Who's ready to explore more space?  If you've joined Squeaks and me here recently, then you already know about the biggest objects in the solar system, which is made up of the sun, the earth, and seven other planets.  The four planets that are closest to the sun, including Earth, are small, solid, rocky worlds.  Those are called the rocky planets.  And the four planets farther away from the sun are much bigger.  They are made mostly of gasses - those are the gas giants.  But there's a lot more in our solar system then just those eight planets.  There are also things like comets and asteroids.  They're a lot smaller, but they're just as interesting.  And they both have one main thing in common - they're basically flying space rocks.  

Let's talk about comets first.  The word comet comes from the Greek word for hairy because some astronomers once referred to comets as hairy stars.  But why?  A comet isn't a star at all, and it doesn't have hair.  It's really a chunk of ice, dust, and rock.  Think of it as like a big dirty snowball in orbit around the sun.  As a comet gets closer to the sun, it's frozen gasses and dust begin to warm up and thaw out.  The gas and dust start to break apart and stream behind the comet, making it look like it has, well, a big hairy tail.  

Our solar system's most famous comet is probably the one known as Halley's Comet.  It's named after English astronomer Edmond Halley, who figured out what it really was.  He had read reports about three comets that were seen flying by the earth many years apart.  But Halley figure out that these three comets were actually the same comet flying past us over and over again.  Based on when the comet had passed by the earth in the past, he predicted when it would come by again - and he was right.  Halley's Comet has been spotted from earth every 75 years or so.  The last time it came close was 1986, meaning we'll probably see it again in 2061.  How old will you be then?  

Now, comets have really bit orbits and spend a lot of their time in the far outer reaches of our solar system.  So let's talk about rocks that come a little closer to the earth - asteroids.

Most asteroids are found between the planets Mars and Jupiter in an area called the asteroid belt.  There are a lot of asteroids cruisin' around in the asteroid belt, but most of them are spaced really, really far apart.  Asteroids sort of look like comets, but they don't have fuzzy outlines or tails.  Actually, they look a lot more like tiny planets - in fact one famous asteroid named Ida even has it's own moon, called Dactyl.  Asteroids are basically broken pieces of unfinished plants left over from the time when the solar system first formed.  They're mostly big chunks of rock with metals in them too.  And as they fly around out there in the asteroid belt they often crash into each other.  Sometimes an asteroid will get bumped clear out of the asteroid belt.  They can even get knocked in our direction.  

If a flying space rock enters the earths atmosphere, which is what we call the layer of gases that surround our planet, it will start to burn up.  Then it's called a meteor - a really fast streak of light that flies through the sky.  You might have heard this called a shooting star, but now you know it's not a star at all.  Most meteors burn up completely before they reach the surface of the earth, but if a hunk of rock is big enough then some of it might still be left by the time it reaches the ground.  What happens if one of these flying space rocks hits our planet?  If that happens then it's called a meteorite.  Most meteorites are still pretty small.  You could probably hold an average size meteorite in your hand.  But very rarely Earth can get hit by a rock that's pretty big.  In fact, most scientists think that a really big meteorite that hit the earth millions of years ago led to the extinction of the dinosaurs.  But don't worry.  Most flying space rocks stay where they are - in space.  

Now who wants to go in the backyard and watch for meteors?  Me too!  See you next time for more SciShow kids.  And remember, if you have a question for any of us here at the fort, let us know by leaving a comment below or emailing us at kids@thescishow.com.