Glint of sunlight shows liquid on Saturn’s largest moon


Washington : A glint of sunlight reflected off a lake on Saturn’s largest moon Titan has confirmed the presence of liquid on its surface.

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The image was captured by NASA’s Cassini spacecraft.

Titan has captivated scientists because of its many similarities to the Earth. Scientists have theorised that Titan’s cold surface hosts seas or lakes of liquid hydrocarbons, making it the only other planetary body besides the Earth believed to harbour liquid.

“This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness,” said Bob Pappalardo, Cassini project scientist, based at NASA’s Jet Propulsion Lab in California.

“It’s an unsettling combination of strangeness yet similarity to the Earth. This picture is one of Cassini’s iconic images,” Pappalardo said.

Cassini scientists had been looking for the glint, also known as a specular reflection, since the spacecraft began orbiting Saturn in 2004. But Titan’s northern hemisphere, which has more lakes than the southern hemisphere, has been veiled in winter darkness.

The sun only began to directly illuminate the northern lakes recently as it approached the equinox of August this year, the start of spring in the northern hemisphere.

Titan’s hazy atmosphere also blocked out reflections of sunlight in most wavelengths. This serendipitous image was captured on July 8, using Cassini’s visual and infrared mapping spectrometer.

In 2008, Cassini scientists using infrared data confirmed the presence of liquid in Ontario Lacus, the largest lake in Titan’s southern hemisphere. But they were still looking for the smoking gun to confirm liquid in the northern hemisphere, where lakes are also larger.

Katrin Stephan of the German Aerospace Centre (DLR) in Berlin, an associate member of the Cassini visual and infrared mapping spectrometer team, was processing the initial image and was the first to see the glint on July 10.

“I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean,” Stephan said. “But we also had to do more work to make sure the glint we were seeing wasn’t lightning or an erupting volcano.”

Team members at the University of Arizona, Tucson, processed the image further, and scientists were able to compare the new image to radar and near-infrared-light images acquired from 2006 to 2008, said a NASA release.

The image was presented Friday at the meeting of the American Geophysical Union in San Francisco.