Cassini Captures Cloud Movement Over Ligeia Mare
If you’ve ever been aboard a sailing ship, you probably know the sensation of the craft cutting through the ocean, wind at your back and a breeze in your face. It’s probably the same sensation you get when you go hang-gliding, or water (or snow) skiing.
It turns out, if you lived on Saturn’s icy but intriguing moon Titan, you could experience the same sensations (provided you could survive the atmosphere and cold temperatures). Of course, your ship would need to be able to withstand the frigid methane sea, and the cold, largely nitrogen (with small amounts of methane and hydrogen) atmosphere.
The clouds would be made of methane, possibly some ammonia, and other hydrocarbons. Feeling the breeze on your face would require you to withstand an atmospheric pressure about 1.5 times that of Earth’s sea level, and near-surface temperatures of about 94 Kelvin (-297 F, or -179 C). Not impossible, but right now, pretty improbable. That’s why we have the Cassini-Solstice Mission — to give us a spacecraft-eye view of what it might look like from above.
So, what would a cloudy, breezy sea day on Titan be like? Cassini scientists just released an animation of clouds blowing across the surface of the northern Titan sea called Ligeia Mare. In the sequence (which you can see here), the clouds blow just over the hydrocarbon-rich sea at speeds of around 7 to 10 miles per hour (3-4.5 meters/second). These images were taken a few weeks ago (late July), and the formation of the clouds and their actions may be harbingers of summer on Titan.
Titan does indeed have seasons during its 30-Earth-year-long year. Each of those seasons lasts about 7 Earth years, giving plenty of time for seasonal change to occur. When Cassini first arrived at Saturn and began studying this moon, its northern pole was pointed away from the Sun, which put it in high winter. At that time, the north polar region was shrouded with a hazy hood. There was a lot of cloud activity in the southern hemisphere (during its summer, when things were a bit warmer (relatively)).
As equinox approached, when both northern and southern hemisphere Titan got equal amounts of light and heat from the Sun, the northern polar hood shrank. Cloud activity continued for a while, until the passing of a large storm in 2010. Then, cloud activity dropped quite a bit. In the approach to northern hemisphere summer (southern hemisphere winter), the northern hood nearly disappeared, and now that we’re starting to see northern summer and southern winter. This latest discovery of clouds above a northern hemisphere ocean could signal summer weather patterns. Their appearance also leads the science team to speculate about whether (or how) the clouds are rela ted in some way to the seas. It’s possible that clouds form over the seas as a matter of course, but it’s also possible that Cassini just happened to catch some clouds racing over the ocean surface as part of a larger-scale circulation pattern.
Cassini will continue studying atmospheric change at Titan during the upcoming northern hemisphere summer (southern hemisphere winter). Already it has given us a great deal of information about the only other world in the solar system (besides earth) that has a fully developed atmosphere (and could possibly be habitable to certain forms of life). Stay tuned!