Search for Life Focuses on Mars, Moons of Jupiter and Saturn—and Earth

It's a good time for aliens—or rather, for tiny critters here on Earth that scientists think might look an awful lot like aliens. That's thanks to three recent papers evaluating some of the weirdest, most hardy terrestrial life we know of and considering how it might fare in extraterrestrial environments.

Our first stop on the trip is to our next door neighbor, Mars. The Red Planet is dry, salty and experiences dramatic temperature swings—much like the Atacama Desert in Chile, where it hardly ever rains.

But when a deluge fell on the desert in 2015, scientists watched as the desert suddenly came to life. So a team sampled all the bacteria they could find and sequenced their DNA—and realized the critters had been there all along, biding their time until they could thrive. And if they can do it here, there's no reason to think similar microbes might not take the same approach on Mars.

Much farther out in the solar system is a frozen moon with a very different environment—Europa, which hides a giant ocean tucked away under an icy crust. Scientists don't know for sure what's going on under there, but they wanted to do a little thought experiment.

The surface of Jupiter's moon Europa. Conditions in some Canadian lakes could resemble Europa and Saturn's moon Enceladus, both of which hide giant salty oceans beneath shells of ice. NASA/JPL-Caltech/SETI Institute

So they took one of the weirdest bacteria scientists have ever discovered, which was found at the bottom of a South African gold mine, where it forms communities all by itself and without ever receiving energy from the sun. Then, they decided to try to figure out whether the microbe could survive off nuclear energy beneath Europa's crust—and found it likely would make itself at home.

Finally, Saturn has a frozen moon much like Europa, called Enceladus. But this moon has an extra trick: It spits giant plumes of hot water and gas out into space. That makes it surprisingly convenient for scientists to figure out what's in all the water trapped under the icy crust—they can just fly a spacecraft through the plumes. That's how they know there's plenty of methane to be found on Enceladus.

Read more: Life on Europa? South Africa Gold Mine Hosts Strange Bacteria That Could Thrive on Jupiter's Icy Moon

And that's intriguing because we have here on Earth a class of primitive organisms that create methane. So in another new study, scientists created Enceladus-like conditions here in a laboratory and looked to see how these critters responded. Again, their results were pretty heartening for those hoping for alien life.

Of course, none of these experiments actually confirm extraterrestrial life, they just keep our options open. They don't even narrow down where we would find it, since there are other strong contenders—Saturn's moon Titan, which has a thick hazy atmosphere, is another likely candidate. That's why the only way to know where we'll find life first is to keep looking.