Solar System: Outer Planets - Jupiter

Giant of the Solar System

Jupiter, the fifth planet from the Sun, is the largest planet in our solar system—bigger than all of the other planets combined! Unlike the inner planets which are terrestrial, Jupiter is a Jovian or gas planet. The images we see of Jupiter are not of its surface, but of the tops of clouds in its atmosphere. The gases that make up these clouds are primarily hydrogen and helium, the lightest and most abundant elements in the universe. A ring system was discovered around Jupiter in 1979 by the Voyager spacecraft. To see the rings from Earth, you would need a telescope with an infrared detector.

Courtesy of NASA JPL

Galilean moons: Named for Galileo who first observed them in 1610. The moons proved the Earth was not the center of motion, as had long been believed. The discovery helped Galileo argue in support of Copernicus's heliocentric (Sun-centered) theory of the motions of the planets.

While various spacecraft have photographed and collected data about Jupiter since the 1970’s, our knowledge of what lies under the atmosphere is very indirect. In 1995, the Galileo Probe was dropped into Jupiter’s atmosphere and was crushed after 57 minutes. The probe found intense thunderstorms and winds exceeding 400 mph (644 km/h). Although scientists had known that Jupiter’s bands of clouds were driven by winds (that blow adjacent bands in opposite directions), they were surprised by the speed and turbulence measured by the probe. The turbulence indicates that the winds are driven more from internal heat rather than solar heat (winds on Earth are driven by solar heat). This means that Jupiter radiates more energy into space than it receives from the Sun.

Jupiter is the fourth brightest object in the sky (after the Sun, the Moon, and Venus), and is easily seen with the unaided eye. With a pair of binoculars you can see four points of light lined up very close to Jupiter, these are Jupiter's four largest moons: Io, Europa, Ganymede, and Callisto (known as the Galilean moons). Each of these four moons is bigger than the planet Pluto! To date, over 50 moons have been discovered around Jupiter. A group of astronomers at the University of Hawaii has found 18 new moons in 2003, and they're still looking for more!

In 2004, Jupiter rises at sunset beginning in late February and stays up all night through mid-April, and can be found in the constellation Leo.

With a small telescope you can see Jupiter’s bands, and its most prominent feature, the Great Red Spot, a hurricane-like storm that is the size of two Earths. The Great Red Spot, which was first spied over 300 years ago, rotates counter-clockwise every six days.