Ice Giants in Brief

Uranus and Neptune are the least explored planets in our solar system:

• Only Voyager 2 has visited, and no mission has returned since the 1980s
• Uranus is tilted 98 degrees, rolling around the Sun on its side
• Neptune has the fastest winds in the solar system, at 2,100 km/h
• Both likely have diamond rain deep in their interiors
• Their mantles may hold superionic water, a metallic form of ice

Neptune's moon Triton is likely a captured Kuiper Belt object. A flagship mission to the ice giants ranks high on scientists' wish list, since they represent a whole class of planet we barely understand.