Sunday Science: Asteroids, Meteors and Comets

Asteroid 2017 BQ6. Image courtesy of NASA/JPL-Caltech/GSSR.

As an asteroid affectionately known as "The Rock" soared past Earth recently, I thought it's time to tackle the differences between some very similar astronomical objects: asteroids, meteors and comets.​

Let's start with asteroids and comets.

Both asteroids and comets are chunks of space debris (usually rocks covered in ice) that orbit around the Sun.

But they come from different places.

Asteroids are rocky, inactive objects that are formed in the warm inner solar system region between the planets of Mars and Jupiter.

Comets are mostly made up of ice embedded with dust particles. They are formed further out, in the colder outer reaches of our Solar System. 

A comet's ices can vaporise in sunlight forming an atmosphere of dust and gas. This atmosphere (also known as a coma) sometimes forms the tail of dust and/or gas you often see trailing behind a comet.

If an asteroid or a comet is nudged out of its orbit by the gravitational pull of the other planets in our solar system, they can pass close to the Earth. 

What about meteors?

OK, this is where we have to introduce three more terms: meteoroid, meteor and meteorite.

A meteoroid is, basically, a tiny piece of space debris. It could be a small asteroid, which forms when bigger asteroids collide, or the debris from a comet, which is formed when a comet passes near the Sun and releases debris that was once embedded in the (now melted) ice of the comet. 

When a meteoroid enters the Earth's atmosphere it burns up, causing a flash of light and is now known as a meteor.

A meteor also goes by another, more common, name - it's a shooting star.

If any of the meteor is not burnt up in the atmosphere and survives its descent to the Earth to land on its surface, then it is known as a meteorite. 

Here's a quick picture from tes.com to help differentiate these cosmological entities:

Extra reading

We know a lot more about comets thanks to ESA's Rosetta mission and there's plenty of information on the differences between comets, asteroids and meteoroids here.

You can find out more about comets here and asteroids here. Or, click here to find out how to catch a meteorite.

​And if you'd like to know what would really happen to you if an asteroid hit Earth, this article is quite shocking.

What is Sunday Science?

Hello. I’m the freelance writer who gets tech. I have two degrees in Physics and, during my studies, I became increasingly frustrated with the complicated language used to describe some outstanding scientific principles. Language should aid our understanding — in science, it often feels like a barrier.
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So, I want to simplify these science sayings and this blog series “Sunday Science” gives a quick, no-nonsense definition of the complex-sounding scientific terms you often hear, but may not completely understand. 

If there’s a scientific term or topic you’d like me to tackle in my next post, fire an email to [email protected] or leave a comment below. If you want to sign up to our weekly newsletter, click here.