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The Double Asteroid Redirection Test successfully changed the trajectory of the asteroid Dimorphos when the NASA spacecraft intentionally slammed into the space rock on September 26, according to the agency.
The DART mission, a full-scale demonstration of deflection technology, was the world’s first conducted on behalf of planetary defense. The mission was also the first time humanity intentionally changed the motion of a celestial object in space.
Prior to impact, it took Dimorphos 11 hours and 55 minutes to orbit its larger parent asteroid Didymos. Astronomers used ground-based telescopes to measure how Dimorphos’ orbit changed after impact.
Now, it takes Dimorphos 11 hours and 23 minutes to circle Didymos. The DART spacecraft changed the moonlet asteroid’s orbit by 32 minutes.
Initially, astronomers expected DART to be a success if it shortened the trajectory by 10 minutes.
“All of us have a responsibility to protect our home planet. After all, it’s the only one we have,” said NASA Administrator Bill Nelson.
“This mission shows that NASA is trying to be ready for whatever the universe throws at us. NASA has proven we are serious as a defender of the planet. This is a watershed moment for planetary defense and all of humanity, demonstrating commitment from NASA’s exceptional team and partners from around the world.”
Neither Dimorphos nor Didymos pose a threat to Earth, but the double-asteroid system was a perfect target to test deflection technology, according to the DART team.
“For the first time ever, humanity has changed the orbit of a planetary object,” said Lori Glaze, director of the Planetary Science Division at NASA.
“As new data come in each day, astronomers will be able to better assess whether, and how, a mission like DART could be used in the future to help protect Earth from a collision with an asteroid if we ever discover one headed our way.”
The DART team continues to gather data by observing the double-asteroid system, and the orbital measurement may become more precise in the future. Currently, there is an uncertainty of plus or minus two minutes.
A new image of Dimorphos, captured by the Hubble Space Telescope, shows that the debris trail’s cometlike tail has split into two. Scientists are still working to understand the significance of the split.
The team is now focusing on measuring how much momentum was transferred from DART to Dimorphos. At the time of impact, the spacecraft was moving at about 14,000 miles per hour (22,530 kilometers per hour). Astronomers will analyze the amount of rocks and dust blasted into space after impact.
The DART team believes that the recoil from the plume “substantially enhanced” the spacecraft’s push against the asteroid, not unlike the release of air from a balloon propels it in the opposite direction, according to NASA.
“Although we have done more to the system than simply change the orbit, we may have left Dimorphos wobbling a bit,” said Tom Statler, DART program scientist at NASA. “So over time, there may be some interaction between the wobble and the orbit and things will adjust. But it’s certainly never going to go back to the old 11 hour 55 minute orbit.”
Astronomers are still investigating the surface of Dimorphos and how weak or strong it is. The DART team’s first look at Dimorphos, provided by DART before the crash, suggests that the asteroid is a pile of rubble held together by gravity.
Imagery continues to return from the Light Italian CubeSat for Imaging of Asteroids, or LICIACube, the mini satellite provided by the Italian Space Agency that tagged along as a robotic photojournalist on DART’s mission.
In about four years, the European Space Agency’s Hera mission will also fly by the double-asteroid system to study the crater left by the collision and measure the mass of Dimorphos.
“DART has given us some fascinating data about both asteroid properties and the effectiveness of a kinetic impactor as a planetary defense technology,” said Nancy Chabot, the DART coordination lead from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “The DART team is continuing to work on this rich dataset to fully understand this first planetary defense test of asteroid deflection.”
The research team chose Dimorphos for this mission because its size is comparable to asteroids that could pose a threat to Earth. An asteroid the size of Dimorphos could cause “regional devastation” if it hit Earth.
Near-Earth objects are asteroids and comets with an orbit that places them within 30 million miles (48.3 million kilometers) from Earth. Detecting the threat of near-Earth objects that could cause grave harm is a primary focus of NASA and other space organizations around the world.
No asteroids are currently on a direct impact course with Earth, but more than 27,000 near-Earth asteroids exist in all shapes and sizes.
Finding populations of hazardous asteroids and determining their sizes are priorities of NASA and its international partners. The design for a space-based telescope called the Near-Earth Object Surveyor mission is currently in review.
“We should not be too eager to say that one test on one asteroid tells us exactly how every other asteroid would behave in a similar situation,” Statler said. “But what we can do is use this test as an anchor point for our physics calculations in our simulations that tell us how different kinds of impacts in different situations should behave.”