ASSESSING THE IMPACT OF THE DART MISSION
Scientists use telescopes around the world, including two at Lowell Observatory, to help determine how much DART changed the orbit of asteroid moon Dimorphos.
Flagstaff, AZ. – Observations of NASA’s Double Asteroid Redirection Test (DART) on the moon of a near-Earth asteroid are reported in five papers published in Nature today. Some of these observations were made using telescopes at research facilities such as Lowell Observatory, where observers used both the 1.1-meter John Hall Telescope and 4.3-meter Lowell Discovery Telescope. Understanding how the impact of the DART spacecraft changed the orbit of the moon sheds light on how this approach might be used to deflect an asteroid in its orbit if one is found on an impacting trajectory with Earth.
Asteroid Didymos (bottom right) and its moonlet, Dimorphos, about 2.5 minutes before the impact of NASA’s DART spacecraft. The image was taken by the onboard DRACO imager from a distance of 570 miles (920 kilometers). This image was the last to contain a complete view of both asteroids. Didymos is roughly 2,500 feet (780 meters) in diameter; Dimorphos is about 525 feet (160 meters) in length. Credit: NASA/Johns Hopkins APL.
The DART mission intentionally impacted a spacecraft into Dimorphos, the moon of near-Earth asteroid (65803) Didymos, on 26 September 2022. The aim of the collision was to change the orbit of the moon, as a demonstration of this planetary defense technique. Estimations of the change in momentum of the moon, a description of how momentum was transferred from the spacecraft to the moon, and a study of ejecta removed during the impact are revealed in the five new Nature papers:
★ Northern Arizona University’s Cristina Thomas and colleagues—including Lowell Observatory’s Nick Moskovitz, Brian Skiff, and Tom Polakis—determine the change in the orbital period of Dimorphos around Didymos after the DART impact. Initial, pre-impact calculations suggested an expected change in the orbital period of around seven minutes. The DART team utilized two independent approaches, one of which was co-led by Moskovitz, to measure the actual change in Dimorphos’ orbit. Both approaches found that the orbital period was reduced by 33 minutes. This much larger number indicates that ejecta removed during the impact imparted significant momentum to alter the orbit of Dimorphos beyond that from just the spacecraft.
★ Ronald Terik Daly and colleagues reconstruct the impact of the DART spacecraft on Dimorphos, which may help with the planning of future missions and could help to predict outcomes with more certainty. They also describe the location and nature of the impact site, noting that it was between two boulders, one of which was grazed by the spacecraft as it made contact with the moon.
★ Jian-Yang Li and colleagues report Hubble Space Telescope observations of the ejecta plume (debris created by the impact), the speed and evolution of which may explain the momentum change caused by the impact.
★ Andrew Cheng and colleagues note that the orbital velocity of Dimorphos reduced after the impact. They propose that the momentum transfer from the spacecraft to the moon was enhanced by recoil from ejecta streams produced by the impact.
★ Observations of Dimorphos before, during and after the impact — made by a global network of citizen science telescopes (including three on Réunion Island and one in Nairobi that captured the moment of impact) — are reported by Ariel Graykowski and colleagues. They estimate the mass and the energy of the ejected dust, and its evolution over time, which may help us to understand the outcomes of impact missions.
“The DART experiment is the world’s first full-scale planetary defense test,” says Moskovitz. “Since impact, it has been thanks to the efforts of telescope observers from around the world that we have gained unprecedented insight into the evolution of this asteroid system and a deep understanding of how DART modified the orbit of Dimorphos.”
Neither Dimorphos nor Didymos poses any hazard to Earth before or after DART’s controlled collision with Dimorphos.
Johns Hopkins Applied Physics Lab built and operated the DART spacecraft and manages the DART mission for NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office. LICIACube is a project of the Italian Space Agency (ASI), carried out by Argotec.
For more information about the DART mission, visit https://www.nasa.gov/dart or https://dart.jhuapl.edu