It’s a question which besets many science fiction writers! Now, in the former days of the 20th century, when not nearly so much was known about other star systems, writers were free and easy with their destinations. C.S. Lewis, who anyway had other motivations in his writing than script scientific accuracy, cheerfully placed parts of his science fiction trilogy on Mars and Venus. E.E. (Doc) Smith had alien habitations all over the solar system, with a wild array of biological adaptations to high gravity, strange atmospheres, or whatever. And when writers got their characters out of the solar system into the galaxy at large, the diversity just kept on growing (except for those authors like Asimov, who for various reasons carefully avoided alien life altogether).

But these days we have a vast amount of data to steer our fiction. In some cases this means that environments get excluded – it would be a brave author indeed who would place a novel like Perelandra on the surface of Venus these days (unless they have a back-story of extensive terraforming). On the other hand, new opportunities for life in previously unconsidered places have emerged – like high up in the Venusian atmosphere, or in liquid oceans underneath the ice coatings of various outer system moons. These are not likely to be, as they say, life as we know it…

On a wider scale, we have a good idea what to look for as regards planets that might support life. Most thinking on the subject supposes that liquid water would be necessary – it’s just too useful a chemical in all kinds of ways to see how it wouldn’t participate in life’s chemistry. So we can plot the Goldilocks Zone for any given star (too close in, and water boils and evaporates… too far out, and it freezes)… but we know from our own solar system that this does not cover all the bases. Close-in planets are probably tidally locked to their sun, and so have a cooler side. Far-out planets may well have orbiting moons with sub-surface water, kept from freezing by a variety of factors.

Back in the day, people used to look for stars relatively similar to our own sun, on the grounds that we kind of knew what we were looking for. But these days, following the extraordinary success of planet-hunting space missions like Kepler (soon to be followed by TESS), we know that many planets circle dim red dwarf stars. For sure, the heat output is much less, but that just means that the Goldilocks Zone huddles close in. And red dwarf stars are immensely long-lived, which gives life time to develop. On the other hand, many red dwarfs also go through erratic flare cycles, potentially blasting their associated planets with X-rays. But for my money, the first place we may find life elsewhere is likely to be circling a red dwarf.

So from the writer’s point of view, it’s a great time to be postulating life elsewhere, but also a rapidly-changing one. New data is pouring in, and new ways of analysing and comprehending that data. It all adds up to a wealth of new ideas and imaginative leads…