You might be surprised to know how many moons are suspected of having oceans underneath their surfaces. Water means life. Therefore, most of these moons have a good chance of containing ecosystems.
Ganymede is incredibly similar to Earth is many respects.
It is the largest moon of Jupiter, which makes it bigger than Pluto and Mercury.
It is the only moon in our solar system that has a magnetic field.
It has an ocean underneath the rocky surface, which could sustain life.
Its atmosphere is considerably thin and contains oxygen.
Gravity on Ganymede is 1.5G.
Ganymede Layers, Artist Illustration
Ganymede is particularly important because it is habitable. The energy from the core heats the ocean underneath the surface, which may lead to life. The heat could also provide a proper environment for a human colony. At the moment, it may sound like science fiction. But in the near future, it may not be.
Callisto, Galileo Spacecraft, NASA
Callisto is the second-largest moon of Jupiter, after Ganymede.
It was discovered by Galileo.
It’s almost the same size as Mercury.
It has an ocean underneath its surface like Ganymede.
It has a very thin carbon dioxide atmosphere.
Callisto may also contain life in its ocean, but the probability is lower than Ganymede’s since the heat that is coming from the core is lower.
Europa’s Surface, False Color- NASA
Europa is the location that is most likely to sustain life in our Solar System.
It is the smallest moon of Jupiter and slightly smaller than our Moon.
It has the smoothest surface of any planet or moon in our Solar System.
It has a thin atmosphere with a considerable amount of oxygen.
In 2012, Hubble Space Telescope detected water plumes on the surface of Europa.
The ocean underneath Europa may have been created by something called Tidal Heat. It is a friction force created inside the moon due to the gravitational changes of Jupiter.
With 200km water plumes and an ocean underneath its surface, Europa is one of the most exciting space objects in our Solar System. It is definitely a future destination for humans’ search for life in space.
Triton was discovered in 1846.
It is the largest moon of Neptune by a huge margin. %99.5 of the mass of all the moons of Neptune belongs to Triton.
It has a cratered, icy surface.
Triton’s surface is so light-colored, it reflects almost all the sunlight. Therefore it is the coldest recorded locations in our Solar System with -235 Celsius.
It is possible that Triton, similar to Europa, may have an ocean underneath its surface due to tidal heating. But more scientific data is required for an exact conclusion.
Titan, True Color, NASA
Titan was discovered in 1655. It is almost the same size as Mercury, making it the second-largest moon in the Solar System.
It most probably has a liquid water ocean mixed with ammonia.
Titan has a tick, mostly nitrogen-methane atmosphere. It is the only moon that has a climate.
Titan’s surface is covered with volcanos that is feeding methane to its surface.
Mimas, Cassini Spacecraft, NASA
Unfortunately, Mimas is a particularly dull moon. It is 200km across and has a solid, rocky surface. It doesn’t have an atmosphere or any kind of action such as geysers.
The thing that is interesting about Mimas, perhaps the only one, is its wobbly orbit. It slightly tilts away or inwards. That is a strong clue for an ocean underneath its surface. Another possible explanation would be an irregularly shaped core, like an American football.
Enceladus, Cassini Spacecraft, NASA
Enceladus was discovered in 1787. It is 500 kilometers across.
Enceladus is a very interesting moon that has geological activity across its surface. We are lucky enough to see it closely in images taken by Cassini spacecraft.
In its fly-by, Cassini discovered water-rich plumes on Enceladus, which provides strong evidence for an ocean underneath.
Honorable Mention: Pluto
Our favorite dwarf planet since 2006 is suspected of having an ocean underneath its surface as well. Ammonia, which is a molecule correlated with life, has been found on Pluto’s surface. There is also compelling evidence that an insulating layer of gas hydrates could be insulating an ocean.