Wocka wocka wocka Mimas wocka wocka

The entire universe in blog form
March 30 2010 7:30 AM

Wocka wocka wocka Mimas wocka wocka

New data from Cassini were just released, showing a thermal map of Saturn's "Death Star" moon Mimas. This map shows where the smallish moon is warmer than in other places, and can reveal a lot about its surface. The scientists expected to see it being warmest pretty much in the middle of the map, since the Sun was shining down on that spot at the time the map was made. As you go progressively farther from that spot, it would get cooler.

What they got, though, was this:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies!  

Advertisement

cassini_titan_pacman

Um. That looks familiar. If the warm part eats that dot in the middle, will the other moons of Saturn turn into ghosts so Mimas can eat them and get points?

Anyway, on the left is the visible light view of Mimas, and on the right is the temperature map. Yellow is warm (well, 92 Kelvin or -290 F) and blue is cooler (77 K or -320 F). That's not at all what was expected! The parts that should be warmest are actually cool, and the cold spots are too warm! Worse, perhaps, is the shape of the boundary. You'd expect a smooth transition from warm to cold, and it would be circular in pattern. Instead, we get this sharp, V-shaped thing!

It's not known why things are so messed up on Mimas. Maybe the distribution of materials on the surface is uneven, causing an odd heating pattern. The warm spots might be covered in a material that is slow to lose heat (so it stays warm long after the Sun sets), and the cooler spots are covered in a material that is very slow to heat up (so they remain cool when the Sun is high in the sky). Maybe the cooler stuff is just coated with something that reflects a lot of heat from the Sun, so it never warms up. I imagine more temperature maps like this one, taken at different parts of the Mimas day, may help sort that out. Emily Lakdawalla at The Planetary Society has a far more in-depth description of this.

This map makes me very happy. Not because a gigantic PacMan hundreds of kilometers across is wocka-wocka-ing across a moon of Saturn (though that helps). It's because this is a complete surprise. No one expected this! Now we have scientists scrambling to figure it out, and that makes scientists happy.

After all, folks, if we had all the answers, and no surprises were left, we wouldn't call it exploration, would we?