Could Earth’s gravity capture an asteroid?

Earth could capture an asteroid, but only under certain conditions. The asteroid would have to be a certain size, traveling at just the right speed, and grazing by Earth at just the right angle. For example, a bus-sized asteroid grazing Earth’s atmosphere might be captured by Earth’s gravity. Afterward, moon’s gravity might pull it into a stable orbit above Earth – to give Earth a second moon.

Planetary scientists believe that asteroid capture was common billions of years ago. The planets are thought to have formed by a process of “accretion” – where small chunks of debris came together to form larger chunks. So there were lots more chunks – what we now call “asteroids” – moving through the solar system back then.

Also, dense gas and dust surrounded the forming planets. When an asteroid passed through this material, drag slowed it down – making capture by a planet easier. Mars’ two small moons were probably captured in this way, as were various satellites of Jupiter, Saturn, Uranus, and Neptune. Now asteroid capture is less common – but it is possible if the right asteroid comes along.

January 25, 2010

Like what you read?
Subscribe and receive daily news delivered to your inbox.

Your email address will only be used for EarthSky content. Privacy Policy
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

More from 

Editors of EarthSky

View All