CATCH a wave. Fleeting features on the face of Titan are probably waves rippling across the moon鈥檚 seas.
As far as we know, Saturn鈥檚 largest moon is the only world apart from Earth to host liquids on its surface, in the form of methane and ethane lakes and seas. The lakes are usually flat and calm, but NASA鈥檚 Cassini orbiter has spotted mysterious intermittent glints. Their reappearance seems to confirm something is afoot.
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鈥淣ow we have confirmation that these seas are not stagnant ponds just sitting there, but there is activity in them,鈥� says Jason Hofgartner of NASA鈥檚 Jet Propulsion Laboratory.
Cassini first spotted a glint in 2013 in Ligeia Mare, a 26,000-square-kilometre sea in Titan鈥檚 north polar region about 50 per cent bigger than Lake Superior. In later observations, the glint disappeared. Another view in 2014 found the bright spot again, and it was gone again by January 2015. The glints could be icebergs, but not much floats in methane, Hofgartner says. Or they could be bubbles.
On Earth, waves ruffled by a breeze are the most common cause of a shimmering sea. That鈥檚 probably true on Titan, too. That is surprising, because Titan鈥檚 lakes appear glassy smooth. But a faint breeze would be enough to ripple the surface according to Hofgartner鈥檚 calculations (Icarus, ).
鈥淚f it is waves, it could be because of the change of seasons,鈥� Hofgartner says. 鈥淭itan鈥檚 year is 30 years long, and it is going toward summer in the northern hemisphere. We would expect that winds would be picking up and it could get more common.鈥�
Cassini is making one last visit in April 2017, in the middle of Titan鈥檚 summer, and may pick up more evidence of the ephemeral shimmers.
鈥淭here are many reasons why we would want to go back to Titan,鈥� Hofgartner says. 鈥淗opefully, one day we would get to observe these from a lander in the sea.鈥�
This article appeared in print under the headline 鈥淲aves ripple surface of Saturn鈥檚 moon鈥�
