What makes an icy moon potentially habitable?

Icy moons are natural satellites in our Solar System that are thought to harbor significant bodies of liquid water beneath their frozen surfaces. Planetary-mass moons like Jupiter's Ganymede, Callisto, and Europa are primary targets for astrobiological study because these subsurface oceans could potentially support extraterrestrial life. Space missions such as the European Space Agency's Jupiter Icy Moons Explorer are designed to investigate these unique worlds and their internal structures.

What we know

• Icy moons such as Ganymede, Callisto, and Europa are targeted for study because they are thought to contain significant bodies of liquid water beneath their frozen outer surfaces. [2]
• Ganymede is composed of approximately equal proportions of silicate rock and water, featuring a fully differentiated body with a liquid metallic core and a potential internal ocean containing more water than all of Earth's oceans combined. [4]
• Planetary-mass moons are large enough that internal partial melting, differentiation, and heating can cause them to become ellipsoidal or spherical in shape, sometimes forming subsurface oceans. [5]
• The European Space Agency's Jupiter Icy Moons Explorer is an interplanetary spacecraft developed to orbit and study Ganymede, Callisto, and Europa. [1, 2]

Still open

• It remains unresolved whether Ganymede possesses an ionosphere associated with its thin oxygen atmosphere.
• The exact cause of the disrupted geology in Ganymede's lighter terrain regions is not fully known, though tectonic activity due to tidal heating is a possibility.

Where to go next

• how it workedHow does the Juice spacecraft plan to study Jupiter's moons?
• how we knowWhat evidence supports the existence of underground oceans on Ganymede?
• the bigger pictureHow do natural satellites form around planets?
• a case in pointWhat makes Ganymede larger than the planet Mercury?
• compared withHow does NASA's Europa Clipper mission compare to Juice?
• an unexpected connectionHow can a moon be larger than a planet yet have less mass?Ganymede is physically larger than the planet Mercury, but its lower density means it possesses less surface gravity and less overall mass.

Sources

• [1]Jupiter Icy Moons Explorer (Wikidata Q63350) · CC0 1.0
• [2]Jupiter Icy Moons Explorer · CC BY-SA 4.0
• [3]Natural satellite · CC BY-SA 4.0
• [4]Ganymede (moon) · CC BY-SA 4.0
• [5]Planetary-mass moon · CC BY-SA 4.0