Titan is a complex world, reminiscent of our own planet in many ways, with mountains, seas, lakes, rivers and rain. Albeit the liquid on this super-cold moon is methane/ethane instead of water, but the visual similarities are striking. Just how geologically active Titan might be in other ways however isn’t really known yet, but a new discovery might provide some clues. What looks like a new small “island“ has appeared in one of the hydrocarbon seas, where it wasn’t before. Is it really an island, or something else?
The odd feature, dubbed “Magic Island,” was first seen near the shoreline of the sea Ligeia Mare in radar images taken by the Cassini spacecraft on July 10, 2013. Ligeia Mare is the second-largest sea on Titan. The “island” was not seen on previous flybys. So just what is it and how did it get there? The bright feature certainly looked island-like against the much darker surface of the surrounding sea.
That was intriguing enough, but then when Cassini looked at the same spot again a few days later, it was gone. It disappeared just as mysteriously as it had appeared. Scientists involved have postulated a few different theories as to what this phenomenon might be. Despite the name, it is not thought to actually be an island. As Jason Hofgartner, astronomer and lead author of the new paper, told BBC News: “‘Magic island’ is a colloquial term that we use within the team to refer to this. But we don’t actually think it’s an island.”
Rather, it is proposed to be something floating on the surface of the sea such as a chunk of methane-ethane ice, similar to icebergs on Earth. It might even be a chunk of organic material, which is widespread on Titan. Or perhaps something like rising bubbles coming up from a volcanic vent below or waves on the surface. An increase in solar energy might be involved, since Titan is now approaching summer in its 30-year seasonal cycle.
“Right now, Titan is basically half way between the vernal equinox (August 2009) – at the beginning of spring – and the summer solstice, the start of summer. It’s roughly equivalent to what we would consider the beginning of May,” said Hofgartner. “As Titan approaches its summer, more of the sun’s energy is being deposited in the northern hemisphere.”
The possibility of methane/ethane icebergs in Titan’s seas and lakes has been discussed before. They could float when the atmosphere is warmer, but sink again when it is cooler. Organic material, if less dense than the surrounding liquid, could also float.
Although Titan’s seas and lakes for the most part are remarkably flat, waves have sometimes been detected which can glint in the sunlight, even under Titan’s thick atmosphere, so this is another conceivable explanation.
Any definitive answers will probably have to wait for a follow-up mission to Titan. Some fascinating concepts being proposed include balloons, airplanes or even a floating lander to bob around in a Titanian lake or sea. John Zarnecki, of the Open University in Milton Keynes who has studied Titan’s waves, sums it all up nicely:
“These are clearly observations that are close to the limit of detectability – and therefore very difficult to interpret. But it looks like something is going on in Ligeia Mare. Titan surprises us at every turn. Is this feature showing us floating solids or gases erupting at the surface – or a phenomenon that we haven’t thought of? After all, we tend to think in terms of Earth-like phenomena. But based on this so far sparse data, any suggestion is likely to be little more than speculation until we get some more supporting information.”
The published paper is available on Nature Geoscience (purchase or subscription).
This article was first published on Spaceflight Insider.