Difference between comets, asteroids and meteors

Hyperaxion October 23, 2020 1:58 am

Comets, asteroids and meteors are different objects, but many people are unaware of the basic differences between them.

We routinely hear about asteroids, comets, and meteors in the news and elsewhere. For this reason, it is important to know the characteristics and differences between these objects.


Asteroids are rocky and have no defined shape.
Asteroids are rocky and have no defined shape.

Asteroids are rocky objects, usually metallic, remnants of the violent past of planets, in other words, they are debris originating from collisions between planets, for example.

Most asteroids in the Solar System are located on the asteroid belt, between the orbits of Mars and Jupiter.

They do not have a defined shape or sufficient gravity to be considered a planet (although very large asteroids are often called planetoids).

Most asteroids we know 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 have a long, shiny tail.
Comets have a long, shiny tail.

Comets are usually formed by gas and ice solidified by the low temperatures of space.

When they approach the Sun, they start to exhibit a long and shiny tail, which appears due to the evaporation of its surface when exposed to solar winds.

They can be categorized as periodic or non-periodic comets.

Periodic comets have very elliptical orbits, while non-periodic ones revolve around the Sun in parabolic orbits, and return to the Sun’s vicinity only once in thousands of years.


Meteorites reaching the Earth's surface.
Meteorites reaching the Earth’s surface.

As we said earlier, a meteoroid is an asteroid less than a kilometer in diameter. When a meteoroid enters the Earth’s atmosphere, it is called a meteor. Meteors have a shiny tail and are often called shooting stars.

Meteors enter the atmosphere at high speeds (around 250,000 kph or 155,342 mph). Consequently, air friction and the resulting high temperature normally destroy most smaller meteors, producing small debris, called meteorites.

Facts about comets, asteroids and meteors that you may not know

  • Whenever a periodic comet orbits at distances close to the Sun, its mass is decreased by the process of sublimation of the ice (sublimation: a transition from solid directly to the gas state).

    Intense solar radiation is responsible for transforming the comets’ ice, formed by water, methane, ammonia, and carbon dioxide, into gases, which form their long tails. That is why any comet can simply disappear after a few thousand years.

  • Halley’s Comet is one of the most famous comets. It completes an orbit around the Sun every 76 years.
  • Every comet has a small atmosphere called a coma, which is formed by the sublimation of gases due to solar radiation. The coma extended by the solar wind forms the comet’s tail.
  • Millions of meteoroids enter the Earth’s atmosphere daily, however, very few manage to reach us. Most are destroyed due to the friction from the air.
  • It is estimated that about 100 tons of comets and asteroids fall towards Earth every day.
  • Astronomical data indicates that, throughout its cosmological history, the Earth was hit by asteroids the size of a soccer field, on average, every 2000 years.
  • Every year a car-sized asteroid enters the Earth’s atmosphere, however, few are able to reach the Earth’s surface.
  • Some asteroids are so massive that they can even have their own moons.
  • One of the largest and most famous asteroids in the Solar System is called Ceres. It is commonly classified as a planetoid because of its 476 km (296 miles) radius.
  • It is estimated that every 10 million years the Earth is hit by asteroids over 5 km (3 miles) long.
  • The last major asteroid impact event on Earth happened about 65 million years ago. This particular event marked the end of the Cretaceous Period, extinguishing much of life on Earth. The asteroid involved in this event was 10 to 15 km (6 to 9 mi) wide.
  • A car-sized asteroid hits the Earth’s atmosphere with an energy similar to the explosion produced by the atomic bomb dropped in Hiroshima, Japan: about 15 kilotons, equivalent to the detonation of 15 thousand tons of dynamite.
  • In 1908, in Tunguska, Russia, an asteroid of about 65 meters destroyed an enormous forest region of 2150 square kilometers (830 square miles). The asteroid in question did not actually hit the ground.

    All the destruction was caused by an air burst due to the asteroid’s explosion 5 to 10 kilometers above the surface, releasing the energy of a thousand nuclear bombs: 30 megatons.

  • A meteorite called Hoba was found in Namibia, on the African continent. It hit Earth 80,000 years ago, and its mass, consisting mainly of nickel and other metals, is around 60 tons.
  • The speed of the asteroid in the Earth’s atmosphere depends heavily on its shape, however, there are cases when these objects reach us at speeds higher than 72 kilometers per second, about 259,000 kph (160,000 mph).
  • The Purdue.edu website offers interactive simulations to calculate the effect of the impact of asteroids on Earth.

If, like us, you are passionate about astronomy, you will surely love any of the following books:


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