Modern Physics

Difference between comet, asteroid and meteor

Comets, asteroids and meteors are distinct and commonly cited objects in our daily lives. There are basic differences between them.

It is common to hear about asteroids, comets and meteors in various places. For this reason, it is interesting to know what each of them is and what their characteristics are.


Asteroids are rocky bodies , usually metallic, remnants of the violent past of the planets, that is, they are debris originated from collisions between planets, for example.

Most asteroids in the Solar System are located between the orbits of Mars and Jupiter , do not have a defined shape or gravity enough to be considered a planet (very large asteroids are often called planetoids). Most asteroids in the Solar System are about a kilometer in diameter, but some can reach hundreds of kilometers. Small asteroids, usually less than a kilometer in diameter, are called meteoroids.


Comets are generally formed by gases and ice solidified by the low temperatures of space. When they approach the Sun , they start to display a long and bright tail, which appears due to the evaporation of its surface when exposed to solar winds. They can be divided into periodic and non-periodic comets: the first ones have very elliptical orbits around the Sun, and the non-periodic ones describe approximately parabolic orbits, being able to return to the vicinity of the Sun only in thousands of years, if they return.


When a meteoroid enters the Earth’s atmosphere, it is called a meteor . Meteors have a bright tail and are often called shooting stars . The high speed (about 250,000 km/h) with which meteors enter the atmosphere together with friction with the air normally destroys most smaller meteors, producing small debris, the so-called meteorites.

In the figure, we have an illustration that shows some meteorites reaching the Earth’s surface.

Facts about comets, asteroids and meteors

  • Whenever a periodic comet orbits at distances close to the Sun, its mass is diminished by the process of ice sublimation (sublimation: going directly from a solid to a gaseous state). Intense solar radiation is responsible for transforming the ice of comets, formed by water, methane gas, ammonia and carbon dioxide, into gases, which give rise to their long tails. It is for this reason that every comet can simply disappear after a few thousand years.
  • One of the most famous known comets is Comet Halley . It completes one orbit around the Sun every 76 years.
  • Every comet has a small atmosphere called a coma, which is formed by the sublimation of gases by solar radiation. The coma extended by the solar wind forms the tail of comets.
  • It is known that millions of meteoroids enter the Earth’s atmosphere daily, however, very few manage to reach us because of their great speed and great friction with the Earth’s atmosphere.
  • It is estimated that around 100 tons of comets and asteroids fall towards Earth every day.
  • Astronomical data indicate that throughout its cosmological history, Earth has been hit by asteroids the size of a football field, on average, every 2000 years.
  • Every year an asteroid similar in size to a passenger car enters the Earth’s atmosphere, however, those that manage to reach the Earth’s surface are rare.
  • Some asteroids are so massive they may even have their own moons.
  • One of the largest and most famous known asteroids in the Solar System is called Ceres. It is commonly classified as a planetoid because of its length of 952 kilometers.
  • It is estimated that every 10 million years the Earth is hit by asteroids more than 5 kilometers across.
  • The last major asteroid impact event with Earth happened about 65 million years ago. This particular event marked the end of the Cretaceous Era, extinguishing much of terrestrial life. The asteroid involved in this event was about 10 kilometers long.
  • An asteroid similar in size to a passenger car hits the Earth’s atmosphere with energy similar to that of the explosion produced by the atomic bomb dropped on Hiroshima, Japan: about 15 kilotons, the equivalent of the detonation of 15,000 tons of dynamite.
  • In 1908, in Tunguska, Russia, an asteroid of a few tens of meters destroyed a huge forest region of 2150 square kilometers (an area the size of the Azores archipelago). The asteroid in question did not actually collide with the ground. All the destruction was caused by the air displacement of the asteroid, which exploded between 5 and 10 kilometers high, with energy close to a thousand nuclear bombs: 30 megatons.
  • A meteorite called Hoba was found in Namibia, on the African continent. It fell to Earth 80,000 years ago, and its mass, consisting mainly of Nickel and other metals, is about 60 tons.
  • The speed of entry of asteroids into Earth depends a lot on their shape, however, there are cases in which these bodies reach us with speeds greater than 72 kilometers per second, about 259,000 km/h.
  • offers interactive simulations to calculate the effect of an asteroid impact on Earth.

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