An asteroid is a rock that orbits the Sun. Most asteroids are found in the asteroid belt, which is between Mars and Jupiter. Some asteroids are found outside the asteroid belt and their orbits can take them close to Earth (yikes!). How big does a rock need to be in order to be classified as an asteroid? There is no definite cut off- some asteroids are a mere few meters in diameter, while the largest asteroid, Ceres, is almost 600 miles wide – but asteroids are generally at least a few meters wide. Smaller rocks and particles are meteoroids.

Comets, like asteroids, orbit the Sun, but consist of ice and dust, not rock. The ice core of comets can vaporize due to sunlight and can form a coma and a bright tail. Note that a comet tail does not trail behind it – instead due to gravity the comet tail points towards the Sun.

Like asteroids, meteoroids are rocks and particles that orbit the sun but are a lot smaller than asteroids. Meteoroids are often pieces of asteroids that have broken off due to collisions but can be from comets or other bodies. Meteoroids can be very small – sometimes just a few millimeters wide.

A Meteor is a meteoroid that enters Earth’s atmosphere and burns up due to the friction of wind resistance. Meteors cause streaks of light in the night sky and are also referred to as “shooting stars.”

Meteorites are meteoroids that don’t completely burn up in the atmosphere and strike the Earth. How many meteorites strike the Earth? According to the Planetary Science Institute,

To date, there have been nearly 1,100 recovered falls (meteorites seen to fall) and nearly 40,000 finds (found, but not seen to fall). It is estimated that probably 500 meteorites reach the surface of the Earth each year, but less than 10 are recovered. This is because most fall into the ocean, land in remote areas of the Earth, land in places that are not easily accessible, or are just not seen to fall (fall during the day).

Some Really Interesting Facts from NASA:

• Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.

• About once a year, an automobile-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface.

• Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area.

• Only once every few million years, an object large enough to threaten Earth’s civilization comes along. Impact craters on Earth, the moon and other planetary bodies are evidence of these occurrences.

• Space rocks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth’s atmosphere and cause little or no damage.

• If a rocky meteoroid larger than 25 meters but smaller than one kilometer ( a little more than 1/2 mile) were to hit Earth, it would likely cause local damage to the impact area.

• We believe anything larger than one to two kilometers (one kilometer is a little more than one-half mile) could have worldwide effects. At 5.4 kilometers in diameter, the largest known potentially hazardous asteroid is Toutatis.

Now for Something Really Crazy

A Bosnian man, Radivoke Lajic, claims that meteorites have struck his house six times! Mr. Lajic has concluded: “I am obviously being targeted by extraterrestrials. I don’t know what I have done to annoy them but there is no other explanation that makes sense. The chance of being hit by a meteorite is so small that getting hit six times has to be deliberate.”