July 22, 2013
Where Did Titan’s Waves Go?
[ Watch the Video: The Mystery Of The Missing Waves Of Titan ]
Lee Rannals for redOrbit.com - Your Universe Online
Surprisingly, Titan is a world full of lakes, seas, river channels, islands, rain and mud. However, one of the big differences between this moon and Earth is that Titan's liquid is not water. Titan is far too cold for liquid water, and instead the moon features an unknown mixture of methane, ethane and various other hydrocarbons.
With all of these wet conditions on Titan, a planetary scientist on the Cassini radar team at Cornell University recently asked: "Where are all the waves?" Alex Hayes says lakes and seas on this Saturn moon are smooth as silk, with no discernible wave action down to the millimeter scale. And as he points out, this is particularly bizarre since scientists know that there is wind on the moon because Titan contains sand dunes to prove it.
Some researchers believe that the lakes are frozen, explaining why there are no waves. However, Hayes points out that scientists have evidence of rainfall and surface temperatures well above the melting point of methane.
Another explanation could be that the lakes on Titan's surface are actually covered with a tar-like substance that damps wave motion. The final, and simpler explanation, proposed by Hayes and colleagues is that the wind on the moon just isn't blowing hard enough.
Titan's northern hemisphere is being held in the grip of winter, when cold heavy air barely moves and seldom reaches the threshold for wave-making. After taking into account the gravity of Titan, the low viscosity of liquid hydrocarbons, and the density of the moon's atmosphere, the researchers concluded that wind would have to blow just one to two miles-per-hour in order to make waves.
Although there haven't been any waves detected yet, Hayes and colleagues say that the wind is coming. The sun crossed Titan's equator heading north four years ago, plunging the moon and its liquid lakes into a long winter season.
"According to [climate models], winds will pick up as we approach the solstice in 2017 and should be strong enough for waves," Hayes says.
When the waters start churning on the distant moon, NASA's Cassini spacecraft will be able to detect them. The spacecraft's radar can detect reflections from wavy lake surfaces, giving them details on wave dimensions and chemical composition. Scientists will also be able to determine the speed of the overlying winds.
Hayes says he is excited about bringing oceanography to another world. "All we need now are some rough seas," he added.
Researchers said in May that this season change could bring hurricanes to Titan as well as waves.
"If you think being a weather forecaster on Earth is difficult, it can be even more challenging at Titan," said Scott Edgington, Cassini's deputy project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We know there are weather processes similar to Earth's at work on this strange world, but differences arise due to the presence of unfamiliar liquids like methane. We can't wait for Cassini to tell us whether our forecasts are right as it continues its tour through Titan spring into the start of northern summer."