Asteroid

An asteroid is a small rocky or metallic body orbiting the Sun. Asteroids are mainly concentrated in the asteroid belt between Mars and Jupiter, where more than a million objects larger than one kilometer in diameter have been cataloged. They are considered to be the fossil remnants of the solar system’s formation, having never been able to coalesce into planets due to Jupiter’s gravitational influence.

Diversity of asteroids

Asteroids come in a wide variety of sizes, compositions, and orbits. The largest, Ceres, measures 940 km in diameter and is classified as a dwarf planet. The smallest are only a few meters in size. There are several spectral classes—primarily C-type (carbonaceous, dark), S-type (silicate, rocky), and M-type (metallic)—which reflect their composition.

Near-Earth asteroids

Some asteroids have orbits that intersect Earth’s—they are called near-Earth asteroids or NEOs (Near-Earth Objects). More than 30,000 NEOs have been cataloged, a fraction of which are considered potentially hazardous. NASA and ESA are closely monitoring these objects to prevent potential collisions. The 2022 DART mission demonstrated that it is possible to deflect an asteroid through kinetic impact.

Asteroid Exploration

Several space missions have visited asteroids. NEAR Shoemaker landed on Eros in 2001. Hayabusa returned samples from Itokawa in 2010, followed by Hayabusa 2 from Ryugu in 2020. OSIRIS-REx brought back samples from Bennu in 2023. The Dawn mission studied Vesta and Ceres. These missions reveal the primordial composition of asteroids and their role in the formation of the solar system.

Did you know?

If we were to gather all the asteroids in the main belt, their total mass would be about 4% of that of the Moon— well below that of a planet. Contrary to what is depicted in science fiction movies, the belt is very sparse—space probes can travel through it without risk of collision.

Frequently Asked Questions

What is the difference between an asteroid and a comet?

An asteroid is primarily rocky or metallic and is generally found in the inner part of the solar system. A comet is rich in ice and dust, originating from the cold outer regions. Comets develop an atmosphere (the coma) and a tail as they approach the Sun.

Can an asteroid destroy Earth?

An asteroid large enough (several kilometers) could cause a mass extinction, such as that of the dinosaurs 66 million years ago. However, no known asteroid poses a threat to Earth in the coming centuries, and monitoring programs now cover most hazardous objects.

Can asteroids be mined?

In theory, yes. Some asteroids contain enormous quantities of precious metals such as platinum. Several companies are exploring the mining of these bodies, but the technological and economic challenges remain considerable.