Laurel, Md. — For the first time in history, a spacecraft from Earth has crashed into an asteroid to test a way to save our planet from extinction.
The spacecraft, NASA’s Double Asteroid Rendezvous Test (DART) probe, crashed into a small asteroid 7 million miles (11 million kilometers) from Earth tonight (September 26) in what the US space agency has announced as the world’s first planetary defense test. Goal: Change the orbit of a space rock called Dimorphos around its larger asteroid parent Didymos to prove that humanity can deflect a dangerous asteroid if it heads towards Earth.
This is something the dinosaurs couldn’t do 65 million years ago when the massive asteroid Chicxulub crashed into the Yucatan Peninsula and caused their extinction.
“The dinosaurs didn’t have a space program to help them, but we do,” Katherine Calvin, NASA chief scientist and senior climate adviser, said ahead of the crash. “Thus, DART represents an important advance in understanding potential future hazards and how to protect our planet from potential impacts.”
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(Image credit: NASA/JHUAPL)
The golf cart-sized DART spacecraft crashed into Dimorphos at 7:14 pm EDT (23:14 GMT) while flying at 14,000 miles per hour (22,500 km/h). The spacecraft was not as big as the probes, but NASA hoped its 1,320 pounds (600 kg) would be enough to move the 534-foot-wide (163 meters) Dimorphos a little faster in its orbit around its parent.
“The spacecraft is very small,” said planetary scientist Nancy Chabot, head of DART coordination at the Johns Hopkins University Applied Research Laboratory (JHUAPL), which oversees the NASA mission. “Sometimes we describe it as a golf cart driving into the Great Pyramid.”
Despite crashing on target, tensions built up at JHUAPL’s DART Mission Control Center as the spacecraft raced toward its target. Most of the last four hours of DART have been automated, with the spacecraft’s navigation system locking onto Dimorphos in its final hour of approach. The main DART camera transmitted photos to Earth every second until the image went black as the spacecraft crashed into the asteroid.
“It’s unnerving,” said Andy Cheng, chief scientist for planetary defense at JHUAPL, who came up with the concept for the DART mission in 2011. The $313 million DART mission launched on November 23, 2021.
(Image credit: NASA/JHUAPL)
Spaceship crash for planetary defense
The DART mission is the first demonstration of what NASA calls a “kinetic striker” for planetary defense: crashing a spacecraft into an asteroid to change its orbit. This is the main method of protecting the Earth if a potentially dangerous asteroid was discovered 5 or 10 years before the expected impact.
“We are changing the movement of a natural celestial body in space. Humanity has never done this before,” said Tom Statler, NASA DART program scientist. “It’s stuff from sci-fi books and really corny Star Trek episodes from my childhood, and now it’s real.”
According to NASA scientists, the risk of a catastrophic asteroid impact with Earth is small, but real. NASA has detected about 40% of large asteroids up to 500 feet (140 meters) wide that could pose a threat to Earth, and regularly scans the skies for more. NASA is also developing a new space sentinel telescope called the Near Earth Object Surveyor, specifically designed to search for dangerous asteroids in the solar system. This mission could be launched by 2026.
But humanity also needs to have methods of deflecting a dangerous asteroid should it be discovered. Hence the DART. “We are very excited every time our space missions protect life on Earth,” NASA Associate Administrator for Science Thomas Zurbuchen told Space.com this morning.
NASA chose Dimorphos, a satellite of Didymos, for the DART strike for several reasons. First, the moon is part of a binary system and revolves around its parent every 11 hours and 55 minutes, which is a short enough period of time for any change in its orbit to be noticeable in ground-based telescopes on subsequent observations.
(Image credit: NASA/Johns Hopkins APL/Steve Gribben)
Didymos and Dimorpos were discovered in 1996 and 2003 respectively and are the first binary asteroid system to be studied in detail. Using a dual asteroid system, rather than a single asteroid, means NASA can use a single spacecraft backed by ground-based telescopes to measure the asteroid’s deflection, rather than requiring an expensive second spacecraft, Cheng said.
