Matter

In space matter occurs in clumps which are held together by gravity. These clumps may be stars, planets, satellites, asteroids, comets, etc.

• Planets:A planet is an astronomical object orbiting a star or stellar remnant that
  • is massive enough to be rounded by its own gravity,
  • is not massive enough to cause thermonuclear fusion, and
  • has cleared its neighbouring region of planetesimals.

• Star:A star is a luminous sphere of plasma held together by its own gravity.

• Asteroids:Asteroids are minor planets. The larger ones have also been called planetoids.

• Satellite:A natural satellite, or moon is a celestial body that orbits another celestial body of greater mass (e.g. a planet, star, or dwarf planet), called its primary.

• Comet:A comet is an icy small Solar System body that, when passing close to the Sun, heats up and begins to outgas, displaying a visible atmosphere or coma, and sometimes also a tail.