An asteroid wiped out the dinosaurs; now The earthlings defend themselves. The sight of saurian fossils in most science museums is a powerful reminder that asteroids can threaten Earth as they orbit our sun, sometimes coming dangerously close to our planet – or, there are 66 million years, too close. Today, scientists tested a method that could save our planet from future disasters. In the past hour, NASA’s Double Asteroid Redirection Test (DART) spacecraft crashed into a small asteroid called Dimorphos.
As DART’s full name suggests, this impact was not accidental. It’s supposed to alter the space rock’s trajectory by a tiny but noticeable amount – a change that observers will carefully confirm and track from afar with a plethora of ground and space telescopes. In the future, if a dangerous asteroid is on a collision course with the Earth, we could use this same technique to deflect it from its course and avoid disaster. “We’re not going to blow up the Death Star,” says Andy Rivkin, DART survey team leader at Johns Hopkins University’s Applied Physics Laboratory (APL), which is leading the mission. “We’re using the spacecraft’s momentum to alter the asteroid’s orbit.”
DART was launched in November 2021 on a collision course with Dimorphos, a small asteroid 160 meters in size that orbits another asteroid, Didymos, which is almost five times larger. For nearly a year, the vending machine-sized, roughly 600-kilogram spacecraft has been catching up with the asteroids, snapping sharper images as it approaches. That was until today, 7:15 p.m. ET, when APL mission control engineers stopped receiving signals from the spacecraft, confirming its self-destructive snap on Dimorphos about 11 million miles from Earth.
“We are entering a new era for humanity,” said Lori Glaze, director of NASA’s planetary science division, in post-impact remarks during the space agency’s live broadcast of the event. . “An era in which we have the potential ability to protect ourselves from something like a dangerous asteroid impact.”
Traveling at approximately 23,000 kilometers per hour, the spacecraft struck the asteroid with the approximate energy of three metric tons of TNT, exploding in a superheated shower of metal and asteroid debris. A small Italian spacecraft called LICIACube (Light Italian Cubesat for Imaging of Asteroids) following three minutes late took images of the impact which will be released in the coming days. However, the real mission has only just begun. Now scientists will observe Dimorphos with everything from ground-based telescopes to deep-space observatories and see exactly how dramatic an impact DART has had on its target. “We demonstrate for the first time that if humanity needed to alter the course of an asteroid, we would be able to do so,” says DART team member Harrison Agrusa of the University of Maryland.
The DART mission was originally conceived about two decades ago, when American and European scientists began discussing a joint mission that could practice an asteroid kinetic deflection technique. Originally called AIDA (Asteroid Impact and Deflection Assessment), the mission would involve NASA’s DART spacecraft and Europe’s AIM (Asteroid Impact Mission) spacecraft, which would orbit the target and observe the impact. Unfortunately, European officials canceled AIM in 2016 due to a lack of funding. In 2019, however, the mission was reborn as the Hera spacecraft (named after the Greek goddess of marriage). But this development reset meant a delayed launch: Hera won’t take off until 2024 and won’t arrive in Didymos until 2026, far too late to see the impact of DART, but still in time to study its lasting effects.
The scientists wanted the DART target to be a binary asteroid, where one asteroid orbits another, because such celestial configurations allow easier measurements of small impact-induced orbital changes. “The deviation is almost instantaneous”, explains Patrick Michel of the National Center for Scientific Research, former principal investigator of AIM and now principal investigator of Hera. In 2013, scientists chose the Didymos system as the target. First discovered in 1996, this larger asteroid got its name (Greek for “twin”) following the discovery of a small orbiting companion in 2003, which was later dubbed Dimorphos, or “having two shapes.” .
Dimorphos completes an orbit of Didymos every 11.92 hours. Asteroids share a similar orbit with Earth but pose no threat because they never approach closer than a few million kilometers to our planet. But their angle of orbit causes Dimorphos to “eclipse” regularly in front of Didymos, making it possible to precisely measure its orbital period. After the impact, various telescopes, including the James Webb Space Telescope and Hubble – and even spacecraft such as NASA’s Lucy probeswhich is currently on its way to visit asteroids near Jupiter, will track this eclipse, allowing scientists to determine how much Dimorphos’ orbit has changed.
DART hit the asteroid almost head-on, meaning it slowed Dimorphos’ orbit. The asteroid is so small, however, that mission scientists didn’t know its exact shape or composition – whether Dimorphos was a rigid, solid object or rather a looser “rubble pile” of rocks and boulders that gently rolled up. accumulated together. During the final moments of its approach, DART sent back images of Dimorphos’ rubble-strewn surface, indicating that the asteroid was far from rock-solid. If that had been the case, the change in orbit could have been barely more than a minute, as DART would have transferred only a relatively small amount of momentum to the asteroid. “We need at least 73 seconds of orbit change” for the mission to be announced as a success, Rivkin says. Instead, the shabby appearance of Dimorphos suggests the strength of the material spitting outward (perhaps up to a few tens of millions of kilograms) could cause a much larger change in momentum, shortening the asteroid’s orbit by 10 minutes or more. Such an event could completely reshape Dimorphos or even bring it down. crazy in Love. “The weaker the asteroid, the larger the crater,” says Sabina Raducan of the University of Bern in Switzerland, a member of the DART team. “Of course we want there to be a lot of deflection and ejecta because it’s more interesting.”
Observations by the telescopes and LICIACube are expected to reveal roughly how much orbit has changed and how much ejecta has been released, with the DART team expected to announce preliminary mission results in December at a meeting of the ‘American Geophysical Union in Chicago. But no one will know for sure how successful the mission was until Hera arrives in 2026. Observations from this spacecraft will accurately measure the mass of Dimorphos and get a more accurate idea of the evolution of its orbit around Didymos, perhaps 10 times better than would otherwise be possible from more distant observations alone. “We’ll understand the magnitude of the surge and we’ll get a better understanding of what Dimorphos is made of,” says APL’s Angela Stickle, a member of the DART team.
This could be crucial information if something like DART is called upon to save Earth in the future. “It’s one of the most important things we’re doing right now,” says Detlef Koschny, deputy director of ESA’s planetary defense office. “We’ve been talking about the need to demonstrate that we can deflect an asteroid for many years.” Although no kilometer-long dinosaur-killing asteroids are known to be on an impact trajectory with our planet, smaller asteroids like Dimorphos are less well constrained, with only an estimated few percent of their total population currently known. “We don’t know enough yet to feel safe,” says Koschny. An impact from a space rock the size of Dimorphos could instantly wipe out a city and cause widespread damage to an entire country, which means there’s good reason to search for such asteroids.
Upcoming telescopes, such as the Vera C. Rubin Observatory, which is expected to come online in Chile later this decade, will better track these asteroids. If we ever find one on a collision course with Earth, the results of the DART mission may well dictate what action we take. “It’s going to validate a tool that we could use,” Rivkin says. To deflect a dangerous asteroid, perhaps a larger version of DART could be used or even a series of DART-sized spacecraft to crash into the offending space rock, one after another, gradually deflecting its fate. “It depends on how much warning time we have,” says Rivkin. It is unlikely that such a perilous event will befall mankind anytime soon. But maybe, in the distant future, our distant descendants will have this little spaceship to thank. “If we can deflect Dimorphos, we can most likely deflect any other near-Earth asteroids,” Agrusa says.