Enlarge (credit: ASI/NASA )

In 2022, NASA's Double Asteroid Redirect Test (DART) smashed into the asteroid Dimorphos in a successful test of planetary defense technology. That success was measured by a significant shift in Dimorphos' orbit around the larger asteroid Didymos. Since then, a variety of observatories have been analyzing the data to try to piece together what the debris from the impact tells us about the structure of the asteroid.

All of those observations have taken place at great distances from the impact. But DART carried a small cubesat called LICIACube along for the ride and dropped it onto a trailing trajectory a few weeks before impact. It took a while to get all of LICIACube's images back to Earth and analyzed, but the results are now coming in, and they provide hints about Dimorphos' composition and history, along with why the impact had such a large effect on its orbit.

Tracing debris

LICIACube had both narrow and widefield imagers on board (named LEIA and LUKE via some carefully chosen backronyms). It trailed DART through the impact area by about three minutes and captured images starting about a minute before the impact and continuing for over five minutes afterward.

Enlarge / The dusty debris from the DART collision dominates this image, but there are boulders present, too. (credit: NASA, ESA, David Jewitt (UCLA) )

NASA's Double Asteroid Redirect Test (DART) mission was a success from the perspective of planetary defense, as it successfully shifted the orbit of an asteroid . But the mission had a scientific element to it, and we're still sifting through the debris of the collision to determine what the impact tells us about the asteroid. That's difficult due to the distance to the asteroid and the low amounts of light that reflect off the debris.

Today, a paper was released by a team that analyzed images of the aftermath using the Hubble Space Telescope. They've spotted dozens of boulders that collectively would have originally made up 0.1 percent of the mass of Dimorphos, DART's target. And while they're all moving very slowly from the site of the collision, some of them should be able to escape the gravity of the double asteroid system.

Knocking rocks

The images taken by DART immediately prior to its demise suggest that Dimorphos was a rubble pile, a mixture of boulders, small rocks, and dust barely held together by their mutual gravitational pull. So what happens when a relatively solid object, like the DART spacecraft, hammers an asteroid at high speed?

Enlarge / Artist’s illustration shows the ejection of a cloud of debris after NASA’s DART spacecraft collided with the asteroid Dimorphos. (credit: ESO/M. Kornmesser)

Last September, the Double Asteroid Redirect Test, or DART, smashed a spacecraft into a small binary asteroid called Dimorphos, successfully altering its orbit around a larger companion. We're now learning more about the aftermath of that collision, thanks to two new papers reporting on data collected by the European Southern Observatory's Very Large Telescope . The first, published in the journal Astronomy and Astrophysics, examined the debris from the collision to learn more about the asteroid's composition. The second, published in the Astrophysical Journal Letters, reported on how the impact changed the asteroid's surface.

As we've reported previously , Dimorphos is less than 200 meters across and cannot be resolved from Earth. Instead, the binary asteroid looks like a single object from here, with most of the light reflecting off the far larger Didymos. What we can see, however, is that the Didymos system sporadically darkens. Most of the time, the two asteroids are arranged so that Earth receives light reflected off both. But Dimorphos' orbit sporadically takes it behind Didymos from Earth's perspective, meaning that we only receive light reflected off one of the two bodies—this causes the darkening. By measuring the darkening's time periods, we can work out how long it takes Dimorphos to orbit and thus how far apart the two asteroids are.

Before DART, Dimorphos' orbit took 11 hours and 55 minutes; post-impact, it's down to 11 hours and 23 minutes. For those averse to math, that's 32 minutes shorter (about 4 percent). NASA estimates that the orbit is now "tens of meters" closer to Didymos. This orbital shift was confirmed by radar imaging. Earlier this month , Nature published five papers that collectively reconstructed the impact and its aftermath to explain how DART's collision had an outsize effect. Those results indicated that impactors like DART could be a viable means of protecting the planet from small asteroids.

Enlarge / A recent Hubble photo shows the 10,000 km tail of debris left behind by DART's impact. (credit: NASA/ESA/STScI/Hubble )

On Tuesday, NASA announced that its first test of a potential planetary defense system was a notable success. The Double Asteroid Redirect Test (DART) successfully smashed a spacecraft into an asteroid in late September, hoping to alter its orbit around a larger companion. Any changes in the orbit, however, would be difficult to pick up and potentially require months of follow-up observations. But the magnitude of the orbital shift was large enough that ground-based observatories picked it up already.

