How big is the asteroid belt

Asteroid belt

The asteroid belt between the orbits of Mars (red) and Jupiter (orange). The earth's orbit is marked in blue.

(Graphic: EasySky)

The asteroid belt, asteroid belt or main belt is the name given to the collection of asteroids and dwarf planets in the solar system, which is located between the orbits of Mars and Jupiter. More than 600,000 such objects are currently recorded in this area.

Any attempt to graphically depict the asteroid belt falsifies the actual image, because the majority of the objects are so small that they cannot be displayed true to scale. Even if several million objects are presumably moving in this huge section of the solar system, the space would appear empty on closer inspection. This has already been proven by many problem-free flights through space probes. So you shouldn't think of the asteroid belt as a dense tangle of boulders. In fact, the total mass of all objects in the asteroid belt is only about 1% of the mass of Mercury, the smallest planet in the solar system. The largest asteroid Ceres (see below) combines about a third of this mass. The rest is distributed among thousands and thousands of objects that form a ring around the sun that is more than 200 million kilometers wide.

The earlier thesis that the asteroid belt was created by the collision or the breaking of a planet is now superseded by the assumption that the objects originate from the time the solar system was formed and that Jupiter's gravitational influence prevented them from growing together into one object.


With an equatorial diameter of 963 km, Ceres is the largest object in the main asteroid belt and is counted among the dwarf planets due to its size and shape. It is almost twice the diameter and four times the mass of Vesta, the second largest object in the asteroid belt.

Ceres was discovered as the first minor planet on January 1, 1801 by the Sicilian priest and astronomer Giuseppe Piazzi. He named the celestial body he discovered after the Roman goddess of agriculture and patroness of Sicily.

The dwarf planet Ceres in size compared to Earth.

(Photos: NASA / JPL / UCLA / MPS / DLR / IDA)

The dwarf planet Ceres has a solid core made of silicate rock and metals, which is surrounded by a mantle that consists primarily of water ice. Overall, Ceres should consist of around 20% water. With its differentiated structure, Ceres differs from the vast majority of asteroids, which mostly consist of material that has survived unchanged since the formation of the solar system 4.5 billion years ago.

CeresAbsolutelyRelativePlanet path
Distance from the sun414 million km2.8 x earth208 m
diameter963 km0.075 x earth0.5 mm
Dimensions9.4x1020 kg0.00016 x earth0.0001 g
Severity acc.0.27 m / s²0.03 x earth
Rotation time9H 4m 30s0.38 x earth
Orbital time4.6 years4.6 x earth
Orbit speed18 km / s0.60 x earth
Light transit time22m 58s


From antiquity to the end of the 18th century, six planets were known in our solar system (Mercury, Venus, Earth, Mars, Jupiter and Saturn) and over the centuries their distances from the sun have been calculated more and more precisely. The distances from planet to planet are greater, the further away they are from the sun. Therefore earlier astronomers suspected a physical law in the consequences of the distances. In the 1760s, the German astronomer createdJohann Daniel Titius an approximation formula which should represent the distances of the planets from the sun by a simple mathematical formula. The formula was published in 1772 by another German astronomer,Johann Elert Bode, which is why this formula is known as the "Titius-Bode series". With their help, the approximate distances of the planets known at the time from the sun can be calculated. In addition, this formula reaffirmed one of the Johannes Kepler expressed assumption that there should be an additional planet between Mars and Jupiter. When the planet Uranus was discovered by chance in 1781, it turned out that its distance from the sun also coincided with the orbit radius predicted by the Titius-Bode series. Encouraged by this, the astronomers began to look for the postulated planet between Mars and Jupiter.

The Sicilian priest and astronomer achieved success for the first time on January 1st, 1801 Giuseppe Piazzi. Its discovery, Ceres, was initially referred to as a planet. The asteroids Pallas, Juno and Vesta discovered in 1802, 1804 and 1807 were also classified as planets. It was only when the number of objects found between the orbits of the planets Mars and Jupiter rose rapidly from the middle of the 19th century that Ceres and the other objects between Mars and Jupiter lost their status as planets. From then on, they were referred to as "minor planets", "planetoids" or "asteroids".

In the past few decades, near-Earth asteroids have become the focus of interest for researchers. Earth orbit cruisers, which can leave the asteroid belt and come close to our home planet, represent a potential danger for the earth and its inhabitants. This is how the mass extinction that occurred 65 million years ago and which, among other things, led to the extinction of the dinosaurs, appears traced back the impact of an asteroid only about 10 km in size.

In 1991 the spacecraft flew Galileo on their way to the planet Jupiter at the approximately 10 km large asteroidGaspa stopped by and explored a minor planet up close for the first time. Since then, around a dozen other planetoids have been examined with space probes. In November 2005, the Japanese spacecraft collected Hayabusa Soil samples from the near-earth asteroid Itokawawhich could then be brought back to earth and examined in earthly laboratories. The NASA spacecraft Dawn pivoted into orbit around the asteroid in 2011 Vesta and researched it for 14 months Ceres second largest celestial body in the asteroid belt. Then she flew to the dwarf planet Ceres further, which she has been orbiting and exploring since the beginning of 2015.


Under favorable circumstances, the asteroid Vesta can barely be seen with the naked eye. Dozens of asteroids can be found with a small telescope, but they only appear as points of light to the observer.

Well-equipped amateur astronomers can contribute to the exploration of the asteroids by determining their rotation time or measuring their precise position and thus contributing to the calculation of an exact orbit. Members of the Linz Astronomical Community also succeeded in discovering around two dozen minor planets in the Davidschlag private observatory (Kirchschlag parish).