The various geological features observed on Didymos helped researchers tell the story of Didymos’ origins. The asteroid’s triangular ridge (first panel from left), and the so-called smooth region, and its likely older, rougher “highland” region (second panel from left) can be explained through a combination of slope processes controlled by elevation (third panel from left). The fourth panel shows the effects of spin-up disruption that Didymos likely underwent to form Dimorphos. Credit: Johns Hopkins APL/Olivier Barnouin
In studying data collected from
NASA’s DART (Double Asteroid Redirection Test) mission, which in 2022 sent
a spacecraft to intentionally collide with the asteroid moonlet Dimorphos, the
mission’s science team has discovered new information on the origins of the
target binary asteroid system and why the DART spacecraft was so effective in
shifting Dimorphos’ orbit.
In five recently published papers
in Nature Communications, the team explored the geology of the binary asteroid system, comprising moonlet Dimorphos and parent
asteroid Didymos, to characterize its origin and evolution and constrain its
physical characteristics.
“These findings give us new
insights into the ways that asteroids can change over time,” said Thomas
Statler, lead scientist for Solar System Small Bodies at NASA Headquarters in
Washington. “This is important not just for understanding the near-Earth objects
that are the focus of planetary defense, but also for our ability to read the
history of our Solar System from these remnants of planet formation. This is
just part of the wealth of new knowledge we’ve gained from DART.”
Olivier Barnouin and Ronald-Louis
Ballouz of Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland,
led a paper that analyzed the geology of both asteroids and drew conclusions
about their surface materials and interior properties. From images captured by
DART and its accompanying LICIACube cubesat – contributed by the Italian Space
Agency (ASI), the team observed the smaller asteroid Dimorphos’ topography,
which featured boulders of varying sizes. In comparison, the larger asteroid
Didymos was smoother at lower elevations, though rocky at higher elevations,
with more craters than Dimorphos. The authors inferred that Dimorphos likely
spun off from Didymos in a large mass shedding event.
There are natural processes that
can accelerate the spins of small asteroids, and there is growing evidence that
these processes may be responsible for re-shaping these bodies or even forcing
material to be spun off their surfaces.
Analysis suggested that both
Didymos and Dimorphos have weak surface characteristics, which led the team to
posit that Didymos has a surface age 40–130 times older than Dimorphos, with
the former estimated to be 12.5 million years and the latter less than 300,000
years old. The low surface strength of Dimorphos likely contributed to
DART’s significant impact on its orbit.
“The images and data that DART collected at the Didymos system provided a unique opportunity for a close-up geological look of a near-Earth asteroid binary system,” said Barnouin. “From these images alone, we were able to infer a great deal of information on geophysical properties of both Didymos and Dimorphos and expand our understanding on the formation of these two asteroids. We also better understand why DART was so effective in moving Dimorphos.”
Based on the internal and surface properties described
in Barnouin et al. (2024), this video demonstrates how the spin-up of asteroid
Didymos could have led to the growth of its equatorial ridge and the formation
of the smaller asteroid Dimorphos, seen orbiting the former near the end of the
clip. Particles are colored according to their speeds, with the scale shown at
the top, along with the continually changing spin period of Didymos.
Maurizio Pajola, of the National
Institute for Astrophysics (INAF) in Rome, and co-authors led a
paper comparing the shapes and sizes of the various boulders and their
distribution patterns on the two asteroids’ surfaces. They determined the physical
characteristics of Dimorphos indicate it formed in stages, likely of material
inherited from its parent asteroid Didymos. That conclusion reinforces the
prevailing theory that some binary asteroid systems arise from shed
remnants of a larger primary asteroid accumulating into a new asteroid
moonlet.
Alice Lucchetti, also of INAF, and colleagues found that thermal
fatigue — the gradual weakening and cracking of a material caused by heat —
could rapidly break up boulders on the surface of Dimorphos, generating surface
lines and altering the physical characteristics of this type of asteroid more
quickly than previously thought. The DART mission was likely the first
observation of such a phenomenon on this type of asteroid.
Supervised by researcher Naomi Murdoch of ISAE-SUPAERO in
Toulouse, France, and colleagues, a paper led by students Jeanne Bigot and
Pauline Lombardo determined Didymos’ bearing capacity — the surface’s
ability to support applied loads — to be at least 1,000 times lower than that
of dry sand on Earth or lunar soil. This is considered an important
parameter for understanding and predicting the response of a surface, including
for the purposes of displacing an asteroid.
Colas Robin, also of ISAE-SUPAERO, and co-authors analyzed the
surface boulders on Dimorphos, comparing them with those on other rubble pile
asteroids, including Itokawa, Ryugu and Bennu. The researchers found the boulders shared similar characteristics,
suggesting all these types of asteroids formed and evolved in a similar
fashion. The team also noted that the elongated nature of the boulders around
the DART impact site implies that they were likely formed through impact
processing.
These latest findings form a more robust overview of the origins of the
Didymos system and add to the understanding of how such planetary bodies were
formed. As ESA’s (European Space Agency) Hera mission prepares to revisit
DART’s collision site in 2026 to further analyze the aftermath of the
first-ever planetary defense test, this research provides a series of tests for
what Hera will find and contributes to current and future exploration missions
while bolstering planetary defense capabilities.
Johns Hopkins APL managed the DART mission for NASA’s Planetary Defense
Coordination Office as a project of the agency’s Planetary Missions Program
Office. NASA provided support for the mission from several centers, including
the Jet Propulsion Laboratory in Southern California, Goddard Space Flight
Center in Greenbelt, Maryland, Johnson Space Center in Houston, Glenn Research
Center in Cleveland, and Langley Research Center in Hampton, Virginia.
For more information about the DART mission:
https://science.nasa.gov/planetary-defense-dart
By Patricia Talbert
Source: NASA’s DART Mission Sheds New Light on Target Binary Asteroid System - NASA Science
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