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By Jacob Siegal, BGR
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.
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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.”
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