NASA’s DART asteroid spewed 2 million pounds of rock into space
The massive tail created by the collision of a spacecraft and asteroid earlier this year is unlocking key information about space rocks and how to handle any such rocks that may one day threaten Earth.
NASA Double Asteroid Redirection Test (DART) slammed into a small space rock called Dimorphos in late September in preparation for the possibility that humans might one day want to deflect a asteroid on a collision course with Land. Within weeks of the impact, the DART team announced that the impact shaved 32 minutes from Dimorphos’ orbit around its larger companion, didymus – in the high range of the team’s pre-launch estimates. Scientists are now sharing additional findings on the impact during the American Geophysical Union’s annual conference taking place this week in Chicago and online.
“DART has been a great success,” Tom Stadtler, program scientist for the DART mission, said during a press conference held Thursday (Dec. 15) in conjunction with the meeting. “I’ve seen these results, I know they’re extremely cool.”
Related: See the first images of the wild DART asteroid crash!
Many of the new results focus on the impressive, kite-like tail produced by impact debris. Mission scientists weren’t sure ahead of time how much debris the DART collision would create, but the impact did not disappoint.
And scientists had a front-row seat, thanks to the Italian hitchhiker’s DART spacecraft, Light Italian Cubesat for Imaging of Asteroids (LICIACube), which was equipped with two cameras and was deployed 15 days before the DART impact, allowing it to fly past Dimorphos just three minutes after impact. Photographs of the tiny spacecraft show great cosmic disorder, with clouds of material billowing out of the space rock.
“The images were really impressive,” said Alessandro Rossi, a member of the LICIACube science team and a scientist at the Instituto di Fisica Applicata Nella Carrara in Italy, during the press conference. “We didn’t expect some of the features we see.”
Scientists are still analyzing the LICIACube data, but the images captured by its two cameras it can offer insight into how big certain debris is, how fast it’s traveling and more, Rossi said. The researchers even think they can see the debris casting a shadow across the orbits of the largest Dimorphos asteroid, Didymos.
The debris offers some insight into the asteroid’s structure, as a solid rock asteroid would produce much less ejecta than an asteroid made of clumped rocks—imagine a tennis ball bouncing off pavement compared to dropping it in a sandbox.
Also, the ejection has solved a key mystery about Dimorphos and Didymos. Scientists suspected that the two space rocks would be made of a similar material, but they had no way to test that theory, either as the spacecraft sped toward its destination or by using ground-based telescopes, neither of which are powerful enough. like to see Dimorphs directly.
Before the impact, scientists could use the light they saw from the system to analyze the composition of the space rock pair in general, knowing that almost all of that light came from Didymos. But in similar data taken just after impact, it’s the flying debris from Dimorphos that’s responsible for most of the light.
Comparison of the two light signatures showed that although there are some slight differences, the material appears to be quite similar between the two asteroids. “We are very excited to see that these two objects are in fact similar in composition,” Cristina Thomas, a planetary scientist at Northern Arizona University who leads the DART observations working group, said during the press conference.
Scientists will be studying Dimorphos Cool Tail for quite some time, including delving into observations taken in the days after the collision, collecting new data to see how the plume changes over time, and comparing observations from different vantage points.
“We have a view of the ejecta column up close, we have a view from the ground, we have a view from hubble space telescopefrom the James Webb Space Telescope“, said Rossi. “So we have many different geometries to compare, and this allows us to clearly characterize the ejecta plume from many points of view.”
Crunching the numbers
During the press conference, the scientists also shared two key numbers that they have calculated since the collision.
First, they have begun to estimate how much debris was blown off the asteroid: at least 2.2 million pounds (1 million kilograms) and possibly as much as 22 million pounds (10 million kg). Given Dimorphos’ total mass of perhaps 11 billion pounds (5 billion kg), the rock might have lost only 0.2% of its material, even if the higher estimate turns out to be correct.
“We’re talking about a very, very small fraction,” Andy Rivkin, a planetary scientist at the Johns Hopkins Applied Physics Laboratory and co-director of DART, told the news conference.
The second number goes to the core of the purpose of the DART mission. DART wasn’t about seeing inside an asteroid, it was about planetary defense. This involves looking for asteroids in orbits that intersect Earth’s and calculating whether the two bodies could ever meet in the same place at the same time.
If scientists ever spot a sizeable asteroid that poses a real threat, humans could try to intervene by speeding up the asteroid’s orbit around the planet. sun so that he misses his appointment with Earth. DART tested a technique for that, called kinetic impact, a fancy name for hitting the asteroid with a heavy, fast-moving object.
However, scientists don’t have a good enough idea of how the characteristics of an asteroid and a collision might interact to produce a specific change in the rock’s momentum in space, making it difficult to know what size spacecraft to launch. , for example.
Scientists use a crucial number, called “momentum transfer factor” or beta, to describe how effective an asteroid impact is. If a spacecraft hits an asteroid head-on in a collision that produces no debris, the space rock will take exactly the momentum the spacecraft had when it crashed, a beta of 1.
A lot of features can affect the beta factor, whether the spacecraft hits a smooth patch or a large rock, for example, the internal structure of the asteroid and the material the asteroid is made of, but let’s put that aside. For simplicity.
Debris being shot from the asteroid into space gives the asteroid extra momentum, gradually increasing the beta factor of the impact. And scientists have now calculated the beta factor of DART’s impact at 3.6. That value means that the asteroid took on more than triple the momentum it would have in a clean impact, and that the debris created by the impact affected the asteroid even more than the spacecraft itself.
“This is very good news for the kinetic impact technique,” Andy Cheng, leader of the DART research team at the Johns Hopkins Applied Physics Laboratory, said during the press conference. “At least in the case of DART, the kinetic impact on the target was really efficient at changing the target’s orbit.”
The calculation also gives scientists much-needed real-world data to understand how an asteroid’s characteristics affect momentum transfer, data that is crucial in determining how massive a kinetic-impact spacecraft needs to be to avoid catastrophe. The successor to DART, that of the European Space Agency Hera spaceshipcurrently scheduled to launch in 2024, it will also play a key role here after it arrives (much more smoothly) at the asteroid pair to study Dimorphos and Didymos up close.
“What we’re trying to get to is being able to look at an asteroid, either from the ground or maybe with a reconnaissance mission, and infer what the response will be if we deploy a kinetic impactor against it,” Stadtler said.
Despite the intriguing findings in terms of science and planetary defense, the mission team stressed that they were far from done with the project.
“From here, now, we can get to our dream list, where we can start to think about the really complicated dynamical effects that were predicted, that we weren’t sure we could observe because we’ve never done this before,” Thomas said. “We look forward to more observations that will allow us to study things in great detail, and I think it’s a really exciting place to be.”
Email Meghan Bartels at firstname.lastname@example.org or follow her on Twitter @meghanbartels. follow us On twitter @spacedotcom and in Facebook.