At 7:14 p.m. EST on September 26, NASA will launch a pre-emptive strike against the dangers of the solar system. Then the agency is supposed to ram a spaceship onto an asteroid 11 million kilometers from Earth. The aim is to throw the harmless space rock into a slightly different orbit to test whether humanity could do such a thing if a dangerous asteroid were ever spotted heading towards Earth1.
The Double Asteroid Redirection Test (DART) spacecraft will meet its end when it crashes into the approximately 160-meter-wide asteroid Dimorphos. “We describe it as going into the Great Pyramid in a golf cart,” says Nancy Chabot, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.
Record number of asteroids whizzing past Earth in 2020
The endeavor is reminiscent of Bruce Willis, who saved Earth by blowing up a wayward asteroid in the 1998 film Armageddon. And the whole event will unfold like a movie when it airs on NASA’s website. DART’s camera will focus on Dimorphos and the larger asteroid it orbits, Didymos, as the spacecraft approaches.
At first, DART won’t be able to distinguish between the two asteroids, but when it gets close enough, its vision will resolve into two points of light. The spacecraft will continue to hurtle toward Dimorphos, taking images once per second and sending them back to Earth until the asteroid’s shattered surface fills the field of view. “We’re very excited to see what it’s going to look like,” says Michelle Chen, a software engineer at the Johns Hopkins lab. Then the footage ends abruptly as DART hits the surface.
After an impact
But the $330 million mission aims to do some science before the credits roll. DART will study the effects of injecting kinetic energy – from a 6.6 km per second impact – into an asteroid. Dimorphos could absorb much of that energy or partially break apart, depending on whether it’s made of solid rock or a loose assemblage of space pebbles2. Small asteroids are “small geophysical and geological worlds,” says Patrick Michel, planetary scientist at the Côte d’Azur Observatory in Nice, France. “We don’t know what DART will see.”
The researchers will get the best overview of the consequences of the collision from another spacecraft that will fly by. An Italian probe called LICIACube is moving slightly behind DART and will zoom past Dimorphos just three minutes after impact. Its cameras take pictures before and after the crash. Unless the impact kicks up a dust cloud big enough to obscure the view, LICIACube will see what’s left of the DART spacecraft3,4. The most exciting images from LICIACube should be available within 24 hours of the crash, says Simone Pirrotta, the probe’s project manager at Italy’s ASI space agency in Rome.
The impact may not leave a crater if Dimorphos absorbs much of DART’s kinetic energy, says Adriano Campo Bagatin, a planetary scientist at the University of Alicante in Spain. Visits to other asteroids have shown how intricate and surprising space rocks can be. As of 2018, for example, NASA’s OSIRIS-REx spacecraft spent two years orbiting and studying the asteroid Bennu, but when it approached to collect a sample, Bennu turned out to be a loose collection of pebbles, arm that reacted in unexpected ways to the sampling.
With Dimorphos, it will be days to weeks before mission scientists can confirm if the test worked. The goal is to speed up Dimorphos’ orbit and reduce the travel time around Didymos by 10–15 minutes (see “Destructive Maneuver”). Scientists will find out if this happened by using telescopes on Earth to observe how Dimorphos blocks light from Didymos and vice versa as the smaller asteroid orbits the larger one.
Observatories on every continent will measure the aftermath of the crash, as will the Hubble and James Webb Space Telescopes. “I will advocate for every single observer,” says Cristina Thomas, a planetary scientist at Northern Arizona University in Flagstaff who leads the observing teams. Changes in Dimorphos’ orbit will likely become visible around October 1-2, or even earlier, depending on how quickly the dust cloud clears after the impact. Researchers will have to wait until 2027 for another close-up, when a European Space Agency mission called Hera visits the asteroid to study the crash site5.
Dimorphos and Didymos are not a threat to Earth – and they won’t be after the test. NASA just wants to understand if they are capable of deflecting a space rock the size of Dimorphos that could devastate a region of Earth if it hit the planet.
The agency scans the cosmos for threatening asteroids, but the project is behind schedule. With the telescopes currently available on Earth, it would take another three decades to complete. And this year, NASA delayed the launch of a long-awaited space telescope that would help hunt down these asteroids from 2026 to no earlier than 2028.
“The most important thing to keep in mind with all of these deflection techniques is that they rely on having enough time to work,” says Amy Mainzer, a planetary scientist at the University of Arizona in Tucson and principal investigator on the proposed telescope. “The key is to find objects well in advance of potential impact.”