Asteroid belt

The asteroid belt is a torus-shaped region in the Solar System. It is centered on the Sun and lies between the planets Jupiter and Mars. This area has many solid, irregularly shaped bodies called asteroids or minor planets. These objects are much smaller than planets and are usually about one million kilometers apart.

The asteroids of the inner Solar System and Jupiter: the belt is located between the orbits of Jupiter and Mars. Sun Jupiter trojans Orbits of planets Asteroid belt Hilda asteroids (Hildas) Near-Earth objects (selection)

The asteroid belt is the innermost and smallest circumstellar disc in the Solar System. Its total mass is thought to be about 3% of the Moon. Most of this mass is in four large asteroids: Ceres, Vesta, Pallas, and Hygiea. Ceres is special because it is big enough to be called a dwarf planet, with a diameter of about 950 km.

The asteroid belt formed from the early solar nebula as a group of planetesimals. These are smaller pieces that help form protoplanets. However, the gravity of Jupiter stopped them from growing into a planet. Because of this, the asteroid belt today has only a small amount of its original mass. Even so, the asteroid belt is an interesting place that helps scientists learn about how planets are made.

History of observation

In 1596, Johannes Kepler's sense of proportion for the planetary orbits led him to believe that an invisible planet lay between the orbits of Mars and Jupiter.

In 1596, Johannes Kepler thought a planet might be between Mars and Jupiter. In 1766, Johann Daniel Titius saw a pattern in the planets' paths and guessed a planet was missing there. This guess grew when William Herschel found Uranus in 1781, which fit the pattern.

On January 1, 1801, Giuseppe Piazzi found a small moving object where the planet was expected. He named it "Ceres" after the Roman goddess of the harvest. He first thought it might be a comet, but it looked more like a planet. Later, another object called Pallas was found nearby. Because these objects looked like stars even in strong telescopes, William Herschel called them "asteroids," meaning "star-like." More asteroids like Juno and Vesta were found after that. As more were discovered, scientists began to call the place where they are found the "asteroid belt." Today, we know of many asteroids in this area, and scientists are still learning more about them.

Origin

The asteroid belt showing the orbital inclinations versus distances from the Sun, with asteroids in the core region of the asteroid belt in red and other asteroids in blue

The asteroid belt is a region between the planets Mars and Jupiter that contains many rocky bodies called asteroids.

Scientists think the asteroid belt formed when small pieces of dust and rock in the early Solar System began to clump together. However, the strong gravity of Jupiter nearby disrupted this process. This stopped these pieces from forming a planet and kept them orbiting the Sun instead.

Characteristics

The asteroid belt is a big area in space between the orbits of Jupiter and Mars. It has many solid objects called asteroids. These asteroids are much smaller than planets and are spread out over a large distance. On average, they are about one million kilometers apart from each other.

The largest asteroids make up most of the belt's mass. The four biggest ones are Ceres, Vesta, Pallas, and Hygiea. Most asteroids are made of rock and metal, and they come in different types based on what they are made of. Some are rich in carbon, while others are made of silicate rocks or metals. The temperature in the asteroid belt changes depending on how far the asteroids are from the Sun.

Collisions

The zodiacal light, parts of which are reflected by interplanetary dust, which in turn originates in part from collisions of asteroids.

The asteroid belt is a busy place where asteroids bump into each other often. When two asteroids hit, they can break into smaller pieces or sometimes stick together if they hit slowly.

Over billions of years, these collisions have changed the asteroids a lot.

Many asteroids in the belt are like piles of rubble held together by gravity. The collisions also create tiny bits of dust, which float around and sometimes enter Earth’s atmosphere as meteorites. Most meteorites we find on Earth come from the asteroid belt. This dust helps create a soft glow in the night sky called the zodiacal light, which appears near the Sun.

Families and groups

Main article: Asteroid family

In 1918, a Japanese astronomer found that some asteroids moved in very similar paths around the Sun. These groups are called families. About one-third of the asteroids in the asteroid belt are part of these families. They share similar colors and paths, meaning they likely came from the same large object that broke apart long ago.

Some well-known families are Flora, Eunomia, Koronis, Eos, and Themis. The Flora family is one of the largest, with over 800 known asteroids. These families help scientists learn more about how asteroids formed and moved over time.

Exploration

Artist's concept of the Dawn spacecraft with Vesta and Ceres

The first spacecraft to travel through the asteroid belt was Pioneer 10, entering the region on July 16, 1972. Since then, many spacecraft have passed through the belt safely. Missions like Pioneer 11, Voyagers 1 and 2, and Ulysses moved through the belt but did not take pictures of asteroids.

The Dawn mission was the first to study asteroids for a long time from orbit. Other spacecraft, such as Galileo, NEAR, and Cassini, took images of asteroids during their flights. In the future, missions like Psyche will orbit the large asteroid 16 Psyche starting in 2029, and Tianwen-2 will visit 311P/PanSTARRS in 2035.