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Unmanned _ Lunar Exploration _ Lunar swirls created by comets?

Posted by: TheAnt Jun 11 2015, 03:32 PM

This piece is not about any specific mission, even though the swirls have been imagined by orbiters.
I might be relevant since it could give an insight for some various features we discuss on this forum.

Posted by: ZLD Jun 11 2015, 05:40 PM

I'm out of the loop as far as these types of simulations. What does such data look like when they say it appears consistent?

Posted by: marsbug Jun 12 2015, 09:18 PM

QUOTE (TheAnt @ Jun 11 2015, 04:32 PM) *
This piece is not about any specific mission, even though the swirls have been imagined by orbiters.
I might be relevant since it could give an insight for some various features we discuss on this forum.

I blogged on this a litte while ago. I can't say my research was PhD level exhaustive (writing the blog is just a hobby) but these patterns seem to be fairly well accepted. Some of the images and the correlaton between the discoloured areas and the local magnetic fields are quite interesting.

Posted by: dvandorn Jun 13 2015, 01:10 AM

Yeah -- I just can't see comets producing the extremely large extent of the swirls as observed. The brightening effects of gas flow over the surface would be darkened over the course of time, such that if the swirls were from such gas transport, we would see them for a relatively short time. Since gas transport just "freshens up" the regolith, the constant rain of small to tiny impactors will darken that kind of thing in timescales far, far shorter than the darkening of rays from impacts.

Also, over a long period of time, you'd expect cometary impacts all over the lunar surface, and in fact they'd have to have happened all over the Moon's globe. We're supposed to believe that they only happened around Reiner Gamma and the few other places we actually see them? I also strongly question that gas transport brightening of the soils would last even a hundred thousand years, much less the 100 million years noted in the article.

Finally, the swirls do seem to be associated with magnetic anomalies. Why would gas transport cause magnetic anomalies? And only in the limited areas where we see the swirls?

I just don't think the comet impact theory works.

-the other Doug

Posted by: TheAnt Jun 13 2015, 07:51 AM

@marsbug: Oh you even wrote a blog about them, Im not the only one who noted this research then. =)

I fully agree with dvandorn that finding these features at the same sites as magnetic anomalies is an odd coincidence so don't think we should embrace this hypothesis fully yet. Unless someone could explain how the impact of a comet create a magnetic field. Nevertheless, with higher resolution images coming up at Ceres, not to mention Pluto, I thought this might be one kind of surface feature we could be on the lookout for in days to come. =)

Posted by: marsbug Jun 13 2015, 11:18 AM

Ah, i thought you were unconvinced that the swirls were a real phenomena, maybe in the same way that many see crepuscular rays as being some kind of optical illusion. Also I was shamelessly taking a chance to mention my blog, but i do also love a chance to point out how much interesting lunar science there still is to do.

Actually i do have a further thought: Many years ago i did my phd on plasma sputterinng, incluxing sputtering of powders. It should be fairly easy to set up powder targets of simulated lunar regolith, and a sputtering atmosphere of solar wind composition and the right energy. Not trivial, but completely do-able. Vararions in magnetic field can also be aarranged, and so we could try to gauge the possible effects of soar wind on regolith and see if it explains the swirls. I expect this has been done, but i don't recall reading any papers on it...

Posted by: TheAnt Jun 13 2015, 01:47 PM

Oh I have no doubt that they're real features, but now that you mention it, it's true that light have to fall in the right angle to make them clearly visible. So the swirls are a bit elusive.

It was however dvandorn who expressed the strongest doubt, and I tend to agree insofar that a second look at the alternative explanations should be looked into. And I think you nailed it there marsbug, since the solar wind is the alternative I had in mind. It would also provide a mechanism to maintain the swirls even in one environment of constant micrometeorite bombardment.

Posted by: dvandorn Jun 13 2015, 06:24 PM

The explanation I have read is that localized magnetic fields redirect some of the incoming solar wind charged particles, "shadowing" the areas in the swirls from solar wind bombardment. The idea is that the solar wind darkens the regolith over time, and the shadowing effect reduces the solar wind flux along the magnetic field lines. Since the swirls can be thought of as a 2D representation of the 3D field lines above these areas of localized magnetic fields (just as a shadow of a 3D object on the floor is a 2D representation of the object casting the shadow), you get swirling patterns of regolith that has not been darkened by the solar wind flux, and thus appear lighter.

There may be other magnetic effects, including electromagnetic lifting and depositing of dust, with the localized magnetic fields affecting the pattern of deposition. I've seen papers about this "levitation" of lunar dust along the dawn terminator (possibly observed by both ALSEP dust detectors and by one of the Surveyors), and I read one theory (sorry, can't remember where) that the magnetic anomalies disrupt that process and cause suspended dust to fall abruptly, or at least be transported along the field lines. That could also explain how the brighter regolith is "freshened" over time.

Again, I think these theories (especially the first one) are somewhat well-accepted. I'd believe them more than the Brown University study.

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