My paper titled ‘Aqueous Alteration on Asteroids: Linking the mineralogy and spectroscopy of CM and CI chondrites’ is a coordinated spectral-mineralogical study of meteorites that experienced interactions with water on their parent bodies. CM/CI carbonaceous chondrite meteorites are low albedo samples that are thought to originate from hydrated asteroids. However, connections between carbonaceous chondrites and asteroids is hampered by the general lack of near-infrared features. Nevertheless, a systematic study of a suite of meteorites with known mineralogy had not before been attempted. We took a suite of 16 meteorites that were known to have experienced different degrees of alteration. The primary measure of degree of alteration is the abundance of hydrated minerals in a meteorite sample. Through collaborations with Dr. Kieren Howard, the mineralogy, including the degree of alteration is well known for each meteorite sample in our suite. We investigated the near-infrared spectral region and the mid-infrared spectral region. We found that, in the near-infrared, the 0.7-mm feature definitively indicates the presence of hydrated minerals but this feature (or the lack of a feature) cannot be used to constrain the composition of meteorites or asteroids alone. Similarly, the slope was uncorrelated to degree of alteration. When we directly compared the mineralogy results to the spectral results, we found continuous spectral changes in the mid-infrared that are directly related to mineralogy. This result can be used to determine the degree of alteration of asteroids remotely, which has not been possible to do before using near-infrared spectroscopy.
In addition to this coordinated spectral-mineralogical study of aqueously altered meteorites, I conducted another laboratory study of least-processed carbonaceous chondrites. This work was published in 2018 with the title ‘Spectral evidence for amorphous silicates in low-metamorphic grade CO meteorites and their parent bodies’. These meteorites have not experienced any parent body processing which is unusual in the meteorite collection. The main evidence of this lack of processing are these strange amorphous materials found only in meteorites that lack all evidence of parent body processing. Currently, it is thought that these materials formed through disequilibrium condensation in the proto-solar disk, making them some of the oldest materials in our Solar System. This work represents the first spectroscopic study of these primitive, least-processed meteorites. We identify two unique spectral features caused by this material allowing us to identify least-processed asteroids and one asteroid, (93) Minerva, that appears to have abundance amorphous materials on its surface. This result may be relevant for target selection for future asteroid missions to primitive, unprocessed bodies.
Another component of my dissertation was to use the results from our first study to constrain the degree of alteration of asteroids using publicly available, archived Spitzer Space Telescope data as well as observations using the Stratospheric Observatory For Infrared Astronomy (SOFIA). This survey, in preparation for publication now, found that asteroids throughout the Main Asteroid Belt appear to be aqueously altered. This implies that either the ‘snow line’ or region of the Solar System where water-ice can exist, was much closer to the sun at the time of asteroid accretion or that the asteroid belt is dynamically well mixed.
I have recently submitted a proposal to the SOFIA telescope to support the Psyche Mission by observing asteroid (16) Psyche. Previous observations of Psyche show that this asteroid a heterogeneous surface and potentially hydrated minerals on its surface. In collaboration with the Psyche Mission Principle Investigator Dr. Lindy Elkins-Tanton, Dr. Zoe Landsman, the leading expert on M-type asteroids and Dr. Tracy Becker, another leading scientist who is supporting the Psyche Mission with ultra-violet observations using Hubble, we proposed to observe Psyche over two rotational periods to confirm the detection of surficial heterogeneity and constrain the composition of Psyche’s surface. If awarded, these observations will occur in Fall of 2020.
——Ongoing and Future work——
Looking toward the future, I proposed a research project to the Planetary Data Archiving, Restoration and Tools Program titled: Meteorite Phase and Grain-size spectral database: A resource for leveraging asteroid mission results. I recently learned that this proposal has been declined, however I am planning to retool and resubmit similar work to the NASA ROSES Solar System Workings Program. Similar to my previous work, I plan to systematically observe meteorites with changing grainsize and phase angle to aid in the interpretation of mission results and remote observations of asteroids. This proposal would fund the creation of a spectral database unlike any other that currently exists: near- and mid-infrared reflectance spectroscopy and mid-infrared emission spectroscopy of a wide variety of meteorites at different phase angles and grain sizes. This laboratory set-up has been created before, however, the effects of grain size and phase angle have not yet been systematically observed for meteorite samples. This database will help us understand the effects of grain size and phase angle on asteroid-relevant materials and hopefully begin to resolve some of the major outstanding questions surrounding interpreting mid-infrared spectroscopy of asteroids. Aspects of this work have been done before—for example, grain size effects are well known for terrestrial materials and phase angle (especially, the opposition effect) has been studied extensively in the laboratory and remotely on Solar System bodies. What makes this work unique is studying these effects on meteorites—highly relevant materials for asteroid observations—and using both reflectance and emission spectroscopy. While we believe that Kirchoff’s law is valid for low albedo materials, relevant for asteroid observations, this has not been validated in the laboratory. This work will help disentangle aspects of mid-infrared spectroscopy that are currently roadblocks to using this wavelength region to its full potential.
As asteroid missions continue to bring back data, I intend to propose to NASA Data Analysis Programs to investigate questions particularly of the OSIRIS-REx target asteroid, Bennu. The OSIRIS-REx mission has confirmed the detection of hydrated minerals on Bennu’s surface. As my expertise lies hydrated meteorites and asteroids, I anticipate proposing research projects related to this mission that would support multiple undergraduate researchers.
In addition to the ongoing projects outlined above, I have several other pending collaborations and research proposals. Firstly, asteroid (93) Minerva appears to be one of the most primitive objects we have identified in the Asteroid Belt. In collaboration with Annika Gustafson, we are planning to obtain rotationally resolved spectroscopy of Minerva using the Discovery Channel Telescope and the Near Infrared High Throughput Spectrometer to determine if there is any surficial heterogeneity. These observations will occur early in the 2020a semester (e.g., before end of February, 2020). We may observe surficial heterogeneity which would imply that Minerva (and least-processed meteorites) accreted relatively late (>4Ma after CAI formation). If heterogeneity is observed, this would imply that Minerva has a crust of primitive materials and a processed interior. If heterogeneity is observed, we will plan follow-up observations with a facility like SOFIA to determine if Minerva is similar to CR meteorites characterized by aqueous alteration or CO meteorites characterized by thermal metamorphism. When the James Webb Space Telescope becomes available, I intend to use this telescope to observe Minerva to help further constrain its surface composition.
New theoretical models of aqueous alteration on asteroids (e.g., Bland and Travis, 2017 Science Advances, 3, 7) can be confirmed using rotationally resolved spectroscopy of hydrated asteroids. As an expert in observations of asteroids in the wavelength region where aqueous alteration can be identified and quantified, I intend to propose observations of asteroids to constrain these new models. These observations may help us understand the overall water-to-rock ratio of asteroids and possible the quantity of water-ice available in early Solar System times. I anticipate submitting this project to the Solar System Observations program of NASA’s Research Opportunities in Space and Earth Sciences.