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Life on Titan? Stand far back and hold your nose!
April 12, 2010
Courtesy of the Royal Astronomical Society
and World Science staff
If life has evolved on Saturn’s frigid moon, Titan, it would
be strange, smelly—and potentially explosive, new research suggests. Methane-ethane lakes on
Titan in an artist's conception (© 2008 Karl Kofoed)
The conclusions come from astrobiologist William Bains, who presents his research at the National Astronomy Meeting in Glasgow, Scotland on April 13.
“Hollywood would have problems with these aliens,” said Bains. “Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible.
“But I think it is all the more interesting for that reason. Wouldn’t it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?” added Bains, referring to the tall extraterrestrials from the movie
Avatar.
Bains, whose research is carried out through Rufus Scientific Ltd. in Cambridge,
U.K. and the Massachusetts Institute of Technology, is studying just how extreme life’s chemistry can be.
Life on Titan, Saturn’s largest moon, is one of stranger scenarios under examination. Titan is twice as large as our Moon and has a thick atmosphere of freezing, orange smog. At ten times our distance from the Sun, it is a frigid place, with a surface temperature of minus 180 degrees Celsius
(minus 292 Fahrenheit). All the water is ice; the only liquids are methane and ethane, filling what scientists believe are ponds and lakes.
“So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive,” said Bains.
This blood would have to contain dissolved chemicals, but few chemicals dissolve easily in liquid methane. Most molecules can’t dissolve in it if they have more than six atoms
not counting easily-dissolved hydrogen. So a metabolism running in liquid methane will have to be built of smaller molecules than in Earth biochemistry, which is typically built of modules of around 10 atoms apart from hydrogen.
You can only build around 3,400 different molecules within the above-described limitations on Titan, Bains said.
In contrast, he added, one can build around 10 million or more different molecules fitting
Earth’s required specifications, although only about 700 are actually used.
“The issue is not how many molecules you can make, but whether you can make the collection you need to assemble a metabolism. It is like trying to find bits of wood in a lumber-yard to make a table. In theory you only need
five. But you may have a lumber-yard full of offcuts and still not find exactly the right five...
so you need the potential to make many more molecules than you actually need. Thus the
six-atom chemicals on Titan would have to include much more diverse bond types [linking the atoms] and probably more diverse elements, including sulphur and phosphorus.”
The elements would have to appear in much more diverse forms, as well as in forms that would be highly unstable on the Earth environment—hence
the explosiveness, he added.
Energy is another factor that would affect the type of life that could evolve on Titan. With sunlight a tenth of a percent as intense on Titan’s surface as on the surface of Earth, energy is probably in short supply. “Rapid movement or growth needs a lot of energy, so slow-growing, lichen-like organisms are possible in theory, but velociraptors are pretty much ruled out,” said Bains.
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If life has evolved on Saturn’s frigid moon, Titan, it would be strange, smelly—and explosive, to us, new research suggests. The conclusions come from astrobiologist William Bains, who presents his research at the National Astronomy Meeting in Glasgow, Scotland on April 13. “Hollywood would have problems with these aliens,” said Bains. “Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible. “But I think it is all the more interesting for that reason. Wouldn’t it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?” added Bains, referring to the tall extraterrestrials from the movie Avatar. Bains, whose research is carried out through Rufus Scientific Ltd. in Cambridge, U.K., and the Massachussets Institute of Technology in the USA, studying just how extreme life’s chemistry can be. Life on Titan, Saturn’s largest moon, is one of stranger scenarios under examination. Titan is twice as large as our Moon and has a thick atmosphere of freezing, orange smog. At ten times our distance from the Sun, it is a frigid place, with a surface temperature of minus 180 degrees Celsius (-292 Fahrenheit). All the water is ice; the only liquids are methane and ethane, filling what scientists believe are ponds and lakes. “So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive,” said Bains. This blood would have to contain dissolved chemicals, but few chemicals dissolve easily in liquid methane. Most molecules can’t dissolve in it if they have more than six atoms other than hydrogen, which dissolves easily because it is light. So a metabolism running in liquid methane will have to be built of smaller molecules than in Earth biochemistry, which is typically built of modules of around 10 atoms apart from hydrogen. You can only build around 3,400 different molecules within the above-described limitations on Titan, Bains said. On Earth, he added, one can build around 10 million or more different molecules fitting the required specifications, although only about 700 are actually used. “The issue is not how many molecules you can make, but whether you can make the collection you need to assemble a metabolism. It is like trying to find bits of wood in a lumber-yard to make a table. In theory you only need 5. But you may have a lumber-yard full of offcuts and still not find exactly the right five that fit together. So you need the potential to make many more molecules than you actually need. Thus the 6-atom chemicals on Titan would have to include much more diverse bond types [linking the atoms] and probably more diverse elements, including sulphur and phosphorus.” The elements would have to appear in much more diverse forms, as well as in forms that would be highly unstable on the Earth environment—hence the explosiveness, he added. Energy is another factor that would affect the type of life that could evolve on Titan. With sunlight a tenth of a percent as intense on Titan’s surface as on the surface of Earth, energy is probably in short supply. “Rapid movement or growth needs a lot of energy, so slow-growing, lichen-like organisms are possible in theory, but velociraptors are pretty much ruled out,” said Bains.