Difference between Asteroid and Comet

The universe is full of celestial bodies, like asteroids, comets, meteoroids and meteors. They are time capsules, which provide historical information about the formation of the universe and its constituents. The main difference between an asteroid and a comet lies inside their composition. Both these celestial bodies are made up of leftover debris when a planet or a moon forms.

As scientists have located it, comets are found in the outermost region of our solar system. In contrast, asteroids are found between Mars and Jupiter. One or two asteroids are not found between Mars and Jupiter, but the entire asteroid belt is found between these two planets. Some say dinosaurs got extinct due to the collision of an asteroid with the Earth. The craters on the moon are also formed due to the falling of asteroids on the moon’s surface.

Asteroids

An asteroid is defined as a minor planet that revolves around the Sun. They do not revolve around the Sun in a circular orbit but revolve around the Sun due to their lightweight. Large asteroids are often termed planetoids. According to scientists, millions of asteroids exist in the solar system. Their sizes vary from a small rock to a gigantic planet.

The first asteroid discovered was Ceres, misinterpreted as a planet. Sir William Herschel was the first astronomer to use the term asteroid, coined from the Greek term, asteroeides, meaning star-like. Till today, millions of asteroids have been found.

Asteroids are mainly composed of minerals and rock. They are rich in carbon, metals and silica. The sizes of asteroids vary greatly. The largest asteroid found to date is approximately 1000 km big. It means we can assume it is a tiny planet.

Only one asteroid is visible to the naked eye, 4 Vesta, which has a reflective surface. The asteroids that may pass close to the Earth can at times be seen with the naked eye, but for a short period.

International Asteroid Day is observed on June 30 every year to educate people about asteroids. According to Stephen Hawking’s book, Brief Answers to the Big Questions, an asteroid collision is the biggest threat to the planet.

Comets

A comet is a small celestial body, ice-like, warms and releases gases when it gets closer to the Sun. The process of releasing gas is called outgassing. This release of gas can be seen in the sky in the form of a comet tail. The same phenomenon is used to describe solar radiation and solar wind.

The term comet is derived from a Latin word, cometa, meaning wearing long hair. Their size ranges from a few meters to tens and hundreds of kilometres. They are made up of ice, small rocky particles, dust, carbon dioxide, carbon monoxide, methane and ammonia. The tail can be up to 15 times that of the Earth’s diameter. One tail can be as long as one astronomical unit.

Comets can be seen from the naked eye and with a telescope as well. Most comets are found near the Kuiper belt, near Neptune’s orbit. However, some comets are also found near the nearest star to the Earth.

Comets differ from asteroids by the atmosphere surrounding their nucleus. The central part of the main body of a comet is known as a coma. At the same time, the gaseous part is known as a tail. To date, there are approximately 4500 known comets. However, the numbers are very small as compared to reality. A few known comets are:

Name	Dimensions (km)	Density (g/cm³)	Mass (kg)
Halley's Comet	15 × 8 × 8	0.6	3×10¹⁴
Tempel 1	7.6 × 4.9	0.62	7.9×10¹³
19P/Borrelly	8 × 4 × 4	0.3	2.0×10¹³
81P/Wild	5.5 × 4.0 × 3.3	0.6	2.3×10¹³
67P/Churyumov–Gerasimenko	4.1 × 3.3 × 1.8	0.47	1.0×10¹³

Difference between asteroids and comets

The tail of the comet is illuminated by the Sun. It is visible when the dust particles of the comet reflect the sunlight. In addition, the gases glow due to ionization. Sometimes, comets can experience sudden outbursts, due to which the size of the comet increases. In 2007, it was seen the last time in Comet Holmes.

Asteroid	Comet
Asteroids are found near the orbits between Mars and Jupiter.	Comets are found near the orbit of Neptune.
They are made up of carbon, silica, metals, dust and rock.	They are made up of carbon dioxide, carbon monoxide, ammonia, dust particles and methane.
The size of the asteroid ranges from a meter to 1000 km.	The size of a comet ranges from a rock to tens of kilometres.
They have only one solid mass, resembling the shape of a planet.	The main body of a comet is known as coma, while its gaseous burnout is known as tail.
Examples: 4 Vesta, Ceres	Examples: Halley, Temple 1, Holmes