In 2022, NASA’s Double Asteroid Redirect Test (DART) smashed into the asteroid Dimorphos in a profitable take a look at of planetary protection know-how. That success was measured by a big shift in Dimorphos’ orbit across the bigger asteroid Didymos. Since then, numerous observatories have been analyzing the information to attempt to piece collectively what the debris from the influence tells us concerning the construction of the asteroid.
All of these observations have taken place at nice distances from the influence. But DART carried a small CubeSat known as LICIACube alongside for the trip and dropped it onto a trailing trajectory a number of weeks earlier than influence. It took some time to get all of LICIACube’s images again to Earth and analyzed, however the outcomes at the moment are coming in, and so they present hints about Dimorphos’ composition and historical past, together with why the influence had such a big impact on its orbit.
Tracing debris
LICIACube had each slim and widefield imagers on board (named LEIA and LUKE by way of some fastidiously chosen backronyms). It trailed DART by the influence space for about three minutes and captured images beginning a few minute earlier than the influence and persevering with for over 5 minutes afterward.
These confirmed that the influence created a complex area of debris. Rather than a easy cone of materials, there have been filaments and clumps of ejecta, all transferring at completely different speeds. One paper, launched in Nature at the moment, tries to catalog rather a lot of it. So, for instance, it identifies one stream of ejected materials that reveals up within the first post-impact images and will be tracked till imaging stops. By this level, it has prolonged over eight kilometers from the influence web site. That works out to be a velocity of about 50 meters a second.
Separately, there was a clump of materials that was seen for a few minute and a half and touring at about 75 meters a second; a second clump moved at about half that price.
The quickest transferring materials they might observe was ejected at about 500 meters a second, which is about 1,800 kilometers an hour (1,100 mph). And that helps drive dwelling LICIACube’s worth, since the very best observations we’ve got at a distance had been achieved by Hubble, and it solely detected objects transferring at half that pace.
Oddly, the ejected materials initially appears to be like reddish in tint however regularly shifts to extra blue over time. The researchers counsel that this might imply that the floor of the asteroid had been reddened by publicity to radiation, and the primary materials to exit the influence got here from the floor. Later, as extra of the fabric got here from the inside, the redness dropped.
Late final 12 months, a separate paper targeted on the scale of the debris cone. Using these, it labored backward to guage the place that cone reached the floor of Dimorphos. Based on that, the researchers concerned estimated that the fabric was coming from a crater that was about 65 meters in diameter.
A weak inside
Tracking all of the complex debris is vital partly as a result of it performed a task within the effectiveness of DART. We know precisely how a lot momentum the DART spacecraft carried into the collision, and we will evaluate that to estimates of the quantity wanted to vary Dimorphos’ orbit. Based on estimates of the magnitude of the orbital change, in addition to the preliminary mass of Dimorphos, it is fairly clear that DART’s momentum cannot account for all of the change. So, a big quantity of the alternate of momentum happened as debris from the influence carried momentum away from Dimorphos.
An further paper takes the LICIACube information on the fabric ejected and makes use of it to attempt to estimate the interior properties of Dimorphos. A mannequin of the physics of the collision was used to check a range of inner compositions for the asteroid that diverse primarily based on their density, quantity of stable rock vs free materials, and different traits. The greatest outcomes got here from a comparatively low-density porous physique that does not have rather a lot of massive boulders close to its floor.
Given that construction, the researchers conclude that DART probably triggered world disruption of its goal’s construction.
Dimorphos’ weak, fragmented construction appears to be like rather a lot like we have seen in visits to what are known as “rubble pile asteroids” like Bennu and Ryugu. The hanging factor about it’s that it is a lot weaker than the construction of its bigger neighbor, Didymos. That’s constant, nevertheless, with fashions of how Dimorphos should have shaped. These posit that Didymos shed materials, some of which stayed gravitationally sure and ended up in orbit.
One method that might occur is by way of a collision, however that could be anticipated to be energetic sufficient to liberate a variety of supplies from Didymos. An various, nevertheless, is that photo voltaic heating might improve the spin of Didymos till it now not had sufficient gravitational pull to carry on to all its materials. In this case, lighter materials is more likely to be shed from the floor first, probably accounting for the comparatively small measurement of the fabric in Dimorphos.
The excellent news is that we’re scheduled to have a fair higher view of the post-impact system in a number of years. In late 2024, the ESA plans to launch a probe known as Hera that may go into orbit across the Didymos/Dimorphos system and supply detailed information on the collision’s aftermath.
The Planetary Science Journal, 2023. DOI: 10.3847/PSJ/ad09ba (About DOIs).
Nature, 2024. DOI: 10.1038/s41586-023-06998-2
Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02200-3