Terrestrial and Extraterrestrial Sloooooow Impacts: My Time at UCF

Today's travels brought me to the University of Central Florida in Orlando where I conducted my doctoral work. I met with my former advisor, Dr. Josh Colwell and several other professors of the Planetary Sciences group in the Physics Department. I took a tour of my own former lab and got to see what new projects the lab group is working on. I was tickled to see that two of my old conference posters still hung on the walls. Such memories!

I started grad school at UCF in January 2010 after gaining my master's degree from the University of Alabama in Huntsville. Up to that point, all of my research had been astrophysics analysis. I had obtained astronomy data from space telescopes and processed that data to make sense of what we were observing. I didn't do observational astronomy myself, so I didn't have the experience of doing any hands-on research.

I could have gotten involved in telescope operation, but instead I decided to try something a bit more alien. I went into experimental planetary science using analog dirt (regolith), reduced gravity, and low pressure in vacuum chambers to transform a terrestrial experiment into simulated extraterrestrial.

My heart has always been on the Moon, so Josh's research appealed to me. He examined low velocity impacts on planetary body surfaces. At the time I began at UCF, NASA's Constellation Program was in motion and so much research was being focused on lunar science. When the direction of NASA's human exploration program became less clear, the research was broadened to any kind of planetary body with a dust or soil surface. The research was also useful for studying the interactions of dust particles in space, such as the early formation of planets or planetary rings. Earth is also a planet, so the research was also translatable to Earth surface impact models.

Much of my research at UCF was focused on the continuation of an impact experiment which involved dropping marbles into granular materials such as small beads, fake lunar regolith, and fake Mars regolith. These experiments were often conducted in a vacuum chamber that was depressurized to minimize air molecule interactions and mimic a space environment. The small heights that the marbles were dropped didn't allow for much speed to build up. We wanted the impacts to be as slow and low energy we could make them.

To get even slower impact speeds, we build a drop tower in the lab. Using the same principle as a roller coaster or amusement park drop ride, drop towers allow for moments of microgravity while the canister is free falling. Our small drop tower gave us less than a second of microgravity, but that was enough. We used light springs to push the marble into the regolith at velocities lower than what we could achieve with a tabletop experiment. To obtain even longer periods of microgravity for our experiments, we used parabolic "ZeroG" aircraft. Last September, they even put an experiment on the International Space Station.

The splash from the impact and the resulting ejecta (ejected particles) informed us about the way that regolith acts. We want to understand how much ejecta is kicked up, how far it spreads, how fast it travels, the tendency for the regolith to be cohesive and stick together, how differently the regolith acts if it's packed more densely, and other characteristics. In more advanced versions of the experiment, a clump of regolith impacted with a regolith surface or two clumps of regolith impacted each other, all at very slow speeds.

Much research has been done to study high velocity impacts, but low velocities impacts have been largely ignored because they're harder to do. By looking at the boundary between whether splash happens or doesn't happen from an impact, we can understand how impact energy is distributed in a material. By throwing clumps together at slow speeds, we can understand when two clumps in space may hit and stick together, forming a larger clump, or hit and break apart, forming pieces, or maybe even just hit and bounce off each other unharmed. Understanding how bodies are formed in space helps us to understand how Earth came to be.

 

I researched at UCF until I obtained a job at CASIS two years ago this March. I also took classes and completed all the requirements for a doctorate in physics except for the dissertation and the defense. This is a topic for a separate entry, but it was the right decision for me to move forward in my career. I accomplished what I had set out to accomplish, learned a ton, and lived some great experiences. I also got my hands dirty for a little while!