There’s nothing major at stake here, other than the demonstration of technology that could one day save civilization.
It is important to note that the targeted asteroid is not a threat to Earth and has done nothing wrong to deserve this attention. But the space collision is a critical moment for the Double Asteroid Redirection Test (DART), NASA’s first “planetary defense” test.
This mission is designed to show how a “kinetic impactor” could deflect a dangerous asteroid that could hit Earth. There are plenty of space rocks that could interrupt our typically peaceful journey around the sun. The general strategy of planetary defense is to alter the orbits of asteroids so that, even if they approach Earth, they pass through without danger.
The DART team members are confident they’ll pull it off, but they admit it’s no slam dunk. The spacecraft could miss. There will be no consolation for scientists and engineers if they have nearly hit the mark. These aren’t horseshoes or hand grenades: proximity doesn’t matter when trying to alter the trajectory of an asteroid.
“The success of the mission is pretty clear: you have to touch this asteroid,” said Elena Adams, an engineer at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, who is leading the mission under contract with NASA. .
The asteroid is called Dimorphos. It measures about 500 feet in diameter. No one knows exactly what it looks like. It’s just a fuzzy drop in telescopes. The first time the Earthlings will examine it closely will be less than an hour before impact.
Dimorphos orbits another larger asteroid, named Didymos (Greek for “twin”), as the two race around the sun. Such “binary” asteroids are common.
The spacecraft was launched last November from California. The larger asteroid essentially serves as the guide star for the mission. But only the smallest asteroid is targeted. When the spacecraft approaches the large Didymos, it should see the small Dimorphos swinging behind its companion. It will be a head-on collision.
Things will surely be tense in the mission operations room in Laurel. The Applied Physics Laboratory handles a lot of classified government research, but occasionally performs nifty space missions. Seven years ago, he successfully flew NASA’s New Horizons spacecraft near Pluto and obtained the first close-up images of the dwarf planet.
This mission is similar in that it is fraught with pitfalls and uncertainties. The spacecraft must autonomously make crucial navigational decisions at the last second. Flying a spacecraft at high speed – around 14,000 miles per hour – into a relatively small asteroid is something no one has ever done before.
If the DART spacecraft misses the target, it will theoretically have a second chance for a shattering encounter with Dimorphos in two years – but the engineers aren’t even thinking about taking a mulligan.
Previous space science missions from NASA and the Japanese space agency have taken samples from asteroids, but these were carefully choreographed rendezvous involving incremental approaches. DART is considering a high speed crash. The scientists and engineers behind the mission say they won’t know if they will hit the asteroid until about 20 seconds before impact.
“Asteroids are extremely dark,” Adams said. “We have to hit something that is the size of two stadiums. You can’t see them until about an hour before you hit them…. Even then, it’s only one pixel in our camera.
Mission engineers are making final adjustments to the spacecraft’s trajectory, but the final approach, in the hours before the anticipated collision, will be automated. A camera on board the spacecraft will capture images of the smaller asteroid while simultaneously helping the vehicle focus on the target.
The final pictures transmitted by the spacecraft’s camera will show a small white dot morphing into something brighter, larger, and more asteroidal. Then, if all goes as planned, Dimorphos will appear so large that it fills the field of vision.
And that will be the last thing anyone will see that the spacecraft will make the ultimate sacrifice.
Telescopes on Earth as well as Webb and Hubble in space will also observe the impact.
The most worrisome asteroids with potentially global climate repercussions are those larger than 1 kilometer in diameter. These are the easiest to spot. More than 95% of the estimated population of these killer rocks have been identified, said planetary scientist Nancy Chabot, head of DART coordination.
Less than half of the asteroids between 140 meters and 1 kilometer have been identified. It is an ongoing effort. Rocks of this size – and Dimorphos is one of them – could wipe out a major city with a direct hit. Chabot said early detection is key to planetary defense.
“It’s something you don’t do at the last minute. It’s something you do years in advance,” she said.
NASA and its partners currently have a catalog of 30,000 objects, said the agency’s planetary defense officer, Lindley Johnson. Scientists can calculate their orbits for a few decades into the future, but as the timeline lengthens, the orbital uncertainties increase.
No dangerous asteroid at the moment appears to be on track to crash into Earth, as far as these things can be calculated, Johnson said. But he will be keeping a close eye on Monday night’s asteroid redirect test.
“We need to have such technology,” he said. “It would be prudent of us to test all of this in advance, so we’re not trying this for the first time when we really need it to work.”
