NASA deliberately crashed a spacecraft into an asteroid on Monday.
It's a test, in case NASA has to deflect a dangerous asteroid headed toward Earth in the future.
There is no risk of that happening anytime soon, but experts say we need to be prepared.
NASA purposefully crashed a spacecraft into an asteroid on Monday, in a first-of-its-kind test to learn how to defend the planet against rogue space rocks.
The experiment should tell us whether hurtling a spacecraft at high speeds into an asteroid is a viable strategy to deflect it. There are no asteroids that pose an immediate threat to human civilization at this time. But experts say it's only a matter of time before an asteroid big enough to wipe out a city crosses paths with Earth.
NASA's 1,376-pound probe traveled about 6.8 million miles before crashing into the asteroid, as part of the Double Asteroid Redirection Test (DART) mission. It did not survive the collision.
"Now is when the science starts," Lori Glaze, director of NASA's planetary science division, said after Monday's collision. "Now that we've impacted, we're going to see for real how effective we were."
"We're embarking on a new era of humankind, an era in which we potentially have the capability to protect ourselves from something like a dangerous, hazardous asteroid impact," Glaze added.
Scientists will be monitoring the trajectory of the asteroid, Dimorphos, which orbits a larger asteroid, Didymos. Neither asteroid pose a threat to the Earth, which is why NASA selected them.
On Monday, the spacecraft provided a nearly real-time feed of its demise starting more than an hour before impact, thanks to its lone instrument - the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO). It took DART's final transmissions 38 seconds to reach Earth.
In the initial images from DRACO, shown above, Didymos and its moonlet Dimorphos appeared as a single white dot. That changed as the spacecraft closed in.
Gradually, Dimorphos emerged as a separate point of light that grew larger and brighter, as in the image shown above. The asteroid ultimately took shape, filling the entire screen until just before impact.
Below, one of the last frames beamed at Earth from DRACO before the DART spacecraft ate it, showing several boulders on the asteroid surface. The team knew the spacecraft successfully smashed into Dimorphos when they lost the spacecraft's signal, which was indicated when the live screen went red. The DART mission operations team at the Johns Hopkins Applied Physics Laboratory erupted in applause after the probe's successful demise.
If all goes according to plan, scientists expect the collision will change the speed of Dimorphos by a fraction of 1%, altering its orbit around Didymos ever so slightly.
The Italian Space Agency's LICIACube, a small satellite which traveled with the spacecraft and is now at a safe distance from it, will beam high-resolution photos of the impact back to Earth. It may take weeks for scientists on Earth to receive that data.
Now that DART has been destroyed during the collision, follow-up observations with ground- and space-based telescopes - including NASA's new infrared eye in the sky, the James Webb Space Telescope - will evaluate the asteroid system to see how much its orbit changed.
Dimorphos has a mass of about 11 billion pounds and is about 525 feet in diameter, and it orbits another, larger asteroid - the 2,650-foot-wide Didymos.about 525 feet wide.
Scientists hope the tiny nudge will be enough to change the trajectory of the space rock.
They will also monitor debris that fly off of the asteroid after the impact.
The Earth is not prepared for a city-killing asteroid
Knowing how to knock a dangerous asteroid off its path is crucial information. But if a city-killer asteroid - that's an asteroid bigger than 460 feet - were headed toward Earth today, odds are scientists would be woefully unprepared.
NASA has organized seven asteroid impact simulations since 2013. A group of international experts was only able to fully stop the asteroid once, mostly because of the limited warning period given in the simulations.
Experts previously told Insider that NASA would need five to 10 years to build and launch a customized mission that could deflect an asteroid.
There's also a risk experts might not spot the rock in time. NASA tracks about 28,000 nearby asteroids. But to date, only about 40% of city-killer asteroids orbiting Earth have been identified, Insider's Morgan McFall-Johnsen previously reported.
This problem is not just theoretical. In recent years, there have been a few times when large space rocks came a little too close for comfort and scientists didn't spot them until it was too late.
In 2019, a city-killer sized asteroid came within 45,000 miles of Earth and scientists only had a few days' warning of the flyby. An asteroid the size of a car flew within 1,830 miles of Earth in 2020 - the closest any known space rock has come without crashing. Scientists only spotted it about six hours before it passed Earth.