.

So far the only spacecraft to orbit Jupiter is the Galileo orbiter, which went into orbit around Jupiter in December 7, 1995. It orbited the planet for over seven years and conducted multiple flybys of all of the Galilean moons and Amalthea. The spacecraft also witnessed the impact of Comet Shoemaker-Levy 9 into Jupiter as it approached the planet in 1994, giving a unique vantage point for this spectacular event. However, the information gained about the Jovian system from the Galileo mission was limited by the failed deployment of its high-gain radio transmitting antenna.

An atmospheric probe was released from the spacecraft in July, 1995. The probe entered the planet's atmosphere in December 7, 1995. It parachuted through 150 km of the atmosphere, collecting data for 58 minutes, before being crushed by the extreme pressure to which it was subjected. It would have then quickly melted and vaporized. The Galileo orbiter itself underwent a more rapid version of the same fate when it was deliberately crashed into the planet on September 21, 2003 at a speed of over 50 km/s, in order to avoid any possibility of it crashing into and possibly contaminating Europa, one of the Jovian moons.

In 2000, the Cassini probe, en route to Saturn, flew by Jupiter and provided some of the highest-resolution images ever made of the planet.

NASA is planning a mission to study Jupiter in detail from a polar orbit. Named Juno, the spacecraft is planned to launch by 2010.After the discovery of a liquid ocean on Jupiter's moon Europa, there has been great interest to study the icy moons in detail.

A mission proposed by NASA was dedicated to study them. The JIMO (Jupiter Icy Moons Orbiter) was expected to be launched sometime after 2012. However, the mission was deemed too ambitious and its funding was cancelled.

In 2007, Jupiter will also be briefly visited by the New Horizons probe, en route to Pluto.

Jupiter's Moons

Jupiter has at least 63 moons. For a complete listing of these moons, please see Jupiter's natural satellites. For a timeline of their discovery dates, see Timeline of natural satellites.The four large moons, known as the "Galilean moons", are Io, Europa, Ganymede and Callisto.

The orbits of Io, Europa, and Ganymede, the largest moon in the solar system, form a pattern known as a Laplace resonance; for every four orbits that Io makes around Jupiter, Europa makes exactly two orbits and Ganymede makes exactly one. This resonance causes the gravitational effects of the three moons to distort their orbits into elliptical shapes, since each moon receives an extra tug from its neighbors at the same point in every orbit it makes. Without this resonance, tidal forces would tend to circularize the moons' orbits over time.

The tidal force from Jupiter, on the other hand, works to circularize their orbits. This constant tug of war causes regular flexing of the three moons' shapes, Jupiter's gravity stretches the moons more strongly during the portion of their orbits that are closest to it and allowing them to spring back to more spherical shapes when they're farther away. This flexing causes tidal heating of the three moons' cores. This is seen most dramatically in Io's extraordinary volcanic activity, and to a somewhat less dramatic extent in the geologically young surface of Europa indicating recent resurfacing.

Classification of Jupiter's moons

It used to be thought that Jupiter's moons were arranged neatly into four groups of four, but recent discoveries of many new small outer moons have complicated the division; there are now thought to be six main groups, although some are more distinct than others.

1. The inner group of four small moons all have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree.
2. The four Galilean moons were all discovered by Galileo Galilei, orbit between 400,000 and 2,000,000 km, and include some of the largest moons in the solar system.

3. Themisto is in a group of its own, orbiting halfway between the Galilean moons and the next group.

4. The Himalia group is a tightly clustered group of moons with orbits around 11-12,000,000 km from Jupiter.

5. Carpo is another isolated case; at the inner edge of the Ananke group, it revolves in the direct sense.

6. The Ananke group is a group with rather indistinct borders, averaging 21,276,000 km from Jupiter with an average inclination of 149 degrees.

7. The Carme group is a fairly distinct group that averages 23,404,000 km from Jupiter with an average inclination of 165 degrees.

8. The Pasiphaë group is a disperse and only vaguely distinct group that covers all the outermost moons.

It is thought that the groups of smaller moons may each have a common origin, perhaps as a larger moon or captured body that broke up into the existing moons of each group.

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Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. It is the brightest natural object in the night sky, except for the Moon, reaching an apparent magnitude of -4.6. Because Venus is an inferior planet, from Earth it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset, for which reason it is often called the Morning Star or the Evening Star.

