Artem has a doctor of veterinary medicine degree.
The Peculiarities of Meteorites
Look at the image on your screen:
What you see is the stereotypical meteorite shown in movies and TV programs. It's big, it's scary, and sort of ugly, although oddly entrancing. But the truth of the matter is less scary than Hollywood. A typical meteoroid, which is a small piece of rock or dust floating in space that may one day enter Earth's atmosphere, has a mass that's about that of a paper clip. That's puny!
I hope you thought that was a pretty interesting little fact. I've actually got an even more interesting little fact for you about meteoroids in this lesson, one about the origin and orbit of meteoroids.
Meteor Showers and the Radiant
If you didn't know already, then you should know that a meteoroid (space dust or rock) produces a meteor when burning up through Earth's atmosphere. If it survives its fall through Earth's atmosphere and hits the ground, it is known as a meteorite.
Let's get on with this lesson then.
If you were to strike a match, it would glow as it burns. If you moved that match through the air, it would produce a trail of smoke behind it. That trail of smoke could give you a clue from which direction you moved the match. When a meteor enters the earth's atmosphere, it also produces a trail, one that can provide clues as to where it came from.
The direction and speed of a meteor can be used to figure out its orbit before entering Earth. One way to do this is to watch for meteor showers. A meteor shower refers to many meteors appearing to come from the same point in the sky over a few hours or days.
The point in the sky from which meteors all seem to come from during a meteor shower is called the radiant, and a meteor is the brief but very bright trail observed in the sky as a small piece of space dust or rock (a meteoroid) enters Earth's upper atmosphere.
The constellation from which a meteor shower seems to radiate gives the meteor shower its name, but the key point here is that the radiant is nothing more than illusion. The meteoroids don't come from that constellation. You'll find out where they come from in a little bit.
One of the most famous meteor showers is the Perseid shower that appears in August. That meteor shower radiates from the constellation Perseus. The reason that the meteors all seem to come from one point in the sky is because they must have been traveling through space in parallel paths.
It's like you standing in the middle of the highway, watching cars traveling in parallel paths on a highway. It will appear that the cars are all coming from the same point on the horizon.
What's a Comet Got to Do With It?
So, I promised in my intro I'd tell you a pretty nifty thing. Meteor showers form thanks to none other than - comets! Yep, it's comets that are responsible for meteor showers. Weird, huh? Tina Turner would surely ask: What's a comet got to do with it?
Well, Tina (or anyone else listening), a comet is basically just a ball of ice and dirt. As a comet orbits the sun, it will shed away dust and other debris from its icy nucleus. This forms a cloud of dust in essentially the same orbit as their parent comet for a long time thereafter.
This cloud, or comet debris, is one of the origins of meteoric material! As Earth passes through this cloud of dust and debris and that comet's orbit around our sun, you get yourself a nice meteor shower!
For example, every October, Earth will pass near the orbit of the famous comet Halley, and we get ourselves a nice Orionid shower.
But you don't always have to wait for a meteor shower to see a meteor. Sporadic meteors, meteors not part of a meteor shower, can be seen on occasion as well.
A few of these sporadic meteors come from the asteroid belt and are thus large and strong enough to survive their fall through Earth's atmosphere to become a meteorite. Meaning, the meteorites we find on the ground almost always originate from the asteroid belt, not from a comet. Thus, another way to define meteoroid is a small piece of a comet or asteroid that is orbiting the sun.
The Parent Bodies of Meteorites
Another lesson goes into many more specifics on the different kinds of meteorites we find on Earth. There are stony ones, iron ones, and stony-iron ones. Their physical characteristics are evidence that they are all fragments of a parent body in the asteroid belt (such as a planetesimal or asteroid).
This body would have differentiated during its formation to have an iron-nickel core and a rocky mantle. That's because this differentiation would've occurred when the body was partially molten. In such a scenario, the heavy stuff (iron and nickel) would have sunk to the bottom while the lighter rock would've floated to the top.
Thus, iron meteorites would have come from this parent body's core. Some of the stony meteorites (called achondrites) would have come from its surface and the stony-iron ones from the boundary of the stony mantle and metallic core.
Over time, collisions would've fragmented these bodies to produce many of the different kinds of meteorites we see today. However, other stony meteorites, the chondrites, likely formed on smaller bodies that never melted, and the delicate carbonaceous chondrites likely formed far away from the sun.
Meteor shower refers to many meteors appearing to come from the same point in the sky over a few hours or days.
The point in the sky from which meteors all seem to come during a meteor shower is called the radiant, and a meteor is the brief but very bright trail observed in the sky as a small piece of space dust or rock (a meteoroid) enters Earth's upper atmosphere.
Again, a meteoroid is a small piece of rock or dust floating in space that may one day enter Earth's atmosphere.
Most meteoroids are very small and arise when a comet spews out a cloud of dust and debris into space along its orbit. Once Earth crosses the comet's orbit, we get ourselves a meteor shower!
However, there are the sporadic meteors, meteors not part of a meteor shower. Some of these sporadic meteors come from the asteroid belt. Meteorites we find on Earth almost always originated in the asteroid belt.
The parent bodies they originate from were once differentiated into rocky surfaces and mantles and metallic cores. Collisions would've broken apart these parent bodies into the three different kinds of meteorites we see today: iron, stony, and stony-iron.
After you've completed this lesson, you'll be able to:
- Define meteor shower, radiant and meteoroid
- Explain the relationship between comets and meteor showers
- Summarize how sporadic meteors appear
- Identify the three different kinds of meteorites we see today
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