Somewhat surprising findings have suggested that Titan’s climate has significantly shifted at some point in the past. Whereas today this moon of Saturn only has bodies of liquid at its poles, evidence points to equatorial regions once being abundant in lakes and seas.
Titan is already known to have bodies of liquid on its surface, but unlike Earth these are composed of liquid hydrocarbons, methane and ethane, rather than water. Nonetheless, the presence of these liquids makes Titan one of the most Earth-like places in the Solar System.
Images from the RADAR instrument on the Cassini spacecraft have shown that Titan has dunes on its surface, with up to 17 percent of its surface believed to be covered in these features. But recent analysis has identified a new feature: mega-yardangs. These are wind-eroded rocky structures and ridges that are formed in soft deposits in empty lake basins. We have numerous examples on Earth. And now scientists have seen some on Titan, too.
Crucially, they were found in Titan’s equatorial regions – suggesting these regions were once notably wetter than their modern dry appearance.
"Finding yardangs at mid-latitudes on Titan means that lakes might have existed there at some point in the moon's past," Nicolas Altobelli, ESA's Cassini-Huygens project scientist, said in a statement. "As they're certainly not there now, it's a strong sign for natural climate change. This just adds to the moon's intrigue – there's much more for us to explore."
Sand dunes and mega-yardangs on Earth. ESA/DLR
Sand dunes and mega-yardangs on Titan. NASA/JPL-Caltech/ASI/ESA
Quite what happened during this change in climate isn’t clear. As the average surface temperature of Titan is currently around -180°C (-290°F), though, it would have had to be significantly warmer in the equatorial regions for liquids to exist there.
The researchers, who published their results in Icarus, came to their conclusion by comparing images of Titan from space, specifically the Cassini missions, with similar images of Earth taken by the TerraSAR-X satellite. Known as comparative planetology, the team was able to identify mega-yardangs both on Earth and on Titan, despite the images of Titan being of a significantly lower resolution.
"Comparing features on different planets is a very powerful approach," said Philippe Paillou of the Université de Bordeaux, France, lead author of the study, in the statement. "It helps us to understand the geology of regions we can't directly access. Fieldwork on Titan is still a dream, but by using Earth's surface as an analogue we can learn huge amounts about Titan's surface, despite it being over a billion kilometres away."