Data from Huygens lander suggest prebiotic conditions on Titan
Although 11 years have passed since ESA’s Huygens probe landed on Saturn’s moon Titan, the data collected by this spacecraft continue to amaze scientists. Recently, a team of researchers led by Martin Rahm of Cornell University has found a chemical trail indicating prebiotic conditions may exist on this moon.
Titan is the largest moon of Saturn. It has a dense atmosphere and a real wealth of liquid hydrocarbon lakes on its surface. Due to this, it is an interesting target for scientists to study complex chemical processes beyond Earth.
The NASA/ESA Cassini mission, which is examining Saturn and its moons, is constantly providing crucial information about these celestial bodies. Moreover, when Cassini deployed the Huygens probe in January 2005 and it successfully landed on Titan’s frigid surface, it sent via Cassini a set of valuable scientific data that allowed researchers to peek into the real nature of this mysterious moon.
Now Rahm and his colleagues revealed new insights about Titan’s possible prebiotic chemistry in a paper published on July 4 in the Proceedings of the National Academy of Sciences. Their main hypothesis states that when sunlight hits Titan’s atmosphere, which is filled with nitrogen and methane, it causes the production of hydrogen cyanide, which is a possible prebiotic chemical key.
“Studies of the chemical composition of the atmosphere and surface of Titan have been underway for many years, and was greatly accelerated by the Cassini-Huygens mission,” Rahm told Astrowatch.net. “The paper published July 4 does not provide new measurements from Titan, rather the team used what had been surmised earlier about this environment to argue for the potential importance of one model compound, and to speculate on its potential to allow for prebiotic chemistry.”
Measurements of the atmosphere and the surface of Titan suggest that hydrogen cyanide-based polymers may have formed on the moon from products of atmospheric chemistry. According to the paper, this makes Titan a valuable “natural laboratory” for exploring potential non-terrestrial forms of prebiotic chemistry.
In order to confirm this theory, scientists have used theoretical calculations to investigate the chain conformations of polyimine, a polymer identified as one major component of polymerized hydrogen cyanide in laboratory experiments.
Rahm noted that polyimine can exist as different structures and may be able to accomplish remarkable things at low temperatures, especially under Titan’s conditions.
The team’s research is another important step toward understanding Titan’s chemistry. However, more work is still needed to make breakthrough discoveries in this field as the chemical environment on this moon is considerably more complicated than was previously thought.
“We focused on the potential roles of one polymer made from hydrogen cyanide, as a model. The actual chemical environment on Titan is considerably more complicated,” Rahm said. “If future observations could show there is prebiotic chemistry in a place like Titan, it would be a major breakthrough. This paper is indicating that prerequisites for processes leading to a different kind of life could exist on Titan, but this only the first step.”
Sending another lander to Titan’s surface could aid in this research. A proposed mission would need to be able to do a careful chemical analysis of different places on the moon’s surface.
“It would need to be capable of characterizing chemical structures stable only at low temperatures, and to possibly observe chemical processes,” Rahm said.
If confirmed, prebiotic conditions on Titan could mean suitable conditions to harbor microbial life there. Hydrogen cyanide is present in comets and is presumed to be a key precursor to the origin of life.
Although there is currently no evidence for this, the paper provides indications that some chemistry may be going on, despite the cold temperature. According to Rahm, in principle, this may allow for prebiotic chemistry which in turn is necessary before there can be any kind of life.
If life were to exist in some form on the surface of Titan, it would need to be very different from that of Earth.
“There is no liquid water, and the temperature is extremely low. The low solar flux also puts limitations on the amount of energy available for metabolism,” Rahm said.
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This is a highly speculative hypothesis, since from what’s written above, the article needs to discriminate between photochemical organic reactions and true biochemical processes. The extreme low temperature on Titan renders reaction rates approaching zero. Granted that Hydrogen Cyanide is a useful prebiotic molecule, but subsequent non-photochemically mediated reactions seem to be unlikely.
Yes, it’s highly speculative, but it sounds like you are also extrapolating from generalities.
The article says “Rahm noted that polyimine can exist as different structures and may be able to accomplish remarkable things at low temperatures, especially under Titan’s conditions.”
This means that they’ve taken the low temperatures and low reaction rates into account, and even in the simplified modeled environment they were able to observe some complex and interesting chemistry. That means that such chemistry is possible on Titan, and that it’s worth sending more landers with the capabilities needed to investigate these possibilities.
I would suggest a lot more laboratory experimentation is required before funding another probe based on this level of speculation. Cryogenic chemistry is routinely done in Earthbound laboratories, particularly in the study of activated complex intermediates. They are essentially “trapped” by cryogenic conditions, and the subsequent forward reaction simply doesn’t proceed due to near zero k, or reaction rate constants. The rate constant of dissociation of the activated complex is completely dependent on absolute temperature.
So.. I’m not extrapolating from generalities, but sound physical chemical principles.
Wouldn’t confirmation of a warm ocean (primarily H20) below Titan’s surface create conditions possible for life – conditions that may or may not not be apparent from Titan’s surface or atmospheric systems? There are Cyanobacteria and even crustaceans capable of thriving around deep sea vents on Earth at temperatures and PH levels we never thought compatible with life until just recently.