Astronomers finally found evidence of rainfall in the northern hemisphere of Titan, Saturn's largest moon. Using images taken by Cassini, they spotted clouds and rains that indicate the beginning of the summer season. 

The images were taken on June 7, 2016, by the near-infrared instrument onboard the spacecraft. While looking at the images, Rajani Dhingra, a doctoral student from the University of Idaho in Moscow, and colleagues spotted a reflective area in the moon that did not appear in previous and subsequent passes made by Cassini. They concluded that the reflective feature is likely the result of sunlight hitting a wet surface.

Details of the study were published in the journal Geophysical Reseach Letter. 

Summer Storms In Titan

The researchers said that the reflective surface was caused by a methane rainfall event, which was followed by a period of evaporation. It covered around 46,332 square miles. 

They also guessed that the methane rainfall occurred over a rough surface where the liquid could settle between the crevices. They argued that if the liquid fell on a smoother surface, it would accumulate into a puddle that would look circular rather than the amorphous pattern photographed by Cassini. 

"It's like looking at a sunlit wet sidewalk," commented Dhingra. 

Titan's Seasons

Scientists have long suspected that rain falls in the northern hemisphere where lakes and oceans of the moon are located. However, it has never been observed before. 

Like Earth, Titan has its own seasons that last about seven and a half Earth years, although it varies because of the orbital eccentricities of Saturn. Models predicted that clouds and rains would manifest in the northern hemisphere before the 2017 solstice but prior to the Cassini images, nothing, not even clouds, had been spotted. 

"We want our model predictions to match our observations," added Dhingra. "Summer is happening. It was delayed, but it's happening. We will have to figure out what caused the delay, though."

Scientists had previously observed rainfall in the southern hemisphere of Titan. 

Dhingra and her colleagues hope that their study could help other researchers find signs of rainfall that have eluded scientists before. She said that the wet sidewalk effect could be used to identify methane rainfall events in the Saturnian moon.