I'm interested in planetary materials, including their early evolution in the solar system, re-creating their exotic properties in the lab, and extracting them sustainably as space resources.
Dec 11, 2:28pm: Ancient Hydrated Silicates in the Martian Deep: Crustal Density, Water Budget, and Astrobiology. 2018 AGU Fall Meeting, Walter E. Washington Convention Center 206.
1. Carbonaceous muds (Recent abstract).
2. Martian clay formation and noble gas sequestration in the pre-Noachian (Recent publication).
3. High fidelity regolith simulants (Recent publication).
My new paper — Evidence for a Widespread Basaltic Breccia Component in the Martian Low-Albedo Regions from the Reflectance Spectrum of Northwest Africa 7034 [whew!] — will come out shortly in the journal Icarus, co-authored by Jack Mustard and Carl Agee. I wanted to give some backstory on how it came to be, to complement the online media blitz. This paper got its beginnings at The Woodlands Waterway Marriott Hotel last March: “Sure, I’ve got some upstairs in my room. I’ll go get it for you.” No, this wasn’t the sound of me scoring drugs, but securing a 0.99 gram chip of the martian meteorite Northwest Africa (NWA) 7034, known as Black Beauty, from Carl. NWA 7034 was already setting the planetary science world on fire, and now I had a piece; at roughly $10,000/g on the open market, a very expensive piece. I put it in my pocket.
Currently there are 79 collected and cataloged rocks known to have made their way from Mars to Earth. These are all basaltic/ultramafic samples, and that makes sense given everything we know about Mars. Pockets of trapped martian atmosphere in some of them confirmed the link beyond any reasonable doubt. But there’s always been a problem. The bulk chemistry of the martian meteorites — collectively the Shergottite, Nakhlite, and Chassignite (SNC) group — doesn’t match Mars’ crust. Neither does their spectral signature, as Vicki Hamilton demonstrated back in 2003 at thermal wavelengths (the story is the same in the visible/near-infrared (VNIR)). After Carl Agee showed that Black Beauty was different, that it was a breccia matching bulk Mars in chemistry, I had an obvious question: what does its spectrum look like?
We started by measuring the solid chip at RELAB, narrowing the aperture down to about a 1 mm spot size. We targeted some of the different clasts in the VNIR, then went back and did a couple additional measurements of more matrix-rich material. The results, in the words of Jack Mustard: “Looks like we’re not in Kansas anymore.” This meteorite was DARK. Like, really dark. It had a few subtle bands from pyroxene, but otherwise the spectra had more in common with a carbonaceous chondrite than an SNC meteorite. Importantly though, it looked like low-albedo martian terrains from OMEGA data. Switching to longer wavelengths with the FTIR, the picture got even richer: NWA 7034 was a much better match for ‘Surface Type 1’ — the majority of the planet that’s interpreted to be unaltered basalt — than any of the SNCs measured before. Now, we didn’t do true thermal emissivity measurements here (we used Kirchoff’s law to convert reflectance to emissivity), so folks at ASU might have some qualms, but we’re confident in the interpretations.
At this point we had enough to publish, but we wanted to get a handle on exactly why Black Beauty is so dark and spectrally featureless at VNIR wavelengths. Fortunately we had contacts at Headwall Photonics, who are doing really cutting-edge work on hyperspectral imaging technology. We brought our NWA 7034 sample up to Fitchburg, MA and measured it at Headwall’s facilities; to our knowledge this was the first time a hyperspectral camera had been used to image a meteorite. The results from hyperspectral images showed that it is the matrix that causes Black Beauty’s spectral properties. You can find clasts of pyroxene and basalt inside NWA 7034 that spectrally resemble the SNCs, but averaging over the entire surface of the chip gives a flat, dark spectrum similar to Mars’ surface, and similar to isolated pixels of the most matrix-rich material. It still isn’t totally clear which aspects of the matrix are most important in causing the meteorite’s low albedo. It could be the incredibly fine grain size, the high magnetite content, or exogenous carbonaceous infall that got incorporated into the breccia. All of these probably play a role. Either way, we argued from our results that most of the low-albedo regions on Mars probably contain a good fraction of brecciated material like NWA 7034, mixed with more intact volcanic rocks, dust and glass (alteration minerals aren’t visible on a global scale). This only makes sense given that Mars hasn’t been resurfaced globally since the heavy bombardment, and its crust should be beaten and battered like that of the Moon.
What’s next? Nothing for now, but currently we’re working with Justin Filiberto on a martian gabbroic meteorite, so stay tuned on that front.