Category Science

What is the Oort cloud?

Cometary periods range from a few years to even ten million years. It is believed
that most of the long period comets emanate from a region extending beyond the orbit of Pluto to a distance of some 100,000 a.u. which contains the bulk of the comets in the Solar System.

According to the currently accepted theory, there are at least a trillion long period comets in this region referred to as the Oort cloud. Comets in the Oort cloud cannot be detected from Earth. The only comets visible from Earth are those that have highly eccentric orbits which brings them near the Sun.

What causes a comet to swerve from the Oort cloud towards the Sun?

According to the currently accepted theory, passing stars and interstellar clouds quite often disturb the equilibrium of the Oort cloud making some comets change their circular orbits and come near the Sun.

It remains a perpetual phenomenon with old comets dying out and new ones displaced from the Oort cloud appearing.

Name the space-probe that made a rendezvous with two comets.

Space probe Giotto was launched from Earth in 1985 on a fifteen-year mission. In 1986 it flew 600 km of the nucleus of Halley’s Comet, and in 1992 within 200 km of Grig-Skjellerup comet. It flew past Erath in 1990.

Can collision of a planet with a large comet or asteroid occur?

Large comets or asteroids are rare phenomena now and hence the possibility is remote. However, such large bodies were abundant in the early history of the Solar System and there is evidence that major catastrophic collisions did occur. Craters and basins hundred or even thousands of kilometers in diameter have been observed on the Moon, Mars and the large satellites of Jupiter. A large comet or asteroid colliding with a small planet or moon can even completely shatter it. Mimas, one of the moons of Saturn, seems to have barely escaped being completely shattered by such a collision but only half of the original moon exists and the other half has been shattered.

Name a recent planet-comet collision.

In July 1994, the comet Shoemaker-Levy-9 collided with Jupiter. The comet split into fragments before impact, and was closely monitored from Earth and space probes.

Is there any possibility of a comet colliding with a planet like the Earth?

There is a possibility that small comets, or small fragments of large comets, may fall on a planet provided the bodies are close and the gravitational pull is appreciable enough. In such cases, it is likely to burn up in the atmosphere sometimes even resulting in a powerful explosion before the comet hits the Earth.

Has a comet fragment actually hit the Earth in Modern times?

An unprecedented explosion occurred on 30th June 1908 in the largely uninhabited Tunguska valley in Siberia and was heard up to 14,000 km away.  At the explosion site neither was there any crater nor signs of impact but the trees around over an area of 3000 sq. km were flattened. Obviously, it must have had the force of a 2 megaton atom bomb. But no atom bombs existed at that time. Could it have been an exploding comet fragment?

What would happen if a comet collides with the Moon?

Since the Moon has no atmosphere, the comet wouldn’t burn up but would directly hit the surface of the Moon. At the point of impact, a crater would be formed. Such craters can be seen on the Moon even with the naked eye. Even in planets like Earth with an atmosphere, impact craters of comets do occur if the comet did not explode or completely burn out before reaching the surface of the Earth. Such an impact crater has been found at Lonar near Pune in Maharashtra.

Are all craters the result of cometary impacts on Earth?

Craters can be caused by impact of comets or asteroids. About a third of the craters on Earth are caused by long period comets and the rest by asteroids. In the case of those observed on the moons of Jupiter, half are caused by asteroids, a quarter by long period comets and the remainder by short period comets.

Is there a possibility of a large comet colliding with the Earth?

There is some evidence that large comets of about ten kilometers in diameter have hit the Erath in the past creating craters of more than 100 km in diameter. Three such craters have been identified on Earth, and there may be some more on the sea beds. If a large comet hits the Earth it would annihilate most species on Earth. There is evidence of periodic large-scale destruction of planet and animal life on Earth through such collisions.

Which are the comets or asteroids most likely to collide with the Erath?

