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Asteroids and comets of the Solar System

Planets are not the only things orbiting the Sun. Asteroids are bodies of rock or metal, almost all gathered in the main belt between Mars and Jupiter; comets are blocks of ice and dust that grow a coma and a tail as they approach the Sun. Here you will find 16 of these bodies, chosen from among the best studied: the large main-belt asteroids, those that pass close to Earth, a Kuiper Belt object and the most famous comets. Each profile gives sizes, orbit, mission history and a 3D model rebuilt from spacecraft data.

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Main-belt asteroids

Most known asteroids orbit between Mars and Jupiter. These are among the largest: together with Ceres, which is a dwarf planet, Vesta, Pallas and Hygiea hold more than half the mass of the entire belt.

3D model of asteroid Vesta, reconstructed from Dawn spacecraft data The brightest of the asteroids Vesta 569 × 554 × 453 km · Orbital period: 3.63 years Read the profile 3D model of asteroid Pallas, reconstructed from ESO Very Large Telescope images The giant on a tilted orbit Pallas 568 × 532 × 448 km · Orbital period: 4.61 years Read the profile 3D model of asteroid Hygiea, reconstructed from ESO Very Large Telescope images A candidate for smallest dwarf planet Hygiea 450 × 430 × 424 km · Orbital period: 5.6 years Read the profile 3D model of asteroid Psyche, reconstructed from ESO Very Large Telescope images The metal world Psyche 278 × 238 × 171 km · Orbital period: 5.01 years Read the profile

Near-Earth asteroids

These are the asteroids whose orbits bring them close to Earth's. That is exactly why they are the easiest to reach: almost all of those below have been visited by a spacecraft, and samples from three of them have been brought back to Earth.

3D model of asteroid Eros, reconstructed from NEAR Shoemaker spacecraft data The first near-Earth asteroid Eros 34.4 × 11.2 × 11.2 km · Orbital period: 643 days Read the profile 3D model of asteroid Itokawa, reconstructed from Hayabusa spacecraft data The rubble pile Itokawa 535 × 294 × 209 m · Orbital period: 557 days Read the profile 3D model of asteroid Bennu, reconstructed from OSIRIS-REx spacecraft data The carbon spinning top Bennu 565 × 535 × 508 m · Orbital period: 436 days Read the profile 3D model of asteroid Ryugu, reconstructed from Hayabusa2 spacecraft data Bennu's dark twin Ryugu 1,004 × 1,004 × 876 m · Orbital period: 475 days Read the profile 3D model of asteroid Apophis, reconstructed from radar observations The asteroid of 13 April 2029 Apophis 340 m · Orbital period: 324 days Read the profile 3D model of asteroid Didymos with its moon Dimorphos, reconstructed from DART spacecraft data The planetary defence target Didymos 818 × 801 × 604 m · Orbital period: 2.11 years Read the profile

Beyond Neptune: the Kuiper Belt

Beyond the orbit of Neptune lies a belt of icy bodies that have remained almost untouched since the birth of the Solar System. Arrokoth is the only one, apart from Pluto and its moons, to have been observed up close.

3D model of Arrokoth, a two-lobed Kuiper Belt object, reconstructed from New Horizons spacecraft data The most distant world ever visited Arrokoth 36 × 20 × 10 km · Orbital period: 294 years Read the profile

Comets

Blocks of ice and dust on very elongated orbits: far from the Sun they are dark and inert, near it they light up. The images show each comet during a perihelion passage, with the coma and both tails computed by the simulation.

3D model of Halley's Comet with coma, ion tail and dust tail, at its 1986 perihelion The most famous comet Halley's Comet 15.3 × 7.2 × 7.2 km · Orbital period: 75.6 years Read the profile 3D model of comet 67P/Churyumov–Gerasimenko with its two-lobed nucleus, coma and dust tail, at its 2015 perihelion Rosetta's comet 67P/Churyumov–Gerasimenko 3.4 km · Orbital period: 6.44 years Read the profile 3D model of comet Hale–Bopp with its coma, blue ion tail and dust tail, at its 1997 perihelion The great comet of 1997 Hale–Bopp 60 km · Orbital period: 2,400 years Read the profile 3D model of comet Swift–Tuttle with its coma, ion tail and dust tail, at its 1992 perihelion Mother of the Perseids Swift–Tuttle 26 km · Orbital period: 134 years Read the profile 3D model of comet Encke with its coma and dust tail, at its 2023 perihelion The comet with the shortest period Encke 4.8 km · Orbital period: 3.3 years Read the profile

Frequently asked questions

What is the difference between an asteroid and a comet?

An asteroid is made of rock or metal and stays inert; a comet holds a lot of ice which, near the Sun, sublimates and forms a coma and a tail. Asteroids generally formed in the warm inner part of the Solar System, comets in the cold outer part. The boundary is not sharp: there are asteroids that shed dust and comets that have gone dormant.

Why do comets have tails?

Because as a comet nears the Sun, the ice in its nucleus turns straight into gas and drags dust along with it. Sunlight and the solar wind push this material away, always in the direction opposite to the Sun: that is why the tail does not trail behind the comet like a wake, and after perihelion it leads the way. There are two tails: one of gas, blue and straight, and one of dust, paler and curved.

How many asteroids are known?

More than a million and a half: in April 2026 the Minor Planet Center had catalogued about 1.57 million, and the number grows by tens of thousands every year. Almost all are small: those more than 100 km across number about two hundred. Known comets are far fewer, about 4,600.

Can an asteroid hit Earth?

Yes, and it has happened many times in the planet's history, but large impacts are extremely rare. Of the known bodies, none currently has a significant chance of hitting Earth in the next century. Apophis, which in 2004 reached level 4 on the Torino scale, the highest ever assigned, has been ruled out for at least a hundred years. In 2022 the DART mission showed that an asteroid's orbit can be deflected.

What is a small Solar System body?

It is the category introduced by the IAU in 2006 for everything that orbits the Sun without being a planet, a dwarf planet or a satellite: almost all asteroids, the comets and most of the objects beyond Neptune. They are leftovers of the material from which the planets formed, and so they preserve information about the origins of the Solar System.

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