Looking for a new home beyond earth? Icy moons in the outer reaches of our solar system could be a contender.
For centuries we have looked up to the stars and wondered if we are alone in the universe. But recently, our search for extraterrestrial life has been less about making contact with an alien race and more about the search for some kind of galactic lifeboat.
To look for life, scientists used to focus on planets in the ‘Goldilocks zone’. A potentially habitable area that’s neither too near or too far from our sun - in other words it’s neither too hot or too cold. But when Cassini started to send back data from the systems of Saturn, scientists began to shift their focus. From planets to moons. Saturn has 62 confirmed moons with more being discovered all the time. And two of those moons, Titan and Enceladus, could be habitable. Thanks to Cassini’s galactic hitch hitcher - a clam shaped probe called Huygens - we were able to pierce Titan’s hazy atmosphere and land on its surface
It's really surprised us. We see dunes. We see these river gullies and channels that have been carved by liquid, but there that liquid is not water. It's methane and ethane. Liquid hydrocarbons that have been forming just like on Earth how we have clouds and rain events, the same thing happens on Titan, but it's with an entirely different set of molecules. It's a fascinating alien world and we're just beginning to scratch the surface in terms of how complex it is and exactly what is present there on the surface.
But with lakes of liquid methane and a surface temperature of minus 290 degrees fahrenheit - how could Titan possibly be habitable? Well, to humans, Titan is one of the least hostile places in the outer solar system. It has a dense, planet-like atmosphere. Meaning, even though it’s colder and gets less light than Earth, it has a dense biochemical make-up that could sustain life.
Titan’s atmosphere is also quite stable. Except for thunderstorms at the poles there are no cataclysmic events to worry about like cyclones, moonquakes or even cosmic rays. If you lived on Titan, you could stand on its surface with just an oxygen mask, and of course, some very very warm clothing.
But maybe the motivation to colonize Titan isn’t necessarily about building Earth 2.0; it might make more sense to think about it as a way-station, a halfway point to the next Earth 2.0. Titan has more hydrocarbon reservoirs, like a larger reservoir than all of them on Earth combined. You need extra gas? Just go to Titan, scoop up some methane, and carry on to find a place where you can survive. It's opening our eyes to the breadth and the possibilities that exist just in our solar system alone.
There is another moon in the Saturn system that scientists are excited about - Enceladus. It’s smaller than Titan - about 310 miles in diameter. And underneath its icy crust is an ocean of water. We had no idea that there were liquid water oceans underneath the icy crusts of some of these moons. This is exciting for us because any place on Earth where we find liquid water, we find life - every time. Enceladus, not only is it a key astrobiology target because of this liquid water, but it is unique in that that liquid water ocean is accessible.
We don’t know the exact energy source that keeps its subsurface ocean liquid. Cassini was able to sample the plumes erupting from its surface. It discovered a hydrothermal chemical makeup similar to what occurs in the depths of Earth’s oceans.
NASA’s next missions to icy moons like Saturn’s Enceladus and Jupiter’s moon Europa, will hopefully be equipped with instruments for oceanic studies. Instruments that are directly targeted to look for organic molecules and the key biosignatures of life as we know it, or even life as we don't know it.
We'll be looking for patterns in organic molecules that are unique only when life is present. The discoveries that Cassini, and spacecraft like Cassini, have made will absolutely help us try to eventually become not a one planet civilization. We can't stay here forever.