Comet? Meteor? Asteroid? So many names for bits of rock in space! But did you know that the words actually mean very specific things? Here’s a quick vocab lesson so that the next sci-fi story you write has accurate science in it!
Planet: Most people know what a planet is, but the word has very specific definition (or meaning). Most importantly, a planet is not a star. Then, a planet must meet these conditions: 1) it must revolve around a star, 2) it must be large enough so that gravity crushes it into a round shape, and 3) it must have cleared the area around its path of other objects in space.
Dwarf Planet: A “dwarf planet” is like a planet but it hasn’t cleared the area around it of other space junk. In our solar system, Pluto is a dwarf planet
Asteroid: Asteroids are like small planets, in that they are hunks of rock that orbit, or revolve around, stars. They don’t fulfil all the conditions to be a planet or a dwarf planet. For example, they are often irregular in shape. Unlike objects like comets, they do not have a tail.
Comet: Comets are another type of rocky object that orbit stars. They are smaller than planets. The main feature of comets is that in addition to rock, they contain different types of ice that heat up, vaporize (or turn into gas) and shoot out and when the comet approaches a star. This gas either forms a mini layer around the comet, or a tail that is sometimes visible on Earth!
Meteoroid: An even smaller lump of rock that orbits a star. Like asteroids, they do not have a tail
Meteor: A meteor is a “shooting star”. When a meteoroid enters Earth’s atmosphere (the layer of gas that surrounds Earth), it burns up, producing light: this is a meteor. It’s different from a comet, because a comet doesn’t usually enter the Earth’s atmosphere.
Meteorite: After a meteoroid enters the Earth’s atmosphere, most of it burns up. However, some of it may survive and crash into the Earth. This part is known as a meteorite. Many ancient peoples used iron found in meteorites to make tools and weapons!
If you want to learn more about space, check out some of our other articles:
Where we Got Our Information
The International Astronomical Union, https://www.iau.org/static/archives/releases/doc/iau0603.doc
The European Space Agency, http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions