[잠깐과학] Asteroids vs comets, visitors to Earth : Donga Science

Asteroids and comets that sometimes come close to Earth and make people nervous! Astronomers always keep a close eye on the movements of the two bodies to prevent them from colliding with the Earth. What is the difference between an asteroid and a comet?

● Asteroid

An asteroid is a celestial body orbiting the sun that is smaller than a planet. Asteroids were created when the solar system was forming 4.6 billion years ago. Due to their small size and lack of gravity, they do not combine into planets and mainly orbit between Mars and Jupiter. This is called the asteroid belt.

An asteroid that falls to Earth and is found on the surface is called a meteorite. Scientists use meteorites to determine the composition of asteroids. Asteroids are rocky masses of carbon, silicon and metals. Unlike comets, they contain very little volatile material and are therefore dense. They differ from comets in that they have no coma or gaseous tail.

An asteroid with a diameter of more than 140m and approaching within about 7.5 million km of Earth is called a ‘potential threat asteroid’. If this asteroid were to collide with Earth, it could destroy an entire area. Because of this, scientists devise strategies to prevent collisions, such as applying physical shocks to asteroids to change their orbits.

Comet. Courtesy of Wikipedia

● Comet

A comet is a celestial body made of ice and dust. Like asteroids, they were formed when the solar system was forming. Comets are similar in size to asteroids, but are less dense because the empty space between the ice is filled with gas. The comet’s nucleus is small, several kilometers long, and looks like a faint spot when it is far from the sun, but forms a long tail as it gets closer to the sun.

Why do comet tails appear? The nucleus of a comet is a solid mass made up of volatile matter. When a comet approaches the sun, the surface of the nucleus evaporates, enveloping the nucleus in a giant gas called ‘coma’. Dust in the coma is then pushed back by the solar wind, which forms the tail of the comet.

The comet’s home is known as the ‘Oort Cloud’, which surrounds the most distant part of the solar system. The Oort Cloud contains pieces of ice and dust, and when it escapes from the cloud under the influence of a celestial body that passes by the cloud, it becomes a comet as it approaches the sun.