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 added some software tools to the site, for now limited to MATLAB scripts used to analyze and manipulate imaging spectroscopy data. Feel free to use however you see fit!
I had the fortune to present at the 2nd workshop for the Mars 2020 landing site selection process last month. Our site, the Nili Fossae Trough, is now among eight remaining sites that will be studied in detail before the third workshop early in 2017:
During the same process for Mars Curiosity, a deep rift emerged between what can be called ‘morphologic’ landing sites versus ‘mineralogic’ landing sites. Morphologic sites tend to be younger in age, with distinct sedimentary layering visible from orbit. Mineralogic sites are rich in alteration minerals and ancient in age, but lack the geologic context needed to fully understand them from orbit. Morphology won out with the controversial selection of Gale Crater, buoyed by a key report of the working group chartered by the MSL project scientist.
That rift has returned this time in a more nuanced form: deltas versus non-deltas. Four of the final eight sites feature deltaic environments: Eberswalde, Holden, SW Melas, and Jezero. Jezero in particular is interesting because its deltas drew sediment from the carbonate and clay-rich Nili Fossae region; however, it’s also the most dangerous site to land and traverse at, and may be culled sooner rather than later for engineering reasons. The other three are more classic ‘morphologic’ sites that bear quite some similarity to Gale.
The appeal of deltaic environments on Mars is their potential, as demonstrated on Earth, to concentrate and preserve organic molecules. This has borne fruit with Curiosity’s success in detecting martian organics in lake sediments at Gale. However, I think an important caveat must be emphasized here. The organics that Curiosity found are simple organic molecules, the kind that cannot be distinguished from those that fall to the surface via meteorites. These do not constitute biosignatures, which must be clear indicators of life. A major goal of the Mars 2020 rover is to seek biosignatures specifically, and simple chlorinated hydrocarbons do not meet this goal. If instead we relaxed the goal to include these types of compounds, then a more effective (and orders of magnitude cheaper) mission would be to the deserts of Morocco, where martian organics are readily found inside meteorites delivered free of charge from the red planet.
There’s no disputing that a trip to a martian delta would likely yield organic molecules, but a deeper question needs to be asked of each of the eight possible landing sites: is there any reason to think that life itself would have been present in the environments recorded in their rock records? This can be laid out like so:
(1) Life is present > (2) Preservation mechanism exists > (3) Biosignature created
It’s a flaw of logic to focus all attention on (2) while ignoring (1), because (1) is really what matters here, even though it’s a tougher question to answer. No biosignatures would be found in a hypothetical preservation environment with perfect fidelity, if the only organic input to that environment is derived from chondritic infall. This is similar to the misguided focus on habitability with no concern for origins of life that plagues the planetary science community. Hopefully we can break out of this narrow focus on organic preservation, and think harder about where and when life could have been present on Mars.
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 (captured powerfully here 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.