Titan, Saturn’s largest moon, is a surprisingly dynamic world, with a dense atmosphere and shallow oceans of liquid methane. Like the fictional land of Westeros in Game of Thrones, the seasons on Titan lasted roughly seven years, and summer must have hit its northern hemisphere in 2016. But, oddly enough, it didn’t come as expected. Now, astronomers have analyzed images from the Cassini spacecraft and found evidence of rain, indicating that summer is finally approaching.
When Cassini first arrived at Titan in 2004, the southern hemisphere of the moon was enjoying summer, and the spacecraft observed a layer of cloud and rain on that half of the moon. Astronomers developed climate models of Titan from Cassini data, which predicted that there would be a similar climate throughout the Northern Hemisphere as the seasons changed.
But it was not like that. According to climate models, the northern summer solstice would start in 2017, but until 2016 no clouds were seen, which puzzled scientists.
“The whole community has been expecting to see clouds and rain at Titan’s north pole, indicating the onset of summer in the north, but despite what the climate models had predicted, we didn’t even see clouds,” says Rajani Dhingra. , study leader. “Some called it the curious case of the lost clouds.”
But clouds may not be the only indicator of a seasonal change in weather. Dhingra and his team found a strange anomaly in an image taken by Cassini on June 7, 2016, which was not shown in images taken during earlier or later flybys. Much of the moon’s surface, measuring about 120,000 square kilometers, had suddenly turned reflective.
This new reflectance was attributed to the “wet soil” effect after the rain. But, of course, we must bear in mind that it would not have been an earthly rain of water as we are used to on Earth: on Titan it rains liquid methane.
Scientists say the shape of the pattern suggests that the rain fell on rough, rocky terrain rather than a smooth surface, which would have produced a more circular reflective spot.
While the predictions may have been misleading, it seems like summer has come to North Titan after all. The next step, scientists say, is to investigate why it was so late, which may require an adjustment of current climate models of Saturn’s largest moon.
Titan has many similarities to our home planet. Like Earth, Titan has seasons and rain. But on the rocky Saturnian moon, it looks a little different. Aside from liquid methane, and scientists aren’t sure exactly why, it rains much less on Titan than it does on our planet. In fact, during Cassini’s 13-year mission, observing Saturn and its moons, it only saw rain on Titan a few times. Also, since Titan’s gravity is about one-seventh the gravity of Earth, raindrops fall more slowly. The methane rain on Titan falls in the same way that snowflakes fall on Earth.
“We want our model predictions to match our observations,” says Dhingra. “This rain detection proves that Cassini’s climate follows the theoretical climate models that we know. Summer is taking place. It was delayed, but there it is. However, we will have to find out what caused the delay, ” he concludes.
Referencia: Rajani D. Dhingra et al, Observational evidence for summer rainfall at Titan’s north pole, Geophysical Research Letters (2019). DOI: 10.1029/2018GL080943
