Aerospace Engineering Prof Named to Asteroid Return Mission

by Chris Carroll

Scientists who research small objects zooming through space rarely get a close-up view of the things they devote their lives to studying. Instead they settle for fuzzy images on computer screens, spectrometry graphs and tables of numbers.

That’s all going to change later this year for Christine Hartzell, assistant professor of aerospace engineering, who uses computer modeling and simulation to study the behavior of dust on the surface of asteroids. She’s one of 13 researchers from around the world recently named to a space mission that’s planned to rendezvous in December with the asteroid Bennu, snatch a small amount of material from its surface and bring it back to earth for study.

As the spacecraft orbits, surveys and then approaches the asteroid 500 meters in diameter for a seconds-long touchdown, Hartzell and her doctoral students will study the camera feed to gather data about how the stream of charged particles from the sun known as solar wind interacts with dust.

Specifically, they’ll look for evidence that electrostatic charges cause the dust to levitate above the asteroid’s surface, an important but little-understood phenomenon.

“We’re interested in this because it’s a potential mechanism for forming features,” Hartzell says. “On the asteroid Eros, in the bottom of craters, we’ve seen very smooth collections of small dust particles. The question is, without air or wind, how does the dust get there?”

Christine Hartzell, assistant professor of aerospace engineering

The mission, which launched in September 2016, is known as OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security—Regolith Explorer). As the name implies, it’s motivated both by scientific curiosity and safety concerns; NASA has calculated a slight chance that Bennu, which passes within about 300,000 kilometers of Earth’s orbit every few years at about 100,000 kilometers per hour, could smash into our planet two centuries from now.

Although it’s not large enough to pose a global threat, it could devastate a wide area anywhere it hit, so NASA is studying how solar energy causes the paths of these rocky orbiting bodies to change subtly over time, as well as how to redirect potentially dangerous near-earth asteroids.

For scientists, Bennu also represents a pristine time capsule that, unlike the planets, has likely changed little in billions of years, providing a glimpse into the infancy of the solar system.

“Holding a meteorite in our hands on Earth, it’s not easy to know which asteroid it came from, so this is a chance to really make that link, and start to tie things together,” says Kevin Walsh, OSIRIS-REx co-investigator and lead scientist for the working group studying the formation of loose, rocky deposits known as regolith on Bennu’s surface. “What we’re really after understanding is how the solar system formed, and how the planets formed.”

The study of electrical charging of dust in the regolith and how that affects movement of material on the surface is a small but key part of the overall puzzle—“an essential and important aid to understanding the surface geology,” he says.

Hartzell came to UMD in 2014 after receiving her aerospace engineering Ph.D. at the University of Colorado Boulder and working as a postdoctoral fellow at the Keck Institute for Space Studies at the California Institute of Technology. In 2015, just a few years into her career as researcher, the International Astronomical Union recognized her contributions to planetary science by naming a main belt asteroid about two kilometers across—(much larger than Bennu, in fact)—9319 Hartzell.

As OSIRIS-REx approaches Bennu, excitement over the December rendezvous is growing for all the scientists involved, including Hartzell, who’s eager not only to gather data and better explain dust levitation, but to get a first real look at the object of her study.

“We don’t really know what the asteroid looks like,” she says. “Is it covered in fluffy dust or boulders? Is the asteroid spherical or shaped like a peanut, or something in between?”