Summer storms brewing up over Titan
Sen—Renewed weather activity on Saturn's moon Titan could finally signal the onset of summer storms that atmospheric models have long predicted.
NASA's Cassini spacecraft captured images of clouds moving across the northern hydrocarbon seas in late July, as it receded from Titan after a close flyby. The spacecraft tracked the system of clouds for more than two days as it developed and then dissipated over the large methane sea known as Ligeia Mare. Measurements of cloud motions indicated wind speeds of around 7 to 10 mph (3 to 4.5 metres per second).
Saturn's largest moon, Titan, is one of the most Earth-like worlds to be found to date. With its thick atmosphere and organic-rich chemistry, Titan resembles a frozen version of Earth, several billion years ago, before life began pumping oxygen into our atmosphere.
Titan's surface is shaped by rivers and lakes of liquid ethane and methane (the main component of natural gas), which forms clouds and occasionally rains from the sky as water does on Earth. A year on Titan lasts about 30 Earth years, with each season lasting about seven years.
Northern Clouds Return to Titan. An image taken on July 21, 2014 using the Cassini spacecraft's narrow-angle camera was reprojected to create this orthogonal view. A streak of methane clouds is seen here, near centre, over the large methane sea known as Ligeia Mare. Image credit: NASA/JPL-Caltech/Space Science Institute
Cassini arrived at Saturn in 2004. For several years after, scientists frequently observed cloud activity near Titan's south pole, which was experiencing late summer at the time. The clouds continued to be observed as spring came to Titan's northern hemisphere.
In late 2010 a huge storm swept across the icy moon's low latitudes and since then only a few small clouds have been observed anywhere on the icy moon. Scientists expected clouds to return sooner, based on computer models of Titan's atmospheric circulation which predicted that clouds would increase in the north as summer approached, bringing increasingly warm temperatures to the atmosphere there.
Sen spoke to Professor John Zarnecki, a leading European space scientist at the UK’s Open University, with a special interest in Titan. He led the team that designed instruments for Cassini's Huygens lander to study its surface when it touched down in January 2005.
Professor Zarnecki told us: "As I'm sitting near the Mediteranean Sea on my holidays watching the storm clouds bubble up after a balmy day, I've just seen the latest data from Titan. They show clouds bubbling up over the sea too—not the Mediterranean but Titan's equivalent, Ligeia Mare!
“Is the underlying physics governing these occurrences the same? They probably are! By comparing the two, we can learn a lot about Titan and the Earth! But I'm glad I'm near the Med with temperatures around 30°C rather than on Ligeia Mare where its more like -170°C!"
An animated sequence of Cassini images shows methane clouds moving above the large methane sea on Saturn's moon Titan. Image credit: NASA/JPL-Caltech/Space Science Institute
Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Laboratory, said in a statement: "We're eager to find out if the clouds' appearance signals the beginning of summer weather patterns, or if it is an isolated occurrence. Also, how are the clouds related to the seas? Did Cassini just happen catch them over the seas, or do they form there preferentially?"
As the Cassini Mission progresses observing Titan's atmosphere and surface for signs of seasonal changes will continue to be a major goal as summer comes to Titan's north and the southern latitudes fall into winter darkness.