Life On Titan Possible Without Water

In this near-infrared mosaic, the sun shines off of the seas on Saturn's moon, Titan. Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho

Saturn’s largest moon Titan is a truly fascinating place. Aside from Earth, it is the only place in the Solar System where rainfall occurs and there are active exchanges between liquids on the surface and fog in the atmosphere – albeit with methane instead of water. It’s atmospheric pressure is also comparable to Earth’s, and it is the only other body in the Solar System that has a dense atmosphere that is nitrogen-rich.

For some time, astronomers and planetary scientists have speculated that Titan might also have the prebiotic conditions necessary for life. Others, meanwhile, have argued that the absence of water on the surface rules out the possibility of life existing there. But according to a recent study  produced by a research team from Cornell University, the conditions on Titan’s surface might support the formation of life without the need for water.

When it comes to searching for life beyond Earth, scientists focus on targets that possess the necessary ingredients for life as we know it – i.e. heat, a viable atmosphere, and water. This is essentially the “low-hanging fruit” approach, where we search for conditions resembling those here on Earth. Titan – which is very cold, quite distant from our Sun, and has a thick, hazy atmosphere – does not seem like a viable candidate, given these criteria.

However, according to the Cornell research team – which is led by Dr. Martin Rahm – Titan presents an opportunity to see how life could emerge under different conditions, one which are much colder than Earth and don’t involve water.

Their study – titled “Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan” – appeared recently in the Proceedings of the National Academy of Sciences (PNAS). In it, Rahm and his colleagues examined the role that hydrogen cyanide, which is believed to be central to the origin of life question, may play in Titan’s atmosphere.

Previous experiments have shown that hydrogen cyanide (HCN) molecules can link together to form polyimine, a polymer that can serve as a precursor to amino acids and nucleic acids (the basis for protein cells and DNA). Previous surveys have also shown that hydrogen cyanide is the most abundant hydrogen-containing molecule in Titan’s atmosphere.

As Professor Lunine – the David C. Duncan Professor in the Physical Sciences and Director of the Cornell Center for Astrophysics and Planetary Science and co-author of the study – told Universe Today via email: “Organic molecules, liquid lakes and seas (but of methane, not water) and some amount of solar energy reaches the surface. So this suggests the possibility of an environment that might host an exotic form of life.”

Using quantum mechanical calculations, the Cornell team showed that polyimine has electronic and structural properties that could facilitate prebiotic chemistry under very cold conditions. These involve the ability to absorb a wide spectrum of light, which is predicted to occur in a window of relative transparency in Titan’s atmosphere.

Another is the fact that polyimine has a flexible backbone, and can therefore take on many different structures (aka. polymorphs). These range from flat sheets to complex coiled structures, which are relatively close in energy. Some of these structures, according to the team, could work to accelerate prebiotic chemical reactions, or even form structures that could act as hosts for them.

“Polyimine can form sheets,” said Lunine, “which like clays might serve as a catalytic surface for prebiotic reactions. We also find the polyimine absorbs sunlight where Titan’s atmosphere is quite transparent, which might help to energize reactions.”

In short, the presence of polyimine could mean that Titan’s surface gets the energy its needs to drive photochemical reactions necessary for the creation of organic life, and that it could even assist in the development of that life. But of course, no evidence has been found that polyimine has been produced on the surface of Titan, which means that these research findings are still academic at this point.

However, Lunine and his team indicate that hydrogen cyanide may very well have lead to the creation of polyimine on Titan, and that it might have simply escaped detection because of Titan’s murky atmosphere. They also added that future missions to Titan might be able to look for signs of the polymer, as part of ongoing research into the possibility of exotic life emerging in other parts of the Solar System.

“We would need an advanced payload on the surface to sample and search for polyimines,” answered Lunine, “or possibly by a next generation spectrometer from orbit. Both of these are “beyond Cassini”, that is, the next generation of missions.”

Perhaps when Juno is finished surveying Jupiter’s atmosphere in two years time, NASA might consider retasking it for a flyby of Titan? After all, Juno was specifically designed to peer beneath a veil of thick clouds. They don’t come much thicker than on Titan!

