Space Facts

Planet Uranus

A Smaller Gas Giant

The planet Uranus as seen from Voyager 2 on January 10, 1986, from 18 million kilometers (11 million miles). The larger view is true color. Inset is a false color view of the same scene, using ultraviolet, violet and orange bands respectively as blue, green and red. The overall blue is from methane while the false color brown is from acetylene. Image Credit: NASA/JPL

Uranus is planet number seven of the Solar system. The planet is named for the Greek titan of the sky, (associated with the Roman god of sky, Caelus, father of Saturn).

The planet Uranus is the third gas giant in sequence from the sun (after Jupiter and Saturn). Uranus is 51,118 kilometers in diameter making it slightly larger than Neptune. The planet is a veritable odd-ball in the Solar family because it is inclined by an angle of 97.53 degrees. Essentially, Uranus is laying on its side. Nearly half of its year, one pole enjoys what little sunlight the planet receives; and the other half of the year, the other pole receieves sunlight.

Uranus rotates once every 17 hours and 9 minutes and takes 84.01 Earth years to revolve about the sun. It is about 14.54 times the mass of Earth, most of which is gaseous. The atmosphere is composed of hydrogen (of course), helium and a high proportion of "ices" such as methane, ammonia and water. Both Uranus and Neptune are, for this reason, sometimes called "ice giants." At 2.869 billion kilometers (1.783 billion miles) from the sun, Uranus is -224 °C cold (49 °K) — not much warmer than Pluto (43 °K). The rocky core of Uranus is estimated to be about 150% the diameter of Earth. That would leave the gaseous and icy layers to be thicker than the diameter of Earth.

Like Jupiter and Saturn, Uranus has a system of rings and a large retinue of moons — five large moons and nearly two dozen smaller ones. The main moons are (with their diameters in kilometers, miles) Miranda (472 km, 293 m), Ariel (1158 km, 720 m), Umbriel (1169 km, 727 m), Titania (1578 km, 981 m) and Oberon (1523 km, 947 m).

Size comparison of gas giant planets with Earth (left to right): Earth, Jupiter, Saturn, Uranus, and Neptune.		The last four planets of the Solar system are called "gas giants" because the bulk of each such planet is gaseous. The other type of planet is called "terrestrials" because of their rough similarity to Earth. The Solar System Facts table gives more comparisons between the planets.

Could Uranus Ever Sustain Life?

With the coldest atmosphere in the Solar system, Uranus could hardly sustain life as we know it. The massive tilt of the planet and the extremely thick atmosphere both work against Uranus sustaining Earthly life. The tilt means that half the planet faces the sun for 42 Earth years, then spends the other 42 of the Uranian year in frigid darkness. The thickness of the atmosphere means Uranus air pressure, if it had a solid surface, would be deadly.

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