A Glint of Sunlight from Titan

Among the trove of discoveries being amassed by NASA's Cassini orbiter are a few that stand head and shoulders above the rest. One of those is the realization that Titan, Saturn's big moon, has lakes of liquid hydrocarbons on its surface.

A couple of years ago, I would have written that as "probably has lakes," because the circumstantial evidence for them was strong &mdash: but not ironclad. The spacecraft had returned images showing large, dark, irregularly shaped blobs in its polar regions, some of which changed shape since Cassini's arrival in 2004. The case got much stronger when radar scans revealed that these enclosures had very smooth surfaces, and an infrared spectrometer found liquid ethane (C₂H₆) within one of them.

Now the Cassini team has found the smoking gun they've been seeking. The image here shows a glint of sunlight reflecting off one of the moon's northern lakes, a region that's been in darkness during the mission until Saturn recently passed through equinox and spring returned to the northern hemisphere. Cassini's visual and infrared mapping spectrometer (VIMS) recorded it at infrared wavelengths near 5 microns, at which Titan's dense, hazy atmosphere appears relatively transparent. VIMS took the image back on July 8th, but it wasn't made public until late last week.

Hints of specular reflection off of liquids on Titan's surface had been seen in 2003, using radar pulses from the giant radio dish at Arecibo, Puerto Rico. But that effort probed a region near 26° south, and there was no way to pinpoint a specific feature associated with it.

Not so with Cassini's sunglint. After careful checking, team scientists traced this specular reflection to the southern shoreline of a lake called Kraken Mare at 71° north, 337° west. One of the moon's biggest pools, Kraken Mare covers about 150,000 square miles, an area larger than the Caspian Sea on Earth.

Apart from its scientific importance, I just find this image visually stunning. I hope you do too.