The VLT observes a double asteroid passing near the Earth at 70 000 km / h

The unique capabilities of the SPHERE instrument on ESO's very large telescope allowed him to obtain the sharpest images of the double asteroid during his ground flight on May 25th. Although this double asteroid is not in itself a threatening object, scientists took the opportunity to repeat the response to a dangerous object located near the Earth, proving that the first-line ESO could play a vital role in global defense.

The International Asteroid Warning Network (IAWN) co-ordinated a cross-cutting observation of the 1999 KW4 asteroid when it flew over the Earth, reaching a minimum distance of 5.2 million km on 25 May 2019. 1999 KW4 is approximately 1.3 km wide. pose no risk to the Earth. As its orbit is well known, scientists have been able to predict this overview and prepare the observation campaign.

ESO joined the campaign with its flagship facility, the Very Large Telescope (VLT). The VLT is equipped with SPHERE, one of the few instruments in the world capable of obtaining images sharp enough to distinguish the two components of the asteroid, distant about 2.6 km.

SPHERE was designed to observe exoplanets; its state-of-the-art Adaptive Optics (AO) system corrects turbulence in the atmosphere by providing images as sharp as if the telescope were in space. It is also equipped with coronographs to mitigate the glare of bright stars, exposing weak exoplanets in orbit.

SPHERE data allowed astronomers to characterize the double asteroid by taking a break from its usual night-time hunting exoplanets. In particular, it is now possible to measure whether the smaller satellite has the same composition as the larger object.

"These data, combined with all those obtained from other telescopes during the IAWN campaign, will be essential for evaluating effective deflection strategies in the event that an asteroid finds itself on a collision course with the Earth." explained the ESO astronomer Olivier Hainaut. . "In the worst case, this knowledge is also essential for predicting how an asteroid could interact with the Earth's atmosphere and surface, which will allow us to limit damage in the event of a collision."

"The double asteroid was firing at more than 70,000 km / h near Earth, making observation with the VLT difficult," said Diego Parraguez, who was flying the telescope. He had to use all his know-how to capture the fast asteroid and capture it with SPHERE.

Bin Yang, VLT astronomer, said, "When we saw the satellite with AO corrected images, we were extremely excited, and at that moment we felt that all the pain and effort was worth it. " Mathias Jones, another TLV astronomer involved in these observations, explained the difficulties. "During the observations, the atmospheric conditions were a little unstable, and the asteroid was relatively weak and moving very fast in the sky, making these observations particularly difficult, and causing the AO system to crash several times. the hard work pays off despite the difficulties! "

Although 1999 KW4 is not a threat of impact, it is strikingly similar to another binary asteroid system called Didymos, which could pose a threat to the Earth in the distant future.

Didymos and his companion called "Didymoon" are the target of a future pioneering planetary defense experiment. NASA's DART probe will have an impact on Didymoon to try to modify its orbit around its larger twin, in order to test the feasibility of asteroid deflection. After the impact, ESA's Hera mission will investigate Didymos asteroids in 2026 to gather key information, including Didymoon's mass, surface properties, and the shape of the DART crater.

The success of such missions depends on collaborations between organizations, and the tracking of objects close to the Earth is a major objective of the collaboration between ESO and ESA. This cooperative effort is ongoing since the first successful follow-up of a potentially harmful NEO in early 2014.

"We are excited to play a role in protecting the Earth from asteroids," said Xavier Barcons, ESO's Chief Executive Officer. "In addition to using the sophisticated capabilities of the VLT, we are collaborating with ESA to create prototypes for a large network to push detection, tracking and characterization of asteroids to a higher level."

This recent close encounter with KW4 in 1999 comes just one month before Asteroid Day, an official United Nations day for asteroid education and awareness, which will be celebrated on June 30th. Events will take place on five continents and ESO will be one of the main participating astronomical organizations. The ESO Supernova Planetarium & Visitor Center will organize a series of activities on the subject of asteroids during the day. Members of the public are invited to participate in the celebrations.

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