The test predicts the effects of the DART impact

A sequence of high-speed camera impact photographs (left to right, top to bottom). The first is two frames before impact, where with higher sensitivity it is possible to distinguish the incoming sphere before impact (the crescent of hypersonic flight through the residual gas in the near vacuum). The following image shows the impact, where the saturated image is approximately 12cm in diameter. The following image is from a numerical simulation of the impact, showing the velocity of the material; the black line delimits the impactor and the target) and the crater at 10 μs measures approximately 6 cm in diameter. The following three images are sequential photographs after the strike. The frames are separated by 12.65 µs; the exposure is 0.29 µs. The experimental images are self-illuminated. Credit: The Journal of Planetary Science (2022). DOI: 10.3847/PSJ/ac854f

On September 26, NASA’s Double Asteroid Redirection Test (DART) spacecraft crashed into Dimorphos, a moon of the near-Earth asteroid Didymos, at 14,000 miles per hour. Prior to impact, engineers and scientists at the Southwest Research Institute performed an experiment to study the cratering process that produces the mass of ejected material and measures the subsequent enhancement of impact momentum.

The experiment, which used a more realistic target than those previously explored, is described in a new paper published in The Journal of Planetary Science.

NASA is not only tracking near-Earth asteroids (NEAs) that could pose a possible impact threat to our planet, but is also exploring technology to deflect the trajectory of a small NEA. Only a small orbital change would be needed to alter an object’s trajectory so that it would pass safely through Earth, as long as the change is applied long enough before the moment of impact.

Changing an asteroid’s momentum through a direct collision delivers a double punch: the direct momentum transfer of the projectile impacting it, pushing it forward, and the asteroid recoiling from the exploding debris from the impact crater, also known as crater ejecta. The ejecta transfers momentum, propelling the target in an “action-reaction” mode, much like a rocket launches when high-velocity gas shoots out from the rear of the vehicle.

“A big question we faced was what the asteroid would actually look like and what its composition would be. Whether we can learn anything from small-scale laboratory experiments is a question that interests us at the moment. highest,” said Dr. James D. Walker, director of Engineering Dynamics at SwRI and lead author of the study.

Walker is a member of the DART investigative team alongside co-authors Dr. Sidney Chocron, Donald J. Grosch, and Dr. Simone Marchi.

The DART mission spacecraft launched from Earth in November 2021. On September 26, it deliberately crashed into the moon Dimorphos to assess whether a spacecraft could deflect an asteroid on a collision course with Earth. Dimorphos orbits the asteroid Didymos, a near-Earth object that has been classified as a potentially hazardous asteroid. DART is designed to move the moon’s orbit around Didymos.

SwRI’s large two-stage light gas cannon, capable of launching projectiles at speeds of up to seven kilometers per second, was used to launch a projectile at an object representing the moon. Because Dimorphos was thought to be a “rubble pile” asteroid made up of pieces of rock bound together by gravity, the moon was represented by a collection of rocks and stones, in this case held together by cement.

“We fired an aluminum sphere, which represented the DART space probe, using the two-stage light gas cannon at the target at 5.44 kilometers per second, which is close to the 6.1 kilometers per second expected from the DART impact,” Walker said.

“Our experiment measured a momentum transfer to the target of 3.4 times the incoming momentum of the spherical aluminum projectile. The number 3.4 is referred to by scientists as the Greek letter beta of impact. Therefore , the ejecta from the crater provided an additional 240% of momentum to deflect the body, beyond that provided by the projectile itself.”

The experiment aimed to study the cratering process and measure the improvement in momentum that would result from the collision. Basically, the pile of rubble was not held in place but was suspended vertically like a pendulum to measure the improved momentum, or recoil, created by impact ejecta.

“It’s important to understand the amount of recoil,” said co-author Dr. Simone Marchi. “It all comes down to the amount of momentum that was transferred to the target from impact, and there was a significant amount of recoil and ejecta material.”

By measuring momentum, the SwRI team could then extract important information that could gauge the difficulty of deflecting asteroids in space. In this latest experiment, the improvement in momentum was higher than seen in the team’s previous experiments. A higher recoil suggests it would be easier to deflect the asteroid.

In the weeks following the impact, NASA announced that DART had successfully pushed the moon. Walker now looks forward to seeing what else can be learned from the mission, including the momentum transfer of the event into space.

“It will take some time to calculate the data, in part because it involves estimating the mass of the moon, which is unknown,” he said. “Once there is agreement on the mass, then the measurement of the change in the moon’s orbit will tell us the momentum transfer. We have a speculative body that we have impacted and what we would really like to know, that’s how height affected things. . It will be a challenge to figure that out.”

The paper appears in The Journal of Planetary Science.