Meteors: Crash Course Astronomy #23

Summary

This script delves into the fascinating world of meteors, meteoroids, and meteorites, explaining the science behind shooting stars and their origins from asteroids and comets. It clarifies common misconceptions, describes the process of meteors burning up in Earth's atmosphere, and touches on the potential hazards of larger meteoroids. The video also discusses meteor showers, the classification of meteorites, and the importance of space programs in preventing catastrophic impacts.

Takeaways

• 🌌 Astronomy studies objects far away, primarily through light, but sometimes we can study physical samples from space.
• 🌠 When you see a 'shooting star', it's actually a meteoroid burning up in Earth's atmosphere, creating a meteor.
• 🔥 Meteoroids, the space debris, are heated to incandescence due to compression of air and not just friction, which is a common misconception.
• 💥 The term 'meteor' refers to the phenomenon of a meteoroid burning up in the atmosphere, while a 'meteorite' is what's left if it survives and hits the ground.
• 🚀 The kinetic energy of a meteoroid, due to its high velocity, is what we see as a bright meteor when it enters the atmosphere.
• 🌌 Sporadic meteors are common and originate from asteroids, while meteor showers are often from cometary debris left in orbit around the Sun.
• 🌌 Meteor showers appear to radiate from a point called the radiant, and are named after the constellation they appear to come from, like the Perseids or Leonids.
• 🌌 The Geminids meteor shower is unique as it originates from an asteroid, 3200 Phaethon, which may act like a comet due to heat vaporizing its surface.
• 🗻 Larger meteoroids can become bolides or fireballs, which are extremely bright and can be the size of a grapefruit.
• 💥 Very rarely, a meteoroid can survive its atmospheric entry and become a meteorite, which can be classified into stony, iron, or stony-iron types.
• 🦕 Large meteorite impacts are rare but potentially catastrophic; plans are being developed to prevent such events, highlighting the importance of a space program.

Q & A

Why is it difficult to study astronomical objects?

Astronomical objects are difficult to study because they are extremely far away, and nearly everything we understand about the Universe comes from light emitted or reflected by these objects, rather than from physical specimens that could be examined in a lab.

What is the term for the phenomenon of a meteoroid becoming incandescent as it enters Earth's atmosphere?

The phenomenon of a meteoroid heating up and streaking across the sky is called a meteor.

What is the difference between a meteoroid, a meteor, and a meteorite?

A meteoroid is the actual bit of solid stuff coming from space. A meteor is the phenomenon of the meteoroid burning up in the atmosphere. A meteorite is the remnant that survives its passage through the atmosphere and lands on the Earth's surface.

Why are meteors often mistaken for stars?

Meteors are often mistaken for stars because they appear as bright streaks in the sky, but they are not stars; they are actually small particles of interplanetary debris burning up in the Earth's atmosphere.

What is the primary source of heat for a meteor as it enters the Earth's atmosphere?

The primary source of heat for a meteor is not friction with air, but rather the compression of air in front of it as it moves at hypersonic speeds, which heats up the gas and, in turn, the meteoroid.

How high above the Earth do most meteors typically burn up?

Most meteors burn up high above the Earth, at altitudes of about 90 to 100 kilometers.

What causes the persistent glowing train left behind by some meteors?

The persistent glowing train left behind by some meteors is caused by the ablated material from the meteoroid's surface, which vaporizes and blows away, leaving a trail that can be influenced by high-altitude winds.

What is the term for random meteors that occur outside of meteor showers?

Random meteors that occur outside of meteor showers are called sporadic meteors.

How do meteor showers form?

Meteor showers form when the Earth passes through a cloud of debris left behind by a comet in its orbit around the Sun, causing many meteors to appear in a short period of time.

What is the radiant, and how is it related to meteor showers?

The radiant is the point in the sky from which meteors in a shower appear to originate. It is named after the constellation in which the radiant is located, and the meteor shower is named accordingly.

Why are astronomers concerned about large incoming meteoroids?

Astronomers are concerned about large incoming meteoroids because they can cause significant damage if they hit the Earth. While such events are rare, the impact could be catastrophic, similar to what is believed to have caused the extinction of the dinosaurs.

What are the three broad categories of meteorites, and what are their characteristics?

The three broad categories of meteorites are stony, which are mostly rock; iron, which are mostly metal; and stony iron, which are a mixture of the two. Stony meteorites are further divided into chondrites, containing chondrules, and achondrites, which lack chondrules and likely originated from larger, once-molten asteroids.

