Science

DART confirmed on target to impact asteroid Dimorphos

NASA DART Double Asteroid Redirection Test
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NASA DART Double Asteroid Redirection Test

DART animation. Credit: NASA/Johns Hopkins APL

DART team confirms orbit of target asteroid

Using some of the world’s most powerful telescopes, the DART research team completed a six-night observing campaign last month to confirm previous calculations of the orbit of Dimorphos, DART’s asteroid target. Dimorphos is in orbit around its larger parent asteroid, Didymos. These observations confirm where the asteroid is expected to be at the time of impact. DART, which is the world’s first attempt to change the speed and trajectory of an asteroid’s motion in space, is testing an asteroid deflection method that could prove useful if such a need arises for planetary defense in the future.

“The measurements the team made in early 2021 were critical in making sure DART got to the right place at the right time for its kinetic impact on Dimorphos,” said Andy Rivkin, co-leader of the DART research team at the Center for Johns Hopkins University Applied Research. Physical Laboratory (APL) in Laurel, Maryland. “Confirming those measurements with new observations shows us that we don’t need any course changes and that we are already right on target.”

Lowell Discovery Telescope Asteroid Didymos

On the night of July 7, 2022, the Lowell Discovery Telescope near Flagstaff, Arizona captured the asteroid Didymos. Credit: Lowell Observatory/N. Moskowitz

However, understanding the dynamics of Dimorphos’s orbit is important for reasons beyond ensuring DART’s impact. If DART manages to alter Dimorphos’s path, the small moon will move closer to Didymos, reducing the time it takes to orbit it. Although measuring that change is straightforward, scientists need to confirm that nothing other than the impact is affecting the orbit. This includes subtle forces like the recoil of radiation from the asteroid’s Sun-heated surface, which can gently push the asteroid away and cause its orbit to change.

“The before-and-after nature of this experiment requires exquisite knowledge of the asteroid system before we do anything to it,” said Nick Moskovitz, an astronomer at the Lowell Observatory in Flagstaff, Arizona, and co-director of the July observing campaign. “We don’t want, at the last minute, to say, ‘Oh, here’s something we hadn’t thought of or phenomena we hadn’t considered.’ We want to be sure that any change we see is entirely due to what DART did.”

Lowell Discovery Telescope Asteroid Didymos

On the night of July 7, 2022, the Lowell Discovery Telescope near Flagstaff, Arizona, captured this sequence in which the asteroid Didymos, located near the center of the screen, moves across the night sky. The sequence here is sped up about 1,800 times. Scientists used this and other observations from the July campaign to confirm Dimorphos’s orbit and anticipated location at the time of DART’s impact. Credit: Lowell Observatory/N. Moskowitz

From late September to early October, around the time of the DART impact, Didymos and Dimorphos will make their closest approach to Earth in recent years. This will put them approximately 6.7 million miles (10.8 million kilometers) apart. Since March 2021, the Didymos system has been out of range of most ground-based telescopes due to its distance from Earth. However, in early July, the DART Investigation Team used powerful telescopes in Arizona and Chile—the Lowell Discovery Telescope at Lowell Observatory, the Magellan Telescope at Las Campanas Observatory, and the Southern Astrophysical Research Telescope (SOAR)— to observe the asteroid system and look for changes in its brightness. These changes, called “mutual events,” occur when one of the asteroids passes in front of the other due to Dimorphos’s orbit, blocking some of the light they emit.

“It was a tricky time of year to get these observations,” Moskovitz said. In the northern hemisphere, the nights are short and it is monsoon season in Arizona. In the southern hemisphere, the threat of winter storms loomed. In fact, just after the observation campaign, a major snowstorm hit Chile, prompting evacuations from the mountain where SOAR is located. This resulted in the telescope being turned off for about ten days. “We asked for six half-nights of observation with the expectation that about half of them would be lost to weather, but we only lost one night. We were very lucky.”

In total, the team was able to extract the timing of 11 new mutual events from the data. Analyzing those changes in brightness allowed scientists to pinpoint how long it takes for Dimorphos to orbit the larger asteroid. Therefore, they can predict where Dimorphos will be located at specific times, even when DART hits. The results were consistent with previous calculations.

“We’re really very confident now that the asteroid system is well understood and we’re ready to understand what happens after impact,” Moskovitz said.

This observing campaign not only allowed the team to confirm Dimorphos’s orbital period and expected location at impact, but also allowed team members to refine the process they will use to determine if DART successfully changed Dimorphos’s orbit. after impact, and for how long

In October, after DART has slammed into the asteroid, the team will once again use ground-based telescopes around the world to search for mutual events and calculate Dimorphos’s new orbit. They expect the time it takes for the smaller asteroid to orbit Didymos to have shifted by several minutes. These observations will also help constrain the theories that scientists around the world have put forward about the dynamics of Dimorphos’s orbit and the rotation of both asteroids.

Johns Hopkins APL manages the DART mission to[{” attribute=””>NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office. DART is the world’s first planetary defense test mission, intentionally executing a kinetic impact into Dimorphos to slightly change its motion in space. While neither asteroid poses a threat to Earth, the DART mission will demonstrate that a spacecraft can autonomously navigate to a kinetic impact on a relatively small target asteroid and that this is a viable technique to deflect an asteroid on a collision course with Earth if one is ever discovered. DART will reach its target on September 26, 2022.

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