Our moon surface is covered with scars
left behind from the countless impacts
throughout its life.
Reminders that the early solar system
was a very violent place.
But amongst this pockmarked backdrop,
one crater stands out.
If you've ever looked closely at the
full moon, you might recognize this,
Tycho crater.
Its long white rays stretch out like
fingers over the lunar surface.
This crater is 85 km across with a
central mountain 2.5 km high, and it was
created by a cataclysmic event, one of
such scale that not only was ejecta
catapulted to the opposite side of the
moon,
but its effects were felt all the way
back here on Earth.
But what collided with the moon to
create this huge scar?
When did it happen?
And how did it impact life here on
Earth?
I'm Alex Mcalgon, and you're watching
Astrum. Join me as we head up to the
lunar surface to learn all there is to
know about our moon's incredible Tycho
crater,
and to explore its greatest mysteries,
many of which are still baffling
scientists to this day.
There are thousands of impact craters on
the moon.
5,000 of which are more than 20 km in
width.
But Tycho, named for the infamous 16th
century Danish astronomer Tycho Brahe,
is one of the most prominent.
Formed by an enormous collision, more on
that later, and stretching 85 km in
diameter, Tycho crater is large enough
to be visible from Earth with the
unaided eye, particularly when the moon
is full.
From its rim to its floor, it is 4.8 km
deep.
To give you a sense of scale, that's
more than twice as deep as the Grand
Canyon here on Earth.
Bright rays emanate from its epicenter,
reaching out thousands of kilometers.
This curious splash pattern is what
happens when a massive object impacts
lunar soil, sending debris flying with
enough force to wrap around the moon
all the way to its opposite side.
Let's take a closer look at some of the
features of Tycho crater and see what
they can teach us about its origins.
After all, a crater of this size must
have come from a pretty violent event.
Perhaps the first thing you'll notice
about Tycho crater is its central
mountain.
Its peak reaches up 2.5 km from the
crater floor and stretches 15 km across
at its widest point.
While much of the regolith that makes up
the moon's surface looks similar to the
untrained eye, NASA's Lunar
Reconnaissance Orbiter discovered that
the peak surface is actually a treasure
trove of interesting and distinctive
textures. Some parts are smooth, others
are blocky. The base is streaked with
fine deposits and there are enormous
gullies.
All these features paint a picture and
through this and other images,
scientists have discovered that the rock
that makes up Tycho's mountain is
actually not the same kind of rock that
forms the crater's basin or its rim.
So, what's this out of place rock doing
here?
It's actually because Tycho is what's
known as a complex crater.
Unlike simple craters whose impact
basins are smaller and look like some
giant has simply scooped out a chunk of
the ground with an extra large spoon,
complex craters are formed by impacts so
large their collision creates recoil in
the bedrock beneath the surface.
Rock that was once buried deep gets
propelled up in the center, forming
peaks that are composed of a very
different sort of rock to the rest of
the crater.
This process is a bit like what happens
when a droplet of water lands in a pond.
The surface is disturbed, water gets
displaced, but then gravity reasserts
itself, and the edges of the newly
formed basin rush in to restore the
equilibrium.
All that inward-rushing water meets in
the middle, and with nowhere else to go,
some is forced upwards.
And when this happens to rock that has
suddenly, violently melted, what was
formerly bedrock is pulled up along for
the ride.
This is one of the reasons scientists
want to study Tycho's peak further. It
offers an excellent opportunity to learn
what the deep interior of the moon is
like.
Surveyor 7, in 1968, discovered that the
surface regolith in the area surrounding
Tycho comprised basalt rock with high
levels of calcium and low levels of
sodium.
But what lies deeper down?
Until we sample the mountain itself,
scientists can only guess how Tycho's
bedrock fits into the broader geological
narrative.
Tycho crater is visible from the Earth
with the naked eye, but to truly
appreciate its features, you need the
right gear. This is true of other
aspects of the moon, too. For instance,
on the 12th of August 2026, the moon as
a whole will be part of a jaw-dropping
solar celestial convergence with our
sun, a solar eclipse. And if you're in
the path for that and want to see it,
your eyes will thank you for choosing
the right solar glasses, like the ones
off their purchase. Now, back to Tycho crater.
There is another feature of Tycho's peak
that tells us much about its history.