What is a bolide, and how does it differ from a regular meteor?

A bolide is an extremely bright meteor, often as bright as the Moon, and is typically the result of a larger meteoroid, about the size of a grapefruit, entering the Earth's atmosphere.

What is the significance of the Chelyabinsk meteor event of 2013?

The Chelyabinsk meteor event of 2013 is significant because it was a large meteoroid impact that caused widespread damage without any prior warning. The event injured over a thousand people due to flying glass from shattered windows and highlighted the need for better detection systems for such threats.

Outlines

00:00

🌌 The Wonders and Science of Meteors

This paragraph delves into the fascination with astronomy and the challenge of studying distant celestial objects. It introduces the concept of meteors as a rare opportunity to examine space debris up close. The script explains the difference between meteoroids, meteors, and meteorites, and clarifies common misconceptions about their formation and appearance. It also touches on the science behind meteors, including kinetic energy, ablation, and the role of atmospheric compression in their incandescence.

05:01

🌠 Meteor Showers and Their Origins

This section discusses the phenomenon of meteor showers, which are named after the constellations from which they appear to radiate. It explains that most meteor showers are caused by the Earth passing through debris left by comets, forming a 'puffy ribbon' of space debris around the Sun. The paragraph also details how to observe meteor showers and mentions the unique case of the Geminids, which originate from an asteroid. Additionally, it covers the rarity and impact of larger meteoroids that can become meteorites upon reaching the Earth's surface.

10:03

💥 The Impact and Aftermath of Large Meteoroids

The final paragraph addresses the potential threat posed by very large meteoroids, using the Chelyabinsk event as a case study. It describes the catastrophic effects of such an event, including the release of energy equivalent to a nuclear explosion and the resulting injuries. The script also discusses the difficulty in detecting and preparing for such incidents, mentioning upcoming telescopes designed to provide early warning. It concludes with a call to action, emphasizing the importance of a space program to prevent a dinosaur-like extinction.

Keywords

💡Astronomy

Astronomy is the scientific study of celestial objects, spaces, and the physical universe as a whole. In the context of the video, astronomy is the central theme, as it discusses the study of celestial bodies and phenomena such as meteoroids, meteors, and meteorites. The script mentions the frustration of studying distant objects and the desire to examine physical specimens from space.

💡Meteoroid

A meteoroid is a small rocky or metallic body in outer space, usually in orbit around the Sun. The script explains that meteoroids are the precursors to meteors and meteorites, and it clarifies that they are not stars, despite the common misconception. The term is used to distinguish the solid matter from the phenomena it causes when entering Earth's atmosphere.

💡Meteor

A meteor, commonly known as a shooting star, is the phenomenon of a meteoroid becoming incandescent from friction with the Earth's atmosphere and appearing as a bright streak in the sky. The video emphasizes that meteors are not stars, and the term is used to describe the visual effect of meteoroids burning up in the atmosphere.

💡Meteorite

A meteorite is a meteoroid that survives its passage through the Earth's atmosphere and lands on the Earth's surface. The script distinguishes meteorites from meteors by stating that if a meteoroid does not burn up completely and reaches the ground, it is then called a meteorite, and it can be studied as a physical specimen from space.

💡Kinetic Energy

Kinetic energy is the energy that an object possesses due to its motion. The video script explains that meteoroids have a high kinetic energy because of their high velocities, which is converted into light and heat when they enter the Earth's atmosphere, creating the bright streaks of a meteor.

💡Ablation

Ablation is the process where a material loses mass due to vaporization. In the script, ablation is described as the vaporization and blowing away of the surface material of a meteoroid as it heats up upon entering the Earth's atmosphere, leaving behind a glowing trail known as a train.

💡Sporadic Meteors

Sporadic meteors are random meteors that occur throughout the night, not associated with a specific meteor shower. The video script mentions that these meteors are typically caused by small meteoroids, often from asteroid collisions, and they are an example of the continuous influx of space debris into Earth's atmosphere.

💡Meteor Shower

A meteor shower is a celestial event during which a large number of meteors are observed to radiate from one point in the night sky, known as the radiant. The script explains that meteor showers are caused by the Earth passing through the debris left by comets, creating a display of many meteors in a short period.

