Jupiter

Jupiter is the fifth largest planet from the Sun within the Solar System. Its diameter is 88,846 miles (142,984 kilometers), more than 11 times that of Earth, and about one-tenth that of the sun. It would take more than 1,000 Earths to fill up the volume of the giant planet. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune.

When viewed from Earth, Jupiter can reach an apparent magnitude of −2.95, making it on average the third-brightest object in the night sky after the Moon and Venus.  Astronomers have studied Jupiter with telescopes based on Earth and aboard artificial satellites in orbit around Earth. Also witnessing a spectacular event in July 1994, when 21 fragments of a comet named Shoemaker-Levy 9 crashed into Jupiter’s atmosphere. The impacts caused tremendous explosions, some scattering debris over areas larger than the diameter of Earth.

Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. The most recent visitor was New Horizons spacecraft in February 2007, and future targets for further exploration of the Jovian system include the possible ice-covered liquid ocean on the moon Europa.

Composition

Jupiter is a giant ball of gas and liquid with little, if any, solid surface. Instead, the planet’s atmosphere is composed of about 86 percent hydrogen, 14 percent helium These dense red, brown, yellow, and white clouds are arranged in light-colored areas called zones and darker regions called belts that circle the planet parallel to the equator. Abundances of heavier inert gases in Jupiter’s atmosphere are about two to three times that of the Sun. Below the roughly 1000-kilometer-thick atmosphere, a layer of liquid hydrogen extends to a depth of 20,000 kilometers. Even deeper, it is believed that there is a layer of liquid metallic hydrogen at a pressure of 3 million bars. The planet core is believed to comprise iron-nickel alloy, rock, etc., at a temperature estimated to exceed 20,000C.

Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other gas giants Uranus and Neptune have relatively much less hydrogen and helium.

Orbit and rotation

Jupiter travels around the sun in a slightly elliptical (oval-shaped) orbit. The planet completes one orbit in 4,333 Earth days, or almost 12 Earth years.

Jupiter rotates faster than any other planet. It takes 9 hours 56 minutes to spin around once on its axis, compared with 24 hours for Earth. Scientists cannot measure the rotation of the interior of the giant planet directly, so they have calculated the speed from indirect measurements. They first calculated the speed using an average of the speeds of the visible clouds that move with interior currents, except for a more rapid zone near the equator.

Jupiter also sends out radio waves strong enough to be picked up by radio telescopes on Earth. Scientists now measure these waves to calculate Jupiter’s rotational speed. The strength of the waves varies under the influence of Jupiter’s magnetic field in a pattern that repeats every 9 hours 56 minutes. Because the magnetic field originates in Jupiter’s core, this variation shows how fast the plant’s interior spins.

Jupiter’s rapid rotation makes it bulge at the equator and flatten at the poles. The planet’s diameter is about 7 percent larger at the equator than at the poles.

Mass and density

Jupiter may have a core made up of heavy elements. The core may be of about the same chemical composition as Earth, but 20 or 30 times more massive. The force of gravity at the surface of Jupiter is up to 2.4 times stronger than on Earth. Thus, an object that weighs 100 pounds on Earth would weigh as much as 240 pounds on Jupiter.

The atmosphere of Jupiter is composed of about 86% hydrogen, 14% helium, and tiny amounts of methane, ammonia, phosphine, water, acetylene, ethane, germanium, and carbon monoxide. These chemicals have formed colorful layers of clouds at different heights. The highest white clouds in the zones are made of crystals of frozen ammonia. Darker, lower clouds of other chemicals occur in the belts. At the lowest levels that can be seen, there are blue clouds. Astronomers had expected to detect water clouds about 44 miles (70 kilometers) below the ammonia clouds. However, none have been discovered at any level.

Jupiter’s most outstanding surface feature is the Great Red Spot, a swirling mass of gas resembling a hurricane. The widest diameter of the spot is about three times that of Earth. The edge of the Great Red Spot circulates at a speed of about 225 miles (360 kilometers) per hour. The spot remains at the same distance from the equator but drifts slowly east and west.

Temperature

The temperature at the top of Jupiter’s clouds is about -230 degrees F (-145 degrees C). Measurements made by ground instruments and spacecraft show that Jupiter’s temperature increases with depth below the clouds. Scientists have discovered no evidence for life on Jupiter. Near the planet’s center, the temperature is much higher. The core temperature may be about 43,000 degrees F (24,000 degrees C) — hotter than the surface of the sun.