Asteroids, Asteroid Belt, Kuiper Belt, Comets, Meteoroid, Meteor and Meteorite

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Other solar system objects include asteroids, comets, meteoroid, meteor, meteorite, etc.

Asteroid Belt

  • Asteroids are remnants of planetary formation that failed to coalesce because of the gravitational interference of Jupiter. They circle the Sun in a zone lying between Mars and Jupiter. The circular chain of asteroids is called the asteroid belt. It lies between 2.3 and 3.3 AU from the Sun.
  • Asteroids (planetoids ― another term for an asteroid) are composed mainly of refractory rocky and metallic minerals, with some ice. They range in size from hundreds of kilometres across to microscopic.


  • Ceres (2.77 AU) is the largest asteroid (946 km in diameter), a protoplanet, and a dwarf planet. It has a mass large enough for its own gravity to pull it into a spherical shape. All asteroids, except Ceres, are classified as small Solar System bodies.

[UPSC Prelims 1997] The group of small pieces of rock revolving round the sun between the orbits of Mars and Jupiter are called:

  1. Meteors
  2. comets
  3. meteorites
  4. asteroids

[UPSC Prelims 1998] Consider the following statements regarding asteroids:

  1. Asteroids are rocky debris of varying size orbiting the sun
  2. Most of the asteroids are small, but some have diameters as large and 1000 km
  3. The orbit of asteroids lies between the orbits of Jupiter and Saturn
Of these statements:
  1. 1, 2 and 3 are correct
  2. 2 and 3 are correct
  3. 1 and 2 are correct
  4. 1 and 3 are correct
  • Ceres (2.77 AU) is the largest asteroid with a diameter of 946 km. Vesta (525 km) is the second largest. So, only statement (1) is correct. Since this question was asked in 1998, the answer was (c) 1 & 2 only.

Kuiper Belt, Pluto, and Charon

  • The Kuiper belt is a great ring of debris like the asteroid belt but consists mainly of objects composed primarily of ice. It extends between 30 and 50 AU from the Sun.
  • Pluto (39 AU) is the largest known object in the Kuiper belt. Charon is Pluto’s largest moon. When discovered in 1930, Pluto was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of a planet.
  • International Astronomical Union’s definition of a planet: a Planet is an object that:
  • orbits the sun;
  • has sufficient mass to assume hydrostatic equilibrium ― a nearly round shape;
  • is not a satellite (moon) of another object, and
  • has removed debris and small objects from the area around its orbit
  • IAU’s definition of Dwarf planet: Dwarf planet is an object that meets planetary criteria except that it has not cleared debris from its orbital neighbourhood.
  • Pluto is a part of the Kuiper belt that contains millions of rocky and icy objects. Also, there are numerous other objects in the Kuiper belt which are of similar size to Pluto. E.g., Eris (diameter: 2,326 km).
  • So, if Pluto is considered a plant, then many other objects like Eris will also have to be considered planets. Hence, Pluto (diameter: 2,377 km) (Kuiper belt) was voted by IAU as a dwarf planet just like Ceres (asteroid belt) and Eris (diameter: 2,326 km) (Kuiper belt).


  • Comets are icy frozen gases (water, ammonia, methane and carbon dioxide) which hold together small pieces of rocky and metallic minerals. They have highly elliptical orbits, unlike the planets which have near-circular orbits.
  • Short-period comets, with an orbital period of a few hundred years, originate in the Kuiper belt. Longer period comets, with orbits of thousands of years, come from the more distant Oort Cloud.

  • Oort cloud is a giant shell of icy bodies that encircle the solar system occupying space at a distance between 5,000 and 100,000 AU.
  • When passing close to the Sun, comets heat up due to the effects of the solar wind upon the nucleus and begins to outgas, displaying a visible atmosphere or coma, and sometimes also a tail.
  • One of the larger comets is Halley’s Comet. The orbit of Halley’s Comet brings it close to the Earth every 76 years. It last visited in 1986.

[UPSC Prelims 2011] What is difference between asteroids and comets?

  1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material.
  2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and Mercury.
  3. Comets show a perceptible glowing tail, while asteroids do not.
Which of the statements given above is/are correct?
  1. 1 and 2 only
  2. 1 and 3 only
  3. 3 only
  4. 1, 2 and 3

Meteoroid, Meteor and Meteorite

  • A meteoroid is any solid debris originating from asteroids, comets or other celestial objects and floats through interplanetary space.
  • A meteor, popularly termed a shooting star or falling star, is the streak of light that appears in the sky when a meteoroid enters the atmosphere (mesosphere) at about 200 km at high speed and burns up because of the friction.
  • In some cases, the meteoroid does not burn up completely and makes its way to the Earth’s surface. The surviving chunk is called a meteorite.
  • The circular depression created on the earth’s surface after the meteorite’s impact is called a meteorite crater. Meteorite impacts are common on all planets and moons in the solar system.
  • The most conspicuous meteorite craters can be found on the surfaces of the Moon and Mercury (because they are geologically inactive due to negligible atmosphere).
  • Largest Meteor Crater: A meteor crater in Arizona (USA) is 1,300 m deep and is the largest meteor crater in the world. It was formed over 10,000 years ago.

Chicxulub Crater

  • Chicxulub crater (Mexico’s Yucatan Peninsula) was caused by a meteor impact that is believed to have wiped out the dinosaurs (mass extinction at the end of the Cretaceous 65 million years ago).

Meteorite Craters in India

  • Lonar Lake (a Ramsar Site) (1.8 km in diameter) in Buldhana District of Maharashtra
  • Dhala crater (14 km in diameter) in Shivpuri district, Madhya Pradesh and
  • Ramgarh crater (3.5 km in diameter) is a potential meteorite crater in the Kota plateau in Rajasthan.

[UPSC Prelims 1995] A meteor is:

  1. a rapidly moving star
  2. a piece of mater which has entered the earth’s atmosphere from outer space
  3. part of a constellation
  4. a comet without a tail
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