Uranus

Uranus is the second outer-most planet in the solar system. Characteristics:

• 14.5 Earth masses.
• 4 Earth radii.
• 17 hours - solar day.
• 84 years - orbital period.
• 19 AU - orbital radius (semi-major axis).
• 0.04717 - orbital eccentricity.
• 97.77° - axial tilt (slightly retrograde, around 90° from typical).

Among the solar system planets, it is easily most similar to Neptune, with a slightly larger radius and a slightly smaller mass. Its 27 known moons include Miranda, Ariel, Umbriel, Titania and Oberon. It has a ring system, and within the solar system, only Saturn's is more extensive and was discovered earlier. Reaching Uranus by spacecraft is a challenge (suitable launch windows are very infrequent) and the only mission to fly near it was Voyager 2 in 1986. A plan for a future (2030s) mission is the Uranus Orbiter and Probe.