Ice on Titan’s lakes and seas: implications for possible life?

Artist's conception of possible ice floes on a Titanian sea.Credit: NASA / JPL-Caltech / USGS
Artist’s conception of possible ice floes on a Titanian sea.
Credit: NASA / JPL-Caltech / USGS

Apart from being composed of liquid methane instead of water, the rivers, lakes and seas of Saturn’s moon Titan are amazingly similar in appearance to those on Earth. The hydrological cycle is also very similar, with Titanian rain replenishing them.

Now, there is another feature that the lakes and seas may have in common with some of those on Earth – ice floes.

Until now, it has been thought that ice floes on Titan were unlikely, because solid chunks of methane ice would sink in liquid methane. But a new study suggests it might be possible, after all. As it turns out, methane ice could indeed float, if the temperature is below the freezing point of methane, about -182˚ C (-297˚ F). If the ice is composed of at least 5% Titanian “air” (mostly nitrogen, like on Earth), then the ice will float.

As Jason Hofgartner, the first author on the paper and a Natural Sciences and Engineering Research Council of Canada scholar at Cornell explains, “We now know it’s possible to get methane-and-ethane-rich ice freezing over on Titan in thin blocks that congeal together as it gets colder – similar to what we see with Arctic sea ice at the onset of winter. We’ll want to take these conditions into consideration if we ever decide to explore the Titan surface some day.”

Areas of the lakes and seas which have shown mixed readings as seen by Cassini in terms of reflectivity could be explained by patches of ice.

The floating ice may even have implications for possible life of some kind on Titan, as it could provide a good niche for pre-biological or biological chemistry to occur.

According to Jonathan Lunine, a paper co-author and Cassini interdisciplinary Titan scientist at Cornell University, “One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life. And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life.”

There has been some debate in recent years regarding possible methane-based life on this fascinating moon, since some of the conditions found on the surface seem to correlate with what some scientific models predicted would be found if methane-based life was present. Other explanations are still possible, but either with or without life, Titan is a hauntingly beautiful and uniquely alien world.

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