💡Bolide

A bolide is a bright and explosive meteor that is larger than typical meteors and can be as big as a grapefruit. The video script uses the term to describe a particularly bright meteor that can occur over Earth, indicating a larger meteoroid that still has significant energy upon impact with the atmosphere.

💡Meteorite Classification

Meteorites are classified into three broad categories: stony, iron, and stony-iron, based on their composition. The script explains that most meteorites found on Earth are stony, while iron meteorites likely originate from the core of a large asteroid, and stony-iron meteorites are rare and can be quite beautiful, with examples like pallasites containing olivine crystals.

💡Chelyabinsk Event

The Chelyabinsk event refers to a large meteor explosion over the Russian city of Chelyabinsk in 2013. The script describes this event as an example of a very large meteoroid entering the atmosphere, causing significant damage due to the shock wave from the explosion, and highlighting the potential danger of such events.

Highlights

Astronomy studies objects far away, often through light, but the desire is to examine physical specimens in labs.

Shooting stars are actually interplanetary debris heated to incandescence as it enters Earth's atmosphere.

Astronomers differentiate between meteoroids, meteors, and meteorites based on their location and state.

Meteors are often tiny, with their kinetic energy resulting from high speeds rather than mass.

The heat of meteors is primarily due to air compression rather than friction.

Meteors typically burn up high above the ground, creating a glowing trail called a train.

Sporadic meteors originate from asteroids and are common but usually small.

Meteor showers are groups of meteors that result from Earth passing through a comet's debris trail.

The radiant point of a meteor shower is the point in the sky from which the meteors appear to originate.

Meteor showers are annual events due to the Earth's consistent orbit intersecting with comet debris.

The Geminids meteor shower is unique as it originates from an asteroid, 3200 Phaethon.

Bolides or fireballs are exceptionally bright meteors that can be the size of a grapefruit.

Meteorites that reach the ground are usually cold and do not cause fires upon impact.

Meteorites are classified into stony, iron, and stony-iron types, with stony meteorites being the most common.

Chondrites and achondrites are two types of stony meteorites with different origins and compositions.

Iron meteorites likely originate from the metallic cores of large asteroids.

Pallasites, a type of stony-iron meteorite, are considered some of the most beautiful due to their olivine crystals.

Meteorite collecting is a hobby that requires caution and purchasing from licensed dealers.

Large meteoroids can cause significant damage, as seen in the Chelyabinsk event in 2013.

Current strategies for preventing asteroid impacts include nuclear devices or space probes to alter orbits.

The rarity of large asteroid impacts does not negate the need for preparedness and a space program.

Transcripts

I love astronomy. You may have noticed. But there’s one really frustrating aspect of

it: Everything we study is really far away.

Nearly everything we understand about the Universe comes from light emitted or reflected

by objects. It’d be nice if we could get actual samples from them; physical specimens

we could examine in the lab.

Welp, sometimes the Universe can be accommodating, and allows us to hold it in our hands.

Cambot, can we get this up on still store?

If you go outside on a clear, dark, moonless night — and you really should — chances

are pretty good that within a few minutes you’ll see a shooting star. It’ll zip

across the sky, a fiery dot leaving a long glowing trail behind it. They’re one of

the most exciting and fun things you’ll see when you look up, and they always get

a gasp and a squeal of delight from people someone who’s stargazing.

What you’re actually seeing is a tiny bit of interplanetary debris: rock, ice, or metal

ramming through the Earth’s atmosphere, heated to incandescence. Most are faint, but

some can be astonishingly bright; I saw one once that left an afterimage on my eye!

Obviously, shooting stars aren’t really stars. So what do we call them?

Sometimes it seems like astronomers use different names for objects to keep things as confusing

as possible. But really, we do that to separate out different things. In this case, the actual

bit of solid stuff coming from space is called a meteoroid.

The phenomenon of the meteoroid getting hot and blazing across the sky is called a meteor.

And finally, if it hits the ground, we call it a meteorite.

I think the second best way to tick off an astronomer is to mix up meteor and meteorite.

Sometimes astronomers can be pretty pedantic about such things.

Oh, the best way to tick off an astronomer? Ask them, “Hey, what’s your sign?”

Amazingly, a typical meteor that you’ll see is due to a meteoroid that’s tiny, probably

smaller than a grain of sand! How can that be?

It’s because they’re hauling mass. You heard me.

The meteoroid is orbiting the Sun, probably at speeds of a few dozen kilometers per second.

