These are NASA’s top 5 biggest asteroid threats and how likely they are to hit Earth

Published: Saturday, 07 September 2024 at 07:32 AM

It’s a famous trope of science fiction: a huge asteroid on a collision course with Earth, and the daring attempts to divert it before a devastating impact.

There are impact craters across the Solar System, revealing how chaotic a place it can be.

But what are the chances of an asteroid hitting Earth? Are asteroids really a threat, and something we should be worrying about?

Artist’s illustration of an asteroid hitting Earth. Credit: Romolo Tavani / Getty Images

Potentially hazardous asteroids

A potentially hazardous asteroid is defined as a space rock with a size larger than 140 metres (459ft), or a brightness of magnitude +22.0 or more, which also has a trajectory that brings it within 0.05 astronomical units (AU) from Earth, or 19.5 lunar distances.

An organisation known as the Minor Planet Center uses data from space and ground-based telescopes to work out asteroid and comet orbits, and make the call on whether an object is a potentially hazardous asteroid or not.

A view of asteroid Bennu, its striking craters and surface covered in boulders, captured by OSIRIS-REx's OCAMS (MapCam) instrument on 28 April 2020 from a distance of 10km. Half of Bennu is bathed in sunlight, and half is in shadow. Credit: NASA/Goddard/University of Arizona — A view of asteroid Bennu, its striking craters and surface covered in boulders, captured by OSIRIS-REx’s OCAMS (MapCam) instrument on 28 April 2020 from a distance of 10km. Half of Bennu is bathed in sunlight, and half is in shadow. Credit: NASA/Goddard/University of Arizona

This essential monitoring is complicated by the fact that asteroids’ orbits can vary over time, as they are affected by the gravitational influence of other bodies or impacts with them.

At the time of writing, NASA estimates that over 90% of potentially hazardous asteroids have been found.

They have identified 35,376 near-Earth asteroids (NEAs) of all sizes, 863 of which are larger than 1km (0.6 miles) across, while 10,909 are 140 metres across or more.

Asteroids over 140 metres across hit Earth about once every 25,000 years; those over 1km strike our planet every 500,000 years.

Here are the top asteroid threats, their size and how likely they are to hit Earth.

	Name	Mass	Size	Earth impact probability	Year of potential impact
1	Bennu	74 million tonnes	0.49km	0.037%	2182
2	29075	78 million tonnes	1.3km	0.0029%	2880
3	2023 TL4	47 million tonnes	0.33km	0.00055%	2119
4	2007 FT3	54 million tonnes	0.34km	0.0000087%	2024
5	1979 XB	390 million tonnes	0.66km	0.000055%	2113

This article appeared in the October 2024 issue of BBC Sky at Night Magazine