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Planet Profile
Composition and Chemistry Because of this, the formation stages of the outer planets had a greater mass of solid material to begin with. This meant that the core bodies for the giant planets had more gravity to the gases hydrogen and helium, which were abundant in the solar nebula. Therefore, the outer planets were able to grow significantly bigger than those that were closer to the Sun. Abundances in the Outer Solar Nebula which includes Jupiter
Our knowledge of the interior of Jupiter was gathered indirectly. (The data from Galileo's atmospheric probe goes down only about 150 km the cloud tops.) Jupiter probably has a core of rocky material that is something like 10 to 15 times the mass of the Earth. Above the core is the main part of the planet in the form of liquid metallic hydrogen. This exotic element is possible only at pressures exceeding 4 million bars, as is the interior of Jupiter (and Saturn). Liquid metallic hydrogen is composed of ionized protons and (like the interior of the Sun but at a far lower temperature). At the temperature of Jupiter's interior, the hydrogen is a liquid not a gas. It is an electrical conductor and the source of Jupiter's magnetic field. This layer also probably contains some helium and traces of "ices". The outermost layer is composed of hydrogen and helium which is liquid towards the interior and a gas further out. The atmosphere that we can see through a telescope is just the very top of this deep layer. Water, carbon dioxide, methane and other simple molecules are also present in trace amounts. Three distinct layers of clouds are believed to exist consisting of ammonia ice, ammonium hydrosulfide and a mixture of ice and water. However, the Galileo probe shows only small indications of clouds (one instrument seems to have detected the topmost layer while another may have seen the second). But the probe's entry point was unusual -- Earth-based telescopic observations and more recent observations by the Galileo orbiter suggest that the probe entry site may well have been one of the warmest and least cloudy areas on Jupiter at that time. Data from the Galileo probe also indicate that there is much less water than expected. The expectation was that Jupiter's atmosphere would contain about twice the amount of oxygen (combined with the abundant hydrogen to make water) as the Sun. But it now appears that the actual amount is much less than the Sun's. Also surprising was the high temperature and density of the upper parts of the atmosphere. Exploration of Jupiter Only six spacecraft, five NASA and one European, have reached beyond the asteroid belt. The challenges of traveling so far away from Earth are great. Flights to the outer planets take years to decades, rather than the few months to reach Venus or Mars. The spacecraft must be very reliable because, even at the speed of light, messages between Earth and the spacecraft take several hours to arrive. If a problem develops near Jupiter, for example, the spacecraft computer must deal with it right then. It would be a disaster if the message had to be sent back to Earth and then be routed back to the spacecraft. These spacecraft also must carry their own energy sources, since ther is not enough sunlight to supply energy to the solar cells. Heaters are required to keep instruments at the right temperature, and spacecraft must have powerful radio transmitters and large antennas if their data are to be transmitted back to Earth a billion kilometers away. The first spacecraft sent to Jupiter were the Pioneers 10 and 11, launched in 1972 and 1973 as pathfinders to Jupiter. One of their main objectives was simply to determine whether a spacecraft could actually travel through the asteroid belt alive. If they got there, they were also instructed to measure the radiation hazards in the magnetosphere of Jupiter. The gas planets do not have solid surfaces, their gaseous material gets denser with depth. What we see when looking at these planets is the tops of clouds high in their atmospheres. Characteristics Jupiter and the other gas planets have high velocity winds which occur only in certain sections of bands of latitude. The winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences between these bands make the colored bands that you see on Jupiter. The light colored bands are called zones, the dark ones belts. The bands have been known for awhile on Jupiter, but the complex vortexes in the regions between the bands were first seen by Voyager. The data from the Galileo probe said that these winds move even faster than thougt (more than 400 mph) and extend down as far as the probe was able to see. They may extend down thousands of kilometers into the interior. Jupiter's atmosphere was also found to be quite turbulent. This shows that Jupiter's winds occur because of its internal heat rather than from solar radiation as on Earth. The colors seen in Jupiter's clouds are probably the result of small chemical reactions of the trace elements in Jupiter's atmosphere, maybe involving sulfur whose compounds take on a wide variety of colors, but the exact reasons are still unknown. The colors are in direct correslation with their altitude: blue lowest, followed by browns and whites, with reds highest. Sometimes we see the lower layers through holes in the upper ones. The Great Red Spot (GRS) has been seen by Earthly observers for more than 300 years (its discovery is usually credited to Cassini, or Robert Hooke in the 17th century). The GRS is about 12,000 by 25,000 km, big enough to hold two Earths. Other smaller but similar spots have been known for decades. Infrared observations and the direction of its rotation indicate that the GRS is a high-pressure region whose cloud tops are significantly higher and colder than the surrounding regions. Similar structures have been seen on Saturn and Neptune. It is not known how these structures can last for so long. Jupiter gives off more energy than it receives from the Sun! The interior of Jupiter is hot: the core is probably around 20,000 K. The heat is generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun It is way too small and its interior is too cool to start a nuclear reaction.) This interior heat probably causes convection deep within Jupiter's liquid layers and is probably responsible for the complex motions we see in the cloud tops. Saturn and Neptune are similar to Jupiter in this aspect, but oddly, Uranus is not. Jupiter is just about as large as a gas planet can be. If more material were to be added, it would be compressed by gravity so that the overall radius would increase only slightly. Very, very interesting! A star can be larger only because of its internal (nuclear) heat source. Jupiter would have to be at least 80 times more massive to become a star. Jupiter has a huge magnetic field, much stronger and bigger than Earth's. Its magnetosphere extends more than 650 million km (past the orbit of Saturn!). Jupiter's magnetosphere is not spherical -- it extends "only" a few million kilometers in the direction toward the Sun. Jupiter's moons therefore lie within its magnetosphere, a fact which may partially explain some of the activity on its moon, Io. Unfortunately for future space travelers and of much concern to the designers of the Voyager and Galileo spacecraft, the environment near Jupiter contains large amounts of energetic particles trapped by Jupiter's magnetic field. This "radiation" is similar to, but much more intense than, that found within Earth's Van Allen belts. It would be fatal to an unprotected human being. The Galileo atmospheric probe discovered a new intense radiation belt between Jupiter's ring and the uppermost atmospheric layers. This new belt is approximately 10 times as strong as Earth's Van Allen radiation belts. More surprisingly, this new belt was also found to contain high energy helium ions of unknown origin. Jupiter has rings like Saturn's, but much fainter and smaller. They were totally unexpected and were only discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth a quick look to see if any rings might be present. Everyone else thought that the chance of finding anything was nada, but there they were!! They have since been imaged in infrared images made by ground-based telescopes and by Galileo. Unlike Saturn's, Jupiter's rings are dark (albedo about 0.05). They're probably composed of very small grains of rocky material. Unlike Saturn's rings, they seem to contain no ice. Particles in Jupiter's rings probably don't stay there for long due to atmospheric and magnetic drag. The Galileo spacecraft discovered that the rings are continuously being renewed by dust formed by micrometeor impacts on the four inner moons, which are very energetic because of Jupiter's large gravitational field. The inner halo ring is broadened by interactions with Jupiter's magnetic field. In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular results. The effects were clearly visible even with amateur telescopes. The debris from the collision was visible for about a year after with HST. When it is in the nighttime, Jupiter is often the brightest "star" in the sky (it is second only to Venus, which isn't that often visible in a dark sky). The four Galilean moons are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a small telescope. There are several Web sites that show the current position of Jupiter (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program such as Starry Night. Jupiter's SatellitesJupiter has 16 known satellites, the four large Galilean moons and 12 small ones.
Jupiter's Rings
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