Classified as a terrestrial planet, it is sometimes called Earth's "sister planet", for the two are similar in size, gravity, and bulk composition. Venus is covered with an opaque layer of highly reflective clouds of carbon dioxide, preventing its surface from being seen from space in visible light; this was a subject of great speculation until some of its secrets were revealed by planetary science in the twentieth century. Venus has the densest atmosphere of all the terrestrial planets, consisting mostly of carbon dioxide. The atmospheric pressure at the planet's surface is 90 times that of the Earth.

Venus' surface has been mapped in detail only in the last 20 years. It shows evidence of extensive volcanism, and some of its volcanoes may still be active today. Venus is thought to undergo periodic episodes of plate tectonics, in which the crust is subducted rapidly within a few million years, separated by stable periods of a few hundred million years.

The planet is named after Venus, the Roman goddess of love; most of its surface features are named after famous and mythological women. The adjective Venusian is commonly used for items related to Venus, though the Latin adjective is the rarely used Venerean; the now-archaic Cytherean is still occasionally encountered. Venus is the only planet in the Solar System named after a female figure, although two dwarf planets - Ceres and Eris - also have female names.

Structure

Venus is one of the four solar terrestrial planets, meaning that, like the Earth, it is a rocky body. In size and mass, it is very similar to the Earth, and is often described as its 'twin'. The diameter of Venus is only 650 km less than the Earth's, and its mass is 81.5% of the Earth's. However, conditions on the Venusian surface differ radically from those on Earth, due to its dense carbon dioxide atmosphere. The mass of the atmosphere of Venus is 96.5% carbon dioxide, with most of the remaining 3.5% composed of nitrogen.

Internal structure

Though there is little direct information about its internal structure, the similarity in size and density between Venus and Earth suggests that it has a similar internal structure: a core, mantle, and crust. Like that of Earth, the Venusian core is at least partially liquid. The slightly smaller size of Venus suggests that pressures are significantly lower in its deep interior than Earth. The principal difference between the two planets is the lack of plate tectonics on Venus, likely due to the dry surface and mantle. This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field.

Geography

About 80% of Venus' surface consists of smooth volcanic plains. Two highland 'continents' make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent is called Ishtar Terra, after Ishtar, the Babylonian goddess of love, and is about the size of Australia. Maxwell Montes, the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km above Venus' average surface elevation. The southern continent is called Aphrodite Terra, after the Greek goddess of love, and is the larger of the two highland regions at roughly the size of South America. Much of this continent is covered by a network of fractures and faults.

As well as the impact craters, mountains, and valleys commonly found on rocky planets, Venus has a number of unique surface features. Among these are flat-topped volcanic features called farra, which look somewhat like pancakes and range in size from 20 50 km across, and 100 1000 m high; radial, star-like fracture systems called novae; features with both radial and concentric fractures resembling spiders' webs, known as arachnoids; and coronae, circular rings of fractures sometimes surrounded by a depression. All of these features are volcanic in origin.

Almost all Venusian surface features are named after historical and mythological women. The only exceptions are Maxwell Montes, named after James Clerk Maxwell, and two highland regions, Alpha Regio and Beta Regio. These three features were named before the current system was adopted by the International Astronomical Union, the body that oversees planetary nomenclature.

Surface Geology

Much of Venus' surface appears to have been shaped by volcanic activity. Overall, Venus has several times as many volcanoes as Earth, and it possesses some 167 giant volcanoes that are over 100 km across. The only volcanic complex of this size on Earth is the Big Island of Hawaii. However, this is not because Venus is more volcanically active than Earth, but because its crust is older. Earth's crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, while Venus' surface is estimated to be about 500 million years old.

Several lines of evidence point to ongoing volcanic activity on Venus. During the Russian Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. While rainfall drives thunderstorms on Earth, there is no rainfall on Venus. One possibility is that ash from a volcanic eruption was generating the lightning. Another intriguing piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which were found to drop by a factor of 10 between 1978 and 1986. This may imply that the levels had earlier been boosted by a large volcanic eruption.

