The last complete image of Dimorphos and its bouldery terrain, taken by the DRACO imager on the DART mission approximately 7 miles from the asteroid. Credit: NASA/Johns Hopkins APL.
NASA’s Double Asteroid Redirection Test (DART) was Earth’s first attempt at launching a spacecraft to intentionally collide with and deflect an asteroid as a planetary defense technique. On September 26, 2022, the DART spacecraft collided with a small asteroid moon called Dimorphos, which orbits a larger asteroid called Didymos. Neither asteroid posed a threat to Earth, but they represented similar celestial bodies that could one day approach and endanger the planet.
In four papers published in the journal Nature on March 1, 2023, the DART team—which includes University of Maryland astronomers—detailed DART’s successful impact, the possible physics behind the collision, observations of the resulting debris ejected from the asteroid and calculations of Dimorphos’ orbital changes. The findings confirm the feasibility of redirecting near-Earth objects like asteroids as a planetary defense measure.
“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,” said Derek Richardson, a professor of astronomy at UMD and a DART investigation working group lead. “With sufficient time, a relatively small change in an asteroid’s orbit would cause it to miss the Earth, preventing large-scale destruction from occurring on our planet.”
DART mission more successful than expected
Richardson and his UMD Department of Astronomy colleagues Professor Jessica Sunshine and Principal Research Scientist Tony Farnham played critical roles in studying the effectiveness of the DART mission to deflect an asteroid from an Earth-bound path.
Farnham was instrumental in computing the geometrical conditions and dimensions needed to interpret observations of the event accurately. Using data from spacecraft engineers and from the Didymos Reconnaissance and Asteroid Camera for Optical Navigation (DRACO), Farnham helped determine what the DART spacecraft was looking at as it approached Dimorphos.
“When dealing with observations from a spacecraft, we need to understand where in space the spacecraft is located with respect to the asteroid, the sun and Earth and where it’s facing at any given time,” Farnham explained. “With this information, we have the context to make our conjectures and evaluate our work.”
Thanks to Farnham’s work, the DART team gained important information about the general timeline of the impact, the location and nature of the impact site, and the size and shape of Dimorphos. To the team’s surprise, they found the small asteroid to be an oblate spheroid, or a slightly squashed sphere-like body, instead of a more elongated shape expected from theoretical predictions.
“Both Didymos and Dimorphos are more squishy in shape—looking more like peanut butter M&Ms and less like peanut M&Ms—than we expected,” Sunshine said. “This shape also challenges some of our preconceptions about how such asteroids form and complicates the physics behind DART because it prompts us to rethink our current models of binary asteroids.”
In addition to Dimorphos’ irregular shape, the scientists also noticed that the asteroid’s surface was noticeably bouldery and blocky. This geomorphic quality likely influenced crater formation, the amount and physical properties of ejecta (debris expelled from impacts), and the momentum of a DART-like impact.
Sunshine, who previously served as the deputy principal investigator for the UMD-led NASA Deep Impact mission, observed that these different textural qualities led to different impact outcomes—critical in evaluating how successfully the DART spacecraft redirected Dimorphos from its original orbit.
“The Deep Impact mission collided with a comet whose surface is made up of small, mostly uniform grains,” Sunshine explained. “Deep Impact resulted in a more uniform fan of debris than the filamentary structures seen after DART’s impact into bouldery terrain. As it turns out, the movement of DART-caused ejecta really had a profound effect on the success of DART’s mission.”
Dimorphos (pictured left), a small asteroid moon, orbits a larger asteroid called Didymos (right). Credit: NASA/Johns Hopkins APL.
Extra push from impact debris shortened Dimorphos’ orbit
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,” explained Richardson, who helped compute and verify the momentum transferred between the DART spacecraft and Dimorphos.
According to Farnham, who calculated the direction of the asteroid’s ejecta, this finding was confirmed when the team measured the asteroid’s orbit had changed more than the team’s more conservative expectations. The difference in orbital periods, or the length of time it takes for a celestial object to complete one rotation around another object, indicates that the orbit of Dimorphos around Didymos had changed.
“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.”
Following up with Hera mission
The DART mission represents a major first step to developing appropriate planetary defense strategies against near-Earth objects like asteroids.
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 and 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,” Sunshine said. “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 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 uniquely 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.”
More information:
Andrew F. Cheng et al, Momentum Transfer from the DART Mission Kinetic Impact on Asteroid Dimorphos, Nature (2023). DOI: 10.1038/s41586-023-05878-z
Citation:
New NASA DART data prove viability of asteroid deflection as planetary defense strategy (2023, March 1)
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NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
