Neptune

Neptune is the outer-most known planet in the solar system. Characteristics:

• 30 AU - orbital radius.
• 17 Earth masses.
• 3.85 Earth radii.

Among the solar system planets, it is easily most similar to Uranus, with a slightly larger mass and a slightly smaller radius.

Neptune has 14 moons, of which one, Triton, is substantial. Triton has a retrograde orbit, suggesting it is a captured minor planet.

Pluto and Neptune have a 3:2 orbital resonance.

The only mission to fly near Neptune was Voyager 2 in 1989.

The term Neptune is also used for Neptune-like extra-solar planets, specifically significantly larger than Earth and smaller than Jupiter or Saturn, and typically a gas planet, perhaps with other Neptune-like characteristics.