- Just before a 280 pound meteorite
crashed into a wheat field in Ensisheim, France,
a resounding boom rocked the local area.
Witnessed by a young boy
on the morning of November 7th, 1492,
it became the earliest recorded
and preserved meteorite landing in the Western world.
Our planet has been rocked, literally,
by more than just this meteorite.
They've left not just themselves as space debris,
but also craters, and even molecules needed for life,
across the world.
But not only have these giant space rocks come to us,
we've started to travel to them,
and they might be a key part of our forays into deep space.
So what are meteors and asteroids,
and why do they matter
to those of us living down here on earth?
(upbeat music)
First up, let's be real.
It's hard to keep asteroids, comets,
meteoroids, meteors, and meteorites straight,
and to figure out which is which,
we really have to go back to the beginning.
The very beginning, like the Big Bang beginning.
At the very start of our universe 13.8 billion years ago,
most scientists think that all matter
existed at a single point
in a ball of infinite density in extreme heat.
Suddenly, it began to expand extraordinarily fast,
creating the material
that composes everything that we know of
in the universe today.
The subatomic particles created at that instant
went on to make atoms,
which then formed molecules and minerals,
matter that then coalesced into clouds
of gases and masses of rock.
Our solar system, like many others,
formed from a dense cloud of gas and dust
that collapsed about 4.6 billion years ago,
a relatively short time ago
compared to the entire universe.
What was first a spiraling solar nebula
went on to become the Sun and planets,
but some of that original gas and dust was leftover,
and a lot of it became asteroids and meteoroids.
Asteroids are rocky objects smaller than a planet
that orbit our sun.
They can be made of many different kinds of elements,
and are categorized based on their composition,
including C-type, S-type, and M-type,
for carbon-rich, stony or silicate, and metallic asteroids.
Their different compositions are primarily a result
of when they were formed in our solar system
and how far away they were from our extraordinarily hot sun.
Many of them are pretty far away,
in the asteroid belt between Mars and Jupiter,
and there are lots of them out there.
We've identified almost a million asteroids so far.
Sometimes, pieces break off of these asteroids
and become meteoroids.
These smaller objects can also come from comets,
which are a lot like asteroids,
but are composed instead of ice and dirt.
You might recognize comets as some of our most beautiful
and stunning celestial visitors,
with two tails that stream away from the sun,
one of ions, and one of dust.
But sometimes, meteoroids can be pulled
out of the asteroid belt
by the gravity of nearby planets, like Mars and Jupiter,
sending them flying out into space.
A small fraction are sent hurdling towards Earth.
Meteoroids that come close to Earth
and burn up in the atmosphere are called meteors.
These are the shooting stars
you've likely made a wish or two on.
And if the meteoroid doesn't completely burn up
in the atmosphere, and fragments land on earth,
they're called meteorites.
There are lots of bits of space dust and debris
hitting the earth all the time,
with an estimated 5 to 300 metric tons of space dust
entering our atmosphere every day.
But you don't really have to worry
about a catastrophic impact any time soon.
Only a tiny fraction of the meteors and meteorites
that crash into our atmosphere
are larger than a centimeter wide.
There are some really big asteroids out there though.
In fact, the largest one, Ceres, is 950 kilometers across,
and is in fact so big that it was reclassified
from an asteroid to a dwarf planet in 2006.
The Chicxulub impactor,
the asteroid that is suspected of killing the dinosaurs,
by comparison, was only 10 kilometers wide.
So Ceres is a really, really big asteroid.
But while there are over 23,000 asteroids
classified as near-earth asteroids,
you shouldn't worry about one hitting earth
in your lifetime,
mostly because they're actually very, very far from Earth
and it would take a long time for something like Ceres
to reach us, likely years or decades,
and so we would have lots of time to spot it
and see something that big coming.
So far, it looks like we're in the clear
for at least to the next hundred years or so.
From the ground, a meteor shower is beautiful
and can seem pretty tame,
with tiny shooting stars streaking across the sky,
but what's actually happening in the sky
is a lot more intense.
As a meteor crashes into our atmosphere,
it compresses the air in front of it.
This increase in pressure
causes the temperature of the air to rise,
which causes the meteor to heat up and glow.
This phenomenon is known as incandescence, where an object
gives off some of its thermal energy as light.
And the meteor can get really hot,
up to 1,650 degrees Celsius,
but usually only the outside few millimeters
gets really heated, melting and creating an exterior crust
that can help identify if that rock you found
is actually a meteorite or just a cool rock.
Meteors crashing towards Earth
can leave minerals up in the atmosphere too.
When we think of the elements that make up our air,
we typically think of gases
like oxygen, nitrogen, and carbon dioxide,
but there are also metals in our atmosphere,
and scientists believe that meteors play a big role
in putting them there.
Iron magnesium, sodium, and other metals
are commonly deposited by meteoroids
as they hurdle through the misosphere,
the middle layer of our atmosphere.
And once meteorites land down here on earth,
they can continue to tell stories about the universe.
When the Ensisheim meteorite crashed into that French field,
it wasn't long before curious locals
began chipping pieces of the space rock off
to keep for themselves or to send to dignitaries.
These pieces have now found their way
to collections around the world.
And because they're are leftover
from the very beginnings of our solar system,
they can tell us a lot about our own planet
and how it formed.
The Ensisheim meteorite was a type of meteorite
known as a chondrite, a type of stony meteorite.
About 86% of all meteorites found on earth are chondrites,
and they retain their primitive chemistry and form.
They represent some of the earliest building blocks
of the rocky planets, including Earth, Mars, and Venus.
And meteorites may also be able to tell us
not just about how our physical planet formed,
but also about how life arose on it.
All of the proteins in our bodies and on this planet
are built by connecting together
a set of molecular building blocks called amino acids.
