Meet DiRAC’s Research Team: Dr. Sarah Greenstreet

Sarah Greenstreet’s research interests involve orbital dynamics of small bodies in the Solar System. This includes studying the long-term evolution of asteroids in the inner and outer Solar System as their orbits change over time and determining their potential to impact the planets. Dr. Greenstreet’s current main focus is working with researchers at the Asteroid Institute as well as Associate Professor and Senior Data Science Fellow Dr. Mario Juric (DIRAC, Department of Astronomy, eScience) to study the threat to Earth due to asteroid impacts and by how much we would need to “nudge” an asteroid out of Earth’s way to avoid an impact.

Dr. Greenstreet is an Asteroid Institute senior researcher and a visiting scientist at the DIRAC center. She joined DIRAC in January 2018 after completing a two-year postdoctoral fellowship at Las Cumbres Observatory in Santa Barbara, CA. She received her Masters in Astronomy in 2011 and her PhD in Astronomy in 2015 from the University of British Columbia in Vancouver, Canada. She also has a Bachelors in Physics with a double minor in Astronomy and Mathematics from Western Washington University in Bellingham, WA, which she earned in 2007.

Dr. Greenstreet is interested in populations of small bodies that undergo unique dynamical phenomena, such as orbiting the Sun on backwards (retrograde) orbits or becoming trapped in orbits around the Sun very near the orbit of a planet where the asteroid and planet appear to “co-orbit” the Sun. Greenstreet also studies the rate at which small bodies in the Solar System impact planets, creating impact craters on their surfaces. Dr. Greenstreet has also used telescopic observations to help refine the orbits of newly discovered near-Earth asteroids, determine physical properties of asteroids of interest to NASA and upcoming targets of the Goldstone and Arecibo radar telescopes, and confirm that predicted asteroids undergo the Yarkovsky effect.

Recently, Greenstreet co-authored a paper with scientists on the New Horizons spacecraft science team to make predictions about the expected number and distribution of impact craters on the surface of the New Horizons flyby target, 2014 MU69 (a.k.a., Ultima Thule), which it flew passed on January 1, 2019. The paper was submitted for publication two weeks before the flyby and published in the Astrophysical Journal in early February 2019. The paper predicted a scarcity of craters on 2014 MU69 due to the number and distribution of craters observed by the New Horizons spacecraft on Pluto and Charon during its fly-through of the Pluto system in July 2015, which was published in Science magazine in March 2019 and co-authored by Greenstreet. Images recently sent back from the New Horizons spacecraft of 2014 MU69 indicate there are, in fact, few impact craters on the surface as Greenstreet’s paper predicted.

Dr. Greenstreeet is also interested in public outreach. She has given public lectures about her research and why asteroids are interesting and important to study at universities, high schools, elementary schools, and other events throughout the Pacific Northwest and southern California, including multiple appearances at the Santa Barbara chapter of Astronomy on Tap, where astronomers give short talks about interesting astronomy research in a bar setting. Greenstreet says, “Talking about the cool research we get to do as astronomers and explaining how scientists do research is, to me, one of the most important parts of the job. We all have a responsibility to share what we learn with the public to keep interest in science fields alive and to inspire the next generation of scientists who will take our research to the next level.”

Learn more about Dr. Greenstreet’s work at