A fisheye view of Titan from about 3 miles above the surface.
Titan is an intriguing world. The largest moon orbiting the ringed planet Saturn, its rich nitrogen and methane atmosphere produce hydrocarbons that rain down on the dunes and fields that lie over an underlying bedrock of water ice. It has, in short, the building blocks for life. But for all its intriguing potential, we’ve only visited this moon once in 2005 with the Huygens probe. But there may soon be a stronger reason to return. In a talk last week at the 246th National Meeting & Exposition of the American Chemical Society, Jonathan Lunine form Cornell and his team presented an interesting idea: Titan might be the laboratory scientists need to understand and explain how life arose on our planet.
Exactly how life sprung up on Earth is a bit of a mystery, but scientists generally agree the story goes something like this: the early Earth had the right kind and amount of simple organic chemicals. As energy was added to this so-called primordial soup, in the form of either sunlight or lightning, these simple chemicals underwent a series of reactions that yielded increasingly complex chemicals. At some point, this chemically complex soup crossed a threshold and the compounds within developed the ability to reproduce themselves. Over many generations, these self-replicating compounds eventually developed into the first DNA strands, forming the first simple organisms. Life had begun.
The main problem with this theory is that it’s really hard to test. Running a billion-year experiment is just plain impractical. And there’s the problem of getting the right primordial matter. All organic matter on Earth have been cycled through living things for billions of years, so we don’t really have the right pre-life matter to study.
But Titan does; aside from the Earth it’s the only body in the Solar System that we know has the right kind and quantity of organic substances on its surface to shed light on how life on Earth might have started. As far as we know from the Huygens lander and the spacecraft that have flown by the planet and measured its atmosphere, the organic materials on Titan, which include deposits of methane and other hydrocarbons as large as Earth’s Great Lakes, are in pristine condition. They’ve never been in contact with any kind of life.
Titan, slgihtly larger than our Moon, against Saturn. via
Titan also has the right kind of energy, sunlight, though the sunlight that reaches Titan is a fraction of what we see on Earth. Titan is nearly a billion miles from the Sun and a just slightly larger than our Moon, and it gets about 1 percent of the sunlight that we get on Earth. This makes for a frigid world. The average surface temperature on Titan is -290°F, a full 160° colder than the coldest recorded temperature in Antarctica. This means that the hydrocarbons that produce natural gas on Earth are frozen solid on Titan.
Nevertheless, sunlight has the right effect on this distant moon. Sunlight strikes Titan's upper atmosphere and breaks the methane and nitrogen compounds in the atmosphere into organic compounds like ethane, acetylene, hydrogen cyanide, cyanoacetylene—all chemicals that we have on Earth.
And there’s a chance that underneath its frozen surface Titan is ripe for life. There’s evidence to suggest that there may be liquid water deep underneath Titan’s frozen surface, and that the floor of these underground seas may be similar to the Earth with hydrothermal vents.
So while Mars continues to capture the public imagination—and admittedly finding evidence of life on our planetary neighbour would be pretty awesome—there are some pretty enticing reasons pushing us to visit Titan. A specially designed probe landed on that distant moon could give us a close up view of what the early Earth might have been like, and how it got like it is today.