The asteroid belt is a wide ring of rocky and metallic bodies that orbit the Sun between Mars and Jupiter, roughly 330 to 480 million kilometres from the Sun. It holds millions of asteroids, but together they weigh only about 3 percent as much as our Moon, and the space between them is huge. Movies show it as a crowded minefield. In reality it is mostly empty, and spacecraft pass through it safely.
This guide covers where the belt is, what is in it, how it formed, the myths that surround it, and the missions that are exploring it.
Asteroid belt facts at a glance
| Fact | Detail |
|---|---|
| Location | Between the orbits of Mars and Jupiter |
| Distance from the Sun | About 2.2 to 3.2 astronomical units (AU), or 330 to 480 million km |
| Total mass | About 3% of the Moon’s mass |
| Largest object | Ceres, a dwarf planet about 940 km wide |
| Number of asteroids | Well over a million catalogued, and millions more too small to track |
| Age | About 4.6 billion years, left over from the early solar system |
| Main types | Carbon-rich (dark), stony (silicate) and metallic |
One astronomical unit is the average distance from Earth to the Sun, about 150 million km.
Explore the belt
The widget below shows the inner solar system from above. Planet orbits are drawn to scale. Select Ceres, Vesta, Pallas, Hygiea or Psyche to learn about them, and turn on Jupiter’s gaps to see where the belt is thinned out.
The asteroid belt, mapped
Look down on the inner solar system, select a large asteroid, and see how empty the belt really is.
How much stuff is in the belt?
Planet orbits are to scale; asteroid dots are only a sample and are drawn far larger than real asteroids. Sizes and distances are rounded. Sources: NASA and the Psyche mission.
What is the asteroid belt?
The asteroid belt is a region of the solar system where rocky and metallic leftovers of planet-building still orbit the Sun. Most are irregular chunks, from tiny pebbles to bodies hundreds of kilometres wide. Only four are larger than 400 km: Ceres, Vesta, Pallas and Hygiea.
Asteroids are not all alike. There are three main groups:
- Carbon-rich (C-type): Dark and the most common, making up roughly three quarters of known asteroids.
- Stony (S-type): Made mainly of silicate rock and metal, and brighter.
- Metallic (M-type): Rich in iron and nickel, and rarer.
The giant Jupiter also keeps a separate crowd of asteroids, called Trojans, sharing its orbit. They are not part of the main belt.
How many asteroids are there?
Astronomers have catalogued well over a million asteroids, and most of them are in the main belt. Estimates suggest there may be around one to two million that are larger than 1 km, and many millions more that are smaller.
But being numerous does not make the belt crowded. The belt is enormous, and the typical distance between asteroids is huge, often hundreds of thousands of kilometres. From the surface of any one asteroid, you would usually not see another with the naked eye.
How did the asteroid belt form?
The belt is what remains of the material that never became a planet. About 4.6 billion years ago, the solar system formed from a spinning disk of gas and dust. Rocks collided and stuck together into larger bodies, and some grew large enough to become small worlds.
In the region between Mars and Jupiter, that process stalled. The huge gravity of Jupiter stirred up the rocks, speeding them up so that collisions broke them apart instead of merging them. A planet never had the chance to form.
Is the asteroid belt a destroyed planet?
No. This is a popular myth. If you added up all the asteroids, they would make less than 1 percent of Earth’s mass, far too little to be a planet, and the asteroids differ too much in composition to have come from one body.
What are the gaps in the asteroid belt?
The belt has gaps called Kirkwood gaps, named after the astronomer Daniel Kirkwood, who spotted them in the 1800s. They appear at distances where an asteroid would orbit the Sun in a simple ratio with Jupiter’s orbit. For example, an asteroid in the 3:1 gap would circle the Sun three times for every one orbit of Jupiter. Jupiter’s gravity gives it a regular tug at the same point in each orbit, and over time it flings the asteroid out of the gap.
These gaps are one reason the belt looks uneven when plotted. You can see them in the widget above. For more about the giant planet that sculpts the belt, read our Jupiter overview.
Ceres, Vesta and the largest asteroids
Ceres was discovered in 1801 by Giuseppe Piazzi and was first called a planet, then an asteroid. In 2006 it was reclassified as a dwarf planet. At about 940 km wide, it holds roughly a third of the belt’s mass. NASA’s Dawn spacecraft orbited it from 2015 to 2018 and found bright patches of salt in the Occator Crater, plus signs of salty water beneath the surface.
