Asteroid was on track to hit Earth. Then something changed

On August 28, 2021, the Mount Lemmon Observatory, located north of Tucson, Arizona, picked by an object cruising in the vastness of space. There was nothing unusual about it like other such objects detected every day beyond Earth. But in the days that followed, this asteroid became a priority as observations from telescopes across the world told a different story.

2021 QM1 was on its way towards Earth with a possibility of hitting the planet, as calculations revealed, in 2052. The object was on a path towards the Sun and was set to come dangerously close to the home planet.

“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,” Richard Moissl, Head of Planetary Defence at the European Space Agency said.

2021 QM1’s orbit as it passed closer to Sun in the sky as seen from Earth, soon after discovery. (Photo: ESA)

COSMIC ALIGNMENT UNFAVOURABLE

While asteroids are regularly observed and catalogued, they are placed on the risk list based on initial observations and then removed after the orbital calculations are refined. However, in the case of 2021 QM1, the asteroid was in no mood to reveal its identity.

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The asteroid’s path brought it closer to the Sun as seen from Earth, and for months it became impossible to see due to our star’s brilliant glare. What worried astronomers was that it was moving away from Earth in its current orbit and by the time it passed out of the Sun’s glare, it could be too faint to detect.

“We just had to wait,” explains Marco Micheli, Astronomer at ESA’s Near-Earth Object Coordination Centre.

Dramatic moonset behind ESO’s Very Large Telescope (VLT), Chile. (Photo: ESA)

ENTERS EARTH’S MOST POWERFUL TELESCOPE

While the James Webb Telescope gets ready for first observation later this month, astronomers brought in the big guns. The European Southern Observatory’s Very Large Telescope (VLT) was primed and as soon as the 50-meter asteroid edged out from the sunlight, astronomers were ready.

“We had a brief window in which to spot our risky asteroid,” explained Olivier Hainaut, Astronomer at ESO. However, it was not that easy as the asteroid was passing through a region of the sky with the Milky Way just behind. The small, faint, receding asteroid would have to be found against a backdrop of thousands of stars.

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But the telescope proved its might. The VLT captured a series of images with thousands of stars filling the background, which were refined and stacked to find the faintest asteroid ever to be observed.

The asteroid was 250 million times fainter than the faintest stars visible to the naked eye from a dark spot.

ESO’s Very Large Telescope captures 2021 QM1 which for months topped risk lists around the glob. This pivotal sighting ruled out Earth impact in the year 2052. (Photo: ESA)

NO IMPACT CONFIRMED

With the fresh observations, the math was refined and the new orbital calculations ruling out an impact in 2052, and 2021 QM1 was removed from ESA’s risk list. However, another 1377 remain.

According to the European Space Agency, more than one million asteroids have been discovered in the Solar System, almost 30,000 of which pass near Earth, with many more expected to be out there.

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