Asteroids, Comets, & Meteoroids
An asteroid is made up of rock, carbon or metal, and orbits the Sun. If it is large, it is called a planetoid, or a Minor Planet. It is formed in the inner solar system, and most are found in the asteroid belt. The largest asteroids are Ceres, Pallas, Vesta, and Hygiea, and the most significant Near-Earth asteroids are Apollos, Amors, and Atens.
A comet is essentially space dirt and chunks of ice, and is formed in the outer solar system. Comets can be predictable if they have been observed and recorded. The most well-known comet is Halley’s Comet, because it circles every 76 years, the next sighting expected in 2062. Other notable comets are Hale-Bopp, which was seen in 1995 and has a 4,200 year cycle, Comet Hyakutake, which was seen in 1996 and only comes around every 9,000 years, and Comet Kahoutek, which was faintly seen in 1973.
A meteoroid is part of an asteroid or comet that is orbiting the Sun. It becomes a meteor when it burns up in Earth’s atmosphere (a shooting star), and a meteorite when it hits Earth.
It is estimated that Earth is hit once a year by an object from space, but we rarely hear about it because the item lands in the water.
However, there is speculation that “dark comets” exist, which do not glow and could escape detection. If one is coming toward Earth, on a direct collision course, we could have little or no warning. These comets don’t glow because as they circle around the Sun, the ice on their surface melts. It is the light reflecting off the ice that helps us see these comets.
Ancient civilizations watched the skies more closely than we do, and thus, it is possible they pinpointed an object coming into Earth’s atmosphere in 2012. NASA agrees that Earth could be hit by a comet, meteorite, or asteroid, but it has a Near-Earth Object Program Office that watches for any threats. So far, they see nothing major that will impact Earth on December 21, 2012.