An asteroid is a small body orbiting the Sun or another star (no asteroid has been discovered in another star yet), due to its small mass, mostly irregular in shape. In the solar system, such bodies are found mainly in the space between Mars and Jupiter, in the so-called main belt. However, others are located beyond the orbit of Neptune, while others may cross the orbit of the Earth and get closer to the Sun than our planet. Bodies larger than 100 m are usually considered asteroids.
According to the current theory of asteroid formation, these are planetesimals (small stone or ice bodies 1-10 km in size that are thought to have formed the solar system), whose accretion to the planet was prematurely terminated by the gravitational influence of Jupiter.
Division of asteroids according to chemical composition:
C-asteroids – whose spectral characteristics resemble carbonaceous chondrites and are the most common (approximately 75% of known asteroids).
S-asteroids – formed by a mixture of nickel iron with silicate minerals (approximately 27% of asteroids).
M-asteroids – formed by practically pure nickel iron (approximately 6% of asteroids).
U-asteroids – not falling into any of the previous groups.
Asteroids according to orbits are divided into:
Objects in the inner solar system
- asteroids orbiting inside the Earth’s orbit: vulcanides (a hypothetical group of asteroids orbiting inside the orbit of Mercury), apohels (asteroids with an aphel of less than 1 AU (150 million km), ie bodies whose entire orbit lies within the Earth’s orbit).
- near-Earth asteroids: Trojans of the Earth (bodies moving in commensurable orbits 1: 1 with the Earth and located in the L4 and L5 liberation centers of the Sun-Earth system), asteroids co-orbital with the Earth (asteroids moving in a path very similar to the Earth’s orbit and close to commensurability 1: 1), Athen’s group (they cross the Earth’s orbit, their orbit is mostly inside the Earth’s orbit, their orbit around the Sun is less than one year), Apollo’s group (they cross the Earth’s orbit, their orbit is mostly inside Earth’s orbits, their orbit around the Sun lasts longer than one year) Cupid’s group (their orbits approach the Earth’s orbit from the outside, but do not cross it)
- asteroids close to Mars: the orbits of the orbit of Mars (their orbits cross the orbit of the planet Mars), the Mars Trojans (asteroids in commensurability 1: 1 with Mars).
- main belt asteroids – orbit in the space between the orbits of Mars and Jupiter, roughlyat distances from 2 AU to 4 AU, and formed largely from a protoplanetary disk in an area where Jupiter’s gravitational influence could not form a single large body.
- asteroids bound to Jupiter: Trojans (values of the large half-axis of their orbits range from 5.05 AU to 5.4 AU, so they move in approximately the same orbit as Jupiter, in commensurability 1: 1), asteroids co-orbital with Jupiter (asteroids , moving along a path very similar to the path of Jupiter and close to commensurability 1: 1).
Objects in the outer solar system
- bodies with perihelion between the orbits of Jupiter and Neptune: centaurs (these are bodies whose entire orbit is located in the space between Jupiter and Neptune), damocloids (these are bodies on very eccentric orbits with perihelion lying inside the orbit of Neptune and afel far beyond its orbit ).
- Neptune Trojans – move in approximately the same path as Neptune, in a 1: 1 range.
- transneptunian bodies – have orbits, most of which lie behind the orbit of the planet Neptune.
Potentially dangerous asteroids Although there is currently no known asteroid that should hit us with certainty, there is already a list of approaching thousands of objects for which this cannot be ruled out in the long run.