Objects in Outer-Space

Comets (Sometimes called dirty snowballs or icy mudballs) are really small solar system bodies. They orbit the sun. When a comet is close enough to the sun; it emits a visible coma. As of 1995, we have cataloged over 850 comets. Comets are only visible when they are near the sun. Otherwise, they are invisible.
Asteroids (sometimes also called minor planets or planetoids) are very small solar system bodies. They orbit the sun. They are smaller than planets; but larger than meteoroids. If we add up the entire mass of each and every asteroid; it would be less than our Moon. 11 Asteroids have been explored by spacecrafts, so far. The largest asteroid is 1 Ceres. It is 974 km in diameter and holds about 25% of the mass of all the asteroids combined.
A black hole is a region of space that has a gravitation field so powerful, that even light cannot escape it's pull. A black hole only has a one way surface, which is called an event horizon. Objects can fall into it. But absolutely nothing can come out. Although its very hard to spot a black hole in the universe. It can often be detected due to it's effect on surrounding matter. Black holes started appearing 300-800 million years after the big bang. It's now believed that at the center of nearly every galaxy, there are super massive black holes. These super massive black holes have huge solar masses. The most massive black hole ever found was estimated to have 18 billion solar masses.
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