Do you see this line running across the
mountain here?
This is a high watermark of a sword.
But before you ask, no, this was not
caused by an ancient lunar water lake
lapping against the mountain, as cool as
that would be.
When the asteroid that impacted the moon
created Tycho crater and pulled that
peak to the surface, the entire crater
floor would have been superheated in the
collision
into a boiling hot pond of impact melt.
Under the softening influence of that
heat and the insidious pull of gravity,
parts of the surrounding rim would have
later broken off and fallen into the
pool, sending tsunami waves propagating
out through the melt.
This mark was formed when a tsunami of
molten rock splashed against the peak's
edges.
Eventually, the melt cooled and formed
the surface we see today, though not
without leaving these fascinating clues
as to their past [music] existence.
Impact melt pooling also explains the
smoother parts of the peak and the
surrounding crater floor.
But that melt can be found elsewhere.
Let's widen our view to the surrounding
landscape of the lunar surface.
These breathtaking Hubble images of
Tycho really showcase the violence that
extended out beyond the crater itself.
In 2013, Tim Krüger and his team of
researchers at the Institute of
Planetology presented a map of more than
3,000 melt pools in the surrounding
area, highlighting where burning
fragments of regolith would have been
flung out of the crust of the moon's
surface by the impact.
By noting that there is one direction
that had fewer melt points than the
others, Krüger and his team were able to
confirm that this hadn't been a direct
blow, but the asteroid had likely come
in at an oblique 35° to 45° angle,
arriving from the southwest.
But, as I mentioned earlier, those balls
of molten rock weren't limited to just
the immediate area.
The Apollo 17 mission landed at the
Taurus-Littrow Valley in the Mons Taurus
Mountains, a location 2,250
km away from Tycho.
One of the primary goals for the mission
was to sample material taken from a
landslide along one of the nearby crater
walls. Specifically, they were targeting
the light mantle, a prominent bright
streak stretching 5 km across the valley
floor from the base of a 2-km tall
mountain known as South Massif.
This site is the only known landslide of
its kind on the moon and is highly
unusual even by lunar standards. It is a
long runout landslide, meaning the
debris traveled an incredibly long
distance across the moon to get there.
And the exact mechanisms of this travel
remained a mystery for decades.
To solve this mystery, astronauts Gene
Cernan and Harrison Schmitt, a trained
geologist, successfully gathered samples
from the site in 1972, bringing back a
total of 110 kg of lunar material. Among
these were two pristine core samples
drilled straight out of the light
mantle.
At the time, officials at NASA knew that
future technology would far surpass
their own research capabilities, so they
stored a portion of these samples away,
completely untouched and sealed for over
five decades.
The time to unseal them came in 2025,
when a team led by geologist Julia
Magnarini from London's Natural History
Museum used medical-grade micro CT scans
to peer inside these cores without
damaging them.
They analyzed clasts, rocky fragments
that broke off the slope of South Massif
during the landslide, and compared their
shape and composition to computer
simulations of the event. And what they
discovered is quite mind-blowing.
As the mountainside began to collapse,
the falling rocks started grinding
against each other with intense force,
eventually coating themselves in their
own dust.
This layer of fine powder lubricated the
giant rocks, allowing huge masses of
debris to collide across the lunar floor
like fluids. This might finally explain
how lunar landslides traveled so far.
But another question still remained
unanswered. What actually triggered this
massive collapse in the first place?
In more analyses of the Apollo 17
samples, scientists found traces of
impact melt glass at the location.
It is believed that these pieces of then
superheated glass were thrown all the
way from Tycho. And remember, that's
more than 2,000 km, causing the
landslide when they crashed into the
slopes of South Massif.
This really gives you a sense of how far
this glass flew.
And no wonder, based on the size of
Tycho crater,
the energy released from the impact that
created it would have been comparable to
30 trillion tons of TNT or 2 billion
nuclear bombs on the scale of the one
used on Hiroshima, all going off at the
same time.
This would create something far brighter
than the small impact flash witnessed by
Artemis two astronauts during their
recent lunar trip.
With a blast that size, some of Tycho's
material would have not just flown
around the moon, but escaped its weak
gravity entirely.
And where would they have gone after
that?
Well, towards the other large source of
gravity in the immediate area,
Earth.
