Latest DART asteroid impact reveals hidden world of far-away asteroids

Astronomers have now seen what happened after the NASA spaceship DART crashed into the asteroid Dimorphos in September 2022.
Christopher McFadden
DART satellite on collision course to the asteroid DIMORPHOS
DART satellite on collision course to the asteroid DIMORPHOS

Makhbubakhon Ismatova/iStock 

NASA's Double Asteroid Redirection Test (DART) spacecraft crashed into the asteroid Dimorphos on September 26, 2022. This was a controlled test of how well our current asteroid-deflecting technology works. This impact happened 11 million kilometers from Earth, and many telescopes, including all four 8.2-meter telescopes of ESO's Very Large Telescope (VLT) in Chile, could see it in great detail.

The first results of these VLT observations have been published in two papers.

Two groups of astronomers used the VLT to watch what happened after the collision and learn more about the asteroid's makeup from the material that was thrown out. One team followed the evolution of the debris cloud for a month with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the VLT. They found that the ejected cloud was bluer than the asteroid before the impact, indicating that it could be made of very fine particles. They also observed other structures, such as clumps, spirals, and a long tail pushed away by the Sun's radiation, which was redder than the initial cloud, suggesting they could be made of larger particles.

MUSE also allowed the team to break up the light from the cloud into a rainbow-like pattern and look for the chemical fingerprints of different gases, but they found no trace of oxygen, water, or propellant from the DART spacecraft.

Using the Focal Reducer/low-dispersion Spectrograph 2 (FORS2) instrument at the VLT, Stefano Bagnulo, an astronomer at the Armagh Observatory and Planetarium in the UK, led another team that looked at how the DART impact changed the surface of the asteroid.

They found that the level of polarization suddenly dropped after the impact, and the overall brightness of the system increased, indicating that the impact exposed more pristine material from the asteroid's interior. Another possibility is that the impact broke up surface particles, sending smaller ones into dust clouds. These studies show the potential of VLT when its different instruments work together.

"When we observe the objects in our Solar System, we are looking at the sunlight scattered by their surface or by their atmosphere, which becomes partially polarized,” explains Bagnulo. This means that light waves oscillate along a preferred direction rather than randomly.

“Tracking how the polarization changes with the orientation of the asteroid relative to us and the Sun reveals the structure and composition of its surface,” he added.

Asteroids are some of the most basic relics of what all the planets and moons in our Solar System were created from, making studying them critical to understanding the formation of the Solar System. The controlled impact of DART made it possible to study an asteroid's makeup in great detail, and the VLT's observations will help astronomers learn more about how asteroids work.

You can view the study for yourself in the journal Astronomy and Astrophysics.

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