There are almost 1,000 impact craters on Venus, more or less evenly distributed across its surface. On other cratered bodies, such as the Earth and the Moon, craters show a range of states of erosion, indicating a continual process of degradation. On the Moon, degradation is caused by subsequent impacts, while on Earth, it is caused by wind and rain erosion. However, on Venus, about 85% of craters are in pristine condition. The number of craters together with their well-preserved condition indicates that the planet underwent a total resurfacing event about 500 million years ago. Earth's crust is in continuous motion, but it is thought that Venus cannot sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust.

Venusian craters range from 3 km to 280 km in diameter. There are no craters smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater.

Atmosphere

Venus has an extremely thick atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The pressure at the planet's surface is about 90 times that at Earth's surface - a pressure equivalent to that at a depth of 1 kilometer under Earth's oceans. The enormously CO2-rich atmosphere generates a strong greenhouse effect that raises the surface temperature to over 400 °C (752°F). This makes Venus' surface hotter than Mercury's, even though Venus is nearly twice as distant from the Sun and receives only 25% of the solar irradiance.

Studies have suggested that several billion years ago Venus' atmosphere was much more like Earth's than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. Venus is thus an extreme example of climate change, making it a useful tool in climate change studies.

Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus' surface does not vary significantly between the night and day sides, despite the planet's extremely slow rotation. Winds at the surface are slow, moving at a few kilometers per hour, but because of the high density of the atmosphere at Venus' surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface.

Above the dense CO2 layer are thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets. These clouds reflect about 60% of the sunlight that falls on them back into space, and prevent the direct observation of Venus' surface in visible light. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well heated or lit. In the absence of the greenhouse effect caused by the carbon dioxide in the atmosphere, the temperature at the surface of Venus would be quite similar to that on Earth. Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days.

Magnetic Field and Core

In 1980, The Pioneer Venus Orbiter found that Venus' magnetic field is both weaker and smaller (i.e. closer to the planet) than Earth's. What small magnetic field is present is induced by an interaction between the ionosphere and the solar wind, rather than by an internal dynamo in the core like the one inside the Earth. Venus' magnetosphere is too weak to protect the atmosphere from cosmic radiation.

This lack of an intrinsic magnetic field at Venus was surprising given that it is similar to Earth in size, and was expected to also contain a dynamo in its core. A dynamo requires three things: a conducting liquid, rotation, and convection. The core is thought to be electrically conductive, however. Also, while its rotation is often thought to be too slow, simulations show that it is quite adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus' core. On Earth, convection occurs in the liquid outer layer of the core because the bottom of the liquid layer is much hotter than the top. Since Venus has no plate tectonics to let off heat, it is possible that it has no solid inner core, or that its core is not currently cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already completely solidified.

Orbit and Rotation

Venus orbits the Sun at an average distance of about 108 million km, and completes an orbit every 224.65 days. Although all planetary orbits are elliptical, Venus is the closest to circular, with an eccentricity of less than 1%. When Venus lies between the Earth and the Sun, a position known as 'inferior conjunction', it makes the closest approach to Earth of any planet, lying at a distance of about 40 million km. The planet reaches inferior conjunction every 584 days, on average.

Venus rotates once every 243 days, by far the slowest rotation period of any of the major planets. A Venusian sidereal day thus lasts more than a Venusian year (243 versus 224.7 Earth days). However, the length of a solar day on Venus is significantly shorter than the sidereal day; to an observer on the surface of Venus the time from one sunrise to the next would be 116.75 days. The Sun would appear to rise in the west and set in the east. At the equator, Venus' surface rotates at 6.5 km/h; on Earth, the rotation speed at the equator is about 1,600 km/h.

If viewed from above the Sun's north pole, all of the planets are orbiting in a counter-clockwise direction; but while most planets also rotate anticlockwise, Venus rotates clockwise in "retrograde" rotation. The question of how Venus came to have a slow, retrograde rotation was a major puzzle for scientists when the planet's rotation period was first measured. When it formed from the solar nebula, Venus would have had a much faster, prograde rotation, but calculations show that over billions of years, tidal effects on its dense atmosphere could have slowed down its initial rotation to the value seen today.

A curious aspect of Venus' orbit and rotation periods is that the 584-day average interval between successive close approaches to the Earth is almost exactly equal to five Venusian solar days. Whether this relationship arose by chance or is the result of some kind of tidal locking with the Earth, is unknown.

