Microbes Found That Survive on the by-Products of Radioactive Decay

In addition to investigating the big questions about life in our Universe (origins, evolution, distribution, etc.), one of the chief aims of astrobiologists is to characterize extraterrestrial environments to determine if life could exist there. However, there are still unresolved questions about the range of conditions under which life can survive and thrive. Placing better constraints on this will help astrobiologists search for life beyond Earth.

To get a better understanding of how ecosystems can exist beneath the ocean floor (so far from the Sun) a team of researchers led by the University of Rhode Island’s Graduate School of Oceanography (GSO) conducted a study on microbes in ancient seafloor sediment. What they found, to their surprise, was that these lifeforms are sustained primarily by chemicals created by the natural irradiation of water molecules.

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Is Titan Hiding an Ocean?

 

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Saturn’s moon Titan just keeps throwing surprises at us. A multi-layered atmosphere thicker than our own? Check. A hydrologic cycle that relies on methane as the operating liquid? Check. Rivers, streams and lakes filled with this same liquid? Check, check and check. And now, scientists are suspecting that Titan may have yet another surprise: a subsurface ocean.

Observations of Titan’s rotation and orbit, carried out by researchers at the Royal Observatory of Belgium using Cassini data, point at an unusual rotational inertia; that is, its resistance to changes in its motion, also known as moment of inertia or angular mass. Basically Titan moves in a way that is not indicative of a solid body of its previously assumed density and mass. Rather, its motion – both around its own axis and in its tidally-locked orbit around Saturn – are more in line with an object that isn’t uniformly solid.

Titan's thick clouds hide its surface well. NASA / JPL / SSI / J.Major

According to the math, Titan may very well be filled with liquid!

Or, at least, have a liquid layer of considerable depth beneath its surface. How far below the surface, how deep and exactly what kind of liquid are all speculative at this point…it’s suggested that it may be a subsurface ocean of yet more methane. This would help answer the question of where Titan gets all of its methane in the first place; methane, – a.k.a. natural gas – is a compound that breaks down quickly in sunlight. In fact, the high-level haze that surrounds the moon like a wispy blue shell is made up of this broken-down methane. So if this stuff is raining down onto the surface in giant, frigid drops and filling streams and lakes, but is still being broken down by ultraviolet light from the Sun to enshroud the entire moon (Titan is BIG, remember…at 5,150 km – 3,200 miles – wide, it’s over a third the size of Earth!) then there has to be somewhere that this methane is coming from.

If these calculations are right, it may be coming from underground.

We propose a new Cassini state model for Titan in which we assume the presence of a liquid water ocean beneath an ice shell… with the new model, we find a closer agreement between the moment of inertia and the rotation state than for the solid case, strengthening the possibility that Titan has a subsurface ocean.

– Rose-Marie Baland et al.

Of course in order for this hypothesis to be proven many more numbers are going to have to be crunched and more data reviewed. And more possibilities considered, too; Titan’s orbital irregularities may in fact be the result of external forces, such as a close pass by a comet or other large body. Still, there’s something to be investigated here and you can bet there’ll be no shortage of attention on a problem as intriguing as this!

Titan may soon be joining the short list of moons speculated to possess subsurface oceans, alongside Jupiter’s Europa and Ganymede and sister Saturnian satellite Enceladus…and who knows how many others?

Read the article on MIT’s Physics arXiv Blog, or you can download the full report here.

Top image credit: NASA / JPL / SSI. (Edited by J. Major.)