So, we’ve covered the far distant worlds which might house adequate enough water sources to sustain life, but what about the ones which we’re actually sure about, the ones we’re a little bit closer to? There are a few different, confirmed sources of water within our own solar system. It might not necessarily be water as we know it, but it’s still liquid, and it still has the potential to sustain life in some sense or another.
Probably the least well known sphere on this list, Enceladus is the sixth largest moon of Saturn, with a diameter of about 500km. From a distance, it looks a bit like the wrinkles you find on the underside of your leg when you’ve been sat in the same place for too long. Said wrinkles are actually huge rifts and craters in the moon’s icy surface. Yes, icy. Enceladus is basically a big ball of ice, occasionally permeated by awesome sounding cryovolcanoes which blast water vapour, sodium chloride crystals and chunks of ice out into space. As a result, it actually snows on Enceladus, but the matter which doesn’t come back down drifts out to form part of Saturn’s E ring.
Ganymede is big; it’s 2% larger than Titan, the second largest moon in the solar system, and a full 8% larger than Mercury. It’s largely made up of silicate rock, but there is a lot of evidence of tectonic activity on the surface which could have been caused by tidal heating. It also has a thin atmosphere of oxygen across the surface, including O, O2, and possibly O3 (ozone). Most importantly though, there is evidence to suggest that, like Enceladus, it has a subterranean ocean.
Ceres is a fascinating little sphere. The dwarf planet sits nestled in the asteroid belt which forms a perimeter between Mars and Jupiter. It is, in fact, the largest body residing in the belt, with a 945km diameter, which makes it the 33rd largest body in the solar system. It’s comprised of rock and ice, as many of the other dwarf planets are (their size necessitates it to some extent), and there’s been talk of a past ocean existing there for years, but then in 2014 some new evidence came to light.
You all saw this coming. Mars remains our best option for beginning the process of interplanetary colonisation, which some have argued is our race’s only chance of survival, in the long term. It’s just unfortunate that it’s a big red rocky ball of boring, at least by comparison to Earth. The thing is, though, it wasn’t always thus. Today, there’s ice on the surface and water vapour in the air, but around 3.8 billion years ago, the atmosphere would have allowed for standing water to exist, and what’s more, it probably covered most of the planet.
5 million cubic kilometres of ice have been logged across the surface of the planet, and as such, if the climate shifted to support liquid water again, the entire planet would be coated in around 35 metres of it, on average, and that’s without taking into account the ice trapped beneath the rocky surface. Numerous outflow channels, lakebeds and deltas have been observed, as well as mineral deposits which could only have formed in water. There is even some evidence to suggest that flowing water may still exist in certain areas, welling up from somewhere below.
It might seem like we know a lot about Mars at this stage, but imagine trying to scour the entire surface of Earth with a team of small robots, it would take centuries. Admittedly Mars doesn’t have quite the abundance of features that Earth does, but even at this point it’s fairly self-evident that it once supported some form of life, and likely could again if the need arose.