Nail-biting research rules out 2052 asteroid impact on Earth

2021 QM1 was first discovered on August 28, 2021, by the Mount Lemmon Observatory in Tucson, Arizona. Initially, the discovery was nothing special since about a dozen new near-Earth asteroids are discovered every dark night. But the following routine observations acquired from telescopes around the globe began telling a more worrying story.

“These early observations gave us more information about the asteroid’s path, which we then projected into the future. We could see its future paths around the Sun, and in 2052 it could come dangerously close to Earth. The more the asteroid was observed, the greater that risk became,” said Richard Moissl, ESA’s Head of Planetary Defence, in a press statement.

It must be noted, however, that orbit calculations based on just a few nights of observations come with uncertainties. This is why asteroids often get onto ESA’s risk list soon after they are discovered and then later get removed. Once more data is gathered, the uncertainties shrink and usually, the asteroid is proven safe. But on this occasion, that wasn’t possible.

As fortune would have it, just as the risk of the asteroid appeared to be increasing, a cosmic alignment was in the works and stood in the way of the observation: the asteroid’s path brought it closer to the Sun as seen from Earth, which meant that for months, it was impossible to see due to the sun’s brightness.

“We just had to wait. But to cap things off, we knew that 2021 QM1 was also moving away from Earth in its current orbit – meaning by the time it passed out of the Sun’s glare, it could be too faint to detect,” explained Marco Micheli, Astronomer at ESA’s Near-Earth Object Coordination Centre (NEOCC), in a press statement. But they were preparing as they were waiting.

The ESO’s Very Large Telescope (VLT), located in the Atacama desert of northern Chile, was primed and ready to observe. The VLT would focus its 8m mirror on the disappearing 50-metre asteroid as soon as it edged out from the sunlight if weather conditions allowed.

“We had a brief window in which to spot our risky asteroid. To make matters worse, it was passing through a region of the sky with the Milky Way just behind. Our small, faint, receding asteroid would have to be found against a backdrop of thousands of stars. These would turn out to be some of the trickiest asteroid observations we have ever made,” explained Olivier Hainaut, an astronomer at ESO, in a press statement.

Over the night of May 24, VLT took a series of new images and once the data arrived, Olivier and Marco began processing them by stacking subsequent observations on top of each other and removing background stars in a time-consuming process. This resulted in the positive detection of the faintest asteroid ever observed.

At the time of observation, 2021 QM1 was 250 million times fainter than the faintest stars visible to the naked eye from a dark spot. Olivier was certain that this small blur was an asteroid. Marco could go one step further and confirm that given its location, it was the asteroid they were looking for.

These new observations were used to refine the projected path of the risky asteroid, ruling out an impact in 2052, and 2021 QM1 was removed from ESA’s risk list, leaving just 1,377 other asteroids on the list.