Thanks to both Cassini and Huygens, we're now more familiar with Saturn and its complex moon, where temperatures can drop as low as hundreds of degrees below freezing. Huygens remains the only spacecraft we've ever landed on a celestial body in the outer solar system. However, that could change if NASA pushes through with its plan to send a sub to find any sign of life in Titan's methane sea.

Update: This piece incorrectly stated that Huygens was the only spacecraft we've landed "outside the solar system." It should have read "outside the inner solar system." We are very much aware that Saturn and its moons are still part of our solar system and apologize for the confusion!