Seven million miles from Earth, a NASA spacecraft crashed head on into a tiny asteroid Monday at a mind-boggling 14,000 mph, the first real-world test of humanity's ability to nudge a threatening body off course before it could crash into Earth.
The asteroid in question, a 525-foot-wide body known as Dimorphos, is actually a moon orbiting a 2,500-foot-wide asteroid named Didymos. Neither poses any threat to Earth, either before or after the impact of NASA's 1,260-pound Double Asteroid Redirection Test, or DART, spacecraft.
But the double-asteroid system offered an ideal target for the $330-million DART mission because the effects of the probe's impact can be measured from Earth by precisely timing how the moonlet's orbital period around Didymos changes as a result of the collision.
Beaming back images of Dimorphos once per second, the DART probe gave scientists a thrilling on-board view as the spacecraft locked on and raced toward its quarry, spotting it for the first time about an hour before impact when the target was still 15,000 miles away.
Covering the final 1,000 miles in about four minutes, DART's camera showed the target growing larger and larger, from a dim point of light until it filled the entire field of view seconds before impact while traveling seven times faster than the bullet from an assault rifle.
"Oh my goodness, look at that!" someone in the control room exclaimed seconds before impact as rocks and boulders rushed into view on Dimorphos' surface.
"It's amazing, guys! Oh my goodness, look at that! Unbelievable!" said Elena Adams, DART mission systems engineer at the Johns Hopkins University Applied Physics Laboratory, who helped oversee the spacecraft's final moments.
Transmissions ceased at the moment of impact as the spacecraft slammed into Dimorphos, disintegrating on impact and blasting out a fresh crater in the rocky surface. Because the collision happened 7 million miles from Earth, the final few images needed 45 seconds or so to cross the gulf and make it into computers and onto NASA's live stream.
And at that moment, after years of planning and a 10-month voyage from Earth to the Didymos-Dimorphos system, flight controllers at APL, where the DART spacecraft was managed, erupted in cheers and applause.
"Congratulations! Boy, the DART team, you really did this one very well," said NASA Administrator Bill Nelson. "I believe it's going to teach us how to one day protect our own planet from an incoming asteroid. So thank you to this international team. We are showing that planetary defense is a global endeavor, and it is very possible to save our planet."
Lori Glaze, director of planetary science at NASA, agreed, saying the DART mission shows "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 asteroid impact."
"What an amazing thing!" she said. "We've never had that capability before."
A small Italian hitchhiker spacecraft known as LICIACube, released from DART earlier this month, attempted to photograph the collision and the debris blasted back out into space, but those images were stored on board and will be relayed back to Earth later.
The Virtual Telescope Project, which offers time on robotic telescopes to professional and amateur astronomers alike, posted views of the double asteroid during the impact that showed a dramatic brightening from presumed clouds of rock and dust blown into space around Dimorphos.
"Planetary defense is a globally unifying effort that affects everyone living on Earth," NASA science chief Thomas Zurbuchen said in a statement. "Now we know we can aim a spacecraft with the precision needed to impact even a small body in space. Just a small change in its speed is all we need to make a significant difference in the path an asteroid travels."
The Didymos-Dimorphos double asteroid system offered an ideal planetary defense test bed because the moonlet's orbit carries it directly in front of and then behind Didymos as viewed from Earth, allowing scientists on Earth to precisely measure slight changes in the combined reflected light from both asteroids.
By timing how the light dims and brightens, researchers have calculated how long it takes Dimorphos to complete one orbit — 11 hours and 55 minutes— and post-impact observations will allow them to determine what effect DART might have had.
Researchers expect the crash to shorten the asteroid's orbital period by about 10 minutes, but it will take a few days to a few weeks for telescopes around the world and in space, including the Hubble and James Webb space observatories, to make the measurements needed to nail down the number.
"The double asteroid redirection test is a test," said Tom Statler, the DART program scientist. "We're doing this test when we don't need to, on an asteroid that isn't a danger, just in case we ever DO need to and we discover an asteroid that IS a danger."
He said the DART mission has two primary objectives, the first being a test "of our ability to build an autonomously guided spacecraft that will actually achieve the kinetic impact on the asteroid."
"The second is a test of how the actual asteroid responds to the kinetic impact," he said. "Because at the end of the day, the real question is, how effectively did we move the asteroid, and can this technique of kinetic impact be used in the future if we ever needed to?"
Unlike Hollywood thrillers like "Armageddon" and "Deep Impact," which imagined piloted flights carrying nuclear bombs to deflect or destroy their targets, DART's goal is much simpler and much less destructive.
While nuclear devices might be a last resort in some future armageddon-class scenario, deflection, not destruction, would still be the goal.
"You just don't want to blow it up, because that doesn't change the direction of all the material," Lindley Johnson, NASA's "planetary defense" officer, told CBS News before DART's launch last November. "It's still coming at you, it's just buckshot instead of a rifle ball."
"What you want to do is just change the speed at which this is all moving by just a bit. Over time, that will change the position of the asteroid and its orbit."
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