NASA's DART Data Validates Kinetic Impact As Planetary Defense Method

After analyzing the data collected from NASA's successful Double Asteroid Redirection Test (DART) last year, the DART team found that the kinetic impactor mission "can be effective in altering the trajectory of an asteroid, a big step toward the goal of preventing future asteroid strikes on Earth." The findings were published in four papers in the journal Nature. From a NASA press release: The first paper reports DART's successful demonstration of kinetic impactor technology in detail: reconstructing the impact itself, reporting the timeline leading up to impact, specifying in detail the location and nature of the impact site, and recording the size and shape of Dimorphos. The authors, led by Terik Daly, Carolyn Ernst, and Olivier Barnouin of APL, note DART's successful autonomous targeting of a small asteroid, with limited prior observations, is a critical first step on the path to developing kinetic impactor technology as a viable operational capability for planetary defense. Their findings show intercepting an asteroid with a diameter of around half a mile, such as Dimorphos, can be achieved without an advance reconnaissance mission, though advance reconnaissance would give valuable information for planning and predicting the outcome. What is necessary is sufficient warning time -- several years at a minimum, but preferably decades. "Nevertheless," the authors state in the paper, DART's success "builds optimism about humanity's capacity to protect the Earth from an asteroid threat." The second paper uses two independent approaches based on Earth-based lightcurve and radar observations. The investigation team, led by Cristina Thomas of Northern Arizona University, arrived at two consistent measurements of the period change from the kinetic impact: 33 minutes, plus or minus one minute. This large change indicates the recoil from material excavated from the asteroid and ejected into space by the impact (known as ejecta) contributed significant momentum change to the asteroid, beyond that of the DART spacecraft itself. The key to kinetic impact is that the push to the asteroid comes not only from colliding spacecraft, but also from this ejecta recoil. The authors conclude: "To serve as a proof-of-concept for the kinetic impactor technique of planetary defense, DART needed to demonstrate that an asteroid could be targeted during a high-speed encounter and that the target's orbit could be changed. DART has successfully done both." In the third paper, the investigation team, led by Andrew Cheng of APL, calculated the momentum change transferred to the asteroid as a result of DART's kinetic impact by studying the change in the orbital period of Dimorphos. They found the impact caused an instantaneous slowing in Dimorphos' speed along its orbit of about 2.7 millimeters per second -- again indicating the recoil from ejecta played a major role in amplifying the momentum change directly imparted to the asteroid by the spacecraft. That momentum change was amplified by a factor of 2.2 to 4.9 (depending on the mass of Dimorphos), indicating the momentum change transferred because of ejecta production significantly exceeded the momentum change from the DART spacecraft alone. DART's scientific value goes beyond validating kinetic impactor as a means of planetary defense. By smashing into Dimorphos, the mission has broken new ground in the study of asteroids. DART's impact made Dimorphos an "active asteroid" -- a space rock that orbits like an asteroid but has a tail of material like a comet -- which is detailed in the fourth paper led by Jian-Yang Li of the Planetary Science Institute.

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