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from https://today.umd.edu/nasas-dart-impact-permanently-changed-the-shape-orbit-of-asteroid-moon

NASA’s DART Impact Permanently Changed the Shape, Orbit of Asteroid Moon UMD-led Study of 2022 Collision Provides New Insights on Geophysics of
Asteroid Formation, Evolution

By Georgia Jiang Aug 26, 2024

illustration shows golden spacecraft hurtling toward an asteroid
An illustration depicts NASA’s Double Asteroid Redirection Test (DART) spacecraft prior to impact at the Didymos binary asteroid system.

Image courtesy of NASA/Johns Hopkins APL/Steve Gribben.

When NASA’s Double Asteroid Redirection Test (DART) spacecraft smashed
into an asteroid moon called Dimorphos as part of an experiment in 2022,
the resulting crater and other changes dramatically reshaped the moon. A
new study led by a University of Maryland astronomer suggests the impact
was so strong it knocked Dimorphos off-kilter, derailing the moon from
its original evolutionary progression.

Now, Dimorphos may start to “tumble” chaotically as it moves back toward gravitational equilibrium with its parent asteroid named Didymos,
according to the paper published Friday in Planetary Science Journal.

The overall DART mission was meant to explore the possibility of
changing trajectories of asteroids that might be headed toward a
collision with Earth. Pre-impact predictions about how DART would change
how Didymos and its moon move in space were correct, said Derek
Richardson, a UMD professor of astronomy and a working group lead on DART.

“But there are some unexpected findings that help provide a better
picture of how asteroids and other small bodies form and evolve over
time,” he said.

One of the biggest surprises was how much the impact with DART changed
the shape of Dimorphos. According to Richardson, the asteroid moon was originally oblate (shaped like a hamburger) but became more prolate
(stretched out like a football) after the DART spacecraft collided with it.

Asteroids like Dimorphos typically become prolate—“an elongated body
that would always point its long axis toward the main body,” he
said.“But this result contradicts that idea and indicates that something
more complex is at work here.”

Furthermore, the impact-induced change in Dimorphos’ shape likely
changed how it interacts with Didymos, he said. Although DART struck
only the moon, the moon and the main body are connected through gravity.
The debris scattered by the spacecraft on impact also played a role in
the disturbed equilibrium between the moon and its asteroid, shortening Dimorphos’ orbit around Didymos.

Interestingly, Didymos’ shape remained the same—a finding that indicates that the larger asteroid’s body is firm and rigid enough to maintain its
form even after losing mass to create its moon.

According to Richardson, Dimorphos’ changes have important implications
for future exploration efforts, including the European Space Agency’s follow-up mission to the Didymos system, known as Hera, slated for October.

The research team is now waiting to find out when the ejected debris
from the impact will clear from the system, whether Dimorphos is still
tumbling in space and when it will eventually regain its previous stability.

“One of our biggest questions now is if Dimorphos is stable enough for spacecraft to land and install more research equipment on it,”
Richardson said. “It could take a hundred years to see noticeable
changes in the system, but it’s only been a few years since the impact. Learning about how long it takes Dimorphos to regain its stability tells
us important things about its internal structure, which in turn informs
future attempts to deflect hazardous asteroids.”

Following its late 2026 arrival at the binary asteroid system containing Dimorphos and Didymos, the Hera mission will assess the internal
properties of both asteroids for the first time, providing a more
detailed analysis of the DART mission and its implications for the future.

“DART gave us insight into complicated gravitational physics that you
can’t do in a lab, and all of this research helps us calibrate our
efforts to defend Earth in the event of an actual threat,” Richardson
said. “There’s a nonzero chance that an asteroid or comet will approach
and endanger the planet. Now, we have an additional line of defense
against these kinds of external threats.”

Topics:
Research
Tags:
AstronomyResearch
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