Asteroids and Bennu

Leftover building blocks

Asteroids are rocky or metallic bodies left over from the formation of the planets about 4.6 billion years ago. Most orbit in the main asteroid belt between Mars and Jupiter, where Jupiter's gravity kept them from forming a planet. Despite movie images, the belt is mostly empty space: spacecraft fly through it without dodging.

Together, all the main belt asteroids have less mass than our Moon.

Near-Earth asteroids

Some asteroids have orbits that bring them close to Earth. NASA and other agencies track them to spot any that could pose a risk. In 2022, NASA's DART mission deliberately crashed into the small asteroid Dimorphos and changed its orbit, the first test of a technique that could one day nudge a dangerous asteroid away.

Visiting Bennu

NASA's OSIRIS-REx launched in 2016 to Bennu, a small, carbon-rich near-Earth asteroid. When it touched down to grab a sample in October 2020, the surface behaved almost like a ball pit, and the sampler sank in. The capsule landed in the Utah desert on September 24, 2023, carrying about 121.6 grams of rock and dust, the largest asteroid sample ever returned.

Scientists have found water-bearing minerals and organic molecules, including amino acids, in the sample.

What comes next

The spacecraft, renamed OSIRIS-APEX, is heading to the asteroid Apophis, which will pass safely but very close to Earth in April 2029. Japan's Hayabusa2 also returned samples from the asteroid Ryugu in 2020. Studying these pristine materials helps answer where Earth's water and the ingredients for life came from.

Can you see an asteroid?

A few large asteroids, such as Vesta, can be glimpsed with binoculars when they are well placed, looking like faint stars that move from night to night. Astronomy apps show their positions. Most meteorites that land on Earth are fragments of asteroids, and some museums let you touch one, which is the closest most of us will get to holding a piece of the early solar system.

← ErisComets →