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30 000 near - Earth asteroids discovered and rising

on 20 October 2022

We have now discovered 30 039 near-Earth asteroids in the Solar System – rocky bodies orbiting the Sun on a path that brings them close to Earth’s orbit. The majority of these were discovered in the last decade, showing how our ability to detect potentially risky asteroids is rapidly improving.

An asteroid is called a near-Earth asteroid (NEA) when its trajectory brings it within 1.3 Astronomical Units (au) of the Sun. 1 au is the distance between the Sun and Earth, and so NEAs can come within at least 0.3 au, 45 million km, of our planet’s orbit.

Currently, near-Earth asteroids make up about a third of the roughly one million asteroids discovered so far in the Solar System. Most of them reside in the asteroid belt between Jupiter and Mars.

Asteroids have been catalogued by astronomers for more than two centuries since the very first asteroid, Ceres, was discovered in 1801 by Giuseppe Piazzi. The first near-Earth asteroid, (433) Eros, was discovered nearly one hundred years later, on 13 August 1898.

The roughly 30 km Eros asteroid was discovered by Carl Gustav Witt and Felix Linke at the Urania Observatory in Berlin and independently by Auguste Charlois at the Nice Observatory. The stony asteroid’s orbit brings it to within around 22 million km of Earth – 57 times the distance of the Moon.

Naturally, large asteroids were discovered first as they are so much easier to see. They were thought of as minor planets, a term still used today. As telescopes get more sensitive, we are finding many more and at a great rate, even those down to tens of metres in size.

Gaia, ESA’s space observatory on a mission to catalogue one billion stars in the galaxy, has also helped us better understand the asteroid risk. Our country is also part of this mission. In Romania, the Astronomical Institute of the Romanian Academy is involved in four working groups of the CU9 (Coordination Unit 9) with regards to access to the GAIA catalogue, in the global GAIA-FUN-SSO network for tracking Solar System objects discovered by the Gaia Mission and in the Gaia Science Alert working group.

More details here.

Image credit: ESA - C. Carreau