Earlier today, I posted a poll about where life could exist in the solar system. It seems Mars is quite popular. You can still vote in the poll with your answer. But now, I’ll examine each of the worlds and you can see what I think. Keep in mind that I am an expert. Okay, not an expert, but I do have a degree in astronomy. So it is my area of expertise.
Mars is the best-known planet in the solar system other than Earth. We’ve had many probes go there, rovers explore the surface, and it’s one of the easiest to observe from Earth. It’s a cold, dry world with most of its water locked up in the polar ice caps or underground. There has been evidence of sudden outflows of liquid water, though it couldn’t last long on the surface, but maybe there are aquifers. There are underground glaciers. There’s a chance there is life in the aquifers. Maybe there isn’t life now, but there may have been early in Mars’ history, as it’s recently been estimated that an ocean covered 20% of the surface. We know it had a wet history. Chances of life now? Quite low. But much better in the past.
We’ve only been studying Ceres up close for a very short time. We don’t know much about it, but there’s a guess about the internal structure. There’s likely a rocky core with a thick ice mantle. That’s covered by a thin dusty crust. Liquid water could exist if it’s warm enough inside. Water vapour was seen in January 2014, so it’s possible there is some sort of icy volcanism or geysers. What we’ve seen of the surface so far shows that it’s rather dark, but a couple bright spots could be ice. Chances of life now? Probably quite low.
This icy moon of Jupiter has been of particular interest for a very long time. It’s almost completely smooth, covered with water ice, and it shows evidence of an active surface, similar to the Arctic polar ice cap of Earth. Thanks to tidal forces exerted on it by Jupiter and other moons of Jupiter, it’s kept warm. That means there’s most likely a vast liquid water ocean under its icy crust. It’s also very likely that there’s underwater volcanism, similar to what we find on the floor of the Earth’s oceans. Those hydrothermal vents are teeming with life, and may give Europa a wonderful chance of supporting simple life, or even some more complex marine life. Because of the thick icy crust, it’s difficult to see what’s beneath. NASA’s recently had a proposal to explore Europa approved, so we could have this chance soon. Chances of life now? Not unlikely, but there’s a decent chance.
The second largest moon in the solar system also happens to be the only moon in the solar system to support a significant atmosphere. In fact, it’s more dense than the Earth’s. The surface of Titan is water ice with liquid hydrocarbon lakes and rivers. It rains and snows ethane and methane. While Earth has a water cycle, Titan has a hydrocarbon cycle. Titan even has cryovolcanoes that may be active. The composition of the atmosphere is said to be similar to early Earth’s, which makes a lot of people excited. However, Titan is extremely cold. There’s also likely a subsurface liquid water ocean, so it could be similar to Europa in that aspect. But on the surface, it’s unlikely we’ll find any life similar to what’s on Earth. Chances of life now? Probably low, but if there is any, it’s probably unrecognisable.
This small moon of Saturn has made planetary scientists very excited. It may be small, but it’s active. It has liquid water under the surface. We know this almost for certain, because it has hundreds of cryovolcanoes in the south polar region spraying out water vapour and other substances such as salt (NaCl). It could have a large salty underground ocean. Organic compounds have also been detected, which makes it an even better candidate for life. Chances of life now? There’s a decent chance, quite similar to Europa.
So, which places have the best chances of life now? I think Europa is number one, though Enceladus may have a good chance, as well as Titan. All three likely have subsurface liquid water oceans. In the past, Mars could very well have had life. We just need to find the fossils if it did. However, in all cases, it’s quite possible that life is single cellular, though Europa’s got a remote chance of multicellular life.
So, with this said, what do you think now? Where do you think life could be hiding? Or do you disagree with me? Let me know in the comments.