There Have Been 30,000 Near-earth Asteroids Discovered
The recent success of NASA's DART mission in deflecting an asteroid from its path could lead one to believe that our planet's defences against approaching asteroids are in order. However, there are several asteroids in space, and the search for potentially hazardous asteroids is a continuing process.
According to the European Space Agency (ESA), there are currently over 30,000 identified near-Earth asteroids. As many asteroids have very eccentric orbits that bring them closer to the sun at different periods, a near-Earth asteroid approaches the Earth at some point during its orbit. Astronomers estimate the distance between the sun and Earth using the Astronomical Unit (AU), and near-Earth asteroids are those that come within 1.3 AU of the sun.
Many near-Earth asteroids are tiny enough to burn up in the planet's atmosphere, while others move in a manner that does not intersect Earth's orbit. If an asteroid has crossed Earth's orbit and is larger than 460 feet in diameter, it is categorised as a Potentially Hazardous Object and will be monitored by astronomers.
To determine whether asteroids are potentially hazardous, however, they must first be detected, which is no simple task. When searching for asteroids, tools such as the ESA's Gaia, a satellite observatory on a mission to map all of the stars in the Milky Way, can provide information on the background stars observed.
Tineke Roegiers, community support for the Gaia mission, said, “Because of Gaia, we know more about the stars in the galaxy, which serve as a backdrop for asteroid observations.” “Asteroid positions are determined relative to these background stars, therefore the more exactly one knows where the stars are, the more precisely one can compute the orbits of asteroids.”
Once an asteroid is discovered, it must be examined several times to calculate its orbit and determine whether it will approach the Earth. “Of course, any asteroid discovered near-Earth qualifies as a near-Earth asteroid, but many are discovered far from home,” said Marco Micheli, an astronomer at the Near-Earth Object Coordination Centre of the European Space Agency.
#PlanetaryDefense means we monitor the skies and search for potentially hazardous near-Earth objects every night. We recently hit a new milestone of more than 30,000 near-Earth #asteroids of all sizes discovered!
— NASA Asteroid Watch (@AsteroidWatch) October 14, 2022
“New objects are detected over time, their motions are examined, and their future positions can be predicted with just a handful of data points from different nights. This can extend decades or even centuries into the future, depending on the quantity and quality of observations.”
If you feel like you hear more about dangerous asteroids today than you did in the past, it may appear that the threat from the sky is expanding, but in reality, we're just much better at detecting them.
“The good news is that more than half of today's known near-Earth asteroids were detected in the last six years,” said Richard Moss, the ESA's head of planetary defence. “This demonstrates how our asteroid vision is improving.” “As this new detection milestone of 30,000 demonstrates, and as additional telescopes and detecting methods are developed, it's only a matter of time before we find them all,”