A Swirly Lava Pool on the Moon

[n2doc]

Phil Plait, Slate
Look, I’ve been doing this a while. I’ve seen it all, right? Fresh craters on the Moon. Rocks rolling on the Moon. Spacecraft crash sites on the Moon. Cripes, even the Apollo landing sites seen from orbit.

So c’mon, Lunar Reconnaissance Orbiter (LRO), you think you can surprise me with a picture of the Moon these days? What’ve you got? A swirly spiral whirlpool of rock or something?



I have to admit, when I saw this picture I literally gasped and smiled. I have never seen anything like this on the Moon, but it was immediately clear what it was: a melt pond. That’s where molten rock (lava, say, or rock molten by a large impact) flows into a depression to form a pond, and then hardens. Usually these have a flattish surface and are circular, but not always. Still, a spiral? That’s really, really weird.

But it’s not hard to think of ways this could’ve formed. Molten material could’ve flowed in off-center, for example, off to the side, forming a current that would spin around, shaped by the pond’s rim (this video of equatorial fakers might help make that clear). Another possibility is a small landslide swirled the cooling material around, pushing it off-center and starting up rotation (though this seems unlikely to me; the ponds don’t take all that long to cool, so the timing would’ve had to have been quick). Perhaps friction sheared the material flowing in, slowing some parts but not others, which again could easily start up rotation.

Whatever started it, I’m more amazed that the action was frozen in time the way it was, the rock hardening in place yet still showing the effects of the spin. The material must have been pretty viscous, or else it would’ve settled into a flat surface. The pond is about a kilometer (0.6 miles) across, by the way.

more

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[Thor_MN]

2. Sand worm pit. Step into that are you are a goner.

[grahamhgreen]

12. Yep. Lost a platoon to those on Ganymede.

[AsahinaKimi]

3. In a few thousand years..

It will probably be a golf course for the elite.

[nikto]

11. How depressingly true, AsahinaKimi

[Maedhros]

4. Lunar basalt is relatively inviscid.

This would allow for the swirling.

[chknltl]

5. Sand in an hourglass phenomenon?

As looked at from the top, sand flowing through a funnel shape forms similar swirls. Is it possible there are similar forces at work here? Maybe there is/was a large hollow below where this material was flowing into before hardening.

[chknltl]

6. "Swirly Thing Alert" from Red Dwarf

http://www.google.com/url?sa=t&source=web&cd=1&ved=0CDkQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DQa_gZ_7sdZg&ei=Wfi7UeOcC8aWqAHLzYDACg&usg=AFQjCNGfqL9dhjK2gKHHonF-TB2vpySzBA

[Spitfire of ATJ]

7. Let's pull the plug on a mission.

[greiner3]

8. To me;

It looks like a spiral galaxy.

Maybe our own?

Conspiracy Theorists anyone?

[n2doc]

9. It's a Map!

Look for the "you are here" sign...

[nikto]

10. I'll just rely on the Mars anomaly talking points...

They're frozen sand dunes.

That is your answer and don't ask any more questions.

[perfessor]

13. Meanwhile, on the other side

The spirals go the other way.