Titan, Saturn's aptly named largest moon, is exactly the kind of place we want to visit: NASA describes it as "one of the most Earth-like worlds we have found to date." It has a dense atmosphere and stable lakes and rivers.
Its air isn't breathable (it's almost entirely nitrogen, with a little methane thrown in instead of oxygen), and its rivers, lakes and oceans are full of liquid methane and ethane. And at -290 Fahrenheit, it's way too cold for a human to chill on. But if you had a breathing mask and the best thermal underwear ever created, you could jump around in gravity a bit weaker than our own moon's and see some surprisingly Earth-like features. You might even see some liquid water spewing out of volcanoes, lava-style.
According to a study published Monday in the Proceedings of the National Academy of Sciences, this bizarro world might have what we call prebiotic conditions — chemicals that could theoretically come together to build and support life as we know it.
(Well, life a lot chillier than we know it.)
"We are used to our own conditions here on Earth. Our scientific experience is at room temperature and ambient conditions. Titan is a completely different beast," Martin Rahm, postdoctoral researcher in chemistry at Cornell and lead author of the new study, said in a statement. "So if we think in biological terms, we're probably going to be at a dead end."
According to Rahm and his colleagues, one of the things that makes Titan utterly unappealing to Earthlings — the abundance of noxious hydrogen cyanide that forms when sunlight hits the hazy atmosphere — could actually help support life.
They showed that it's possible, at least hypothetically, for hydrogen cyanide to react with some of the other molecules found on Titan to produce molecular chains or polymers, including one called polyimine.
That wouldn't mean much under earthly conditions. But at Titan's temperatures, they say, polyimine could potentially have the kind of properties that would support microbial evolution. It would be flexible, according to the researcher's models, allowing it to adopt more than one structure, and its ability to absorb sunlight might help it provide energy for life in the primordial ooze.
Not even this computer modeling showed exactly how life would come together on Titan, so it's a little early to go alien hunting. But polyimine is at least one way that the evolution of life might theoretically be possible there.
"This paper is indicating that prerequisites for processes leading to a different kind of life could exist on Titan, but this is only the first step," Rahm said.
With a whole lot of luck, there might indeed be microbes wriggling around the seas of Titan. But we probably won't know until we check it out for ourselves: The Cassini and Huygens missions gave us tantalizing glimpses of Titan and a treasure trove of data on its thick, hazy atmosphere, but sending a probe to its surface would tell us once and for all what kind of life-giving processes are going on there. Of course, we'd have to be extremely careful not to contaminate any microbial life we found: The reason NASA's Mars rovers aren't allowed to traipse through areas where we've seen signs of liquid water is that they aren't sterile enough to guarantee no Earth microbes would hitch a ride and colonize Martian marshes.
But that doesn't mean a mission to Titan is out of the question. We'll be looking for life on at least one other moon sometime soon.
NASA is in the early planning stages for a robotic mission to Europa sometime in the next few decades. Europa, a moon of Jupiter, is very different from Titan: Like all the other bodies in the solar system (save Earth, of course) it lacks any stable liquid on its surface. But Europa is covered by a subsurface ocean. Because its icy crust is made of mostly water, scientists hope this moon's seas contain liquid water as well — creating a hostile but potentially habitable environment not unlike subglacial lakes here on Earth.