Venus is currently moonless, though the asteroid 2002 VE68 presently maintains a quasi-orbital relationship with it. According to Alex Alemi and David Stevenson of the California Institute of Technology, their recent study of models of the early solar system shows that it is very likely that, billions of years ago, Venus had at least one moon, created by a huge impact event.

About 10 million years later, according to Alemi and Stevenson, another impact reversed the planet's spin direction. The reversed spin direction caused the Venusian moon to gradually spiral inward until it collided and merged with Venus. If later impacts created moons, those moons also were absorbed the same way the first one was. The Alemi/Stevenson study is recent, and it remains to be seen what sort of acceptance it will achieve in the scientific community.

Observation

Venus is always brighter than the brightest stars, with its apparent magnitude ranging from -3.8 to -4.6. This is bright enough to be seen even in the middle of the day, and the planet can be easy to see when the Sun is low on the horizon. As an inferior planet, it always lies within about 47° of the Sun.

Venus 'overtakes' the Earth every 584 days as it orbits the Sun. As it does so, it goes from being the 'Evening star', visible after sunset, to being the 'Morning star', visible before sunrise. While Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported 'unidentified flying object'. In 1973, future U.S. President Jimmy Carter reported having seen a UFO in 1969, which later analysis suggested was probably the planet, and countless other people have mistaken Venus for something more exotic.

As it moves around its orbit, Venus displays phases like those of the Moon: it is new when it passes between the Earth and the Sun, full when it is on the opposite side of the Sun, and a crescent when it is at its maximum elongations from the Sun. Venus is brightest when it is a thin crescent; it is much closer to Earth when a thin crescent than when gibbous, or full.

Venus' orbit is slightly inclined relative to the Earth's orbit; thus, when the planet passes between the Earth and the Sun, it usually does not cross the face of the Sun. However, transits of Venus do occur in pairs separated by eight years, at intervals of about 120 years, when the planet's inferior conjunction coincides with its presence in the plane of the Earth's orbit. The most recent transit was in 2004; the next will be in 2012. Historically, transits of Venus were important, because they allowed astronomers to directly determine the size of the astronomical unit, and hence of the solar system. Captain Cook's exploration of the east coast of Australia came after he had sailed to Tahiti in 1768 to observe a transit of Venus.

A long-standing mystery of Venus observations is the so-called Ashen light - an apparent weak illumination of the dark side of the planet, seen when the planet is in the crescent phase. The first claimed observation of ashen light was made as long ago as 1643, but the existence of the illumination has never been reliably confirmed. Observers have speculated that it may result from electrical activity in the Venusian atmosphere, but it may be illusory, resulting from the physiological effect of observing a very bright crescent-shaped object.

Studies of Venus
Early Studies

Venus was known in the Hindu Jyotisha since early times as the planet Shukra. In the West, before the advent of the telescope, Venus was known only as a 'wandering star'. Several cultures historically held its appearances as a morning and evening star to be those of two separate bodies. Pythagoras is usually credited with recognizing in the sixth century BC that the morning and evening stars were a single body, though he espoused the view that Venus orbited the Earth. When Galileo first observed the planet in the early 17th century, he found that it showed phases like the Moon's, varying from crescent to gibbous to full and vice versa. This could be possible only if Venus orbited the Sun, and this was among the first observations to clearly contradict the Ptolemaic geocentric model that the solar system was concentric and centered on the Earth.

Venus' atmosphere was discovered as early as 1790 by Johann Schröter. Schröter found that when the planet was a thin crescent, the cusps extended through more than 180°. He correctly surmised that this was due to scattering of sunlight in a dense atmosphere. Later, Chester Smith Lyman observed a complete ring around the dark side of the planet when it was at inferior conjunction, providing further evidence for an atmosphere. The atmosphere complicated efforts to determine a rotation period for the planet, and observers such as Giovanni Cassini and Schroter incorrectly estimated periods of about 24 hours from the motions of markings on the planet's apparent surface.

Ground-based Research

Little more was discovered about Venus until the 20th century. Its almost featureless disc gave no hint as to what its surface might be like, and it was only with the development of spectroscopic, radar and ultraviolet observations that more of its secrets were revealed. The first UV observations were carried out in the 1920s, when Frank E. Ross found that UV photographs revealed considerable detail that was absent in visible and infrared radiation. He suggested that this was due to a very dense yellow lower atmosphere with high cirrus clouds above it.

