Sunday, July 10, 2016

Data from Huygens Lander Suggest Prebiotic Conditions on Titan

An image of Titan’s surface, as taken by the European Space Agency’s Huygens probe as it plunged through the moon’s thick, orange-brown atmosphere on Jan. 14, 2005. Today, Cornell scientists have chemical evidence that suggests prebiotic conditions may exist there. Credit: ESA/NASA/JPL-Caltech/Univ. of Arizona

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 the Cornell University, has found a chemical trail, indicating that 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. NASA/ESA Cassini mission which examines Saturn and its moons, is constantly providing crucial information about these celestial bodies. Moreover, when in January 2005 Cassini deployed the Huygens probe and it successfully landed on Titan’s frigid surface, it sent a set of valuable scientific data that allows researchers to peek into the real nature of this mysterious moon.

Now, Rahm and his colleagues, reveal new insights about Titan’s possible prebiotic chemistry in a paper published July 4 in the Proceedings of the National Academy of Sciences. Their main hypothesis is that when sunlight hits Titan’s atmosphere 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. 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,” Rahm told Astrowatch.net.

Measurements of the atmosphere and the surface of Titan suggest that hydrogen cyanide-based polymers may have formed on the moon’s from products of atmospheric chemistry. According to the paper, this makes Titan a valuable “natural laboratory” for exploring potential nonterrestrial forms of prebiotic chemistry. In order to confirm this theory, the 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 they may be able to accomplish remarkable things at low temperatures, especially under Titan’s conditions.

The team’s research is another important step towards understanding Titan’s chemistry. However, much more work is still needed to make breakthrough discoveries in this field as chemical environment on this moon is considerably more complicated than it 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. Much more work is needed,” Rahm admitted.

“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,” he added.

Future lander that would land on Titan’s surface could aid in this research. A proposed mission would need to be able to do 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 noted.

If confirmed, prebiotic conditions on Titan could mean a suitable conditions to harbor microbial life there. Hydrogen cyanide is present in comets and is believed to be a key precursor to the origin of life. Although we currently have no evidence for this, the paper provides indications that some chemistry may be going on, despite the cold temperature. According to Rahm, this, in principle, may allow for prebiotic chemistry, which in turn is necessary before there can be any kind of life.

However, 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 concluded.

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