What would we do if we spotted a dangerous asteroid on a collision course with Earth? Can we safely deflect it to avoid impact?
Last year, NASA’s Double Asteroid Redirection Test (DART) mission tried to see if a “kinetic impactor” could do the job: ram a 600-kg spacecraft the size of a refrigerator into an asteroid the size of an Aussie Rules football field .
The early results of this first real test of our potential planetary defense systems looked promising. But the first scientific results are only now being published: five papers in Nature have recreated the impact and analyzed how it altered the asteroid’s momentum and orbit, while two studies examine the debris knocked off by the impact.
The conclusion: “Kinetic impactor technology is a viable technique to defend the Earth if necessary.”
Small asteroids could be dangerous but are difficult to spot
Our solar system is filled with debris left over from the early days of planet formation. Today, about 31,360 asteroids are known to be loitering in Earth’s neighborhood.
Although we have our eyes on most of the large, kilometer-sized ones that could wipe out humanity if they hit Earth, most of the smaller ones remain undetected.
A little over ten years ago, an 18-meter asteroid exploded in our atmosphere over Chelyabinsk, Russia. The shockwave smashed thousands of windows, wreaking havoc and injuring around 1,500 people.
A 150-meter asteroid like Dimorphos would not wipe out civilization, but it could cause mass casualties and regional devastation. However, these smaller space rocks are harder to find: we think we’ve only spotted about 40% of them so far.
The DART Mission
Suppose we spied an asteroid that size on a collision course with Earth. Could we nudge it in a different direction and steer it away from disaster?
It’s theoretically possible to hit an asteroid with enough force to change its orbit, but is it actually possible? That’s what the DART mission wanted to find out.
In particular, the “kinetic impactor” technique was tested, which is a fancy way of “hitting the asteroid with a fast-moving object.”
The asteroid Dimorphos was a perfect target. It was in orbit around its larger cousin Didymos in a loop that lasted just under 12 hours.
The impact of the DART spacecraft should alter that orbit slightly, slowing it just a little, shrinking the loop and cutting off its round trip by an estimated seven minutes.
A self-piloting spaceship
In order for DART to demonstrate that kinetic impactor technology is a potential tool for planetary defense, it needed to demonstrate two things:
that its navigation system could autonomously maneuver and target an asteroid during a high-speed encounter
that such an impact could change the orbit of the asteroid.
In the words of Northern Arizona University’s Cristina Thomas and colleagues, who analyzed the changes in Dimorphos’ orbit as a result of the impact, “DART successfully achieved both.”
The DART spacecraft steered its path from Dimorphos using a new system called Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav), which used the onboard camera to position itself for maximum impact.
More advanced versions of this system could allow future missions to choose their own landing sites on distant asteroids where we can’t map the debris pile terrain well from Earth. That would save the hassle of a first scouting tour!
Dimorphos itself was one such asteroid before DART. A team led by Johns Hopkins University’s Terik Daly used high-resolution imagery of the mission to create a detailed shape model. This gives a better estimate of its mass and improves our understanding of how these types of asteroids will respond to impacts.
The impact itself created an incredible cloud of material. Jian-Yang Li of the Planetary Science Institute and colleagues have described in detail how the ejected material was thrown up by the impact and poured into a 1,500 km long tail of debris that was visible for almost a month.
Material flows from comets are known and documented. Composed mostly of dust and ice, they are considered harmless meteor showers when they cross Earth.
Asteroids are made of rockier, stronger material, so their currents could pose a greater hazard if we encounter them. It is very exciting to record a real example of the formation and evolution of debris trails in the wake of an asteroid. Identifying and monitoring such asteroid streams is a key goal of planetary defense efforts like the Desert Fireball Network that we run from Curtin University.
A bigger result than expected
How much did the impact change Dimorphous’ orbit? Much more than expected. Instead of changing by seven minutes, it had gotten 33 minutes shorter!
This larger-than-expected result shows that the change in Dimorphos’ orbit is not solely due to the impact of the DART spacecraft. Most of the change was due to a recoil effect from all the ejected material that flew into space, which Ariel Graykowski of the SETI Institute and colleagues estimated to be between 0.3% and 0.5% of the asteroid’s total mass.
A first success
The success of NASA’s DART mission is the first evidence of our ability to protect Earth from the threat of dangerous asteroids.
At this stage we still need some advance warning to apply this kinetic impactor technique. The sooner we intervene in an asteroid’s orbit, the smaller the change we need to make to keep it from hitting Earth. (To see how this all works, you can play with NASA’s NEO Deflection app.)
But should we? This is a question that must be answered if we ever need to divert a dangerous asteroid. If the orbit changed, we would have to be sure that we weren’t pushing it in a direction that would affect us in the future.
However, we are getting better and better at spotting asteroids before they reach us. We’ve seen two in just the past few months: 2022WJ1, which struck over Canada in November, and Sar2667, which landed over France in February.
With the opening of the Vera Rubin Observatory in Chile later this year, we have much more to discover in the future.
R. Terik Daly et al., Successful kinetic impact into an asteroid for planetary defense, Nature (2023). DOI: 10.1038/s41586-023-05810-5
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
Cristina A. Thomas et al, Change in orbital period of Dimorphos due to DART kinetic impact, Nature (2023). DOI: 10.1038/s41586-023-05805-2
Jian-Yang Li et al, Ejection from DART-produced active asteroid Dimorphos, Nature (2023). DOI: 10.1038/s41586-023-05811-4 Ariel
Graykowski et al, Light Curves and Colors of the Ejecta from Dimorphos after the DART Impact, Nature (2023). DOI: 10.1038/s41586-023-05852-9
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Citation: New Results from NASA’s DART Planetary Defense Mission Confirm We Could Deflect Deadly Asteroids (2023 March 4) Retrieved March 4, 2023 from https://phys.org/news/2023-03-results-nasa- dart-planetary-defense. html
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