PASADENA, Calif. – A new discovery has been made by NASA’s Cassini Solstice Mission. The spacecraft revealed data tying a shift in seasonal sunlight to a reversal in the circulation of the atmosphere of Saturn’s moon, Titan, at unexpected altitudes.
There is definitive evidence at Titan’s south pole showing sinking air where it was upwelling earlier in the mission. Thus, the key to circulation in the atmosphere of Titan is a certain slant of light.
In addition to the evidence of sinking air, Cassini also found complex chemical production in the atmosphere at up to 400 miles above the surface. This means the atmospheric circulation extends about 60 miles higher than previously thought.
Compression of the sinking air as it moved to lower altitudes produced a hot spot above the south pole. Scientists were also able to see very rapid changes in the atmosphere and pinpoint the circulation reversal to about six months—around the August 2009 equinox—when the sun shone directly over Titan’s equator. The circulation change meant that within two years of equinox, some gases increased 100-fold—much more extreme than anything seen so far on Titan.
The results also suggest that a detached layer of haze, first detected by NASA’s Voyager spacecraft, may instead be the region where small haze particles combine into larger, more transparent, clumped aggregates that eventually descend deeper into the atmosphere and give Titan its characteristic orange appearance.
These findings were published in the journal Nature. Nick Teanby, the study’s lead author and a Cassini team associate, said, “Cassini’s up-close observations are likely the only ones we’ll have in our lifetime of a transition like this in action. It’s extremely exciting to see such rapid changes on a body that usually changes so slowly and has a ‘year’ that is the equivalent of nearly 30 Earth years.”
Titan is the only moon in our solar system to have both a solid surface and a substantial atmosphere. Titan has been described as a pre-biotic Earth and could help scientists better understand how life arose on our own world.
“Understanding Titan’s atmosphere gives us clues for understanding our own complex atmosphere,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory. “Some of the complexity in both places arises from the interplay of atmospheric circulation and chemistry.”
The pole on Titan experiencing winter is usually pointed away from Earth, but since Cassini has been in orbit around Saturn (the spacecraft arrived in 2004), the moon has been studied from angles unattainable from Earth.
According to NASA’s mission page, it is a top priority to see Titan’s surface in the act of changing, and thanks to Cassini these changes can be watched as they develop over time.
Cassini instruments recently obtained images of the formation of haze and a vortex over Titan’s south pole. The composite infrared spectrometer (CIRS) data also revealed changes in hard-to-detect vertical winds and global circulation.
“Next, we would expect to see the vortex over the south pole build up,” said Mike Flasar, the CIRS principal investigator at NASA’s Goddard Space Flight Center. “As that happens, one question is whether the south winter pole will be the identical twin of the north winter pole, or will it have a distinct personality? The most important thing is to be able to keep watching as these changes happen.”
The Cassini Solstice mission is scheduled to last through September 2017 and is named for the Saturnian summer solstice that will occur in May 2017.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA), and the Italian Space Agency. NASA’s Jet Propulsion Laboratory manages the mission for NASA’s Science Mission Directorate.