Jupiter

Introduction

Jupiter is the fifth and largest planet in our solar system. This gas giant has a thick atmosphere, 39 known moons, and a dark, barely-visible ring. Its most prominent features are bands across its latitudes and a great red spot (which is a storm).

Jupiter is composed mostly of gas. This enormous planet radiates twice as much heat as it absorbs from the Sun. It also has an extremely strong magnetic field. It is slightly flattened at its poles and it bulges out a bit at the equator.

Size

Jupiter’s diameter is 88,700 miles (142,800 km). This is a little more than 11 times the diameter of the Earth. Jupiter is so big that all the other planets in our Solar System could fit inside Jupiter (if it were hollow).

Mass and gravity

Jupiter’s mass is about 1.9 x 10²⁷ kg. Although this is 318 times the mass of the Earth, the gravity on Jupiter is only 254% of the gravity on Earth. This is because Jupiter is such a large planet (and the gravitational force a planet exerts upon an object at the planet’s surface is proportional to its mass and to the inverse of its radius squared).

A 100-pound person would weigh 254 pounds on Jupiter.

Length of a day and year

It takes Jupiter 9.8 Earth hours to revolve around its axis (this is a Jovian day). It takes 11.86 Earth years for Jupiter to orbit the sun once (this is a Jovian year).

Jupiter is made up of gases and liquids, so as it rotates, its parts do not rotate at exactly the same velocity. It rotates very rapidly, and this spinning action gives Jupiter a large equatorial bulge; it looks like a slightly-flattened sphere (it is oblate).

Orbit

Jupiter is 5.2 times farther from than the Sun than the Earth. On average, it is 480,000,000 miles (778,330,000 km) from the sun.

At aphelion (the place in its orbit where Jupiter is farthest from the Sun), Jupiter is 815,700,000 km from the Sun. At perihelion (the place in its orbit where Jupiter is closest to the Sun), Jupiter is 749,900,000 km from the Sun.

Jupiter has no seasons. Seasons are caused by a tilted axis, and Jupiter’s axis is only tilted 3 degrees (not enough to cause seasons).

Moons

Jupiter has four large moons and dozens of smaller ones (there are 39 moons known so far). More moons are being found all the time.

Galileo first discovered the four largest moons of Jupiter, Io (which is volcanically active), Europa, Ganymede (the largest of Jupiter’s moons, pictured at the left), and Callisto in 1610; these moons are known as the Galilean moons. Ganymede is the largest moon in the Solar System.

For more information on Jupiter’s moons, click here.

Rings

Jupiter has faint, dark rings composed of tiny rock fragments and dust. These rings were discovered by NASA’s Voyager 1 in 1980. The rings were investigated further when Voyager 2 flew by Jupiter. The rings have an albedo of 0.05; they do not reflect very much of the sunlight that they receive.

For more information on Jupiter’s rings, click here.

Temperature

The cloud-tops average 120 K = -153°C = -244°F.

Discovery

Jupiter has been well-known since ancient times. It is the third-brightest object in the night sky (after the moon and Venus).

Comet SL-99 hits Jupiter

Shoemaker-Levy 9 (SL-9) was a short-period comet that was discovered by Eugene and Carolyn Shoemaker and David H. Levy. As the comet passed close by Jupiter, Jupiter’s gravitational forces broke the comet apart . Fragments of the comet collided with Jupiter for six days during July, 1994, causing huge fireballs in Jupiter’s atmosphere that were visible from Earth.

Spacecraft visits

Jupiter was first visited by NASA’s Pioneer 10, which flew by Jupiter in 1973. Later fly-by visits included: Pioneer 11, Voyager 1, Voyager 2, Ulysses, and Galileo.

Name and symbol

Jupiter was named after the Roman primary god, Jupiter.

Activities and links

• Jupiter coloring page
• Find It!, a quiz on Jupiter.
• Jupiter Cloze: A fill-in-the-blanks activity on Jupiter.
• Interactive Jupiter Puzzle
• How to write a report on a planet - plus a rubric.