Spectroscopic observations in the 1900s gave the first clues about Venus' rotation. Vesto Slipher tried to measure the Doppler shift of light from Venus, but found that he could not detect any rotation. He surmised that the planet must have a much longer rotation period than had previously been thought. Later work in the 1950s showed that the rotation was retrograde. Radar observations of Venus were first carried out in the 1960s, and provided the first measurements of the rotation period which were close to the modern value.

Radar observations in the 1970s revealed details of Venus' surface for the first time. Pulses of radio waves were beamed at the planet using the 300 m radio telescope at Arecibo Observatory, and the echoes revealed two highly reflective regions, designated the Alpha and Beta regions. The observations also revealed a bright region attributed to mountains, which was called Maxwell Montes. These three features are now the only ones on Venus which do not have female names.

The best radar images obtainable from Earth revealed features no smaller than about 5 km across. More detailed exploration of the planet could only be carried out from space.

Exploration of Venus
Early Efforts

The first robotic space probe mission to Venus, and the first to any planet, began on 12 February 1961 with the launch of the Venera 1 probe. The first craft of the otherwise highly successful Soviet Venera program, Venera 1 was launched on a direct impact trajectory, but contact was lost seven days into the mission, when the probe was about 2 million km from Earth. It was estimated to have passed within 100,000 km from Venus in mid-May.

The United States exploration of Venus also started badly with the loss of the Mariner 1 probe on launch. The subsequent Mariner 2 mission enjoyed greater success, and after a 109-day transfer orbit on 14 December 1962 it became the world's first successful interplanetary mission, passing 34,833 km above the surface of Venus. Its microwave and infrared radiometers revealed that while Venus' cloud tops were cool, the surface was extremely hot - at least 425°C, finally ending any hopes that the planet might harbor ground-based life. Mariner 2 also obtained improved estimates of Venus' mass and of the astronomical unit, but was unable to detect either a magnetic field or radiation belts.

Atmospheric Entry

The Venera 3 probe crash-landed on Venus on March 1, 1966. It was the first man-made object to enter the atmosphere and strike the surface of another planet, though its communication system failed before it was able to return any planetary data. Venus' next encounter with an unmanned probe came on October 18, 1967 when Venera 4 successfully entered the atmosphere and deployed a number of science experiments. Venera 4 showed that the surface temperature was even hotter than Mariner 2 had measured at almost 500°C, and that the atmosphere was about 90 to 95% carbon dioxide. The Venusian atmosphere was considerably denser than Venera 4's designers had anticipated, and its slower than intended parachute descent meant that its batteries ran down before the probe reached the surface. After returning descent data for 93 minutes, Venera 4's last pressure reading was 18 bar at an altitude of 24.96 km.

Another probe arrived at Venus one day later on October 19, 1967 when Mariner 5 conducted a flyby at a distance of less than 4,000 km above the cloud tops. Mariner 5 was originally built as backup for the Mars-bound Mariner 4, but when that mission was successful, the probe was refitted for a Venus mission. A suite of instruments more sensitive than those on Mariner 2, in particular its radio occultation experiment, returned data on the composition, pressure and density of Venus' atmosphere.[40] The joint Venera 4 Mariner 5 data were analyzed by a combined Soviet-American science team in a series of colloquia over the following year, in an early example of space cooperation.

Armed with the lessons and data learned from Venera 4, the Soviet Union launched the twin probes Venera 5 and Venera 6 five days apart in January 1969; they encountered Venus a day apart on May 16 and May 17 that year. The probes were strengthened to improve their crush depth to 25 atmospheres and were equipped with smaller parachutes to achieve a faster descent. Since then current atmospheric models of Venus suggested a surface pressure of between 75 and 100 atmospheres, neither were expected to survive to the surface. After returning atmospheric data for a little over fifty minutes, they both were crushed at altitudes of approximately 20 km before going on to strike the surface on the night side of Venus.

