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Maryland Astronomers Were Central to Planetary Defense Mission That Smashed Into Asteroid Moon Last Year
Illustration by NASA/Johns Hopkins APL
Humanity now has the ability to change the trajectories of near-Earth objects like asteroids to defend the planet, a group of four research papers about NASA’s Double Asteroid Redirection Test (DART) confirmed today in the journal Nature. The mission, which slammed a spacecraft into a small asteroid moon and changed its orbit last September, includes several University of Maryland astronomers.
“We can’t stop hurricanes or earthquakes yet, but we ultimately learned that we can prevent an asteroid impact with sufficient time, warning and resources … preventing large-scale destruction from occurring on our planet,” said Derek Richardson, a professor of astronomy at UMD and a DART investigation working group lead.
The four papers, which include more than ten UMD faculty, staff, students and alums as co-authors, detailed DART’s successful impact, the possible physics behind the collision, observations of the resulting debris ejected from the asteroid moon Dimorphos and calculations of its orbital changes.
Among the findings: The DART spacecraft was not the sole provider of momentum in the impact with Dimorphos. An additional shove was caused by violent spews of debris when the spacecraft slammed into the diminutive asteroid moon.
“There was so much debris ejected from the impact that Dimorphos was pushed approximately 3.5 times more effectively compared to being hit by the DART spacecraft alone,” said Richardson, who helped compute and verify the momentum transferred between the DART spacecraft and Dimorphos.
According to UMD Principal Research Scientist Tony Farnham, who calculated the direction of the asteroid’s ejecta, this finding was confirmed when the team measured that the asteroid’s orbit had changed more than the team’s more conservative expectations.
“Pre-impact, we expected the impact to shorten Dimorphos’ orbit by only about 10 minutes,'' Farnham said. “But after the impact, we learned that the orbital period was shortened even more, reducing an ordinarily 12-hour orbit by slightly more than 30 minutes. In other words, the ejected material acted as a jet to push the moon even further out of its original orbit.”
The DART team anticipates that the upcoming European Space Agency Hera mission launching in October 2024 will unravel more information about the DART impact site. By 2026-27, the Hera spacecraft will revisit the binary asteroid system containing Dimorphos and Didymos (a larger asteroid the small moon orbits) to assess the internal properties of both asteroids for the first time, providing a more detailed analysis of the DART impact’s effects on the system and the geophysics behind solar system formation.
“We still don’t know a lot about Dimorphos and Didymos because we have only seen the outsides,” said UMD astronomy Professor Jessica Sunshine. “What is their internal structure like? Are there differences in porosity between the two? Those are the types of questions we need to answer to really see how effective our deflections are and how celestial bodies like those asteroids form and evolve.”
While the Hera mission is still in the construction phase, research from both DART and its predecessors like Deep Impact (a 2005 UMD-led NASA mission to collide with a comet for which Sunshine was deputy principal investigator) still offer a wealth of information on how humans can develop additional ways to defend Earth from approaching asteroids and comets.
Thanks to a legacy of kinetic impact-testing initiatives and planetary defense research led by the late Distinguished University Professor of Astronomy Mike A’Hearn, UMD astronomers are equipped to evaluate and advance planetary scale impact experimentation. Richardson, Sunshine, Farnham and their colleagues hope to honor the work that led up to DART by continuing to help pioneer new methods of asteroid threat mitigation.
“These papers are simply the very first results about the DART mission to be published,” Farnham said. “But there are dozens of studies currently underway that will help us further our understanding of the impact and implications for planetary defense while uncovering more interesting phenomena.”
Other UMD-affiliated DART research contributors and co-authors include astronomy Principal Research Scientist Ludmilla Kolokolova, Adjunct Assistant Professor of astronomy Matthew Knight, astronomy Ph.D. student Carrie Holt, and alums Harrison Agrusa M.S. ’19, Ph.D. ’22, Jian-Yang Li M.S. ’02, Ph.D. ’05, Stephen Schwartz M.S. ’07, Ph.D. ’13 and Patrick A. Taylor ’03. The Johns Hopkins University Applied Physics Laboratory built the DART spacecraft and manages the mission for NASA.
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