How many astronomical objects do you know about? A comet is one of the astronomical objects which is a small body of the solar system. Let’s dig in and find out more about comets.
LEARNING OBJECTIVES
By the end of this topic, you are expected to;
A comet refers to an icy, small body of the solar system that, when passing near the sun, warms and starts to release gases. This process is known as outgassing. This produces a coma, or a visible atmosphere, and sometimes a tail is also produced. These phenomena are as a result of the solar wind and the solar radiation acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and they are made up of loose collections of dust, ice and small rocky particles. The coma may be up to 15 times the diameter of the earth. The tail may stretch one astronomical unit. If sufficiently bright, it is possible to see a comet from the earth without the help of a telescope.
Comets normally have highly eccentric elliptical orbits and have a wide range of orbital periods that range from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, lying beyond the orbit of Neptune. Long-period comets are said to originate in the Oort cloud. This is a spherical cloud made up of icy bodies that extend from outside the Kuiper belt to halfway the nearest star. Long-period comets are set in motion towards the sun from the Oort cloud by gravitational perturbations that are caused by passing stars and the galactic tide.
Comets can be differentiated from asteroids by the presence of an extended atmosphere that is gravitationally unbound that surrounds the central nucleus of a comet.
PHYSICAL CHARACTERISTICS
NUCLEUS
The nucleus refers to the solid, core structure of a comet. Cometary nuclei are made up of an amalgamation of dust, rock, water ice and frozen ammonia, methane, carbon dioxide and carbon monoxide.
The general appearance of the surface of the nucleus is dry, rocky and dusty. This suggests that ices are hidden beneath the crust. In addition to the gases mentioned above, the nuclei also contain several organic compounds like ethane, ethanol, hydrogen cyanide and methanol.
COMA
The streams of dust and gas that are released from a comet form an extremely thin atmosphere around the comet and it is known as the coma. The force exerted on the coma by the solar wind and radiation pressure of the sun causes a big tail to form that points away from the sun.
The coma is generally composed of water and dust. Water makes up to 90% of the volatiles outflowing from the nucleus when the comet is within 3 to 4 astronomical units of the sun.
TAILS
Comets remain inactive and frozen in the outer solar system, this makes it extremely difficult to detect from the earth due to their small size. As a comet approaches the inner solar system, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, they carry dust away with them. The streams of dust and gas each form their own distinct tail. These tails slightly point in different directions.
ORBITAL PERIODS
Many of the comets are small bodies of the solar system with elongated elliptical orbits that take them close to the sun for a part of their orbit and then out into the further reaches of the solar system. Comets are mainly classified depending on the length of their orbital periods. The longer the period, the more elongated the ellipse. We have; short period and long-period comets.
EFFECTS OF COMETS
They include;
FATE OF COMETS
Some of the fates of comets include;
