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Infrared images of Saturn\u2019s icy moon Titan<\/p>\n
NASA\/JPL-Caltech\/St\u00e9phane Le Mou\u00e9lic, Virginia Pasek<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
The seas of Saturn\u2019s moon Titan have weird \u201cmagic islands\u201d that seem to appear and disappear over the course of hours to weeks. These so-called islands might actually be porous, sponge-like clumps of snow that slowly fill up with fluid and then sink.<\/p>\n
Titan\u2019s thick atmosphere is full of complex organic molecules that can clump together and fall down to the moon\u2019s surface like snow. Xinting Yu at the University of Texas at San Antonio and her colleagues thought the \u201csnow\u201d could be responsible for the magic islands. To test their idea, they used what we know about these atmospheric compounds and how they are expected to interact with Titan\u2019s seas.<\/p>\n
Typically, we expect any solids on the surfaces of these seas to sink immediately because the liquid on Titan is methane rather than water. While water molecules tend to cling to one another and push away other materials, methane easily grabs on to other molecules, so a pool of liquid methane has very little surface tension.<\/p>\n
<\/p>\n \u201cWater molecules just love themselves to the exclusion of some types of molecules,\u201d says Michael Malaska at NASA\u2019s Jet Propulsion Laboratory in California, who was not involved in this work. \u201cBut put methane on the same surface and it will crawl all over.\u201d That means that the methane oceans and lakes on Titan should immediately swallow up any solids, even those that might otherwise be expected to float.<\/p>\n But that clearly doesn\u2019t happen with the magic islands, which appeared as ephemeral bright spots in observations from the Cassini spacecraft. \u201cFor us to see the magic islands, they can\u2019t just float for a second and then sink,\u201d Yu said in a statement. \u201cThey have to float for some time, but not for forever, either.\u201d<\/p>\n The researchers found a solution to this problem: if large chunks of snow amassed on the shore, they could form ices that are full of holes, like sponges. When these porous \u201cicebergs\u201d broke off from the land, they could float on Titan\u2019s seas for long enough to match the Cassini observations. This would work if, the researchers calculated, the sponge-like structures contained enough empty space \u2013 a minimum of about 25 to 50 per cent depending on the exact composition of the ice.<\/p>\n This doesn\u2019t mean that the mysterious islands are definitely porous icebergs, though. \u201cWe are narrowing the different scenarios for the magic islands, but we still don\u2019t yet know the answer,\u201d says Malaska. Other possible explanations include bubbles of nitrogen gas, waves caused by wind or solid sediments in the oceans. But this does provide evidence that Titan\u2019s transitory islands could actually be floating matter from this strange world\u2019s atmosphere.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n