EENS Graduate Student Spotlight: Alan Braeley

From Boston Skies to Martian Ice

I have always enjoyed exploring. Growing up, I would explore Boston and the surrounding region with friends. We loved camping in the mountains and watching the skies. I was always a dreamer and was pretty drawn to science fiction and the margins of human experience. In 2013 I decided to study astronomy at the University of Massachusetts Amherst. There I participated in instrumentation research, helping to build the TolTEC astronomical camera  with Professor Grant Wilson.

During my time working on TolTEC, I realized I needed to improve my software skills to continue opening a path in space science. Instead of applying directly to graduate school, I worked as a software engineer for Baystate Health in Springfield, MA. Here I maintained and built software interfaces for the hospital system during the COVID pandemic.

Although work consumed my thoughts at this time, I knew I wanted to continue growing my career in space science. The Winter of 2020-2021 I applied to the Ph.D. program here at Tulane to work with Professor Jennifer Whitten, a planetary scientist whose work I followed and enjoyed reading about, especially her work on NASA missions to Mars (Mars Reconnaissance Orbiter) and Venus (VERITAS). I was lucky enough to get a Ph.D. offer, and I knew what my next step would be as soon as I got it.

Unraveling Mars' Climate History

Now I study the ice caps of Mars. On Earth, we experience something called Milankovich Cycles, which refer to the changing of certain orbital parameters, like the tilt of the Earth. Over time, these parameters change, leading to a multitude of major changes for life here on Earth, like the causing of ice ages. The ice caps on Earth preserve a record of what the climate was like when they formed, and so we sample the ice and use it to study the climate during different climates in terrestrial history.

The same is true for Mars. The tilting of Mars (called its “obliquity”) causes sunlight to more-directly hit the ice caps, which causes the ice to sublimate and move equatorward, leaving dust behind at the ice caps. Eventually there is enough of a dust layer left behind that the remaining ice beneath it is protected from the solar energy. Over time, Mars tilts back to being more vertical, leading to less direct sunlight in the polar regions and more direct sunlight in the equatorial regions. At this point, ice migrates back to the poles, forming newer, cleaner layers of ice at the top of the ice caps.

Examples of Martian polar ice cap structures studied using SHARAD radar data from the Mars Reconnaissance Orbiter

Research Tools: Seeing Beneath the Surface

The Martian ice caps are studied with many kinds of instruments, but I use a radar sounder on the Mars Reconnaissance Orbiter, the Shallow Radar (SHARAD). The data generated here gives insight into the subsurface composition of the ice caps, in particular the porosity, density, and composition. These data basically provide a slice through the ice caps so we can see what is happening below the surface.

Dissertation Research: Three-Part Investigation

Chapter 1: The North Polar Layered Deposits (NPLD)
The first chapter of my dissertation focuses on the northern ice cap, called the North Polar Layered Deposits (NPLD). A collaborator of mine, Dr. Bruce Campbell, processed SHARAD data by splitting it into high- and low-frequency images, creating a new “multiband” dataset. This allows me to look at the radar sounder data and map out radar reflectors, which are caused by changes to the actual layer properties (thickness, density, porosity, composition). Prior research shows that different frequencies create resonant echoes in the SHARAD data as a function of layer thickness. These resonant echoes are recorded as multiband reflectors – reflectors that denote the radar behavior of groups of layers, rather than changes to one layer. I surveyed radargrams spanning the top 400-m of the NPLD and found a majority of multiband reflectors populate a particular region of the NPLD, a lobe called Gemina Lingula. The way the NPLD ice cap has been built up over time is an active field of research, but previous efforts concluded that the main lobe and Gemina Lingula may have distinct depositional histories. These results support that theory. This paper is currently in review at the Journal of Geophysical Research: Planets.

Chapter 2: The South Polar Layered Deposits (SPLD)
The second chapter of my dissertation is set at the South Polar Layered Deposits (SPLD), the ice cap at the Martian south pole. Similar to the results from the first chapter, multiband reflectors were found to most densely populate a particular lobe of the SPLD. Both research projects use machine learning clustering algorithms to compare the depths of multiband reflectors beneath the surface of the poles. The multiband reflectors cluster at specific depths, indicating that a particular layer thickness regime persisted at a particular time in the past. The two projects indicate that the formation of ice of these ice caps varied over time, either due to changes in deposition of water ice and/or the amount of water preserved and the volume of dust deposited on their surfaces.

Chapter 3: Understanding Radar "Fog"

My final chapter takes a different approach to studying the ice caps. Rather than using radar sounder data to look at signals from previous Martian climate regimes, I am looking at regions where normal reflector signals are replaced with a fuzzy, "foggy" radar behavior. The source of the fog in radar data is a mystery, but one of the primary suspects is surface roughness. With roughness at just the right scale the radar signal can be bounced around, creating a foggy appearance in the radar sounder data (i.e., radargrams). I am using a fractal geometry technique called the Hurst exponent to test whether surface roughness is associated with the foggy radar signal. The Hurst exponent indicates whether a surface is smoother, rougher, or is exhibiting random behavior at specific length scales. This work will allow us to potentially establish a connection between the radar fog and roughnesses at pertinent length scales.

Looking to the Future

After finishing my work at Tulane, I plan to work in geographic information systems (GIS) engineering initially, but my ambition is to start a nonprofit to leverage my love of planetary science and interest in climate change activism.