As it approaches the Earth, our planet’s gravity accelerates it an additional 11 kilometers

per second — Earth’s escape velocity. And when it enters our atmosphere it’s moving

incredibly fast, up to 70 km/sec or more.

The energy of motion is called kinetic energy. If you want to get something moving, you have

to give it energy, and if you want it to stop, you have to take that energy away. This kinetic

energy depends on the mass of the object and how fast it’s moving. In fact, it depends

on the square of the velocity; double its speed and it’ll have four times the kinetic

energy.

Meteoroids may usually be small, but they’re screaming fast, and have a huge amount of

kinetic energy. As they hit our atmosphere they slow from their ridiculous orbital speed

to nearly a standstill, and all that energy has to go somewhere. It gets converted into

light and heat, and that’s what we see as a meteor.

A big misconception about meteors is that they get hot due to friction with air. Actually,

a far bigger contributor to their heat is compression. One of the most basic laws of

physics is that when you compress a gas it heats up. And a meteoroid coming in at hypersonic

speeds compresses the air in front of it a lot, heating it hugely. The gas can reach

temperatures of thousands of degrees Celsius for a few seconds.

The air radiates away this heat, in turn heating up the meteoroid. The material on the surface

vaporizes and blows away—a process called ablation. That ablated material leaves a glowing

trail behind the meteor, which we call a train. Sometimes it can glow for several minutes,

getting twisted up in high altitude winds, leaving behind an eerie, ghost-like persistent

train. This all happens high above your head, about 90 – 100 km above the ground.

Typically, from any one location, you can see a few meteors per hour. It may not seem

like much, but when you add them up all over the planet you find the Earth is getting pelted

to the tune of about 100 tons of material a day. But again, most of these meteoroids

are teeny tiny.

Those random meteors are called sporadic meteors. They tend to be rocky in composition, and

generally come from asteroids. If two asteroids smack into each other, the collision can eject

little bits of material that then orbit the Sun on their own. If their orbit crosses the

Earth, then you have a potential meteor. It may take a few million years, but at some

point the Earth and the meteoroid are at the same place at the same time, and boom.

But sometimes meteoroids travel in packs. When that happens, we can get meteor showers,

many dozens or even hundreds of meteors per hour. With one exception, those don’t come

from asteroids: They come from comets.

When a comet orbits the Sun, the ice on it turns to gas, dislodging dust and gravel mixed

in. This material leaves the comet and tends to stay more or less in the same orbit as

the comet itself. Over time, that material gets scattered all along the orbit, creating

a puffy ribbon of tiny pieces of space debris around the Sun.

When the Earth plows through that cloud of debris, we get a meteor shower.

From our viewpoint on Earth we see meteors shooting across the sky, apparently radiating

away from a single point. That’s a perspective effect; it’s like driving through a tunnel

and seeing the tiles on the wall and ceiling flying past you, all apparently coming from

a point ahead of you. The point in the sky where the meteors come from is called the

radiant, and the shower is named after the constellation the radiant’s in. So we have

the Perseid meteor shower, the Leonids, the Camelopardalids. Or the Camelopardalids.

And, since the Earth hits a specific comet stream around the same time every year, the

showers are annual. The Perseids are in August, and the Leonids in November.

Watching a meteor shower is easy: Just go outside and look up! Generally, they’re

better after local midnight. The Earth plows into the meteoroids, so facing the direction

of Earth’s orbital motion means more meteors, just like you get more raindrops on the front

windshield of your car than than on the back when driving through a storm. After local

midnight you’re on the part of the Earth facing into the orbit, so you see more meteors.

By the way, if you happen to be on the International Space Station, you have to look down to see

a meteor. In 2011, astronaut Ron Garan photographed a Perseid burning up below him! But don’t

worry: The odds of the Space Station getting hit are extremely low. Space is big.

Oh, and that one exception I mentioned before? That’s the annual Geminids shower, which

occurs in December. That comes from the asteroid 3200 Phaethon, which is on an orbit that takes

it very close to the Sun. It’s possible it gets so hot that the rock vaporizes, making

it act like a comet.

The vast majority of meteoroids are small and tend to burn up in our atmosphere. But

they can be bigger. A bolide, or fireball, is an extremely bright meteor, and those can

be about the size of a grapefruit. Those happen pretty often somewhere over the Earth. I’ve

seen a few myself.