The order and composition of amino acids in a protein
gives that protein its shape and function.
And while the first amino acids on earth
could have been generated by chemical reactions
right here on our planet,
we've also found extraterrestrial amino acids in meteorites,
suggesting that these small celestial visitors
may have brought amino acids to our planet.
Organisms here on earth
use what are called left-handed amino acids
to build proteins.
This handedness refers to something called chirality.
Molecules are chiral when you can make two versions of them
with identical chemical compositions,
but mirror image 3D shapes.
This is just like your hands,
they're mirror images of each other,
but you can't lay one on top of the other
and get them to match up.
Your thumbs will poke out in opposite directions.
And chirality is really important.
Some enzymes in our bodies
are only able to metabolize sugars of one-handedness,
and some drugs like ibuprofen are only effective
in one form, say the left-handed or the right-handed form,
even though they have the same chemical composition.
This can be because one confirmation
fits into an enzyme or binding partner,
while the other does not.
Scientists aren't sure why life on earth
is mostly made up of left-handed amino acids.
It's possible that meteorites
brought more left-handed amino acids
to earth than right-handed ones,
but how exactly would that have happened?
There are many hypotheses,
but we're going to talk about just one,
the neutron star hypothesis.
As matter in the early solar system heated and cooled,
ices of carbon monoxide, carbon dioxide,
methanol, ammonia, and water that coated dust grains
were formed into amino acids.
They were likely created
in both left and right-handed configurations
at pretty equal concentrations.
So the neutron star hypothesis proposes that when this dust
covered in amino acids traveled past a neutron star,
the light emitted by the star may have selectively destroyed
either right or left-handed amino acids,
leaving meteoroids with an excess of one or the other.
This initial excess could then be further amplified
as amino acids formed and crystallized,
creating a kind of snowball effect
of one type overtaking the other.
And scientists have found an excess
of left-handed amino acids in meteorite samples.
So when those early asteroids crashed down to earth,
they might've added to the supply
of organic compounds necessary for life.
And asteroids' impacts on life
may not have happened only on earth.
NASA's Curiosity Rover found evidence
that asteroids hitting the surface of Mars
may have also created some of the key ingredients for life.
But let's go back to 1492 France.
While only one person saw the huge stone fall to the sky,
the sound of the crash was heard up to 150 kilometers away.
Meteorites can cause sound in three ways.
They can create a sonic boom
as they hurdle through the atmosphere,
they can create an explosion when they break up in the sky,
or they can create a loud noise when they hit the ground.
In the case of the Ensisheim meteorite,
The noise may have come from a sonic boom or an explosion.
to see what a Sonic boom is,
let's start with this jet plane,
which is traveling at 200 meters per second,
less than the speed of sound,
which is 343 meters per second, at 20 degrees Celsius.
The soundwaves it's making propagate out in all directions.
But if we speed the jet up to 400 meters per second,
it will overtake the waves ahead of it,
pushing air molecules out of its way,
creating a wake like a boat pushing through water.
The super fast object creates a cone
of overlapping soundwaves and pressurized air,
which spreads down and out and hits the ground.
This is a sonic boom,
and you'd hear it as the edge of the cone passed over you.
But the loud boom heard from the Ensisheim meteorite
may have also been caused by an explosion
before it hit the ground.
Some of these types of explosions
have happened more recently.
In 1908, a fireball exploded over the forests of Siberia,
in a region known as Tunguska.
It flattened over 80 million trees
and smashed windows over 35 miles away.
NASA recently released these pictures
of a fireball exploding over the Bering Sea in 2018.
Luckily, this happened over an unpopulated area.
Scientists estimated that the explosion
released 173 kilotons of energy,
or 10 times the energy released by the atomic bomb
that destroyed Hiroshima.
So asteroids and meteors have left a lot behind
when they come to us.
But what about if we go to them?
Well, we've already started to.
NASA's Galileo mission was the first
to fly by an asteroid, back in 1991.
And in 2005, Japan's Hayabusa spacecraft
landed on asteroid, Itokawa, collected samples,
and brought them back to Earth five years later.
And JAXA's Hayabusa2 mission
recently collected samples from the asteroid, Ryugu,
making their way back to earth at the end of 2020.
NASA's OSIRIS-REx mission
is trying to replicate their success,
landing on Bennu, a near-earth asteroid,
and trying to back samples in 2023.
And we hope to learn a lot by going out to these asteroids,
not just where we came from, but also where we're going.
There could be some really valuable stuff out there.
Some asteroids contain lots of valuable metals,
like platinum.
In planets, these metals
tend to be really deep underground and hard to mine.
Asteroids could actually be an easier way
for us to find these metals.
And crazily, while you can't own an asteroid,
the United States passed legislation in 2015
that says you can own anything you mine from one.
NASA is even planning a mission
to a 226 kilometer-wide asteroid called 16 Psyche.
It's suspected to be full of iron, nickel, and gold
worth more than our entire global economy.
I'm not gonna lie,
I'm kind of excited about a space gold rush,
or even better, a platinum rush.
But we may not even want to bring the stuff
we mine out of asteroids back to earth.
If we're trying to go farther and farther out into space,
we're gonna need lots of fuel to do it.
Some companies have proposed mining water
from chondrite asteroids to produce fuel
for long distance space travel.
They could split the water into hydrogen and oxygen,
a pretty common fuel combo in rockets today.
Or even just heat it up
and use steam to propel the spacecraft forward.
But that water could also be useful to astronauts
as both drinking water,
and a pretty efficient radiation shield.
The nuclei and molecules are what block cosmic radiation,
and water has more nuclei per volume than metal,
which makes it a more efficient shield.
So if you can get there and mine it,
all of that sweet, sweet space water can be yours.
(adventurous music)