A peculiar flash of light glinting from Saturn's largest moon confirms what's been suspected for years: liquid lakes exist on the surface of Titan!
[Click to entitanate.]
The image above was taken on July 8, 2009 by the Cassini spacecraft. Light can reflect off the surface of liquids, producing a little sparkle or glint, called a specular reflection. Knowing that earlier images had shown what look to be lakes of liquid methane on Titan, they kept their eyes open for Cassini's images of the moon to show such a glint. There are lots of lakes in the northern hemisphere of Titan, making the odds better it would be seen there, but it was only last year that spring sprung in Titan's northern latitudes. That's when it was finally possible to see sunlight plinking off of any purported standing liquid.
And that's what we're seeing here. They checked to make sure this wasn't some other source of light like lightning or geologic activity, and were able to trace the position of this glint to the shores of a monstrous lake called, appropriately, Kraken Mare. It's a sprawling 400,000 square kilometers, bigger than the Caspian sea!
Titan's atmosphere is thick and hazy, so visible sunlight isn't strong enough to produce a glint. The image was taken at 5 microns, well into the infrared, where Titan's atmosphere is essentially transparent. Cassini was about 200,000 km (120,000 miles, about half the distance of the Earth to the Moon) away from Titan when the image was taken.
It's a cool picture! It looks a lot like images of Earth taken from space. I don't mean the color or fuzziness -- both due to Titan's smoggy air -- but just the way our brain recognizes how a flash of light like that is from liquid. We have to double check our brains, of course, since we're easily fooled, but the confirmation of it satisfies some part of my own brain that likes to categorize things.
And it also brings home, so to speak, just how Earthlike this alien world is. It has a thick atmosphere, weather, and a hydrological cycle... except where we have water, Titan has methane. And of course it's incredibly cold there; water would be frozen into ice literally as hard as rock. But liquid on the surface harkens to another part of our brain, the piece that asks if life could arise in such a place.
The answer is, of course, we don't know. Not for sure. But we can't rule it out, either.
The more we learn about Titan -- and everywhere in our solar system -- the more intriguing and beguiling it gets. I know that even now scientists are planning the next generation of exploratory spacecraft. I hope one of them will take a much closer, and much wetter, look at this giant satellite world.