Asteroids

Asteroids are marvelous celestial objects, not only because they played a huge role in water formation on Earth through various collisions with Earth's surface, but because they are so complex. Asteroids are irregularly shaped, rocky objects that usually are considered small objects or minor planets. They are rocky fragments that were left over from 4.6 billion years ago when the solar system formed. 

 The average asteroid is very complex because it has a diameter of 20 km, a density of 0.3 g/cm^3, and an albedo of less than .05. They also have an average surface temperature of 100 degrees Fahrenheit. 

 Asteroids are also very interesting because they fall into three different categories based on their compositions; C-type (carbonaceous) asteroids, S-type (sillicaceous) asteroids, and M-type (metallic) asteroids. C-type asteroids are greyish and are the most common asteroids. They make up 75 percent of all known asteroids in the solar system. S-type asteroids are reddish and greenish in color and they make up 17 percent of all known asteroids. M-type asteroids are red in color, consist of mostly nickle, and are located mostly in the middle of the asteroid belt. 

 Asteroids orbit the Sun in elliptical orbits in the asteroid belt that is located between Mars and Jupiter. The asteroid belt is made up of many different sized asteroids. The asteroid belt holds more than a million asteroids, of which 200 are larger than 60 km in diameter and 750,000 are larger than 1 kilometer in diameter. Half of the mass that is found in the asteroid belt comes from the four largest asteroids. The four largest asteroids are Ceres, Vesta, Pallas, and Hygiea. 

 The total mass of all the asteroids in the solar system is less than the mass of the Moon, but asteroids are still very dangerous. Many asteroids collided with the Earth in the past. The asteroids that collided with the Earth, depending on their sizes, caused great amounts of damage. Therefore many astronomers study the orbital paths of asteroids and believe that these earlier collisions, together with earlier comet collisions, contributed to water formation on Earth's surface.