Some asteroids called Earth grazers regularly pass close to Earth. Asteroid Hermes has passed within 77,000 km from Earth. Other smaller objects may also graze or collide with the Earth. However, with advances in technology, scientists might know well in advances in technology, scientists night know well in advance of any comet or asteroid likely to collide with Earth and deflect or destroy then using rockets and nuclear bombs.

Why was the appearance of a comet conceived to be a bad omen in ancient times?

Ancient people thought that comets caused calamities on Earth. Even in recent times people have been scared that gases from a comet’s tail would poison life on Earth.

Is it possible to see details of comets with the naked eye?

Comets can sometimes be seen with the naked eye. One can even identify their tail and the head. Once in a few thousand years, comets have appeared when even the luminous gas jets have been visible to the naked eye. The ‘swastika’ symbol is believed to be a representation of a comet with multiple gas jets and has been considered an auspicious symbol in many countries from the period of yore. Also the “Menorah” used in Jewish ceremonies is believed to be a representation of a comet with multiple tails.

How does a comet group come into being?

When a comet comes very close to the Sun the nucleus is subjected to various forces due to gravity, heat, pressure within and the force of its jets. Sometimes, these may cause the nucleus to crack up into fragments. If such fragments continue in orbit close together, they are called a comet group. In 1846, the comet Biela was observed to split into two fragments which moved together with each part showing all the characteristics of a comet including head and tail.

Is a comet always visible from the Earth?

A comet normally emits no light of its own and can be seen only when it reflects light from the Sun. since the comets are extremely tiny, they are not visible when they are far from the Sun. A comet, however, develops a vapour cloud for a short period when it is near the Sun, which enables it to reflect more of the Sun’s light and become more visible. The gases in the vapour cloud also emit light when the ultraviolet light from the Sun falls on them. Consequently most of the comets are visible from earth only during a portion of their total period of orbit. However, some short period comets like Encke are always visible through telescopes.

What is the shape of the solid portion of a comet?

The solid portion of a comet is of irregular shape, since its gravitation is too weak to make the material assume a spherical shape as in the case of the planets.

Continue reading “The Solar System”

What is meant by the tail of a comet?

When the solar wind strikes the vapour cloud of a comet, it deflects and scatters the dust and gases, and part of the vapour cloud, with the result that the comet appears to have a ‘Tail”. The size of the tail depends on the density of the dust and gas present in the cloud. The tail is more prominent when the comet is very near the sun.

Is the comet’s tail always situated behind the comet?

The tail is caused by the solar wind which blows from the Sun. hence, the tail always points away from the Sun and has no relation to the direction of motion of the correct. The tail can therefore be at the rear, in front, or at the side of the comet.

How long is the tail of a comet?

Cometary tails can be short or long. However, some comets have been observed to have extremely long tails with the length even exceeding the distance from the Earth to the Sun.

Are there different colours of cometary tails?

Some cometary tails contain very few dust particles and give out a faint  blue light. Some other cometary tails contain a large number of dust particles which reflect the Sun’s light, making the tail appear yellow.

Do cometary tails maintain a constant shape?

Cometary Tails do not maintain a constant shape. Some of such shape changes can be spectacular. Tails may remain straight or curved, or lengthen, or may even detach and disappear. Tails can exhibit bright spots which appear like ‘knots” along the tail. Some comets may even multiple tails.

How dense are the gases in a comet’s tail?

It is usually in the order of less than 1000 gas molecules per cubic centimeter. It is, more or less, close to a perfect vacuum. The tail is consequently almost completely transparent and stars can even be seen through it.

What would happen if the Earth were to pass through the tail of a comet?

In 1910, Halley’s Comet was due to approach the Sun and it was thought that the Earth would pass through the tail of the comet. There was a worldwide scare that poisonous gases in the tail of the comet would annihilate all species on Earth. Conan Doyle, the creator of “Sherlock Holmes”, even wrote a story on this theme called “The Poison Belt”. Bur the density of gases in the comet’s tail is extraordinarily low and is incapable of exerting any noticeable effect on any living creature. Over the millions of years of its existence, the Earth must have passed through the tails of many such comets without any apparent ill effects.