Europa Europa is the fourth largest moon of Jupiter and a satellite that boasts hardly any volcanic peaks higher or deeper than a few thousand feet. This indicates that Europa’s surface is quite geologically young and possibly floats on a liquid layer beneath.
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Tidal forces from Jupiter’s gravitational interaction generate enough heat to maintain a liquid interior ocean. However, due to its distance from the Sun, the surface remains frozen.
Europa also possesses a very thin oxygen atmosphere, created when radiation breaks apart water molecules on the icy surface.
A study published in the journal Astrobiology in 2007 estimated that the oxygen level in Europa’s ocean might be comparable to the deep oceans of Earth, further supporting the moon’s potential for hosting life.
Ganymede
Ganymede, the largest moon of Jupiter, is more than 8% larger than Mercury, but only about half its mass. This low mass suggests that Ganymede is composed of rock and water.
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In the 1990s, the Galileo spacecraft discovered that Ganymede has its own magnetic field, implying a hot, molten iron core. This internal heat would melt the ice and create an immense subsurface ocean.
Callisto
Callisto, the second largest moon of Jupiter, is nearly as large as Mercury but only one-third its mass, indicating it contains about 50% water. A peculiar aspect of Callisto is its surface being entirely covered with impact craters.
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Today, Callisto is geologically dead. A study published in a journal showed that the ice never completely melted during Callisto’s formation process.
However, it’s known that Callisto has a subsurface liquid ocean.
Pluto
Pluto is too small to generate enough internal heat to maintain a molten core. Radioactive decay beneath its surface provides only 2% of the radiative energy emitted outward. However, this is sufficient to melt lighter elements and enable heavier silicate minerals to sink.
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According to NASA, Pluto’s surface is frigid, covered with solid nitrogen, methane, and carbon monoxide.
Furthermore, research conducted at Purdue University indicates that water within Pluto behaves similarly to molten magma beneath Earth’s crust.
Ceres
Ceres is the largest object in the asteroid belt and the only dwarf planet in the Solar System. Initially, it formed as a mix of rock and about 10% ice.
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During its early formation, the heat generated from the decay of heavier elements melted the ice, causing most of the rock to sink into the core.
Over billions of years, convection currents carried heat away from the core, allowing the interior to almost freeze back into solid form. However, Ceres still appears to have some subsurface liquid water.
The Herschel space observatory has observed water vapor escaping into space from Ceres at a rate of 13.2 pounds per second. The total water content in Ceres’ icy crust is greater than all the freshwater on Earth.