Further Reading: PNAS

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Huygens Data Confirms Presence Of Methane Fog At Titan’s South Pole

Titan's dense, hydrocarbon rich atmosphere remains a focal point of scientific research. Credit: NASA

Titan is a moon shrouded in mystery. Despite multiple flybys and surface exploration conducted in the past few decades, this Cronian moon still manages to surprise us from time to time. In addition to having a dense atmosphere rich in hydrocarbons, which scientists believe may be similar to what Earth’s own atmosphere was like billions of years ago, it appears that methane is to Titan what water is to planet Earth.

In addition, methane fog was also observed by the Cassini space probe back in 2009 as it conducted a flyby of Titan. But recent findings by a team of researchers from York University indicates that the Huygens lander also detected fog during its short time on the surface. This evidence, combined with the data obtained by Cassini, have helped to shed light on the weather patterns of this mysterious moon.

In a paper that appeared in arXiv on March 14th, Dr. Christina Smith – a postdoctoral student from York University’s Center for Research in Earth and Space Sciences (CRESS) – described how the Huygens probe’s Side Looking Imager (SLI) obtained information that has since been analyzed to identify potential atmospheric features. These features show that Titan experiences meteorological phenomena which were not previously known.

In total, the team looked over 82 SLI images, which were all taken after the lander reached the surface. These were then calibrated, processed and examined for signs of atmospheric features. Of these, six showed evidence of an extended horizontal feature that differed in radiance from what was predicted at higher and lower regions. No other discernible features were detected.

The team concluded that this feature most likely originated from the presence of a fog bank close to the horizon that rose and fell during the period of observation. This indicated that it had recently rained in the area, which was a rather surprising find. Much like the observations made in 2009, the presence of methane fog shows that Titan has an active methane hydrological cycle.

In essence, this means that methane on Titan is subject to the same transfer process as water is here on Earth. Basically, liquid methane on the surface evaporates and is exchanged with the atmosphere, where it condenses to form fog banks and rain clouds. As Christina Smith told Universe Today via email:

“We initially set out to see if we could see features such as clouds from the Huygens SLI data, but the features we found don’t seem to be consistent with clouds and more likely are caused by a fog bank rising and falling over the time of observation. Fog had been seen before from orbit but never from the surface of Titan – this is what makes this work so exciting. This work is also a great example of how new insights and new findings can be made from “older” data sets.”

Looking over this old data for the sake of making new discoveries was made possible, in part, because of the ongoing investigations conducted by Martian rovers and their respective science teams. Brittany Cooper – an undergraduate research assistant at York University’s Center for Research in Mass Spectrometry, and the second author of the paper – explained via email:

“We applied a technique of image analysis developed by Mark Lemmon for use with the Mars Exploration Rovers that was adapted by John Moores for use on the Mars Phoenix lander mission. This analysis method allowed the faint, barely observable atmospheric features captured by the Huygens’ probe Side Looking Imager (SLI) on Titan to be amplified and more easily discerned.”

For years, scientists have understood that on Titan, methane is analogous to water. It exists in solid form, in liquid form (especially around the north pole where several large methane lakes exist), and in gaseous form in the atmosphere. However, what they did not know was whether or not there was an active cycle, where liquid methane on the surface was replenished through evaporation, condensation, and rain.

But this evidence, combined with the Cassini probe data, confirms that on Titan, there is active transfer process between the liquid methane and the atmospheric methane. And where atmospheric humidity reaches 100%, methane fogs will form. Just the latest in a long line of fascinating discoveries to emerge from this mysterious moon!

Further Reading:

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Scientists Discover 101 Geysers Erupting at Saturn’s Intriguing Icy Moon Enceladus

Scientists analyzing the reams of data from NASA’s Cassini orbiter at Saturn have discovered 101 geysers erupting from the intriguing icy moon Enceladus and that the spewing material of liquid water likely originates from an underground sea located beneath the tiny moons ice shell, according to newly published research. The geysers are composed of tiny […]