Europa and Enceladus are ice-shelled moons hiding liquid-water oceans beneath their frozen surfaces. Tidal flexing from their giant parent planets kneads their rocky interiors, and where that heat escapes at the seafloor it can drive hydrothermal vents — exactly the kind of chemistry-rich, energy-rich environments where life first appeared on Earth. This cutaway shows the rocky core, the ocean, and the ice shell in cross-section, with a vent plume rising from the seafloor and a cryobot mission descending to sample it.
NASA's Cassini spacecraft flew directly through Enceladus's south-polar plumes and detected water vapour, salts, silica nanograins, and organic molecules — strong evidence for active hydrothermal chemistry on its seafloor right now, without ever having to drill through the ice.
A cutaway 3D model of an icy moon's ice shell, subsurface ocean and seafloor hydrothermal vent — tune vent heat output and ice thickness, then launch a cryobot to melt through the ice and dive to the vent.
The layered structure of an ice-shelled ocean world — rocky core, liquid ocean, ice shell — and how a seafloor vent's heat output and the ice shell's thickness together shape how promising, and how reachable, a target is for astrobiology.
Switch between Europa and Enceladus, drag the heat and ice-thickness sliders to see the plume and biosignature score respond, then click "Launch cryobot" to watch a probe melt through the ice and travel to the vent.
Enceladus's ice shell is thin enough near its south pole that its ocean vents plumes directly into space — Cassini flew through them and detected the chemical fingerprints of hydrothermal activity without landing at all.