Using the European Southern Observatory’s (ESO) VLT Ground Telescope in Chile, two teams monitored the evolution of the debris generated after the first controlled impact to deflect an asteroid for a month.

The first controlled collision in the history of a spacecraft against an asteroid to voluntarily divert its trajectory was not just a milestone to make the so-called planetary defense a reality and have some chance of protecting the Earth from a future collision of one of these space rocks. The impact of NASA’s DART probe against the asteroid Dimorphos, the past September 26, was a golden opportunity for astronomers investigating the composition of these celestial bodies, in whose material ones believe that this is the key to the origin of life In the land.

The impact at 22,530 kilometers per hour took place 11 million kilometers from Earth, which is a lot, but a very reasonable distance not only for space telescopes. James Webb It is hubblethat captured the moment, but also for the most powerful terrestrial telescopes such as the VLT (Very Large Telescope or Telescopio Muy Grande) that the European Southern Observatory (ESO) has in the Atacama Desert, in Chile.

Prepared for this astronomical milestone, four 8.2-meter telescopes that make up the VTL pointed to the asteroid system formed by the small Dimorphos (160 meters in diameter), the spacecraft’s target, and Didymos, the 700-meter asteroid orbited by the smaller one. Neither of these two bodies presented a risk to Earth, so they were chosen to test a controlled deflection technique that, announced by NASA two weeks later, was successful because the orbit of the asteroid Dimorphos was changed around Didymos in 32 minutes, more than expected. .

Thus, astronomers were able to witness in real time the fall of the DART spacecraft (acronym for Double Asteroid Redirection Test which also means dart in English) and monitored it the following month. This Tuesday, two of the teams that used data from ESO’s Chilean telescope are presenting the results of their monitoring of the system formed by these two asteroids.

“Impacts between asteroids occur naturally, but we can never know in advance,” says Cyrielle Opitom, an astronomer at the University of Edinburgh and lead author of one of the papers. In her opinion, the DART mission “has been a great opportunity to study a controlled impact, almost as if you were in a laboratory.”

debris cloud

The team led by Opitom followed the evolution of the debris cloud generated after the spacecraft collided with the asteroid for a month with the Multi Unit Spectroscopic Explorer (MUSE) instrument on the VLT, whose results are shown in the collection of Photos taken between September 26th and October 25th. Scientists saw that the cloud of ejected material was bluer than the asteroid itself before the impact, indicating that the cloud could be composed of very fine particles. In the hours and days that followed, other structures developed, including cumulus clouds, spirals and a long tail powered by solar radiation. The spirals and tail were redder than the initial cloud, so they could have been formed by larger particles, according to his hypothesis.

The MUSE instrument allowed them to split the cloud’s light to look for the chemical signatures of the different gases present. In particular, They looked for oxygen and water in the ice exposed by the impact, but found nothing. “Asteroids are not expected to contain significant amounts of ice, so detecting any trace of water would have been a real surprise”, says Opitom, who also found no traces of propellant fuel from the DART spacecraft, a possibility they considered remote because “the The amount of gas left in the powertrain tanks wouldn’t be huge. Plus, some of it would have traveled too far to be detected with MUSE by the time we started looking.”

The second DART investigation published on Tuesday focused on how the surface of the asteroid was altered. “When we look at objects in our Solar System, we are looking at sunlight that is scattered by its surface or its atmosphere, which becomes partially polarized. By tracking how the polarization changes with the asteroid’s orientation relative to us and the The Sun reveals the structure and composition of its surface,” said Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium in the UK and leader of the work.

Using the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument on the VLT, they detected that the level of polarization suddenly dropped after impact. At the same time, the overall system brightness has increased. One possible explanation is that the impact exposed more pristine material from within the asteroid. “Perhaps the material brought to the surface by the impact was inherently brighter and less polarizing than the material at the surface, because it was never exposed to the solar wind or solar radiation”, proposes Bagnulo, referring to another possibility: that the impact destroyed the particles in the surface, thereby ejecting much smaller particles into the debris cloud.

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