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ESA and ESO rule out the threat of 2006 QV89 for this September
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Asteroid 2006 QV89, a small object 20 to 50 meters in diameter, has been in the news lately, because of a very small 1-in-7000 chance of impact with the Earth on 9 September 2019.

In general, when an asteroid is found to have a possibility of impact with Earth, additional astrometric observations are acquired. When these are added to the orbit solution for the object, they allow our knowledge of the possible risk to be refined, often excluding any chance of collision.

However, the case of 2006 QV89 is peculiar: the object was discovered in August 2006, and then observed for only ten days. After that it became unobservable, and has not been seen since. Now, after more than a decade, we can only predict its position with very poor accuracy. As a result, astronomers cannot easily re-observe it, because no one knows exactly where to point a telescope.

Nevertheless, there is a way to obtain the information we need.

While we do not know the object's trajectory exactly, we do know where it would appear in the sky if it were indeed on a collision course with our planet. Therefore, we can simply observe that small area of the sky, and check to see that the asteroid is, hopefully, not there.

This way, we would indirectly exclude any risk of an impact, even without actually seeing the asteroid.

This is precisely what ESA and the European Southern Observatory did on 4 and 5 July, as part of the ongoing collaboration between the two organisations to observe high-risk asteroids using ESO's Very Large Telescope (VLT).

Teams obtained very ‘deep’ images of a small area (about one arcminute in width – the Moon appears to be 30 arcminutes wide seen from Earth) in the sky where the asteroid would have been located if it were on track to impact Earth in September.

Our images reached a limiting magnitude fainter than 27, while the asteroid would have been magnitude 24 at that time.

Nothing was seen.

With the object not present in the expected area on either of the two nights, we can conclude that it is not on a collision course for this year. Having not seen the object on two nights reinforces the ‘non-detection’, since possible contamination with background stars would have affected different parts of the region.

This approach to rule out possible impacts via negative observations was first proposed by Andrea Milani and collaborators back in 2000. It was subsequently tested by us last year using Pan-STARRS archival images on a lower-risk asteroid, 2017 XO2. This is the first time the technique has been used with observations acquired specifically for this purpose, and the first reported case of ruling out a high-risk impact possibility.

VLT image

Image of the region of the sky corresponding to possible impact trajectories of 2006 QV89 in 2019, acquired on 5 July 2019 with the ESO’s VLT. The segment delimited by the three red crosses in this image corresponds to the area where the asteroid would have appeared had it been on a collision course. The image has been processed to remove background star contamination, so the object would have appeared as a single bright round source inside the segment. Raw images are available on the ESO archive.

Credit: ESO/O. Hainaut and ESA