Are There Planets Better at Supporting Life Than Earth?

A new study may have found exoplanets that are warmer and waterier than our own.

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The potentially habitable exoplanets we currently know of (PHL @ Arecibo via America Space)

There is, in this crazy world, one thing we know for sure: Our world is the world. Our planet is the planet -- for creating life, for supporting life, for letting us humans and our fellow species become what we are. And so, as we take our first tentative steps from a warm, watery Earth out into the universe, we set our sights toward the worlds that look like the one we know -- toward planets that are, in their way, "Earth-like." 

But: What if there are planets that are better at being Earth-like than Earth itself? What if there are worlds that are more homey than home? What if other planets are better at supporting life than our own?

It's a possibility, actually, according to new work coming out of Ohio State -- and just a little bit of cosmic conjecture. A team of astronomers and geologists at the university, using data gathered by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory in Chile, made a study of eight stars that are "solar twins" to our sun -- similar in factors like size, age, and composition -- and measured the amounts of radioactive elements those stars contain. Combining those analyses with theories about the conditions that made Earth hospitable to life, the team has made an exciting, if preliminary, finding: that the terrestrial planets orbiting those stars could be hotter and more dynamic than Earth. Which might make them, according to the theory, more hospitable to life than Earth.

What the team was looking for, in particular, were elements like thorium and uranium, which along with potassium, warm Earth's interior. This heat affects its plate tectonics and, according to the scientists, the way it retains its water. Though the functions of that heat-to-plate-to-liquid interaction aren't fully understood -- it's "one of the great mysteries in the geosciences," the study's advisor, Wendy Panero, put it -- scientists have speculated that the forces of heat convection in the mantle, the ones that move Earth's crust, have some kind of role in regulating the amount of water in the oceans. "It seems that if a planet is to retain an ocean over geologic timescales, it needs some kind of crust 'recycling system,' and for us that's mantle convection," Unterborn said.

Which means, in turn, that plate tectonics could also be a key indicator of a planet's hospitality to life. Particularly for microbial life -- since microbial life on Earth, the study's authors point out, benefits from subsurface heat. (Take the single-celled microbe archaea, some of which live not off the energy of the sun, but rather off the heat rising from inside the Earth.) And that indicator, the team reasoned, can be approximated by analyzing a given exoplanet's sun: the more thorium in the star, say, the more likely a terrestrial planet formed around that star would be to support life.  Since it would stand to reason that the planets that orbit around those suns contain more thorium, as well, that would suggest that the interiors of those exoplanets are warmer than ours -- and also that those planets are more geologically active than Earth. And that would mean that they are more likely than Earth to retain the liquid water that supports life. 

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Megan Garber is a staff writer at The Atlantic.

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