The Asteroid Belt is a vast collection of rocks both large and small, orbiting the Sun in a belt that is mostly in a zone of space between Mars and Jupiter. Currently there are more than 1.3 million known asteroids that are more than 1 kilometer in length. Far more smaller asteroids are thought to be in the asteroid belt, bringing the total to many millions.
Most asteroids orbit the Sun between Mars and Jupiter, but not all. Many other asteroids orbit the Sun from inside the orbit of Mercury all the way out to the orbit of Neptune. All of these rocky bodies that orbit the Sun inside the orbit of Neptune are referred to as Minor Planets. Beyond the orbit of Neptune they’re known as trans-Neptunian objects, or Kuiper Belt objects. The “former” planet Pluto has now been reclassified as a Kuiper Belt object, but this reclassification is still a point of controversy.
Ceres is the largest asteroid in the main asteroid belt. It has a diameter of more than 1000 kilometers, large enough to be classified as a dwarf planet. Its large size and total mass contain enough gravity for it to be contracted into a spherical shape. Ceres contains approximately one third of the total mass of the entire asteroid belt. By comparison, the next largest asteroids in the belt, Vesta and Pallas, are both roughly the same size at 500 km in diameter, and are not spherical in shape. They are referred to as “minor planets” with all of the other asteroids. The Minor Planetary Center keeps a large catalog of all known asteroids and their current location in the sky.
NASA is currently working on mission plans to send probes to asteroids as scouting missions to investigate the feasibility of mining asteroids for precious metals and other key raw materials. One asteroid in particular, known as Psyche, appears to be very rich in heavy metals such as iron, nickel and gold. In October of 2023 NASA launched an exploration mission to Psyche, its planned rendezvous is in August, 2029.
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Tracking Evolution in the Asteroid Belt