The Oceans Of Titan
I’m not quite sure what to make of this yet (and it being 6:00 am as I type might have something to do with that). But this story might be the astronomy story of the year, if it means what I think it means.
Like usual, Phil Plait at Bad Astronomy has the scoop.
A startling result from the Cassini mission has just been announced: Titan, Saturn’s giant moon, may have an ocean of water and ammonia under its surface.
Huh? How’d they do that? Relatively easily, it appears. Stuff on the surface of Titan is floating around.
Titan’s period is well-studied, and Cassini has visited Titan many times. Astronomers used the known landmarks and rotation period of Titan to predict what they will see with each visit… and they found landmarks like lakes and mountains that were far afield of where they were expected, as much as 30 kilometers (19 miles). A solid body will rotate as such, making these features very predictable. If the landmarks weren’t where they should be, then it must mean that Titan isn’t a solid body.
The more detailed story is that the crust, the surface layer of the moon must be decoupled, separate, from the interior. The only way for that to be is for there to exist a liquid layer between the surface and the core. Titan is far too cold and is comprised of the wrong material to have a hot mantle like the Earth does. Instead, scientists think it has an ocean 100 km below its frozen surface. Given the composition of the surface and the known density of Titan, they suspect it is made of liquid water and ammonia. The crust floats over this chilly liquid, and as winds blow on the surface the crust drifts, causing the predictions of landmark locations to be off.
At NASA’s Cassini Mission web-site, they’re being a bit more circumspect and cautious with the pronouncement, using words like “evidence points to…”. That’s wise.
Despite the fact that we happen to be awash in it, liquid water is a rare item in the Solar System. There’s evidence of quite a large amount being on Mars in the distant past, but there’s been no (solid) evidence of any being there now (We did think that we found some early last year, but that didn’t pan out). There’s pretty solid evidence of oceans beneath the ice encrusted surface of Jupiter’s moon Europa (You know, the one place that the late, great Arthur C. Clarke told us not to go), and Saturn’s moon Enceledas, which is known to have H2O spewing geysers. And now it looks like Titan can be added to that short list.
And of course, that’s significant, because only in the presence of liquid water do you have a chance of finding something that is recognizable as life.