The Cassini probe recently spotted a monstrous ice cloud in the moon’s low- to mid-stratosphere. The ice clouds have been seen at an altitude of about 124 miles (200km). This is the first time any spacecraft has seen the onset of a Titan winter.
Existence of the polar cloud suggests the onset of winter is rapid and harsh. NASA says that the system peaking at an altitude of about 124 miles is much bigger than previously discovered ice storms. Currently, a giant polar vortex brews on Titan with winter setting in on the satellite’s South Pole.
The new cloud was found in the lower stratosphere, where temperatures are even colder. The ice particles are made up of a variety of compounds containing hydrogen, carbon and nitrogen.
Carrie Anderson, the lead researcher behind the discovery, was quoted as saying by DailyMail.com that the new cloud spans about 5 degrees in latitude.
Anderson introduced the findings November 11th at the Assembly of the Division of Planetary Sciences of the American Astronomical Society in Maryland.
The storm appears to have occurred as sinking gases, a mixture of smog-like hydrocarbons and nitrogen-bearing chemicals called nitriles, encounter colder and colder temperatures on the way down. Different gases will condense at different temperatures, resulting in a layering of clouds over a range of altitudes.
Five degrees in latitude means the cloud is about 150 miles (240km) across. Using the Composite Infrared Spectrometer, or CIRS, Cassini’s infrared instrument detected the new cloud. Scientists expect it to have a low density, which is similar to Earth’s fog.
This is not the first time that an impressive cloud has been spotted by the probe, it has happened before, but the new discovery has shed more light on why the storms form, and also suggests that they could be far stronger than previously observed.
For the past few years, Cassini has been catching glimpses of the transition from fall to winter at Titan’s South Pole, the first time any spacecraft has seen the onset of the season on the moon.
A Titan season will last about seven and a half years, according to Earth’s calendar. This means that the South Pole will still be enveloped in winter in 2017 when the Cassini mission ends.
Anderson of NASA’s Goddard Space Flight Center said that when the infrared data is considered, this ice cloud has stood out like nothing seen before.
If the ice clouds at Titan’s pole and rain clouds on Earth are compared, there are several similarities.
Water tends to evaporate from the surface in rain clouds and encounters cooler temperatures as it rises through the troposphere.
Clouds form when the water vapour reaches an altitude where the temperature and air pressure combination is apt for condensation.
When it comes to methane clouds in Titan’s troposphere, they are formed in a similar manner but the polar clouds on the moon form higher in the atmosphere through a different process.
Cassini had arrived at Saturn during mid-winter at Titan’s north pole in 2004. Because of the north pole transitioning into springtime, the ice clouds were then disappearing.
Meanwhile, new clouds have been forming at the south pole.
The build-up of these southern clouds is an indication about a change in the direction of Titan’s global atmospheric circulation.
Scientists have been able to uncover more about the nature and severity of Titan’s winter as they analyze the size, altitude and composition of the polar ice clouds present. Cassini’s camera has captured images of the ice clouds and scientist have concluded that the temperatures at the south pole must get down to at least -238 degrees Fahrenheit (-150 degrees Celsius).
Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory, said that Titan’s seasonal changes continue to excite and surprise.
‘The opportunity to see the early stages of winter on Titan is very exciting,’ said Robert Samuelson, a Goddard researcher working with Anderson added.
Cassini will provide more clues for scientists to analyze and learn more about Saturn and Titan.