At Play in the Magnetic Fields of the Lord

Astroeremology is something I’ve had an armchair interest in for a number of years. Back when I first started nosing around it, bouncing ideas off PSU professors like Alex Ruzicka, I was quite taken with one geologic mystery of Mars in particular. Are any of you are familiar with the magnetic lineations the Mars Global Surveyor detected back in 1997? They’re similar – in appearance, at least – to the ones found in the Earth’s crust that led to the discovery of sea floor spreading: evidence that greatly strengthened the theory of plate tectonics. As I’m sure you’re all aware, the notion of any similar activity on Mars, even historically, is a controversial one. And given how long ago the Martian planetary dynamo shut down, the stripes there probably do tell a different geologic story. I mean, they might be hotspot artifacts or some other relic of ancient plate tectonics. Personally, though, although it may only be my chronic impishness flaring up, I agree with Ruzicka’s hypothesis that at least some of those lineations are magnetic paleodunes.

I realize this notion is complicated by a number of unanswered questions – e.g., Could highly magnetized ores be formed by eolian deposition? And even if they could, how might that happen in the absence of an atmospheric water cycle like Earth’s? &c.

I had an idea about this, based on the following (quite possibly bone-headed) assumptions: 1. Eolian deposition is routine on Mars. 2. Some sand dunes lithify. 3. Not all dunes that lithify need to do so in the context of precipitation. 4. Dunes that lithified in a post-precipitation Martian climate might do so if: 

• The obliquity of Mars changed – as it is wont to do occasionally. 

• As a result, the surface of the planet changed position relative to sun, exposing its massive CO2 ice fields in the southern polar region to increased temperatures, some of which melted. 

• Enough CO2 was released to thicken the atmosphere slightly (creating a situation in which both wind patterns changed and small quantities of groundwater were not immediately sublimed away). 

• Wind got shut off to particular dune field. 

• Subsurface ice melted slightly, owing to elevated global temperatures. 

• Moisture wicked up into the dune (because of the new temperature gradient), where it facilitated diagenesis. 

But who knows, really? If they are paleodunes, they may have formed in the context of rain in some remote eon of Martian history. By counting the number of impact craters, measuring their size, and looking for evidence of previously observed erosion patterns, we should be able to date paleodune fields to known geochronological benchmarks, at the very least. If someone – or something – would take a closer look, all sorts of interesting, better-informed questions might be asked. This sort of thing didn’t exist back then, so it may be that MOLA, HRSC, and other instruments have helped sort the mystery out already. If so, I haven’t read about it.

If we (where “we” = “someone, anyone, please”, although there is nothing but an orogeny of other priorities to stop me from acquiring a student edition of ArcGIS Pro and looking back into this myself) do identify topography consistent with paleodunes in those cratered highlands, I’d love to see us drop a robot down to check them for magnetite, limonite, and other hematitic precipitate cements one would expect to see in a lithification process that involved extremely slow, very low T/P redox reactions – which would probably have reinforced the remnant magnetism in the hematite dust.

And, heck, if those magnetic lineations aren’t dunes, that’s probably even more interesting.

2 Responses to “At Play in the Magnetic Fields of the Lord”

  1. CP Says:

    Really enjoyed this one, brother.

  2. wchambliss Says:

    Glad to hear it!

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