Aster Cowart's Research Page


Research Description

My research work has generally revolved around image processing, analysis, and interpretation. To put it plainly, it is doing geology on another planet through a camera. Photographs can contain a surprising depth of information, allowing geologists to measure the properties of rocky surfaces. This can be as simple as looking at a photo and seeing sand, gravel, and boulders and interpreting that the surface has been broken up by some geologic process. It can be as complex as using specialized photographic filters to measure the composition of the rock to infer how it formed. It spans scales ranging from an entire planet in a single photo to entire photos for a single sand grain. My work has focused on using as many sources of information as possible to learn about Mars' geologic history.

Currently, I am a postdoctoral researcher working at the Planetary Science Institute (PSI) with Dr. Aileen Yingst, the current Principal Investigator for the Mars Hand Lens Imager (MAHLI) onboard the Curiosity rover. MAHLI is a camera with a macro lens mounted on Curiosity's arm turret, and is capable of taking in-focus images from a range of only 2 cm from the surface. At these distances, MAHLI is capable of resolving sediment grains ~40-60 microns in size. My work is to measure changes in grain size and rock texture from MAHLI images as it travels through the thick clay and sulfate bearing sedimentary rocks in Gale Crater. These measurements will allow us to reconstruct the hydrology of the Gale Crater lake, as well as geochemical processes which may have altered the lake sediments after they were buried.

Prior to starting work at PSI, I conducted my dissertation work at Stony Brook University under Dr. Deanne Rogers. This work was focused on identifying and characterizing large rocky exposures in the Martian cratered highlands. These rocks were likely formed within the first billion years of Martian history. These rock exposures appear to span the planet's transition from a dynamic geologic and hydrologic system to the relatively inactive, arid world we see today. These rocks also record a time period which has been almost totally erased from Earth's geologic record by plate tectonics. As such, they provide an interesting point of comparison which might inform us of geological processes occurring early in the history of terrestrial planets. Finally, the Martian geological system began shutting down at roughly the same time we start seeing strong signals of life here on Earth. Ancient Martian rocks probably have a lot to say about the early evolution of a planet and life, and an important first step to understanding this record is knowing where to look in the first place. Finding and studying these bedrock exposures used a combination of orbital remote sensing techniques.

Much of this analysis involved thermal infrared imaging of the surface by the Mars Odyssey Thermal Emission Imaging System (THEMIS). This camera measures light emitted from the Martian surface at 100 m/pixel scales at 8 wavelengths between 7-14 microns. This region of the electromagnetic spectrum is dominated by absorbed light reradiated as heat, so measuring the surface's brightness can be used to calculate the surface's temperature. Because rocks change temperature more slowly than sandy or dusty material, temperature measurements can be used to identify rock. Additionally, in this wavelength region, bonds between silicate molecules absorb a small number of photons, with the exact wavelength of photons absorbed dependent on the distance between the molecules. This distance changes depending on the general organization of the silicate molecules (e.g. chains vs. sheets), allowing us to determine the general composition of these rocks and make first-order interpretations regarding the sources of these rocks, such as whether they originated from Mars' mantle or crust.

Additionally, I use visible light imaging to perform geomorphologic analysis of the Martian surface. This work primarily makes use of the Mars Reconnaissance Orbiter Context Camera (CTX), which is capable of resolving landforms ~20 m in size on the surface. I used images taken by this camera to look for landforms which may be related to the formation of ancient rock (such as channelized deposits or lava flow margins) and/or processes which subsequently modified these exposures (such as modern soil convection driven by freeze-thaw cycles). This camera also helped measure how well surfaces retain craters. Surfaces of a given age are thought to accumulate craters at a predictable statistical rate, with small craters being much more common than large craters. Small craters, however, are prone to erosion and are more easily removed from the surface than larger craters. Qualifying or quantifying this removal rate can be used to infer how resistant the rock is to erosion.

Another source of visible light data is the Mars Reconnaissance Orbiter High-Resolution Imaging Science Experiment, which is essentially a half-meter (~20 in) telescope pointed at the Martian surface. Images taken with this camera can resolve details as small as a meter across, allowing for analysis of extremely small-scale features like rock layering and fracture properties. This instrument is particularly useful for understanding local-scale processes on the Martian surfaces, and bridges the gap between orbital observations and the scale of observations that might be made by a rover like Curiosity.

Page last updated: June 9, 2022