Eight other worlds in our solar system might have life beyond Earth
Ethan Siegel

We aren’t going to be haring off to other star systems any time soon, so yeah, let’s look more locally.

Ethan didn’t mention Saturn itself, but maybe he should have. Like Venus, there is an atmospheric depth on Saturn where temperatures and pressures are downright Earth-like. In fact a very respected physicist, Robert Forward, wrote a speculative science fiction book in 1997 suggesting airborne life might exist on Saturn and sent his fictional characters to go interact with it. It’s a fun read.

Ceres is a planetoid in the asteroid belt which may have a liquid ocean far beneath its surface. It’s between Mars and Jupiter in its orbit, and easier to reach than either (since Mars has a steeper gravity well to overcome, and Jupiter’s moons are farther away). If it does have liquid water, we should presume it also has an energy source — perhaps radioactive decay at its core — to keep the water from freezing solid.

It’s even possible that the solar system’s comets might harbor life, and could have been the vehicles by which microbes first got to the Earth (after it had cooled down somewhat). Visits to comets might also prove fruitful.

Venus, Titan and Pluto will be tough nuts to crack. All of space beyond Earth is hostile to human survival, but those three are especially difficult due to nasty temperature extremes (and in the case of Venus, a corrosive atmosphere). It’s even hard to design robotic explorers that can survive in those three places. We’ll spend money more wisely by investigating the liquid water possibilities and by rendezvousing with a comet or two. Penetrating into Venus’ and Saturn’s atmospheres might be interesting as well, but there are more obvious places to look for life first. Titan and Pluto are just about the last places to look, not because life is impossible in those places (we don’t know if it is), but because it’ll be much harder to engineer survivable missions for those destinations.

The first place to look is probably Enceladus. A robotic probe could collect water sprayed into orbit from its geysers and analyze it without our having to worry about landing a craft on the surface, which is more challenging (and expensive). I’d put a comet rendezvous near the top of my wish list, too. Europa might be the most probable to harbor life, of the various candidate destinations we might explore, but it won’t be simple or easy to get down through Europa’s ice crust to search for it. Ditto with Ceres. We can get a probe to Ceres more easily than just about anywhere else, but once there, its crust is a formidable obstacle to any investigation of water-based life.

We know enough to have lots of questions and to stimulate our curiosity. Exploring our system for signs of life won’t be fast or easy, but it sure will be fun — a lot more fun than orbiting endlessly on the ISS, where it’s absolutely certain that the only life present is from Earth.

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