Asteroids are made of rocky and/or iron-nickel material and most are found in an orbit between Mars and Jupiter. Most are pitted with impact craters and dust left from collisions with other objects in the solar system. A group of asteroids orbit the sun called Near-Earth Asteroids because they are somewhat close to the Earth and occasionally may cross Earth’s orbit.
Any asteroid falling from the sky would have a tremendous amount of energy. Here’s a typical example. In 2028, the asteroid 1997XF11 will come extremely close to Earth but will miss the planet. If something were to change and it did hit Earth, what you would have is a mile-wide asteroid striking the planet’s surface at about 30,000 mph. An asteroid that big traveling at that speed has the energy roughly equal to a 1 million megaton bomb. It’s very likely that an asteroid like this would wipe out most of the life on the planet.
There are obvious craters on Earth (and the moon) that show us a long history of large objects hitting the planet. The most famous asteroid ever is the one that hit Earth 65 million years ago. It’s thought that this asteroid threw so much moisture and dust in to the atmosphere that it cut off sunlight, lowering temperatures worldwide and causing the extinction of the dinosaurs.
The amount of dust and debris thrown up into the atmosphere would block out the sun and cause most living things on the planet to perish. If an asteroid that big were to land in the ocean, it would cause massive tidal waves hundreds of feet high that would completely scrub the coastlines in the vicinity.
In other words, if an asteroid strikes Earth, it will be a really, really bad day no matter how big it is. If the asteroid is a mile in diameter, it’s likely to wipe out life on the planet. Let’s hope that doesn’t happen anytime soon!
Comets are believed to be in long eliptical orbits that take them from beyond the orbit of Uranus to around the sun. These objects are found in the Kuiper Belt between Uranus and Neptune and the Oort Cloud from way out beyond Pluto.
The name “comet” comes from the Greek meaning “long-haired” because of their tails. Chinese astronomers record several observations as well. Comets throughout history have been thought to bring bad luck but these are just natural phenomena of the solar system.
The nucleus of a comet is like a ball of rock and dirty snow. As these objects get close to the sun the frozen gases and dust begin to heat and cause a long tail of vaporized gases, dust and debris to flow behind them. As it melts a cloud of gases and dust forms a coma. The head of the comet is the nucleus and coma together. Because of their orbits we can see them come back from time to time. Halley’s Comet appears about every 76 years, for example.
Meteors, known also as shooting stars, are usually sized from a grain of sand to about a softball. As the meteor enters the Earth’s atmosphere it becomes very hot due to friction like when you rub your hands together for a few moments. They become bright and seem to streak across the sky.
When the Earth enters a meteoroid stream left by a comet it produces a meteor shower. These showers can be predicted and come every year or so. They are named after the constellation that the meteors appear to be coming from.
These meteor showers can have over 100 meteors an hour and be quite spectacular. The best way to view these events are reclining or laying on the ground so you can see the whole sky without neck strain.
Meteors that survive the intense heat of friction with our atmosphere and hit the ground are called meteorites. Scientists have collected over 10,000 meteorites for study. These are made up of parts called Breccia, Carbonaceous Chondrites, Chondrites, and Chondrules.