Meanwhile, a lot of hardware is also picking up the debris that shot out from the impact, giving scientists a lot of information about the collision and the asteroid.

New orbit, who dis?

Dimorphos is less than 200 meters across and cannot be resolved from Earth. Instead, the binary asteroid looks like a single object from here, with most of the light reflecting off the far larger Didymos. What we can see, however, is that the Didymos system sporadically darkens. Most of the time, the two asteroids are arranged so that Earth receives light reflected off both. But Dimorphos' orbit sporadically takes it behind Didymos from Earth's perspective, meaning that we only receive light reflected off one of the two bodies—this causes the darkening.

Enlarge / Nailed the landing. (credit: NASA, ESA, CSA )

At a press conference shortly before NASA's Double Asteroid Redirection Test (DART) spacecraft smashed into an asteroid, a reporter tried to get a sense of just what would happen as a bunch of metal and electronics smashed into a pile of rubble left over from the birth of the Solar System. "Give us a sense of this combat between our spacecraft and this rock," the reporter asked a scientist at the Applied Physics Lab.

"The spacecraft's going to lose," APL's Nancy Chabot quipped back.

The amazing thing about that loss is that we got to experience it in real time, as the last image from DART's onboard camera cut out after only a small fraction of it was transmitted to Earth.

Enlarge / One of the last images from DART. (credit: NASA/APL)

About 24 hours prior to its collision, NASA's Double Asteroid Redirect Test (DART) probe performed its last course correction based on commands sent by ground controllers. "It's pointed to within a football field of the central body," said Bobby Braun of the Johns Hopkins Applied Physics Lab (APL). "That last maneuver was spot-on."

Even at this late stage, DART's onboard camera couldn't resolve its ultimate target, the small asteroid Dimorphos, so the central body it was targeting is the partner Dimorphos orbits, called Didymos. DART's onboard navigation couldn't start navigating toward its target until it could see it, which was only expected to occur about 90 minutes before impact. At that point, the navigation started adjusting DART's course to get it heading straight at Dimorphos. Ground controllers, separated by about a minute of communications time, could only watch.

"Space is full of moments, and we're going to have a moment tonight, hopefully," said Braun.

Enlarge / The DART spacecraft is prepared for launch. (credit: NASA/Johns Hopkins APL/Ed Whitman )

Monday will see NASA's first attempt at real-world testing of a technology that it hopes can protect the Earth from the dangers posed by impacts from large asteroids. The Double Asteroid Redirect Test, or DART, will smash a spacecraft into a small asteroid called Dimorphos at 7:14 pm US Eastern time in the expectation that the impact will alter Dimorphos' orbit around the nearby large asteroid Didymos. If successful, then we can have some confidence that we can alter the orbit of small objects that pose a threat of colliding with Earth, sending them off into orbits where they no longer create a risk of catastrophic impact.

There are still things that can go wrong. As we detailed earlier , the camera on DART won't even be able to resolve its target until under two hours prior to the collision, and the final trajectory to impact will be handled by its on-board software, rather than controllers on Earth.

NASA will be hosting pre- and post-impact briefings for the press, which Ars will be attending, so expect updates later today. One option if you want to watch for yourself is coverage on NASA TV, which will start at 6 pm US Eastern.

Enlarge / An artist's conception of DART's electronics in the last moments before they suffer catastrophic failure. (credit: NASA )

This coming Monday, NASA will broadcast its first attempt to modify the orbit of an asteroid, a capability that will be essential if we detect an asteroid that poses a threat of colliding with Earth. The planetary defense effort is focused on a craft called DART, for Double Asteroid Redirection Test, which will target a small asteroid called Dimorphos that orbits the larger 65803 Didymos, forming a binary system. If all goes according to plan, DART will direct itself to a head-on collision that slows Dimorphos, altering its orbit around Didymos. NASA has repeatedly emphasized that there's no way for either asteroid or any material released by the collision to pose a threat to Earth.

Ars will be at the mission control center in the Johns Hopkins Applied Physics Laboratory (APL) for the planned collision, which will also be broadcast live on NASA's YouTube channels. While we'll know immediately whether the collision occurred as planned, it may take several months before we're certain that Dimorphos' orbit was successfully modified.

To get you ready for Monday's festivities, we've put together a background on the DART mission and the planned follow-up observations.