The Planets and Other bodies in the Solar System

Comets

Comets are objects with leading heads and bright tails in the sky. Sometimes they can be seen at night. They are composed mainly of rock, ice, dust, and frozen gases. A combination of all of these components gives the comet a shiny appearance. As the comet passes near the sun, it leaves a tail of dust. Comets orbit around the sun far beyond the limits of Pluto (Fig 1.4). They can be seen from the Earth only when their orbits overlap that of the Earth. This is because other times their orbits are very far away.

Asteroids

Asteroids are solid heavenly bodies revolving around the sun, but are too small to be called planets. Tens of thousands of these minor planets are gathered between the orbits of Mars and Jupiter. The largest asteroid has a diameter of just less than 800 kilometres. These bodies can only be seen with a telescope because they are very far away from the Earth.

Asteroids are found in a portion of the solar system called asteroid belt. As the name suggests, this is a belt where asteroids are most likely to occur. The section is found between Mars and Jupiter. The largest of the existing asteroids is called Ceres, with a diameter of approximately 930 kilometres.

Meteors

Meteors are pieces of hard matter falling from outer space. They can be seen when they come close to the Earth, at about 110-145 kilometres above the Earth’s surface, whereas as a result of friction with the atmosphere, they become hot and usually disintegrate. But when they don’t disintegrate completely in passing through the atmosphere, they teach the Earth's surface as large boulders known as meteorites. These bodies are usually made of nickel, iron and silica. Sometimes meteors reach the Earth’s surface with such a force that they make large holes or craters called meteor craters.

Natural satellites

A natural satellite or moon (in the most common usage) is an astronomical body that orbits a planet or minor planet (or sometimes another small solar system body).

The largest known satellite is the moon. Other planets also have large moons, e.g., Jupiter’s Galilean moons (Ganymede, Callisto, Io, and Europa), Saturn’s moon (Titan) and Neptune’s moon (Triton).

Four dwarf planets are also known to have natural satellites: Pluto (Charon, Hydra, Nix, Kerberos, and Styx); Haumea (Hiʻiaka and Namaka), Makemake [S/2015 (136472) 1]; and Eris (Dysnomia). As of January 2012, over 200 minor-planet moons have been discovered.

Most of the 178 known natural satellites are irregular moons, while only 19 are large enough to be round. Ganymede, followed by Titan, Callisto, Io and Earth's Moon are the largest natural satellites in the solar system.

There are two known meteorites in Tanzania. One is found in Mbozi district in Mbeya region and another is in Malampaka in Kwimba district of Mwanza region. These meteorites fell from space and reached the Earth in 1930 and they formed large holes on the Earth’s surface.