Some reflections on why I do what I do: I hadn't heard of the field of planetary science until I started grad school, but I stuck to it because I found that it brought together a lot of things I like: telling stories, solving problems, listening to the natural world, learning constantly, and working with good and knowledgeable people. I've enjoyed physics, math, and computer programming since high school (thanks entirely to the teachers I had), which largely explains why most of what I do on a daily basis involves building and running code, and thinking about the results. I particularly enjoy applying ordinary physics to unusual situations, which I think is why I'm drawn to the "airless" bodies of our solar system (really, they have very, very thin atmospheres), which are home to a wonderful variety of strange environments, with different compositions, temperatures, and past and present processes. This also explains why I've never been able to look away for long from the Moon, the nearest of those airless worlds, with so many stories to tell.
Ghosts of Atmospheres Past: The Origins of Water on the Moon and Mercury
Understanding the origin and distribution of water throughout the solar system has long been a key driver of planetary exploration. One of the most intriguing findings in recent years has been the detection of water ice in dark, shadowed regions near the poles of the Moon and Mercury, where temperatures are so cold that water and other volatile ices can remain stable over billions of years. These polar deposits provide a unique record of the delivery of water to the inner solar system, but in order to interpret this record, it is important to understand the sources that may have delivered these volatiles. These are some of the questions I am particularly interested in:
• Could Mercury's polar water ice deposits have been delivered by a relatively recent comet impact?
• How has the lunar atmosphere changed over time, and what traces of these atmospheres remain today?
• How does the contemporary lunar volatile cycle operate?
There are many different ways to address these questions. In my work, I use a Direct Simulation Monte Carlo (DSMC) code to model the origin and transport of water (and other volatiles) on the Moon and Mercury in the past and present. DSMC is a computational method that simulates gas behavior by modeling the motion of a large number of representative molecules and the exchange of energy between molecules during collisions. DSMC was originally developed by the late Dr. Graeme Bird, whose website has some great resources on the method. I use the PLANET DSMC code developed at the Computational Fluid Physics Lab (CFPL) at the University of Texas at Austin. I contributed (together with many other excellent people) to the development of the code as a PhD student, and continue to use it for independent projects, supported by NASA's Solar System Workings program, and Solar System Exploration Research Virtual Institute (SSERVI) teams LEADER and ICE Five-O.
• Could Mercury's polar water ice deposits have been delivered by a relatively recent comet impact?
• How has the lunar atmosphere changed over time, and what traces of these atmospheres remain today?
• How does the contemporary lunar volatile cycle operate?
There are many different ways to address these questions. In my work, I use a Direct Simulation Monte Carlo (DSMC) code to model the origin and transport of water (and other volatiles) on the Moon and Mercury in the past and present. DSMC is a computational method that simulates gas behavior by modeling the motion of a large number of representative molecules and the exchange of energy between molecules during collisions. DSMC was originally developed by the late Dr. Graeme Bird, whose website has some great resources on the method. I use the PLANET DSMC code developed at the Computational Fluid Physics Lab (CFPL) at the University of Texas at Austin. I contributed (together with many other excellent people) to the development of the code as a PhD student, and continue to use it for independent projects, supported by NASA's Solar System Workings program, and Solar System Exploration Research Virtual Institute (SSERVI) teams LEADER and ICE Five-O.
Worlds of Many Wavelengths: Radiative Transfer Modeling & Remote Sensing
Much of planetary science is ultimately rooted in understanding how electromagnetic radiation interacts with planetary surfaces: this is how we know the temperature, composition, and texture of worlds across the solar system. Most of my work in this area is in support of NASA's Lunar Reconnaissance Orbiter (LRO) mission, which will forever be engraved on my heart. Current projects include the following:
Radar: Modeling the radar response of ice-rock mixtures at different observing geometries, in order to better understand the distribution of sub-surface ice at the lunar poles, and to make sense of the remarkable LRO Mini-RF dataset.
Infrared: Investigating thermal emission under lunar environmental conditions to support the LRO Diviner experiment, in collaboration with some amazing colleagues who do pathbreaking experimental work in labs at APL (Dr. Ben Greenhagen), Stony Brook University (Prof. Tim Glotch), and the University of Central Florida (Prof. Kerri Donaldson Hanna).
Optical: Modeling the scattering of polarized light by planetary surfaces, in order to support experimental work in the Planetary Surface Texture Lab at APL (led by the irreplaceable Dr. Dave Blewett).
These projects involve a set of Monte Carlo radiative transfer codes, which model the interaction of radiation with a medium of interest (in these cases, a planetary regolith) by tracking the propagation of a large number of representative "energy bundles" through the medium.
Radar: Modeling the radar response of ice-rock mixtures at different observing geometries, in order to better understand the distribution of sub-surface ice at the lunar poles, and to make sense of the remarkable LRO Mini-RF dataset.
Infrared: Investigating thermal emission under lunar environmental conditions to support the LRO Diviner experiment, in collaboration with some amazing colleagues who do pathbreaking experimental work in labs at APL (Dr. Ben Greenhagen), Stony Brook University (Prof. Tim Glotch), and the University of Central Florida (Prof. Kerri Donaldson Hanna).
Optical: Modeling the scattering of polarized light by planetary surfaces, in order to support experimental work in the Planetary Surface Texture Lab at APL (led by the irreplaceable Dr. Dave Blewett).
These projects involve a set of Monte Carlo radiative transfer codes, which model the interaction of radiation with a medium of interest (in these cases, a planetary regolith) by tracking the propagation of a large number of representative "energy bundles" through the medium.
Understanding the Impact of Exploration on Space Environments
How do we change (temporarily or permanently) the environments of the other worlds that we visit? Understanding the answer to that question is important to carrying out meaningful and responsible science.
One aspect of this that I have been working on is developing computational tools (based on the DSMC code mentioned above) to model the propagation and persistence of spacecraft exhaust gases in the lunar environment. The motivation behind this project was to determine how gases released by lunar landers during their descent to the surface might affect measurements of the surface and exosphere by scientific instruments onboard. Besides helping to understand environmental impact, measurements like these can also tell us a great deal about how exospheres and surfaces interact on the Moon and other airless bodies.
This work was initially supported by the SSERVI DREAM2 team, and now the LEADER team (which aims to understand the lunar environment and its two-way connection with human systems) and will support investigations by several instruments set to be delivered to the lunar surface soon, as well as the exciting VIPER mission. There's lots of interesting and important work to be done!
One aspect of this that I have been working on is developing computational tools (based on the DSMC code mentioned above) to model the propagation and persistence of spacecraft exhaust gases in the lunar environment. The motivation behind this project was to determine how gases released by lunar landers during their descent to the surface might affect measurements of the surface and exosphere by scientific instruments onboard. Besides helping to understand environmental impact, measurements like these can also tell us a great deal about how exospheres and surfaces interact on the Moon and other airless bodies.
This work was initially supported by the SSERVI DREAM2 team, and now the LEADER team (which aims to understand the lunar environment and its two-way connection with human systems) and will support investigations by several instruments set to be delivered to the lunar surface soon, as well as the exciting VIPER mission. There's lots of interesting and important work to be done!