An aerial view of the surface of Titan, captured by ESA’s Huygens lander in 2005. Data sent back by
the Cassini-Huygens mission remains our primary source of knowledge about this moonThe blotches on this
false-colour images of Titan
are thought to be lakes of
liquid methane and ethanePHOTO: NASA X2, ESOTITAN
Parent planet: Saturn
Orbital period: 15.945 days
Radius: 0.404 Earth radii
Mass: 0.0225 Earth mass
Planetary Habitability Index: 0.64
This moon of Saturn is an altogether more alien
place, sitting under obscuring clouds that are rich in organic molecules.
Its surface was revealed by ESA’s Huygens lander that parachuted down
in 2005. During the descent, the craft made some intriguing electrical
measurements. Combined with measurements of the way the moon’s
gravitational field differs from place to place, they strongly suggest of
an ocean beneath the surface.With all the organic molecules in the atmosphere and on the surface
of Titan, there’s a strong chance the ocean would be full of them too,
increasing the chances of life. But could we sample this ocean to test
that hypothesis? “That’s the question,” says Lunine. “There’s nothing
spewing out of that ocean onto the surface of Titan.”
But maybe we don’t need to go deep to find life on this particular
moon. There is liquid on the moon’s surface, but it’s not water.
Liquid methane and ethane pool in lakes and seas at the moon’s
polar regions, the largest of which is about the size of the Caspian
Sea on Earth. Could life be based on methane rather than water?
Lunine thinks so. Together with some chemical engineering
colleagues, he found a theoretical biochemistry that could work for
methane, but testing it is going to be extremely hard. “It’s very hard
to ‘cook up’ biochemistry in the lab,” he says, “It’s probably easier
just to go to these places and look. It would be interesting to land
on one of Titan’s seas and see what’s going on.”SCIENCE