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Where to look for signs of life on Titan



Looking down on Titan with Cassini. Some of the large lakes filled with methane and ethane are visible through the haze. Credit: NASA / JPL-Caltech / SSI.

Recent findings, published in the journal Astrobiology suggest that large craters are the key places to find the building blocks of life on Saturn's largest moon Titan.

Titan is an icy space covered with organic molecules, in which liquid methane lakes are surrounded by a dense, hazy atmosphere of nitrogen and methane that raises the question: Why is there no life on this strangely Earth-like world? Perhaps it is the mild temperature of -1

79 degrees Celsius (-300 degrees Fahrenheit) on the surface that would likely prevent any biochemical reactions from taking place. But is there any place on Titan where you could hope that biomolecules like amino acids could form? A Team Wanted to Find Out

Using images and data from the Cassini spacecraft and the Huygens probe, scientists were led by Dr. Catherine Neish, a planetary scientist specializing in impact craters at the University of Western Ontario, chasing the best place to search for biological molecules on the titanium surface. Life, as we know it, is based on carbon and uses liquid water as a solvent. The surface of Titan contains abundant carbon-rich molecules (hydrocarbons) that have been shown to form amino acids, the building blocks of proteins needed for life when exposed to liquid water in laboratory simulations.

This is the problem: titanium is far too cold for liquid water on the surface. Although this is not a favorable scenario for the formation of viable molecules, there is hope

Clear Crater

Radar measurements by Cassini, orbiting Saturn for 13 years, have revealed Titan's visually dense atmosphere revealing the terrain this enigmatic world. What was revealed was unexpected – Titan is active. Cassini's radar revealed lakes, dunes, mountains, river valleys, and not many craters, suggesting that processes are taking place to recharge Titan and fill or erode older craters. It was monumental to discover a world like the Earth that was nine times as far from the Sun.

With such a familiar landscape on earth, where would be the best places to look for signs of life? Although methane lakes may have been the obvious choice, Neish and her colleagues found craters and cryovolcanoes instead (regions where liquid water erupts under Titan's icy surface) are among the most appealing places. Both properties promise to melt the icy crust of titanium into liquid water, a necessary step in the formation of complex biomolecules.

Dr. Morgan Cable, a technology specialist in the Systems Implementation and Concepts department of NASA's Jet Propulsion Laboratory in Pasadena, California, is an expert in "tholine" (organic matter that results when simple gas mixtures are exposed to cosmic radiation). She commented, "When we mix Tholine with liquid water, we make amino acids very fast, and any place where liquid water is on Titan or near its surface could be the precursors of life – biomolecules – for life It would be important to know it, and that is really exciting. "

Sotra Facula is a cryovolcan on Titan. This image, built from radar topography with superimposed infrared colors, shows the caldera of the volcano, mountainous peaks and thin, bright rivers leading away from the cryovolcan. Credit: NASA / JPL-Caltech / USGS / University of Arizona

Craters are the best

With both cryovolcanoes and craters as literally hot spots for melting on Titan, what feature is that you should put your money on? For Neish, the answer is definitely craters, though there are not as many on Titan as on our moon.

"Craters have truly emerged as the clear winners for three main reasons," says Neish to Astrobiology Magazine. "One thing is, we're pretty sure there are craters on Titan.

Cratering is a very general geological process and we see circular features that are certainly craters on the surface," she says.

The second point is that craters would probably produce more melt than a cryovolcan, which means that "they need longer to freeze [the water] for longer," Neish says, adding that liquid water is the key to complex cryogenics is chemical reactions.

"The last point is that impact craters should produce water that has a higher temperature than a cryovolcan," says Neish. Hotter water means faster chemical reaction rates, which is promising for the formation of vital molecules.

"Water could remain liquid in these environments for thousands of years or even longer," says Cable

Cryovolcanoes, on the other hand, they're not that hot. "When a cryovolcan breaks out, it typically breaks directly at the melting temperature of the ice, and we think that each & # 39; lava & # 39; [in this case, a slushy form of water] on the Titan will be heavily doped with ammonia, which pretty much prevents the freezing point, so that's the case, lava would be pretty cold, "says Neish.

Sotra Facula is a cryovolcan on Titan. This image, built from radar topography with superimposed infrared colors, shows the caldera of the volcano, mountainous peaks and thin, bright rivers leading away from the cryovolcan. Credit: NASA / JPL-Caltech / USGS / University of Arizona

Cryovulcanism turns out to be an obscure and elusive process to put the last nail in the coffin for these icy volcanoes. Imagine ice that is less dense than water and floats in a glass of water. "It's pretty hard to get the water up on the ice when you have such density contrast," says Neish. "Cryovulcanism is the more difficult thing and there is very little evidence of it on Titan."

In fact, cryovolcanism on Titan might not really be. "Sotra Facula [a mountainous feature on Titan that appears to have a caldera-like depression] is perhaps the best and only example we have of a cryovolcan on Titan." Neish adds. "So it is much rarer, if it exists at all."

In-situ measurements

Sinlap (112 kilometers / 70 miles in diameter), Selk (90 kilometers / 56 miles) and Menrva (392 kilometers / 244 miles) craters, which are the largest fresh craters on Titan are prime locations to look at when we finally have the opportunity to search for biomolecules in these craters. A probe would have to land on Titan and take measurements to make such a discovery. But are these goals the next candidates for a future Titan mission? Not everyone is convinced.

"We do not know where to look for such results ourselves," says Dr. David Grinspoon, Senior Scientist at the Planetary Science Institute. "I would not use it to lead our next mission to Titan, it's premature."

Instead, Grinspoon wants to spy more places on Titan. "Because there is so little we know about the planet, it makes more sense to first characterize a number of environments," he says.

Nevertheless, the search for the building blocks of life on this cold world, though titan is baffled, has to start somewhere, and the result of this research gives us not one, but three potential candidates for starting this search, with hopefully much more more.


Further information:
Changes in the surface brightness of titanium indicate cryovulcanism

Further information:
Catherine D. Neish et al. Strategies for the detection of biological molecules on titanium, Astrobiology (2018). DOI: 10.1089 / ast.2017.1758

Reference Number:
astrobiology

Source ::
Astrobiology Magazine


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