Very rarely, an incoming meteoroid will survive all the way to the ground and become a meteorite.

Sometimes, the immense pressure of ramming Earth’s air causes the incoming meteoroid

to crumble or even explode, raining down dozens or hundreds of smaller pieces. Typically,

they slow rapidly after their blaze of glory, and simply fall the rest of the way to the

ground. The air up there is cold, and their interiors are cold from being in space so

long. So, despite what you might think, meteorites don’t cause fires when they hit the ground.

In fact, they can be quite chilly!

Meteorites are classified into three broad categories: Stony, which are mostly rock;

iron, which are mostly metal; and stony iron, which are a mixture of the two. The majority

of meteorites we find are stony.

The stony meteorites are subdivided into two kinds: Chondrites, and achondrites. Chondrites

contain chondrules, small grains of minerals. These are very primitive, and are thought

to have condensed out of the original disk of material that formed the solar system.

Their age can be found by looking at ratios of elements in them formed from radioactive

decay. The oldest known meteorite formed 4.568 billion years ago: Before the Earth itself

formed!

Achondrites don’t have chondrules in them. Most likely they came from a bigger asteroid,

one that was once molten through, mixing the minerals. A big collision disrupted the parent

body, creating the achondritic meteoroids.

Iron meteorites most likely come from the center of a large asteroid, one big enough

that metals fell to the center via gravity. Again, a big impact blew the asteroid up,

scattering its material around the asteroid belt, and with some on orbits that eventually

intersected Earth.

Stony irons are the rarest. Some have green or orange crystals of a mineral called olivine

embedded in a web of metal. Called pallasites, they may be the most beautiful of all meteorites.

I actually collect meteorites. It’s fun but can be a somewhat pricey hobby. If you’re

interested, make sure you get ‘em from a licensed dealer. We have links to some in

the dooblydoo.

Of course, on occasion the meteoroid coming in can be a tad bigger. And when that happens,

well, all hell can break loose.

On February 15, 2013, residents of the Russian city of Chelyabinsk got a rude awakening.

At 9:20 a.m. local time, a rock about 19 meters across came in at a low angle. It got nearly

as bright as the Sun as it slammed into the atmosphere, and the pressure of its passage

broke it up into several chunks, which broke up again. In a moment’s time, the sudden

energy released was equivalent to the detonation of a half million tons of TNT — as much

as a small atomic bomb!

While no one was killed, over a thousand people were injured by flying glass, shattered by

the explosion. No doubt they were at their windows gawking at the huge vapor trail in

the sky when the shock wave hit.

There was no warning for this event; the asteroid was essentially too small to detect while

it was out in space. Well, for now at least. Telescopes are coming online soon that should

be able to find smaller asteroids and give us some warning. Astronomers are more worried

about ones roughly a hundred meters across or bigger; these can do serious damage on

a city-wide scale or larger, but at the moment aren’t easy to spot much in advance.

And what do we do if we do see one headed our way? As of right now, there’s not much

we can do. Studies have been done to determine the best course of action; maybe lobbing a

nuke at it, or simply ramming it with a spaceprobe to change the orbit and make sure it misses

Earth. These ideas look good on paper, but they haven’t been tested yet. We’re still

a few years from that.

The good news is that objects that size hitting the Earth are rare; maybe once every century

or three. But if we do nothing, it will happen eventually. As science fiction writer Larry

Niven points out, the dinosaurs went extinct because they didn’t have a space program.

Hopefully, we’re smarter than they were.

Today you learned that meteors are small bits of interplanetary debris sloughed off by asteroids

and comets. When the Earth plows through the stream emitted by a comet we get a meteor

shower. Meteors burn up about 100 km above the Earth, but some survive to hit the ground.

Most of these meteorites are rocky, some are metallic, and a few are a mix of the two.

Very big meteorites can be a very big problem, but there are plans in the works to prevent

us from going the way of the dinosaurs.

Crash Course Astronomy - hey Crash Course, meteors! Cool!

Crash Course Astronomy is produced in association with PBS Digital Studios. Head over to their

channel for even more awesome videos. This episode was written by me, Phil Plait. The

script was edited by Blake de Pastino, and our consultant is Dr. Michelle Thaller. It

was directed by Nicholas Jenkins, the script supervisor and editor is Nicole Sweeney, the

sound designer was Michael Aranda, and the graphics team is Thought Café.