NASA’s Cassini spacecraft swoops down to make its 100th flyby of Saturn’s moon Titan.

Ten years ago, humanity knew Titan as a fuzzy orange ball about the size of Mercury. Scientists knew it had a nitrogen atmosphere — the only known world with a thick nitrogen atmosphere besides Earth. But what might lie beneath the hazy air was still just a guess.

On March 6, NASA’s Cassini spacecraft swooped down within 1,500 kilometers of Titan to conduct its 100th flyby of the Saturn moon. Each flyby gives humanity a little more knowledge of Titan and its striking similarities to Earth. Even with its cold surface temperatures of minus 179 degrees Celsius (94 kelvins), Titan is like early Earth in a deep freeze.

Since its 2004 arrival at Saturn, Cassini’s radar instrument has identified remarkable surface features on Titan. The features include lakes and seas made of liquid methane and ethane, which are larger than North America’s Great Lakes, and an extensive layer of liquid water deep beneath the surface. Organic molecules abound in Titan’s atmosphere, formed from the breakup of methane by solar radiation.

Shown above is an artist’s conception of a possible model of Titan’s internal structure.

For more on Titan and Cassini, see the NASA press release.