MSU professor involved in NASA’s DART mission explains science behind historic event
NASA’s Double Asteroid Redirection Test, or DART, successfully slammed into an asteroid in space last Monday in the first-ever attempt to deflect an asteroid using kinetic impact.
The DART mission launched into space 10 months ago on a trajectory to Didymos, an asteroid system that posed no threat to Earth. The system consists of two asteroids: Didymos and a smaller asteroid orbiting Didymos, Dimorphos, which was the final target.
Before crashing into the asteroid, which measures 530 feet in diameter, DART filmed Dimorphos up close and the video was broadcast live around the world.
Among those watching was Seth Jacobson, who works in DART’s Dynamics Task Force. He is an assistant professor in the Department of Earth and Environmental Sciences at MSU. Jacobson gathered with friends and colleagues in a restaurant to watch the small white dot in the middle of the black screen grow until it was the only object in the frame and the cameras slammed into it .
According to Jacobson, although the chances of success increased as the spacecraft approached the asteroid, he still feared something might go wrong. When the collision happened, Jacobson was relieved and thrilled to see the asteroid he had been studying for years up close.
“It was fantastic,” Jacobson said. “We have been studying the Didymos-Dimorphos system from the ground for a long time, and when we study from the ground, we never get any kind of detailed information about the appearance of the surface, or about the very precise shapes of the objects. So to see it appear, as we approached the asteroid, was really cool. It finally became a real object, and all of these characteristics of its surface and its shape were revealed. It was really fun .
Jacobson first heard of the mission about a decade ago, when he said it was still just a “blackboard sketch.” But he officially got involved in the mission about two years ago.
As a member of the Dynamics Working Group, Jacobson’s role is to characterize the binary asteroid system visited by the DART mission, before and after impact. This work will help estimate the amount of momentum transferred from the spacecraft to Dimorphos.
To do this, the team will analyze data from various sources over the next two months. The team has data from the spacecraft itself regarding the speed and mass of the spacecraft before impact, as well as observations of the asteroid and ejecta. The team will also look at data from ground-based observatories and space observatories like the Hubble Space Telescope.
With images from ground-based telescopes, the team will use a light-curve technique to determine Dimorphos’ trajectory. Jacobson said the technique will be particularly effective because Dimorphos passes between Earth and Didymos, and behind Didymos, on each orbit. This means scientists can precisely time when Dimorphos passes in front of and behind Didymos down to the millisecond.
According to Jacobson, NASA’s decision to target this system will help the team in several ways.
“One of the reasons we chose a binary asteroid system that has two members…is because we can very precisely measure this little orbit of Dimorphos around Didymos, and we can do that from the floor, which is really good,” Jacobson said. “It is much more difficult to measure – at such a level of precision – a single asteroid moving around the sun, for example. So the fact that it is a small system means that we can make very precise measurements.
Once the data is collected, the team will be able to quantify momentum transfer, for which they use a parameter called beta. Beta is calculated by dividing the extra momentum the target asteroid picks up by the momentum provided by the spacecraft. Jacobson said he expects the transferred momentum to be greater than the spacecraft’s initial momentum due to ejecta thrown up by the asteroid.
NASA has images of the DART mission on its website. Once Jacobson and his team create an accurate beta estimate, NASA will be better equipped for future hazards an asteroid could create.
“If we can get an accurate estimate of that value, then we know that whenever we need to run this experiment for real, then we can apply the beta, that number that we’ve now verified experimentally, to our predictions for what we need to do to accomplish the task of potentially saving a city or the planet from impact.
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