What is a NEO?
A NEO (near-Earth object) is an asteroid or comet that comes within 50 million kilometers (30 million miles) of Earth’s orbit, representing a possible danger to our planet.
Using the cut-off for asteroid diameter of 1 meter, there are estimated to be more than half a billion near-Earth asteroids. Although more than 30,000 of these have already been discovered, that represents only a small fraction of the total. But because it’s easier to find larger objects, we think we have found more than 90% of the asteroids 1 kilometer (0.6 miles) and above. The biggest threats to our planet are the least likely to sneak up on us, but there are still many smaller asteroids lurking in the darkness of space that could still be dangerous to us.
Planetary defense is the effort to find, track, and characterize near-Earth objects and prepare technologies for deflecting them in case one is ever headed our way.
What is a meteoroid?
A meteoroid is a rocky or metallic object in space with a diameter of less than 1 meter (3.28 feet). Very tiny meteoroids — with mass smaller than 1 gram or so — are often called micrometeoroids or space dust.
What is a meteorite?
If part of a meteoroid, asteroid, or comet makes it to the ground, it is called a meteorite.
What is a meteor?
A meteor is the streak of light that occurs when an object (e.g., an asteroid or meteoroid) hits the Earth’s atmosphere at high speed causing the object to heat up and glow.
Meteors are also known as shooting stars, although they aren’t actually stars at all.
Meteor showers happen when the Earth passes through debris shed by a comet or asteroid. They reoccur at about the same time every year when Earth comes around in its orbit and passes through the debris again.