Surface Science

Venera 7 represented a concerted effort to return data from the planet's surface, and was constructed with a reinforced descent module capable of withstanding a pressure of 180 bar. The module was pre-cooled prior to entry and equipped with a specially reefed parachute for a rapid 35-minute descent. Entering the atmosphere on 15 December 1970, the parachute is believed to have partially torn during the descent, and the probe struck the surface with a hard, yet not fatal, impact. Probably tilted onto its side, it returned a weak signal supplying temperature data for 23 minutes, the first telemetry received from the surface of another planet.

The Venera program continued with Venera 8 sending data from the surface for 50 minutes, and Venera 9 and Venera 10 sending the first images of the Venusian landscape. The two landing sites presented very different visages in the immediate vicinities of the landers: Venera 9 had landed on a 20 degree slope scattered with boulders around 30-40 cm across; Venera 10 showed basalt-like rock slabs interspersed with weathered material.

In the meantime, the United States had sent the Mariner 10 probe on a gravitational slingshot trajectory past Venus on its way to Mercury. On February 5, 1974, Mariner 10 passed within 5790 km of Venus, returning over 4,000 photographs as it did so. The images, the best then achieved, showed the planet to be almost featureless in visible light, but ultraviolet light revealed details in the clouds that had never been seen in Earth-bound observations.

The American Pioneer Venus project consisted of two separate missions. The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978, and remained there for over thirteen years studying the atmosphere and mapping the surface with radar. The Pioneer Venus Multiprobe released a total of five probes which entered the atmosphere on December 9, 1978, returning data on its composition, winds and heat fluxes.

Four more Venera lander missions took place over the next four years, with Venera 11 and Venera 12 detecting Venusian electrical storms; and Venera 13 and Venera 14, landing four days apart on March 1 and March 5, 1982, returning the first color photographs of the surface. All four missions deployed parachutes for braking in the upper atmosphere, but released them at altitudes of 50 km, the dense lower atmosphere providing enough friction to allow for an unaided soft landing. Both Venera 13 and 14 analyzed soil samples with an on-board X-ray fluorescence spectrometer, and attempted to measure the compressibility of the soil with an impact probe. Venera 14, though, had the misfortune to strike its own ejected camera lens cap and its probe failed to make contact with the soil. The Venera program came to a close in October 1983 when Venera 15 and Venera 16 were placed in orbit to conduct mapping of the Venusian terrain with synthetic aperture radar.

The Soviet Union had not finished with Venus, and in 1985 it took advantage of the opportunity to combine missions to Venus and Comet Halley, which passed through the inner solar system that year. En route to Halley, on June 11 and June 15, 1985 the two spacecraft of the Vega program each dropped a Venera-style probe (of which Vega 1's partially failed) and released a balloon-supported aerobot into the upper atmosphere. The balloons achieved an equilibrium altitude of around 53 km, where pressure and temperature are comparable to those at Earth's surface. They remained operational for around 46 hours, and discovered that the Venusian atmosphere was more turbulent than previously believed, and subject to high winds and powerful convection cells.

Radar mapping

The United States' Magellan probe was launched on May 4, 1989 with a mission to map the surface of Venus with radar. The high-resolution images it obtained during its 4 and a half years of operation far surpassed all prior maps and were comparable to visible-light photographs of other planets. Magellan imaged over 98% of Venus' surface by radar and mapped 95% of its gravity field. In 1994, at the end of its mission, Magellan was deliberately sent to its destruction into the atmosphere of Venus in an effort to quantify its density. Venus was observed by the Galileo and Cassini spacecraft during flybys on their respective missions to the outer planets, but Magellan would otherwise be the last dedicated mission to Venus for over a decade.

Current and Future Missions

The Venus Express probe was designed and built by the European Space Agency. Launched by the Russian Federal Space Agency on November 9, 2005, it successfully assumed a polar orbit around Venus on April 11, 2006. The probe is undertaking a detailed study of the Venusian atmosphere and clouds, and will also map the planet's plasma environment and surface characteristics, particularly temperatures. Its mission is intended to last a nominal 500 Earth days, or around two Venusian years. One of the first results emerging from Venus Express is the discovery that a huge double atmospheric vortex exists at the south pole of the planet.

Japan's aerospace body JAXA is planning to launch its Venus climate orbiter, the PLANET-C, in 2010. Future flybys en route to other destinations include the MESSENGER and BepiColombo missions to Mercury.

