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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.

The con­clu­sions come from as­tro­bi­ol­o­gist Wil­liam Bains, who pre­s­ents his re­search at the Na­tional As­tron­o­my Meet­ing in Glas­gow, Scot­land on April 13.

Methane-ethane lakes on Ti­tan in an art­ist's con­cep­t­ion (© 2008 Karl Ko­foed)


“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.