New Study Suggests Alien Life May Be Hiding on Freezing Cold Planets
Radioactivity deep in a planet's crust could keep water liquid and habitable beneath a frozen surface, a recent study suggests.
Water on exoplanets may be more common than we thought, and that could be good news for alien-hunters.
A few recent discoveries hint that the so-called habitable zone (the region where temperatures are just right for liquid water on the surface of a planet) around red dwarfs is actually blasted by stellar winds and strong radiation that strip away planets’ atmospheres and leave only bare, irradiated rock — which seems like discouraging news for alien-hunters.
That’s a question JWST will shed more light on over the next few months, but in the meantime, a recent study offers some hope. Exoplanets farther out from their stars are out of range of the worst of the stellar flare bombardment, but they’re also too cold for liquid water to exist on their surfaces; if these worlds have water at all, it’s probably ice, which isn’t exactly hospitable. But a recent study suggests that you shouldn’t judge an exoplanet by its frozen surface; on average, one planet in every star system could have liquid water hidden underground.
“Our work shows that water can be found in places we had not much considered,” said Rutgers University planetary scientist Lujendra Ojha, who presented his work at a recent geochemistry conference in France. “This significantly increases the chances of finding environments where life could, in theory, develop.” Ojha and his colleagues published their work in the journal Nature Communications.
What Lies Beneath
Radioactive elements are part of the ingredients mixed into most rocky objects in space, and they produce heat as they decay. Earth’s interior gets part of its heat from radioactive potassium, thorium, and uranium decaying deep in the crust and mantle. Radioactive elements even heated rocky objects in the early Solar System enough to melt rock and metal. Ojha and his colleauges modeled how much heat an Earth-sized planet could generate this way, without help from sunlight or tidal friction. It turned out that “many more than we had thought” could actually crank out enough heat to maintain underground lakes or seas.
How many more? Ojha and his colleagues’ model predicts that an average of one planet in every star system could have liquid water hidden beneath an icy exterior.
Beneath the ice of Antarctica lies Lake Vostok, a liquid water lake. Vostok Station, shown here, was built on the surface of the ice so scientists could study the lake from above.
Hidden oceans beneath an icy surface aren’t a wild idea; in our own Solar System, Saturn’s moon Enceladus and Jupiter’s moons Europa and Ganymede all have worldwide oceans of liquid water sloshing around beneath miles of icy crust. Those icy moons get much of their internal heat from the tidal pull of the gas giants they orbit, but Ojha and his colleagues say heat from radioactive elements decaying in a planet’s interior could also do the trick.
Our own planet proves it’s possible. Beneath Arctic permafrost in parts of Canada, and beneath the ice of Antarctica, lie lakes of chilly — but liquid — water. Heat produced by radioactive elements in Earth’s crust keeps the water warm enough not to freeze.
“There is even some evidence to suggest that this might even be happening currently in the south pole of Mars,” says Ohja.
Water, With a Grain of Salt
Of course, water doesn’t automatically mean life. Water is just one of the ingredients required to turn chemistry into biology; life also needs a source of energy and a bunch of nutrients, like electrolytes and phosphorus (not to mention luck). Liquid water is the biggest and most obvious habitability hurdle, though.
If there’s life hidden beneath the surface of an alien world, however, we may never actually know. We can send rovers to search for life (past or present) beneath the surface of Mars, and we can send probes to sample the oceans of Europa and Enceladus, but when it comes to planets orbiting other stars, all we can do is stare through a telescope. And while life on the surface of a planet might leave traces in its atmosphere, underground life probably won’t.
“The major challenge is to devise ways to detect these habitats by future telescopes,” says University of Puerto Rico astronomer Abel Mendez, in a statement commenting on the recent study.
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