Cassini-Huygens at Saturn (NASA/ESA, 2004–2017)

Cassini-Huygens delivered over 450,000 images and 635 GB of data during its 13-year Saturn mission, but its most transformative discovery was the geysers on Enceladus. In 2005, the spacecraft observed plumes of water ice, salt, and organic molecules erupting from the moon’s south pole—evidence of a global subsurface ocean in contact with a rocky seafloor, creating conditions more favorable for life than any other location in the solar system. This finding, which exceeds the biological potential of Mars, was followed by the Huygens probe’s landing on Titan, the first ever in the outer solar system. Cassini’s revelations have reshaped the search for extraterrestrial life, making icy moons a top priority for future exploration.