Extraterrestrial Life

Eyeball Planets May Be Our Best Bet for Finding Alien Life

There's only one place in the entire universe that we know for sure supports life, and you're standing on it. We haven't been looking for long, though, and our ability to scope out other planets is still pretty limited. According to the Drake Equation, however, there's a good chance that we're not completely alone.

The problem is that we've been looking for solar systems like our own, and stars like our sun are not especially common. Planets like our planet orbiting them are even rarer. But maybe we shouldn't be looking for Earth-like planets. According to Laboratoire d'Astrophysique de Bordeaux astronomer Sean Raymond, we should be looking for eyeball planets instead.

Artist's impression of the exoplanet TRAPPIST-1f, located in the Aquarius system of TRAPPIST-1. Originally created for NASA as part of their announcement of discoveries in the TRAPPIST-1 system on 22 February 2017. According to NASA, both TRAPPIST-1e and TRAPPIST-1f are depicted as "covered in water, but with progressively larger ice caps on the night side."

An Eye in the Sky

Our sun is a yellow dwarf, but the most common — and oldest — type of star in the galaxy is a red dwarf. They're everywhere, and that makes them pretty easy to find. Since they're also relatively dim, their habitable zone (the zone a planet can orbit around it and still support life) is smaller than that of stars like ours. But that's good news, too, since the closer a planet is to a star, the easier it is for us to spot it here on Earth.

But a close orbit also means that a planet is likely to be tidally locked, meaning that one side of the planet always faces the sun (just like how the same side of the moon is always facing the Earth). A planet tidally locked to its sun wouldn't have a day-night cycle, so one half of the planet would be encased in ice and the other would bake under constant sunlight. Not exactly a hospitable environment — or is it?

A planet like that would look a lot like an eyeball. Think of the hot spot facing the sun as the pupil. But that pupil would have a surrounding iris as well — a strip of land with a more temperate climate, where liquid water would be able to flow. And it would flow, since melting ice from the frozen half would trickle into huge rivers flowing towards the desert half. Once it reached that blazing region, the water would evaporate, precipitate, and begin all over again.

The result? Any residents of that ring of life would be living in perpetual twilight, with a never-setting sun. Still, they'd certainly be living. Since these planets are so much more plentiful and so much easier to spot, we'll almost certainly find our celestial neighbors there before we find them anywhere else.

The Search Is On

So how many of these "eyeball planets" are there? Probably a lot, and they're going to come in several different flavors. The kind we've been discussing so far have all been tidally locked, but there are other possible formations. Depending on how swiftly the planet rotates, the landscape of such a planet might form a striped pattern or a double-eyeball pattern where both the western and eastern hemispheres have their own hotspots.

What those spots are like might vary too. Instead of a barren desert where it's too hot for water to stay in liquid form, the planet could be so far out in its orbit that it's cool enough for oceans — and in that case, there would be just one large, warm ocean on the side facing the sun. Whether we find aliens there or not, we should be giving serious consideration to these types of planets when it comes to humanity's eventual interstellar destination.

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Learn more about the search for extraterrestrial life in "Exoplanets: Hidden Worlds and the Quest for Extraterrestrial Life" by Donald Goldsmith. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Reuben Westmaas June 23, 2017

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