Missing: Titan’s waves. If found report to NASA

By Kruti Shrotri

Titan is one of the most intriguing bodies in our solar system. The largest of Saturn’s sixty-two moons, it is the only planetary object other than Earth known to have rivers and lakes on its surface. Like Earth, it also has rain, winds and an atmosphere, rendering it a possible contender for exotic life.

However, unlike Earth, Titan’s thousands of lakes are not made of water. Rather, they are made of methane and ethane, kept liquid by the chilling -180°c surface temperatures. It is these lakes that have been recently puzzling scientists.

NASA’s Cassini spacecraft has been exploring Saturn and its moons since 1997. In May last year, radar observations from its probe indicated that one of Titan’s largest lakes, Ligeia Mare, was exceptionally still, bearing no waves, at least not greater than a millimetre in size. Yet, there are definitely winds on Titan: the dark sand dunes that cover its landscape are evidence of them. So if there is wind, why are there no waves?

NASA Goddard Space Flight CenterResearchers have considered a number of theories, including the theory that the lake, which is thought to be liquid, is actually frozen. Another theory suggests that the lake is covered by a sticky substance, preventing waves from forming on its surface. However, no evidence to support either of these theories has been found.

The most likely theory is that the winds simply haven’t been strong enough for Cassini to see any waves. In fact, studies have shown that the winds on Titan would have to blow between at least one to two miles per hour for the lake to bear waves, higher than the estimated wind speeds of the last few years.

So will Cassini ever see any waves? Summer is approaching on Ligeia Mare, bringing stronger winds with the warmer weather. For the first time, researchers have found possible evidence of waves: a bright spot appearing and then suddenly vanishing in images from Cassini.

Whether this vanishing spot really is evidence of waves on Titan is yet to be determined, for researchers believe that it could also be explained by rising bubbles or floating solids. But whatever it turns out to be, it is certainly indicative of another dynamical process on this lively and exotic moon.


Image: ‘NASA’s Cassini Spacecraft Finds Ingredient of Household Plastic in Space’ by NASA Goddard Space Flight Center under creative commons license