For the first time, NASA’s Cassini spacecraft has recorded the effect of changing seasons on Saturn’s Earth-like moon Titan.Titan is the second-largest moon in our solar system and the only one to have an atmosphere similar to our own on Earth. Images from Cassini’s ISS camera show a change in the direction of atmospheric circulation on Titan; an event which only happens once every 15 years and is never visible from Earth.
"Cassini's up-close observations are likely the only ones we'll have in our lifetime of a transition like this in action," said Nick Teanby, the study's lead author who is based at the University of Bristol, UK. "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."
The change, visible in the form of a vortex at Titan’s south pole, marks a shift in Titan’s seasons as it entered Winter in 2011. The changing seasons on Titan are comparable to our seasons on Earth due to the tilt of Titan’s axis, which is at a similar angle to the sun as our own. However, a year in Titan’s takes place at a markedly more relaxed pace than our own; taking 29.5 Earth years as this is the time it takes Saturn to orbit the sun.
The scientists were able to record the season change in detail by tracking the shifts in chemical tracers and Titan’s atmospheric temperature using infra-red spectroscopy. They were surprised to find that the changes occurred much higher up in the atmosphere than expected, at altitudes of over 450km. Their findings are published today in the journal Nature.
"Understanding Titan's atmosphere gives us clues for understanding our own complex atmosphere," says Scott Edgington, a Cassini project scientist at NASA's Jet Propulsion Laboratory, California.
Teanby also added: "Our results provide a powerful new constraint for atmospheric models of Titan. Titan provides a natural laboratory for an Earth-like atmosphere in the cold outer solar system. So, these results could eventually lead to a more complete understanding of atmospheric processes on Earth, other Solar System planets, and the many exoplanetary systems now being discovered."
Cassini, NASA’s robotic spaceship has been exploring some of the most distant parts of our solar system since 2004. While Cassini orbits Saturn, a second part of the ship 'Huygens' landed successfully on Titan in 2005, the first landing to take place in the outer-solar system. Titan is also the only object, other than Earth, in our Solar system which appears to have stable bodies of liquid on its surface.