NASA’s Cassini orbiter has been dead for well over a year now, but its incredible discoveries continue to trickle in as researchers pore over data and images it collected while it was active.
Consequently, studies focused on the orbiter’s findings continue to crop up on a regular basis, such as a recent study from University of Idaho in Moscow doctoral student Rajani Dhingra, who, along with her colleagues, found evidence of rainfall on the north pole of Saturn’s largest moon, Titan, in an image taken on June 7th, 2016. This indicates that summer had arrived on the moon’s northern hemisphere later than climate models had predicted.
“The whole Titan community has been looking forward to seeing clouds and rains on Titan’s north pole, indicating the start of the northern summer, but despite what the climate models had predicted, we weren’t even seeing any clouds,” said Dhingra, lead author of the study. “People called it the curious case of missing clouds.”
Dhingra and her colleagues spotted a reflective feature near the north pole of Titan in the aforementioned image — a feature which covered approximately 46,332 square miles — which had never appeared before, and didn’t appear when Cassini passed by again. Dhingra concluded that the reflective nature of the feature was due to sunlight reflecting off of a wet surface, which she believes was the result of a methane rainfall event.
This is the first time summer rainfall has ever been observed on Titan. While Earth experiences four seasons over the course of a year, a single season on Titan lasts seven Earth years. When Cassini reached Titan, clouds and rainfall were observed in the southern hemisphere, signaling a southern summer. Climate models predicted the rain would move to the northern hemisphere “leading up to the northern summer solstice in 2017,” but the clouds still hadn’t appeared by 2016. The images above should help reseachers understand why this was the case.
We want our model predictions to match our observations. This rainfall detection proves Cassini’s climate follows the theoretical climate models we know of,” Dhingra said. “Summer is happening. It was delayed, but it’s happening. We will have to figure out what caused the delay, though.”