JUPITER
NASA/ESA/GSFC/UCBerkeley/JPL-Caltech/STScI
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Formation Jupiter is thought to be the oldest of the planets. It formed from gases remaining in the solar nebula, following the Sun's formation 4.5 billion years ago. Jupiter became the largest planet in the Solar System by far. It has more than double the mass of all the other planets put together. It is a gas giant, and not surprisingly, it is made of the same two gases as the Sun- hydrogen and helium.
Jupiter likely formed closer to the Sun and then migrated to its current orbit about 4 billion years ago. Because of its enormous mass, it is possible that Jupiter influenced both the formation and the orbits of the inner terrestrial planets. Though Jupiter is the largest planet in the Solar System, it has the shortest day- only 9 hours 53 minutes. |
(NASA/Lunar and Planetary Institute)
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Structure, Atmosphere and Magnetoshpere Jupiter is one of the four gas giant planets, composed mostly of atmospheric and compressed gases. It likely has a small, solid core, equal to 1-2 Earth masses. Whether this core is truly “solid” or "diffuse", mixing with the over-laying mantel, is currently undecided.
Jupiter's upper atmosphere consists mostly of hydrogen (90%) and helium (10%) with traces of other elements (methane, water vapor and ammonia). Toward the interior the gravitational and atmospheric pressure converts the gaseous atmosphere to a liquid. At depths of more than 10,000 km, the liquid hydrogen’s electrons are freed, and the hydrogen behaves like a metallic conductor of electricity (“metallic hydrogen”). Jupiter’s interior temperature is estimated to be approximately 20,000 degrees K- much hotter than the surface of the Sun. This source of this heat is not well understood. It may be the result of ongoing contraction of the planet under its extreme gravity. |
Cloud bands on Jupiter (NASA/JPL/University of Arizona)
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Jupiter has the deepest atmosphere of any planet in our Solar System- over 5,000 km. in altitude. By comparison, the Earth's atmosphere is 100 km high, and the International Space Station orbits the Earth at an altitude of about 350km.
Jupiter's upper cloud deck is about 50 km. thick, showing several distinct light and tawny-coloured bands. The light-coloured bands are comprised of water and ammonia ice; the tawny-coloured bands are thought to be convection cells rising from the warmer interior and carrying compounds such as phosphorus, sulfur and hydrocarbons. This region is highly electrically charged, producing lightning that is 1000 times more powerful than that seen on Earth. |
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The “Great Red Spot” is a massive storm, akin to a hurricane on Earth. Wind speed is estimated to be 430-680 km/h. It is larger than the entire Earth, and was first observed more than 300 years ago. The rotational period is about 6 Earth days, and it appears to be decreasing in size. Occasionally, there are smaller dynamic weather systems nearby.
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(NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Justin Cowart)
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Jupiter’s magnetic field is 14 times stronger than Earth’s. It is thought to be caused by eddy currents in Jupiter’s metallic hydrogen interior. All of Jupiter’s major moons orbit within the magnetosphere. The solar wind causes a long tail in the magnetosphere on the lee side of Jupiter, which extends nearly to the orbit of Saturn. It is the largest structure in the Solar System. The strong magnetism surrounding Jupiter traps and accelerates charged particles, resulting in intense radiation belts which are hazardous to spacecraft.
Moons Jupiter has a total of 79 known moons. The four largest ones are called the Galilean moons - Io, Europa, Ganymede and Callisto. Their first verifiable observation was by Galileo in 1610 using the newly-invented telescope; however, it is possible Ganymede was observed in 362 BCE by Chinese astronomer Gan De. Galileo’s observation dealt a serious blow to the belief in a universe where all celestial objects orbited around the Earth. The Galilean moons change their positions on a nightly basis. They can be seen with any small telescope and most binoculars.
 NASA/JPL/University of Arizona
Io is the innermost Galilean moon and is slightly larger than our moon. It has more than 400 active volcanoes and over 100 mountains. Some are taller than Mount Everest. It is the most geologically active body in the solar system.
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 (NASA/JPL-Caltech/
SETI Institute)
Europa is second closest to Jupiter and slightly smaller than our moon. It has a smooth surface of ice which likely covers a water ocean, maintained in its liquid state by tidal flexure from Jupiter’s gravity. The presence of liquid water suggests the possibility of life, making it an object of great scientific interest.
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 (NASA/JPL)
Ganymede is the third closest to Jupiter and the largest moon in the Solar System. Larger even than the planet Mercury, Ganymede has a liquid iron core producing its own magnetic field. Its rocky surface resembles that of our moon, but with icy regions. Ganymede has an extremely thin atmosphere of oxygen and ozone.
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 (NASA/JPL/DLR)
Callisto is the last of the Galilean moons. It is slightly smaller than the planet Mercury. It is a mixture of ice and rocky material. Callisto shows no signs of ancient geological activity. Because it is one of the most heavily cratered moons in the Solar System, its surface is thought to be among the oldest. It has an extremely thin atmosphere, however conditions for life may exist in subsurface oceans.
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Missions There have been nine NASA-led missions to Jupiter: Pioneer 10&11, Voyager 1&2, Galileo, Ulysses, the Cassini-Huygens probe (with ESA and ASI), New Horizons, and Juno. Only Galileo and Juno were orbital missions, while the rest were flybys. The Galileo mission entered orbit in 1995, conducting multiple flybys of the Galilean Moons as well as making many observations of the planet, including the impact of comet Shoemaker-Levy 9. The Juno spacecraft (shown) arrived in 2016 and is budgeted until 2025. It is intended to study Jupiter's composition, its atmosphere, magnetosphere, mass distribution and gravity.