Imagine what this would have looked like
for the dinosaurs alive back then.
One night, the moon would suddenly flash
with a brilliant light as the impact had
crashed headlong into its surface.
And for those ancient dinosaurs that
missed the main event, there was still a
show.
The moon would have borne a strange,
glowing, orange scar for many nights to
come, the signature of the red-hot
impact melt still cooling on its
surface.
But as spectacular as that show would
have been, it wasn't until hours or days
later, once the debris had cleared the
380,000
km between the moon and the Earth, that
the real fireworks [music]
would have begun.
Within hours of being jettisoned into
space, most of the molten moon rock
would have resolidified into hard
meteorites.
Upon entry into Earth's atmosphere, that
rock would start heating up again.
30% would have burned up entirely,
lighting up the sky. But the remaining
70% would have hit the ground,
bombarding the planet with tiny or
larger fragments over the course of days
to weeks.
Enough material would fall that, if it
were spread out, estimates from a lunar
and planetary science conference predict
it would have covered the entire Earth
in a layer 0.1 to 0.3 mm thick. And of
course, in reality, there would have
been larger fragments here and there.
But, there is one mystery when it comes
to this day of raining rock and glass.
When exactly did it happen?
And unfortunately, the answer is we're
actually not quite sure.
When the Apollo astronauts brought their
sample of glass back to Earth, cosmic
ray exposure dating placed the Tycho
crater event at around 108 million years
ago, right at the end of the early
Cretaceous period.
This makes Tycho crater relatively young
by lunar crater standards, and explains
why the crater is still so pristine, and
its rays are so bright. There's not been
time for them to get disturbed by later,
smaller meteor impacts.
You think that locating small pieces of
asteroid impact glass, known [music] as
tektites, that's a similar point in the
fossil record, would have been easy.
But, in the whole world, there are
actually only five known fields of
tektites created by meteors,
>> [music]
>> and none of them are related to Tycho.
There is other evidence that is equally
bizarre.
In her doctoral thesis, researcher Elena
Martin from the Lund University in
Sweden demonstrated [music] that Tycho
could be older than 117 million years.
She did this by searching for that Tycho
meteor layer in sediment deposited on
the floor in the Pacific Ocean,
examining samples with ages ranging from
103 to 117 million years old.
And yet, she found Tycho meteorites in
precisely none of them.
One grain was found that could have come
from the moon, but it did not match the
chemical composition expected from Tycho
specifically.
So, it is still not clear exactly when
the asteroid that impacted Tycho
occurred.
That's something only further study will
be able to confirm.
But while analysis of ancient impacts
like Tycho is limited to samples and
computer models,
sometimes we do get to watch the moon
get a brand new scar in real time.
In late spring of 2024, a space rock
traveling at extraordinary speed slammed
into the lunar surface, punching a fresh
crater 225 m across, roughly the width
of two football pitches end-to-end.
Thanks to NASA's Lunar Reconnaissance
Orbiter Camera, scientists were able to
capture the high-resolution before and
after images of the site.
It is the largest fresh crater ever
observed during the orbiter's entire
17-year mission, more than three times
the size of the previous record holder.
It stretches 43 m deep, features steep
walls, and is surrounded by shattered
boulders up to 13 m wide.
Deep inside, scientists [music] even
detected dark, glassy rock flash melted
by the intense [music] energy of the
collision.
According to models, an impact of this
scale on any given patch of lunar ground
is a true once-in-a-century event,
expected only once every 139 years.
So, catching it this soon after
formation is an astounding feat of the
LRO mission.
While going to the moon seems like a
rare and noteworthy thing,
Tycho crater demonstrates that exchange
between the moon and the Earth happens
more regularly than you might think.
Across the eons, these two bodies have
proven to be a dynamic system where
material from the one can sometimes, if
conditions are right, find their way to
the other.
Astronauts are returning to the surface
of the moon in 2028.
Perhaps in time, once NASA has finished
[music] building its moon base,
humanity will make their way to Tycho
crater itself, and through careful study
of its slopes or by climbing [music] its
peak, will answer once and for all all
the numerous questions about Tycho's
origins.
Until then, if we want to learn more
about Tycho crater, there is always that
layer of rock and tektites to find.
We don't need to go to the moon. We have
Tycho crater at home.
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