While Didymos and Dimorphos are classified as “potentially hazardous asteroids,” they do not pose a collision threat to Earth in the foreseeable future, which NASA measures in decades and centuries. DART was expected to accelerate Dimorphos about 10 minutes faster in its orbit around Didymos without posing the risk of changing the binary system’s orbit to get closer to Earth.
And just 7 million miles away, Didymos and Dimorphos are the closest to Earth they will be in the next 40 years. The signal only takes 38 seconds to complete the one-way journey from DART to Earth, according to NASA.
“So this is the right asteroid at the right time, and that time is now,” Chabot said.
Dimorphos also appeals to astronomers because its size is similar to those asteroids that NASA is most worried about due to a collision with Earth. It is also what NASA calls an S-type asteroid, a rocky variety that is one of the most common types of asteroids in our solar system.
“We do think something like DART would be big enough to take on an asteroid the size of Dimorphos,” planetary scientist Mallory DeCoster, a fashion designer on the DART working group at JHUAPL, told reporters hours before the impact.
However, DART is the first mission of its kind, and mission scientists didn’t know exactly what to expect from Dimorphos. Is the asteroid a solid, massive rock, or more of a pile of sandy debris? And what was its exact form? Variables like these can determine how effective a DART-like asteroid deflection will be.
Angela Stickle, head of the DART working group at JHUAPL, said the team’s simulations and models suggest the spacecraft is likely to create a crater up to 65 feet (20 m) wide.
“We expect it to be catastrophically fragmented,” Stickle said of the DART spacecraft as it hit the target. “Of course, there is a possibility that DART fragments may remain on Dimorphos.”
Read more: NASA’s DART Asteroid Impact Mission Explained in Pictures
Simply hitting Dimorphos was an engineering feat, NASA said, as the DART spacecraft sent a photo every second as it approached its target.
The spacecraft also had witnesses to its death. A few weeks before the impact, DART launched a small cubesat called LICIACube to follow it and watch the asteroid fall. Photos from this cubesat should reach Earth a few days after the impact and show a close-up of the impact and ejection it picked up from Dimorphos.
Has the first test of humanity’s planetary defense succeeded?
Other spacecraft also observed the accident.
NASA’s new James Webb Space Telescope, the Hubble Space Telescope and the Lucy spacecraft tracked the crash from their respective vantage points throughout the solar system during its own mission to the asteroid. On Earth, an extensive network of ground-based telescopes have been trained on the event and will monitor the Didymos-Dimorphos binary over time to see how much faster Dimorphos is now moving in its orbit.
“Our requirements are for 73 seconds, but we actually think we’ll change by about 10 minutes,” Statler said.
It will take time to know if the DART strike was successful as a planetary defense test.
(Image credit: NASA/Johns Hopkins APL/Nancy Chabot/Mike Halstad)
More than three dozen telescopes around the world, including at least one on every continent, will track the Didymos-Dimorphos asteroid system over the next six months to see exactly how effective the test has been. The first radar observations of the impact could happen as early as Tuesday (September 27), said Christina Thomas, a planetary scientist at Northern Arizona University who leads the DART observation task force.
“We will watch Didymos until he can’t be watched,” Thomas said.
The observation campaign attracted volunteer groups from students and universities around the world, each hoping to add their observations to the DART effort.
“There are a lot of them,” Thomas said of the number of ground-based telescope teams. “It’s very interesting to lose count.”
The European Space Agency is planning its own mission to the Didymos-Dimorphos asteroid system to track the impact of DART. This mission, called Hera, will launch a spacecraft to the asteroid in 2024, and by 2027 it will begin orbiting a binary asteroid system to study space rocks and the DART-created Dimorphos crater.
“Asteroid impact technology is a really big challenge,” Chabot told reporters hours before the crash. “But there’s a lot going on after that.”
Email Tariq Malik at tmalik@ or follow him @tariqjmalik. Follow us @Spacedotcom, Facebook and Instagram.