Venus in Human Culture
Historic Connections

Babylonians:
One of the brightest objects in the sky, Venus has been known since prehistoric times and has had a significant impact on human culture from the earliest days. It is described in Babylonian cuneiformic texts such as the Venus tablet of Ammisaduqa, which relates observations that possibly date from 1600 BC. The Babylonians named the planet Ishtar (Sumerian Inanna), the personification of womanhood, and goddess of love. The Ancient Egyptians believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti. Likewise believing Venus to be two bodies, the Ancient Greeks called the morning star, Phosphoros (Latinized Phosphorus), the "Bringer of Light" or Eosphoros (Latinized Eosphorus), the "Bringer of Dawn". The evening star they called Hesperos (Latinized Hesperus) (the star of the evening), but by Hellenistic times, they realized the two were the same planet. Hesperos would be translated into Latin as Vesper and Phosphoros as Lucifer ("Light Bearer"), a poetic term later used to refer to the fallen angel cast out of heaven. The Romans would later name the planet in honor of their goddess of love, Venus, whereas the Greeks used the name of her Greek counterpart, Aphrodite (Phoenician Astarte). One of the oldest surviving astronomical documents, from the Babylonian library of Ashurbanipal around 1600 BC, is a 21-year record of the appearances of Venus (which the early Babylonians called Nindaranna). The ancient Sumerians and Babylonians called Venus Dil-bat in Akkadia it was the special star of the mother-god Ishtar; and in Chinese it is Jin-xing, the planet of the metal element. In India, Venus is called Shukra Graha (the planet Shukra) which is named after a powerful saint Shukra. The word 'Shukra' is also associated with semen, or generation.

Hebrews:
To the Hebrews it was known as Noga ("shining"), Helel ("bright"), Ayeleth-ha-Shakhar ("deer of the dawn") and Kochav-ha-'Erev ("star of the evening").

Maya:
Venus was important to the Maya civilization, who developed a religious calendar based in part upon its motions, and held the motions of Venus to determine the propitious time for events such as war. Venus was considered the most important celestial body observed by the Maya, who called it Chak ek, "the Great Star", possibly more important even than the Sun. The Mayans monitored the movements of Venus closely and observed it in daytime. The positions of Venus and other planets were thought to influence life on Earth, so Maya and other ancient Mesoamerican cultures timed wars and other important events based on their observations. In the Dresden Codex, the Maya included an almanac showing Venus's full cycle, in five sets of 584 days each (approximately eight years), after which the patterns repeated (since Venus has a synodic period of 583.92 days). 2012

Maasai:
The Maasai people named the planet Kileken, and have an oral tradition about it called The Orphan Boy. In western astrology, derived from its historical connotation with goddesses of femininity and love, Venus is held to influence those aspects of human life.

India:
In Indian Vedic astrology, Venus is known as Shukra (Hindi:, meaning "clear, pure" or "brightness, clearness" in Sanskrit. One of the nine Navagraha, it is held to affect wealth, pleasure and reproduction; it was the son of Bhrgu and Ushana, preceptor of the Daityas, and guru of the Asuras.

China:
Early Chinese astronomers called the planet Tai-pe, or the "beautiful white one". Modern Chinese, Korean, Japanese and Vietnamese cultures refer to the planet literally as the metal star (Chinese), based on the Five elements. Lakotan spirituality refers to Venus as the daybreak star, and associates it with the last stage of life and wisdom.

Australia:
Venus is important in many Australian aboriginal cultures, such as that of the Yolngu people in Northern Australia. The Yolngu gather after sunset to await the rising of Venus, which they call Barnumbirr. As she approaches, in the early hours before dawn, she draws behind her a rope of light attached to the Earth, and along this rope, with the aid of a richly decorated "Morning Star Pole", the people are able to communicate with their dead loved ones, showing that they still love and remember them. Barnumbirr is also an important creator-spirit in the Dreaming, and "sang" much of the country into life

Greece:
Early Greeks thought that the evening and morning appearances of Venus represented two different objects, calling it Hesperus when it appeared in the western evening sky and Phosphorus when it appeared in the eastern morning sky. They eventually came to recognize that both objects were the same planet; Pythagoras is given credit for this realization. In the 4th century BC, Heraclides Ponticus proposed that both Venus and Mercury orbited the Sun rather than Earth.

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