ESO/M. Grain Fair
Last September, the Double Asteroid Redirect Test (DART) successfully smashed a spacecraft into a small binary asteroid called Dimorphos, altering its orbit around its larger companion. We are now learning more about the aftermath of that impact, thanks to his two new papers reporting data collected by the European Southern Observatory’s Very Large Telescope. The first paper, published in the journal Astronomy and Astrophysics, looked at debris from the impact to learn more about the asteroid’s composition. The second, published in the Astrophysical Journal Letters, reports how the impact changed the surface of the asteroid.
As previously reported, Dimorphus is less than 200 meters in diameter and cannot be resolved from Earth. Instead, from here the binary asteroid looks like a single object, with most of the light reflected off the much larger Didymo. However, you can see that the Didymos system dims sporadically. In most cases, the two asteroids are positioned so that Earth receives light reflected from both. However, Dimorphus’ orbit is sporadically behind Didymus, meaning that as seen from Earth, it only receives light reflected from one of the two celestial bodies. This causes it to darken. By measuring the duration of the darkening, we can tell how long it takes for Demorphos to orbit and how far apart the two asteroids are.
Before DART, Demorphos’ orbit took 11 hours and 55 minutes. After the collision he is shortened to 11 hours and 23 minutes. 32 minutes (about 4%) less for those who aren’t good at math. NASA estimates that the orbit is now “tens of meters” closer to Didymos. This orbital shift was confirmed by radar images. Earlier this month, Nature published his five papers that collectively reconstruct the impact and its aftermath to explain how the DART impact had such a profound impact. These results indicate that impactors like DART may be a viable means of protecting the Earth from small asteroids.
The cameras closest to the collision (named Luke and Leia) were mounted on the LICIACube, a DART-mounted cubesat, and separated weeks before the collision. LICIACube was equipped with two cameras. Last October, the Italian Space Agency, which conducted the LICIACube mission, released some early images, including a distant view of the impact, a close-up taken shortly after, and an animation showing the sudden brightness after impact.
The ATLAS project and one of the Las Cumbres Observatory telescopes captured images of the Didymos/Dimorphos system gently past the background stars from an Earth perspective (most of the light is reflected from the much larger Didymos). At the moment of impact, the object became noticeably brighter and the debris gradually moved to one side of the asteroid.
Evolution of the debris cloud ejected after NASA’s DART spacecraft collided with the asteroid Demorphos.
Why is the study of debris important? Asteroids are relics from when our solar system was created, so they can tell astronomers something about the early history of this corner of the universe. As it moves, it is hit hard by small meteorites and the solar wind. This causes erosion, or “space weathering,” so looking at the asteroid’s surface doesn’t always tell you how it formed. The DART impact ejected pristine material beneath Demorphos’ weathered crust, and was expected to give astronomers a better glimpse into the asteroid’s past.
