Asteroids and the Asteroid Belt
Rocky and metal leftovers from the birth of the planets, and the spacecraft that brought pieces of them home.
Asteroids are rocky or metallic bodies left over from the early Solar System. Most travel in the main asteroid belt between Mars and Jupiter, but others share Jupiter's orbit, cross the paths of the inner planets or pass near Earth. They range from boulders to bodies hundreds of kilometers wide, and many are loose piles of rubble held together by weak gravity.
The belt is far emptier than movies suggest. Its total mass is less than that of the Moon, and the rocks are spread across an enormous region, so spacecraft cross it without special maneuvers. Astronomers sort asteroids by what they are made of, mostly dark carbon-rich types, stony types and metal-rich types, and by where they orbit.
This category covers both the science and the missions. NASA's Dawn studied Vesta and then Ceres. Japan's Hayabusa and Hayabusa2 brought back material from the asteroids Itokawa and Ryugu. NASA's OSIRIS-REx delivered a sample from Bennu to Earth in 2023, and NASA's DART spacecraft hit the small moonlet Dimorphos in 2022 to test whether a collision can change an asteroid's path.
Planetary defense gets its own guide because the topic attracts exaggeration. Space agencies track near-Earth asteroids, publish their orbits and explain the odds openly. Our guides report those statements with the date they were checked, and they leave out scenarios that no agency has put forward.
Start with what asteroids are for the basics. After that, follow your curiosity: a giant like Vesta, a sample mission like OSIRIS-REx and Bennu, or the 2029 flyby of Apophis.
The nine guides
What Are Asteroids? Types, Sizes and Where They Live
A plain-language guide to asteroids, from the 530 km giant Vesta to rocks under 10 m, with the main compositional classes and the zones where they gather.
The Asteroid Belt Is Mostly Empty Space
Where the main belt sits, how little material it holds, what carves its Kirkwood gaps, and why Jupiter kept a planet from forming there.
Vesta: The Giant Asteroid Visited by Dawn
Vesta has a core, mantle and crust, a basin nearly as wide as itself, and a family of meteorites that landed on Earth. Here is what Dawn showed in 2011 and 2012.
Near-Earth Asteroids: What They Are and How They Are Tracked
How astronomers define, count and follow asteroids whose orbits come close to Earth, and why a label like "potentially hazardous" is not a prediction.
Planetary Defense Explained: DART and What Comes Next
What agencies actually do to watch for hazardous asteroids, the numbers from the DART impact on Dimorphos, and the missions that will check the results.
OSIRIS-REx and Bennu: Bringing Asteroid Dust Home
The mission's key dates, how the touch-and-go grab worked, how much material came back, and the findings from amino acids to sugars, as of November 2026.
Hayabusa and Hayabusa2: JAXA's Asteroid Sample Missions
How two Japanese spacecraft reached near-Earth asteroids and returned samples, what the grains revealed, and the 2026 Torifune flyby of Hayabusa2's extended mission.
Lucy and the Trojan Asteroids of Jupiter
What Trojan asteroids are, why they ride along Jupiter's orbit, and a dated tour of Lucy's flybys, from the main-belt rehearsals to the Patroclus and Menoetius pair.
Asteroid Apophis and Its 2029 Close Flyby
Why Apophis worried astronomers in 2004, how radar data in 2021 ended the concern, and which spacecraft and telescopes will watch the April 2029 flyby.