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Mission to Test Technology for Defending Earth Against Potential Asteroid or Comet Hazards Hits Target

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DART spacecraft 

This illustration depicts NASA’s Double Asteroid Redirection Test (DART) spacecraft prior to impact at the Didymos binary asteroid system. 

Credit: NASA/Johns Hopkins APL/Steve Gribben.

NASA’s Double Asteroid Redirection Test (DART) spacecraft successfully hit its target Sept. 26, and now scientists are analyzing to what degree the kinetic impact changed the trajectory of Dimorphos, the asteroid moonlet of Didymos. 

The mission is a test to see if hitting a body headed for Earth with a small spacecraft could redirect the threat away from us. 

Five Planetary Science Institute scientists, Jian-Yang Li, Eric Palmer, Steven Schwartz, Amanda Sickafoose and Jordan Steckloff are working on the DART mission. 

The mission will attempt to slightly change an asteroid’s motion in a way that can be accurately measured using ground-based telescopes. DART’s target Dimorphos is approximately 530 feet (160 meters) in diameter, and orbits Didymos, approximately 2,560 feet (780 meters) in diameter. Since Dimorphos orbits Didymos at much a slower relative speed than the pair orbits the Sun, the result of DART’s kinetic impact within the binary system can be measured much more easily than a change in the orbit of a single asteroid around the Sun. 

“This is the first time that humans have tried to actually alter the path of an asteroid. This is the type of thing that blockbusters movies are made of!” said Sickafoose, a DART Investigation Team member.

Sickafoose’s team has been taking six-hour blocks of images using a 1-meter telescope in Sutherland, South Africa to derive Didymos’ light curve on the days leading up to the impact, the impact itself, and will then take more light-curve observations following impact. “Our site is also well placed to observe the impact itself. Changes in brightness near the impact time can be compared with models to help determine the physical properties of Dimorphos.  Combining light-curve observations from many sites over a long period of time will allow accurate determination of changes to Dimorphos’ orbit as a result of the impact,” Sickafoose said. 

“By observing the Didymos system before and after the impact, we are supporting the primary goal of determining how much the path of the satellite is altered. Right now, Dimorphos has an orbital period of roughly 11.9 hours. Changes to this orbital period after the impact would indicate the effect of the spacecraft,” Sickafoose said. “Taking images of the impact itself can be used to compare with models of ejecta formation and distribution, which should help constrain the physical properties of the asteroid.”

“The DART mission is a test to see how effective a kinetic impact is in changing the orbit of an asteroid. We are using this binary asteroid system for this test because it provides a clear and accurate technique to measure the change in orbit,” Palmer said. 

“I will be building the digital terrain model for Didymos, the binary asteroid system’s primary.  Additionally, I am responsible for updating and testing the software needed to generate the shape model,” Palmer said. “My part supports our scientific understanding of asteroids, especially binary asteroids.” 

Li is leading the NASA Hubble Space Telescope observations of the impact, and also participating in the analysis of the images of Didymos and Dimorphos to be collected by the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) onboard DART and the LEIA camera onboard the Light Italian CubeSat for Imaging Asteroids (LICIACube) to study the surface albedo of the asteroids.

“I'm currently a Participating Scientist on the mission, but I've been involved with it for a while,” Schwartz said. “It was conceived as a more coordinated set of two missions, NASA’s DART and the European Space Agency’s Asteroid Impact Mission. 

Steckloff is on the mission’s investigative team. “My main interest is in the behavior of the asteroid regolith and topography in response to the DART impact.  Are we going to trigger landslides and landscape evolution? How will any impact-induced seismic activity contribute to landscape evolution?  What are the physical properties of the asteroid material – for example, cohesive strength? 

“In short, my interests are on changes to a rubble pile in response to a known impact. This has less to do with the primary goal of the DART mission to determine the efficacy of current kinetic deflection technology, but more to do with what we can learn from a known impact into a rubble pile asteroid,” Steckloff said. 

The spacecraft, about the size of a golf cart and weighing 1,210 pounds, or 550 kilograms, slammed into Dimorphos at roughly 4 miles per second (6 kilometers per second). Scientists estimate the kinetic impact will shorten Dimorphos’ orbit around Didymos by several minutes. 

Dec. 4, 2022

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