I'm interested in diverse topics within planetary science, particularly surface mineralogy, comparative planetology and origins of life.
Currently working on:
Martian impact glasses: spectral properties, distributions, and astrobiology implications.
Martian meteorites: NWA 7034 (Black Beauty), NWA 6963, spectroscopic links to the surface.
Mars2020 landing site selection: mapping activities.
I've started putting together some short videos to accompany my publications, acting as a middle ground between peer-reviewed articles and popular science websites. Check out the first one below:
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.
Gravity by Alfonso Cuarón has taken in $716,392,705 in worldwide box office sales as of the time of writing. At a conservative estimate of $8/ticket, just under 90 million people saw the Clooney & Bullock flick in theaters. I think the only good thing about this is that 90 million people willingly paid to watch a film about space, and I just hope those same people go see Interstellar by Chris Nolan. Quite frankly, the message of Gravity is abysmal and discouraging. Ignore the impressive special effects, let go the scientific nitpickings, and think about the message this movie sends filmgoers home with: Space is a deadly and unforgiving place, and humans have no business being there. The final frame features Bullock, back on solid earth after her near-death catastrophe, grasping soft mud and crying in relief at the safety of terran ground. The message couldn’t be more clear: we belong on the surface, and it was folly to ever experiment by venturing upwards to the sky.
And why were Clooney and Bullock in space to begin with? Those in the know will recognize a Hubble repair mission, but Cuarón shows no hint of NASA’s scientific purpose, or goals, or of humanity’s aspirations to explore. His astronauts are fucking around with jetpacks in low-earth orbit, wasting taxpayer money, because that’s what he (and maybe most of the general public) thinks astronauts do. Of course the public can be forgiven for thinking this way, given the lull in human exploration since Apollo (thanks, Nixon), but Cuarón deserves no respite for writing and carrying through with such a dispiriting movie. Everything he gets wrong, though, Nolan gets right in Interstellar: Earth is not a safe haven to hunker down on, especially given humanity’s utter lack of stewardship for this planet. Whether it be global warming, plague, or asteroid impact, we are not safe here. We must leave the Earth to survive, and should anyways because of our unwavering instinct to explore. Interstellar’s opening act shows us what happens when we follow the logical conclusions that Gravity spells out: the dereliction of our species. But there is hope, and the tone of Nolan’s film is optimistic: if only we retain some sliver of curiosity, of pioneering (here captured powerfully by McConaughey’s character), there are infinite planets lying out there in wait. The same ingenuity that now lets us see new planets being born, and find tens of thousands of them, will one day carry us to one of these new worlds.
Interstellar is a deep, emotional, powerful film, and smug potshots at the technical details will completely miss the point and impact it delivers.
The European Space Agency is soliciting landing site proposals from the community for its 2018 (2020?) ExoMars rover, but it may not be worthwhile writing a 6-page submission. A cursory glance shows the baseline engineering requirements for the landing ellipse rule out practically every scientifically interesting location on Mars, except Mawrth Vallis. On the one hand this is a good thing: Mawrth is an outstanding landing site packed with layers of ancient clay minerals that are mostly lacking at sites like Gale Crater. Mawrth was voted as the fourth-best choice for the MSL Curiosity rover at its first landing site selection conference, and made it to the final four-candidate shortlist (only Holden Crater was initially ranked higher and remained in the final four). On the other hand, it seems rather pointless to go through a protracted series of conferences, powerpoint presentations and publications to reach a foregone conclusion. Is it really worth it, just to uphold the appearance of a democratic process? The community has already demonstrated its esteem for Mawrth, and not many feelings are likely to be crushed when it gets announced in the end.
The ExoMars rover can land between 5 degrees south and 25 degrees north latitude (half as large a swath as MSL had access to), and the ellipse is a sprawling 104 by 19 kilometers large (the final MSL ellipse was 25 by 20 km). More limiting is the elevation requirement: ExoMars must land in a flat location lower than -2 km below the MOLA datum, leaving out scientific gems like Nili Fossae and Meridiani Planum. Below is a table of the top proposed landing sites for MSL Curiosity, ranked by their scores as voted by participants at the initial selection conference. Beside each I have indicated why the site is inaccessible to ExoMars:
|MSL Proposed Site||Reason for ExoMars exclusion|
|Nili Fossae Trough||Too high, ellipse too large|
|Holden Crater||Too far south|
|Terby Crater||Too far south|
|Mawrth Vallis||All clear!|
|Eberswalde Crater||Too far south, too high, ellipse too large|
|Gale Crater Northwest Fan||Ellipse too large|
|West Candor||Too high, ellipse too large|
|Northern Meridiani||Too high|
|Juventae Chasma||Ellipse too large|
|Nilo Syrtis||Too far north, ellipse too large|