Vesta is about 525 km wide and the second most massive asteroid. Dawn orbited it in 2011 and 2012. A giant impact scooped out a huge basin near its south pole, and pieces of Vesta have fallen to Earth as meteorites.
Pallas is about 510 km wide, with an orbit tilted about 35 degrees away from the plane of the planets.
Hygiea is about 430 km wide and nearly round, so it may one day be classed as a dwarf planet.
Dawn was also the first spacecraft to orbit two different bodies beyond Earth, thanks to its efficient engines. Read how they work in our guide to ion propulsion.
Is the asteroid belt dangerous for spacecraft?
No. Pioneer 10 became the first spacecraft to cross the belt, between 1972 and 1973, and many probes have followed without a problem. NASA has said that the chance of hitting an asteroid while crossing it is far less than one in a billion. Mission planners do not even need to steer around asteroids. They aim for particular ones only when they want to visit them.
Which missions are exploring the asteroid belt?
- Dawn (NASA, 2007–2018): Orbited Vesta and then Ceres.
- Lucy (NASA): Launched in 2021 to visit Jupiter’s Trojan asteroids. On the way, it flew past the main-belt asteroids Dinkinesh in 2023 and Donaldjohanson in 2025. Its first Trojan flyby, at Eurybates, is planned for 2027.
- Psyche (NASA): Launched in October 2023 to study the metal-rich asteroid Psyche, which is about 226 km wide. It flew past Mars in May 2026 for a gravity boost and is due to arrive in 2029.
- Tianwen-2 (China): Launched in 2025 to visit a near-Earth asteroid, with plans to continue to a main-belt comet.
Schedules can change, so check each mission’s official page for the latest news.
Is the asteroid belt the only asteroid region?
No. Several regions hold small bodies.
| Region | Location | Made of |
|---|---|---|
| Main asteroid belt | Between Mars and Jupiter | Rock and metal |
| Jupiter Trojans | Share Jupiter’s orbit | Dark rock and ice |
| Near-Earth asteroids | Orbits that come close to Earth | Rock and metal |
| Kuiper Belt | Beyond Neptune | Ice and rock, far more massive than the asteroid belt |
Most asteroids that come near Earth began in the main belt and were nudged inward by Jupiter’s gravity. Planetary defence tests, such as NASA’s DART mission in 2022, which changed the orbit of a small asteroid called Dimorphos, are practising how we might deflect a dangerous one. For the full picture of where these regions fit, see our Solar System guide.
Common myths about the asteroid belt
- “It is a dense field of rocks.” False. The belt is mostly empty space.
- “It is a planet that blew up.” False. There is not enough material, and the asteroids are too different from each other.
- “Spacecraft have to dodge asteroids.” False. Collisions are extremely unlikely.
- “The metal asteroid Psyche is worth quintillions of dollars.” That headline figure is a thought experiment, not a real market value. NASA’s mission is about science, to learn about the cores of planets.
Some of the moons in our solar system, like Mars’s Phobos and Deimos, may be captured asteroids. See how many moons each planet has.
Frequently asked questions
Where is the asteroid belt?
Between the orbits of Mars and Jupiter, about 2.2 to 3.2 astronomical units from the Sun.
How many asteroids are in the asteroid belt?
Well over a million have been catalogued, and there are probably millions more that are too small to see from Earth.
What is the largest object in the asteroid belt?
Ceres, a dwarf planet about 940 km wide.
How much does the asteroid belt weigh?
About 3 percent of the Moon’s mass.
Is the asteroid belt crowded?
No. The space between asteroids is vast, so spacecraft can pass through safely.
Did the asteroid belt come from a planet?
No. It is leftover material that never formed a planet, because Jupiter’s gravity kept stirring it up.
Can asteroids from the belt hit Earth?
Some can. Jupiter’s gravity occasionally sends asteroids toward the inner solar system, which is why astronomers watch for near-Earth objects.
Key takeaways
- The asteroid belt lies between Mars and Jupiter and holds only about 3 percent of the Moon’s mass.
- It contains millions of asteroids, but they are far apart.
- It formed from material that Jupiter’s gravity kept from becoming a planet.
- Ceres is the largest object and a dwarf planet. Vesta, Pallas and Hygiea follow.
- Dawn, Lucy and Psyche have explored or are exploring it.
Continue exploring in our Solar System guide.
Sources
- NASA: Asteroids
- NASA: Psyche mission
- NASA JPL: Psyche spacecraft prepares for Mars flyby
- NASA: Dawn mission
- NASA: Lucy mission
Related posts :
How Many Moons Does Each Planet Have? (2026 Count)