For a few tense days this January, a roughly 70-metre asteroid became the riskiest observed in over a decade. Despite the Moon’s attempt to scupper observations, the asteroid is now known to be entirely safe.

Initial observations of an asteroid dubbed ‘2022 AE1’ showed a potential Earth impact on 4 July 2023 – not enough time to attempt deflection and large enough to do real damage to a local area should it strike.

Worryingly, the chance of impact appeared to increase based on the first seven days of observations, followed by a dramatic week ‘in the dark’ as the full Moon outshone the potential impactor, ruling out further observations. As the Moon moved aside, the skies dimmed and ESA’s Near-Earth Object Coordination Centre (NEOCC) took another look, only to find the chance of impact was dramatically falling.

It has since been confirmed that 2022 AE1 will not impact Earth and has been removed from ESA’s risk list.

The Palermo scale is used by planetary defenders to categorise and prioritise the impact risk from near-Earth objects (NEOs) by combining the potential date of impact, the energy they would strike with and the impact probability.

There are asteroids out there that will certainly hit Earth but are so small they are almost imperceptible as they burn up in our atmosphere. Others might be giant, extinction-level event asteroids which could do immense damage but are travelling in orbits around the Sun that are entirely safe.

Values less than -2 on the Palermo Scale reflect events with no likely consequences; those between -2 and 0 indicate situations that merit careful monitoring, and positive values generally indicate situations that merit some level of concern.

More details here.

Image credit: ESA/NEOCC