Uranus

The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel, although he originally thought it was either a comet or a star. It was two years later that the object was universally accepted as a new planet, in part because of observations by astronomer Johann Bode.

Size and Distance

With a radius of 15,759.2 miles (25,362 kilometers), Uranus is 4 times wider than Earth

Orbit and Rotation

Uranus makes a complete orbit around the Sun in about 84 Earth years (30,687 Earth days).

• Its equator is nearly at a right angle to its orbit, with a tilt of 97.77 degrees-possibly the result of a collision with an Earth-sized object long ago.
• For nearly a quarter of each Uranian year, the Sun shines directly over each pole, plunging the other half of the planet into a 21-year-long dark winter.

Potential for Life

Uranus’ environment is not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to.

• There are 27 known moons orbiting Uranus, most of which are roughly half water ice and half rock.

Formation Uranus took shape when the rest of the solar system formed about 4.5 billion years ago, when gravity pulled swirling gas and dust in to form this ice giant.

Uranus is made of water, methane, and ammonia fluids above a small rocky center, and rotates in the opposite direction as most other planets.

Magnetosphere

Uranus has an irregularly shaped magnetosphere. Magnetic fields are typically in alignment with a planet’s rotation, but Uranus’ magnetic field is tipped over: the magnetic axis is tilted nearly 60 degrees from the planet’s axis of rotation.

• Auroras on Uranus are not in line with the poles like they are on Earth, Jupiter and Saturn.

Structure

Uranus is one of two ice giants in the outer solar system (the other is Neptune). Most (80 percent or more) of the planet’s mass is made up of a hot dense fluid of “icy” materials-water, methane and ammonia-above a small rocky core. Near the core, it heats up to 9,000 degrees Fahrenheit (4,982 degrees Celsius).

• It is the second least dense planet; Saturn is the least dense of all.

Atmosphere

Mostly hydrogen and helium, with a small amount of methane and traces of water and ammonia

• Wind speeds can reach up to 560 miles per hour (900 kilometers per hour) on Uranus
• Winds are retrograde at the equator, blowing in the reverse direction of the planet’s rotation. But closer to the poles, winds shift to a prograde direction, flowing with Uranus’ rotation

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