DART confirmed on target to impact asteroid Dimorphos

NASA DART Double Asteroid Redirect Test

DART animation. Credit: NASA/Johns Hopkins APL

DART team confirms orbit of targeted asteroid

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

“The measurements taken by the team in early 2021 were critical to ensuring DART arrived at the right place and time for its kinetic impact on Dimorphos,” said Andy Rivkin, DART research team co-lead at Johns Hopkins University Applied Sciences. Physics Laboratory (APL) in Laurel, Maryland. “Confirming those measurements with new observations shows us that we don’t need course changes and that we are already well on track.”

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. Moskovitz

However, understanding the dynamics of Dimorphos’ orbit is important for reasons beyond ensuring the impact of DART. If DART manages to change Dimorphos’ path, the moon will move closer to Didymos, reducing the time it takes to orbit around it. While measuring that change is easy, scientists need to confirm that nothing but impact affects orbit. This includes subtle forces such as radiation recoil from the asteroid’s sun-warmed surface, which can push gently on the asteroid and alter its orbit.

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

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 is accelerated about 1800 times here. Scientists used these and other observations from the July campaign to confirm Dimorphos’ orbit and its expected location at the time of the DART’s impact. Credit: Lowell Observatory/N. Moskovitz

In late September to early October, around the time of the DART impact, Didymos and Dimorphos will be closest to Earth in recent years. This puts them about 6.7 million miles (10.8 million kilometers) away. Since March 2021, the Didymos system has been out of reach of most ground-based telescopes due to its distance from Earth. However, in early July, the DART research 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 (SOAR) Telescope — to observe the asteroid system and look for changes. in its brightness. These changes, called “mutual events,” happen when one of the asteroids passes in front of the other due to Dimorphos’ 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 in Arizona it is monsoon season. In the southern hemisphere, the threat of winter storms loomed. Shortly after the observation campaign, a major snow storm hit Chile, prompting evacuations from the mountain where SOAR is located. This resulted in a shutdown of the telescope for nearly ten days. “We requested six half-nights of observation with some expectation that about half of that would be lost to the weather, but we only lost one night. We’ve been really lucky.”

In total, the team was able to extract the timing of 11 new reciprocal events from the data. By analyzing those changes in brightness, scientists were able to determine exactly how long it takes Dimorphos to orbit the larger asteroid. This allows them to predict where Dimorphos will be at specific points in time, including when DART makes an impact. The results were consistent with previous calculations.

“We are really confident now that the asteroid system is well understood and we are set up to understand what happens after the impact,” Moskovitz said.

This observation campaign not only enabled the team to confirm the orbital period of Dimorphos and its expected location at the time of impact, but it also enabled the team members to fine-tune the process they will use to determine whether DART is compatible with success changed the orbit of Dimorphos after the impact, and by how much.

In October, after DART hits the asteroid, the team will again use ground-based telescopes around the world to look for reciprocal events and calculate Dimorphos’ 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 narrow down theories that scientists around the world have put forth about Dimorphos’ orbital dynamics and the rotation of both asteroids.

Johns Hopkins APL manages the DART mission for:[{” 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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