Comets are said to be the cosmic snowballs of frozen gases and rock and dust that orbit the Sun. When frozen they are the size of a small town along with a tail. The dust and gases combine together and form a tail that stretches away from the Sun for millions of miles. There are likely billions of comets that are orbiting our Sun in the Kuiper Belt and even more distant Oort Cloud. Here, we are going to discover more factors related to this topic that is comet astronomy.
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Size of Comets
The comets phenomena which we are studying are due to the effects of solar radiation and the solar wind that are acting upon the nucleus of the comet. A comet has a nucleus which ranges from a few hundred meters to tens of kilometres across and these are composed of loose collections of ice, and dust, and small rocky particles. A comet is generally said to be up to 15 times the planet Earth's diameter while the tail may stretch beyond one astronomical unit. If sufficiently bright then a comet may be seen from planet Earth without the aid of a telescope and may subtend an arc of 30°.
Composition of Comets
Comets have been observed and recorded as well since ancient times by many cultures. Comets are said to be distinguished from asteroids by the presence of an extended, as well as a gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed as the coma which is the central part immediately surrounding the nucleus and the tail which is a typically linear section consisting of dust or gas blown out from the coma by the light of Sun pressure or out streaming solar wind plasma.
However, we can say that the comets which were extinct that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble asteroids which are small.
As a comet that generally approaches the inner Solar System solar radiation that generally causes the volatile materials which are within the comet to vaporize and stream out of the nucleus which is carrying dust away with them.
Origin and Life of Comets
The origin of comets can be determined from their parameters of the orbital. The comets that take less than 200 years to orbit the star Sun and are thought to originate from the Kuiper Belt. The Kuiper Belt exists beyond the orbit of Neptune and was hypothesised by the Dutch-American astronomer Gerard Kuiper. It’s now thought to contain around 1000 billion comets with it.
Comets with longer periods that are more than 200 years are thought to originate from the Oort Cloud. The Oort Cloud is a spherical cloud of comets that have been orbiting the Sun from over 1.5 light-years from the edge of the Kuiper Belt. This is said to be a third of the distance to the closest star extrasolar which is Proxima Centauri.
Comets vs Asteroids
The asteroids are thought to have a different origin from comets but they have formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between comets and asteroids.
The asteroids earlier were distinguished from comets because they do not have enough capacity of the material of vaporising when they are close to the Sun. And so they do not produce a coma but we can say that the line between asteroids and comets is ambiguous.
This is because comets eventually lose all of their volatile material. They are then called ‘extinct’ comets. The material which is volatile has also been observed on objects in the asteroid belt with water vapour detected on the dwarf planet Ceres in 2014.
Study of Comets
The institute of NASA and the ESA launched the first spacecraft to fly past a comet. The ICE stands for the International Cometary Explorer. It's said to be a primary mission to study the interaction between the Earth’s magnetic field and the solar wind. In 1958, the mission of ICE’s was extended and it flew through the tail of the comet Giacobini-Zinner. It also flew through the tail of Halley’s Comet, a very famous comet which was from a distance of about 28 million km the following year.