Impacts and early Earth habitability

The early Earth is expected to have experienced a number of large impacts during the tail end of accretion. This late veneer could have contained impactors that sterilized the planet through surface melting or ocean vaporization. Alternatively, large projectiles could have delivered reducing iron that generated transient reducing atmospheres favorable for the origin of life. We have been conducting simulations of large impacts on the Earth to investigate their role in either aiding or inhibiting Earth's early habitability.

Oceans on Mars

We examined the timing of oceans on Mars from evidence of shoreline deformation. We found that the deformation of the Martian shorelines can be explained by deformation due to the emplacement of Tharsis. This suggests that an early Martian ocean existed prior to or during the early stages of Tharsis, and points to a close link between Tharsis volcanism and the evolution of oceans on Mars.

Origin of the Martian Crustal Dichotomy

We are investigating a hybrid origin of the Martian Crustal Dichotomy, the stark difference in surface elevation and crustal thickness between Mars' northern and southern hemispheres. The two main theories of dichotomy formation are Giant Impact and Degree-1 mantle convection. While a giant impact can explain the shape of the dichotomy boundary, degree-1 mantle convection with subsequent plume migration can explain why Tharsis forms on the dichotomy boundary. We study a hybrid model in which a giant impact in the northern hemisphere of Mars causes an initial variation in crustal thickness and composition. We find that a superplume develops under the enriched, thicker, and insulating southern crust, which could result in melt residue causing subsequent migration until the emplacement of Tharsis on the dichotomy boundary. A hybrid model can therefore explain the shape of the dichotomy boundary, as well as potentially the timing and location of Tharsis formation.

Related to this is the remanent crustal magnetic signatures on Mars. The magnetic signatures display a unique pattern of lineations. We found this pattern might be explained by a magmatism expanding radially from a superplume in Mars' southern hemisphere.

Origin of the Martian Moons

Although the moons of Mars, Phobos and Deimos, have been thought to be captured asteroids, there is growing evidence and acceptance that these moons formed as a result of a giant impact. We investigated if a giant impact would have produced a large enough debris disk to form the Martian moons. Using Smoothed Particle Hydrodynamics (SPH) simulations of planetary impacts, we find that Phobos and Deimos could have formed from a giant impact - the same impact responsible for initiating the Martian crustal dichotomy.

Formation of Earth's Moon

Although the Earth's Moon is thought to have formed from a single giant impact, large-scale collisions were a common process during planetary accretion. Since each of these impacts had the potential to produce a moon, we examined what happens when satellites produced by separate impacts dynamically interact. We used the Mercury-T code to examine the orbital evolution of multiple-moon systems with direct computation of tidal interactions.

Impact processes in the solar system

In addition to SPH simulations, I've used the CTH hydrocode to examine planetary impacts on a variety of bodies, including Titan and Mars.

Searching for meteorites with machine learning

In order to better understand the composition of asteroid families, we much connect fresh meteorite falls to their pre-impact orbits. This is done by imaging the trajectories of the meteorites as they enter the atmosphere and finding the corresponding fragments. However, locating the fragments with a human search is tedious. As part of the 2016 NASA Frontier Development Lab, we studied if machine learning could be used to help identify meteorite fragments in the field. We developed a framework using machine learning to classify images from a quadcopter drone to determine if the images contained meteorite fragments.

Planet 9

I have been conducting a search for Planet 9 in data from the South Pole Telescope. We haven't found it yet.