Cassini found hydrogen erupting from Enceladus
Saturn's tiny moon Enceladus sprays geysers of water from a subsurface ocean. NASA's Cassini spacecraft flew through these plumes and detected molecular hydrogen plus silica, signs that warm water is reacting with rock at the ocean floor. Those same water-rock reactions power chemical-energy-based life at deep-sea hydrothermal vents on Earth, with no sunlight needed.
