Happy Asteroid Day, folks! A threatening space rock that had been hovering near the top of hazardous potential-impact lists has officially been ruled out. Originally thought to potentially hit Earth in 2052, we can all now breathe a sigh of relief.  

The 50-meter-wide asteroid 2021 QM1 was first spotted in August 2021 by the Mount Lemmon Observatory in Arizona. So far, so normal. A dark sky and a good observatory can spot around a dozen near-Earth objects a night, according to the European Space Agency (ESA).

 Routine follow-ups looked less positive, however.

“These early observations gave us more information about the asteroid’s path, which we then projected into the future,” said Richard Moissl, ESA’s Head of Planetary Defence, in a statement.

“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.”

However, just as information was looking a little concerning, the asteroid's path brought it close to the Sun as seen from Earth, meaning the glare of our star outshone everything in its vicinity and it was impossible to carry on tracking the space rock.

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

“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.”

Luckily, the European Southern Observatory’s Very Large Telescope (VLT) was ready to jump into action the minute the asteroid was visible again – it still wasn't easy to spot, though.

“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,” Olivier Hainaut from ESO said. “These would turn out to be some of the trickiest asteroid observations we have ever made”.

In fact, it turned out to be the faintest asteroid ever observed. 

With a magnitude of 27 on the scale used by astronomers to indicate brightness, QM1 was 250 million times fainter than the faintest stars still visible to the naked eye. The scale decreases in numbers the brighter the object. Betelgeuse, the 10th brightest star in the sky, is 0.42 and the Sun is -27, for comparison.  

Images of the asteroid on May 24 allowed astronomers to refine the risky asteroid's path, ruling out a 2052 impact and removing it from the high-risk list. 

There are, of course, 1,377 that remain.