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General History

Jupiter was discovered in 1610 by Galileo, who noticed the four large moons around Jupiter and saw that they were moving around the planet. The discovery of these moons helped show people that the Earth was not the center of our universe, which led to more people supporting Copernicus' heliocentric model of the solar system. The Great Red Spot on Jupiter was discovered by Cassini or Robert Hooke in the 17th century.

Cultural Significance

Jupiter, the Roman counterpart to the Greek’s Zeus, is named after the Roman word “Jove,” the Greek Zeus, who was the King of all the Gods.

Size & Scale

Jupiter’s gasses reflect a lot of the Sun’s light back to Earth, it is a bright planet—the fourth brightest in the solar system. Jupiter is the fifth planet from the sun, which would imply that its orbit around the Sun is longer than that’s of Earth. However, Jupiter travels at 29,000 miles per hour, taking only 11.86 Earth years or 4331 Earth days to complete one orbit. Jupiter also rotates with intense speeds, every ten hours, making seasons on the planet impossible.


Jupiter radiates more energy into space than it receives from the Sun. Because of the extremely hot temperatures of the core, a convection current creates complex motions in the clouds on Jupiter.

If more material were added to Jupiter, it would only increase slightly in size because the gravity would compress it. So, Jupiter is approximately as large as a gas planet is able to be. Jupiter’s gravitational pull is 2.53 times that of Earth. Imagine weighing over twice of what you weigh now. That would be like experiencing Jupiter’s gravity!

Jupiter’s magnetic field extends past the orbit of Saturn! It is so strong that it would be immediately fatal to an unprotected human being.

Jupiter has rings that are smaller and fainter than Saturn’s (Saturns’ rings are about a million times more massive than Jupiters’). They are composed of small grains of rocky material and are very dark. Because of Jupiter’s magnetic field, the contents of the rings are constantly being recycled. The rings contain no ice, unlike Saturn’s. This means that less light will be reflected by those dark particles. The material of those rings are constantly being pulled into Jupiter; however, impact from asteroids on the moons constantly replenish the loss of those particles in the ring.

Physical Features

Jupiter is a gas planet, which means that it does not have a solid surface. However, as you move closer to the center of the planet, the gaseous material gets denser. This has a lot to do with the strong gravity on Jupier, 2.53 times Earth’s.

Jupiter is 90% hydrogen and 10% helium. This composition is very similar to that of the Solar Nebula, which started the solar system.

The interior of Jupiter is hard to determine as solar probes only measure about 93 miles into the surface of Jupiter. However, scientists think that the core of Jupiter is probably a rocky material with a mass 10 to 15 times that of Earth’s.

The majority of the planet is made up of liquid metallic hydrogen. This rare form of hydrogen can only occur at extreme pressures, which is the case on Jupiter. Liquid metallic hydrogen is a conductor and accounts for the magnetic field around Jupiter.

The outer layer is mainly hydrogen and helium, starting in a liquid form and changing to gaseous as the distance increases from the core.

There are three distinct layers of clouds on Jupiter: ammonia ice, ammonium hydrosulfide, and an ice/water mix.

Jupiter has high winds that can be more than 400 mph. The winds are confined to a specific latitude and spin in opposite directions, which makes colored band on the surface of Jupiter. The light colored bands are called zones and the dark ones are called belts. They are visible on Jupiter’s surface. The current theory for those winds is that Jupiter produces a massive amount of heat from its core, causing the winds to be so rapid. This is similar to hot air causing those powerful hurricanes to form on Earth’s surface. The more hot air present, the stronger the storm.

The colors of Jupiter’s clouds correlate with the altitudes. Lowest to Greatest: Blue, brown, white, red. The colors of Jupiter’s atmosphere are created when different chemicals reflect the Sun’s light. Most of Jupiter is hydrogen and helium, but the top of its clouds are composed of ammonia crystals, which explains the blue, with trace amounts of water ice and droplets, and possibly ammonium hydrosulfide. Powerful storms on Jupiter are created by the planet’s convection. That allows the storms to bring material, such as phosphorus, sulfur and hydrocarbons, from closer to the planet’s core to the tops of the clouds, causing the white, brown, and red spots that we see dotting the Jovian atmosphere.

The Great Red Spot is a large oval on Jupiter’s surface that is large enough to hold two Earths! It is a high-pressure area where the cloud tops are higher and colder than the areas around it.

Orbiting Bodies

Jupiter has four large moons. Io, Europa, Ganymede, and Callisto. They are known as Galilean moons. Io, Europa, and Ganymede orbit together and evolve their orbits together. Callisto will be locked into this orbit as well after a few hundred million years.

Jupiter has 63 known satellites. Fifty of those moons are named, but 13 still have yet to receive one.

The moons are named after other figures in Zeus’ life. The four largest moons are named after Zeus’s lovers.

Io has volcanism that is constant. Europa and Ganymede (Two of Jupiter’s moons) have a gravitational pull that causes Io to bulge in and out like the tides do on Earth. This creates a massive amount of heat under the surface, and the heat searches for anyway to escape. When it does escape, it spews out as magma on the moon’s surface! The surface of Io is constantly renewing itself, because of this process!


  • (1973) Pioneer 10 was the first spacecraft to fly close to Jupiter. It transmitted data on the magnetic fields and energetic radiation. It sent back images of Jupiter and measurements.
  • (1974) Pioneer 11 was the second spacecraft to fly by Jupiter. It flew three times closer to Jupiter than Pioneer 10 did. It showed Jupiter’s polar regions.
  • (1979) Voyagers 1 and 2. Voyager 2 explored the moons of Jupiter. They created a time-lapse video of how Jupiter changed from Voyager 1 to Voyager 2.
  • Launched 1989, Probe decent 1995 Impact:(2003) Galileo had 10 scientific instruments and a probe that learned a lot about Jupiter. It found the radiation above the clouds, helium concentration, Io’s(the third largest moon of Jupiter) volcanism, evidence for liquid water oceans under Europa’s(The fourth largest moon of Jupiter) surface. The probe measured the temperature, pressure, chemical composition, cloud characteristics, sunlight, and lightning. The probe went 124 miles into Jupiter’s atmosphere before being destroyed. The probe was sent into Jupiter by its controllers in order to prevent contaminating possible bacterial ecosystems on some of the moons. The probe was more than likely crushed by Jupiter’s immense gravity.
  • (1992) Ulysses passed by Jupiter. This was done to take advantage of Jupiter’s gravitational pull, allowing the probe to be in a final orbit around the sun to see its north and south poles.

Purdue Connections

Michael J. McCulley (Captain, USN, Ret.)

BS '70, M.S. '70, Metallurgical Engineering, Purdue University

He was the pilot aboard STS-34, Atlantis, October 1989, where the crew successfully deployed the Galileo spacecraft on its six-year journey to Jupiter, where it began its two-year exploration of the planet and its moons. During this mission, the crew also operated the Shuttle Solar Backscatter Ultraviolet Instrument (SSBUV) to map atmospheric ozone. He has logged a total of 119 hours and 41 minutes in space.