have shaped the history of our planet more than you might imagine.
We Earthlings have got used to looking
up to an empty, inky expanse of night
sky, adorned only by the familiar
spattering of the brightest stars, the
subtle smudge of the Milky Way, and of
course, our lone moon.
But what if our night sky didn't always
look like this? If Earth once had rings,
how would it have looked then?
To really paint a picture for you, let's
imagine we're standing on the surface of
this ancient, ringed Earth.
For starters, the rings aren't shiny and
bright like Saturn's, because we're too
close to the sun for ice to persist.
Instead, Earth's rings are made of rock,
rich in silicates [music]
and low in iron.
Rocks don't reflect light, at least not
efficiently. They absorb it. So, the
traces you see overhead are pale and
dusty.
But, this doesn't make them any less
dramatic.
And what you see from the surface varies
wildly depending on where you're
standing.
At the equator, you don't see a ring at
all, just a thin line from one horizon
to the other.
As you move 20° from the equator in
either direction, the rings appear in
their full majesty, taking up a
significant portion of the sky.
40° away, they appear like an elongated
rainbow stretching across entire cities.
Here, the bottom of the rings are
blocked by the curvature of the Earth.
And 90° away, at the poles, the ring is
barely visible at all, hiding just
[music] beyond the horizon like a
permanent twilight.
At night, [music] things get really
surreal.
At the equator and poles, not much
changes, but in the mid-latitudes, night
takes on a whole new meaning.
Dust in the rings scatters daylight from
the day side of the planet onto the
night side, a phenomenon known as
ringshine.
The rings glow brighter than the moon,
which fades into obscurity.
At these latitudes, darkness becomes a
[music] thing of the past.
However, you never see the full ring.
As much as the sun traces an arc across
the sky in the day, so the Earth's
shadow traces an arc across the rings in
the [music] night.
It sounds like a world from a
science-fiction novel, except it's not.
Researchers have actually found evidence
that Earth may have had skies like this
millions of years ago.
Imagine what standing in a ring's shadow
would have been like. A strange twilight
would sweep across the earth, bringing
darkness where there should have been
daylight. The thought of it evokes the
similarly unforgettable moments when our
moon blocks out the sun in a solar
eclipse. If you need a reminder of that
particular sight, one is coming on
August 12th this year to Europe and will
even be partially visible in parts of
America. It promises to be an
once appeared in our skies? If you look into the geological record,
you'll notice something strange around
the 466 million year mark. All across
the globe, limestone formations from the
Ordovician period show a sudden 100 to
1,000-fold spike in key elements
associated with meteorites, specifically
L-chondrites.
For decades, the prevailing theory
stated that these L-chondrite deposits
all originated from one apparent body.
That body broke apart somewhere in the
asteroid belt, scattering [music] debris
throughout the inner solar system. Some
of these fragments collided with Earth,
leaving impact craters dotted all over
the planet.
But in 2024, Andy Tomkins and his team
at Monash University, Australia, noticed
something unusual.
They analyzed 21 craters using tectonic
plate reconstruction models to determine
where each impact site would have been
466 million years ago.
Accounting for continental drift and
plate movement, the data points started
falling into place.
If these impacts had come from random
asteroid belt debris, we would expect to
see a global distribution of impact
sites strewn across our planet. But
Tomkins' analysis revealed something
else entirely.
All 21 impact sites fell within 30° of
where the equator would have been back
then.
It seemed too unlikely to just be a
coincidence.
So, Tomkins and his team ran the
numbers.
The odds that 21 impacts would all land
within that narrow equatorial zone was 1
in 25 million.
As I said, very unlikely.
Still, there could be a non-obvious
reason for this pattern.
To be sure, the researchers compared the
spatial clustering of these impacts to
more recent impact events on Earth. They
found that the modern impact craters
from the last 40 million years didn't
really form clustered groups on Earth's
surface. They followed the pattern you'd
expect for a shower of random space
debris.
But the Ordovician impacts were a
different story.
They were all clustered together, almost
as though something had guided them
there.
So, how does a rock shower from the
asteroid belt explain this crater
pattern on Earth?
To answer this, scientists turned their
attention to our next-door neighbors. If
this was truly an asteroid belt breakup,
we would find evidence all over the moon
and Mars, too.
Mars sits closer to the asteroid belt
than we do. Any fragments flying through
space should have collided with the red
planet harder and more frequently than
they did with us.
And the surface of the moon, without an
atmosphere to protect it, is essentially
a permanent record of everything that's
ever hit it. So, did this mysterious
asteroid leave any clues behind?
That's exactly what Anthony Lagain and
his team wanted to find out in 2022.
The researchers examined 49 large
craters on Mars, 45 on Earth, and 91 on
the moon to determine if there were any
spikes in impact frequency over the last
600 million years.
Earth, as we already saw, showed a jump
in impacts about 460 million years ago.
But Mars and the moon did not.
Lagain thought this spike on Earth could
be due to preservation bias.
The craters in question formed in
tropical regions with favorable
preservation conditions, and that
created an apparent cluster around
Earth's equator.
He argued that our planet wasn't pelted
in a thin belt, rather that only those
impacts have survived until now.
But Tompkins had a different idea.
What if the asteroid that caused the
Ordovician meteor shower didn't break up
in the asteroid belt, but right here in
[music] Earth's orbital space?
What if a massive asteroid passed close
enough to Earth that our planet's
gravity tore it apart? And what if those
fragments didn't scatter across the
inner solar system, but stayed right
here in orbit?
What if 460 million years ago
Earth had rings?
When you think of rings, your mind jumps
to Saturn, the iconic illuminated arcs
circling the queen of the solar system.
And though not as epic, all four gas
giants have rings of their own.
But, as it turns out, rocky planets can
have rings, [music] too. They just don't
last as long for various reasons we'll
discuss later.
Before we get to all that, we need to
work out how an asteroid could
spontaneously fracture above Earth 466
million years ago.
As an asteroid gets closer to our
planet, the side [music] facing the
planet experiences a stronger
gravitational pull than the side facing
away from it. This difference is called
the tidal force, the same phenomenon
that causes the moon to raise ocean
tides on our shore.
For most objects, their internal gravity
is strong enough to hold them together.
But, the closer to the planet they get,
the stronger the tidal forces grow.
If the orbiting object gets too close,
there comes a point when the tidal
forces of the planet eventually rip it
apart.
The distance at which this happens is
called the Roche limit. It isn't a hard
and fast distance, since it varies
depending on a few things, namely the
planet's mass and radius, and the
object's density and composition. For
example, the Earth's Roche limit for a
rigid body made of solid rock, like the
Ordovician L chondrite asteroid we've
been talking about, is about 3,100 km
above the surface of the planet.
For a pile of rubble loosely held
together by gravity, it is about 15,800
km above the surface.
So, fairly possible.
Next, we need to know what happens to
the fragments once this near-Earth
asteroid breaks up. How do they end up
in a neat circular orbit around the
equator?
Well, when the asteroid breaks apart,
its total momentum is conserved among
its fragments. Most remain trapped
within Earth's Hill sphere, the region
of space where Earth's gravity dominates
over the sun's, keeping them in orbit
around our planet.
At first, these fragments follow chaotic
elliptical paths. Some swing close to
Earth, others arc further out.
But over time, they collide with [music]
each other.
Each collision transfers momentum, and
gradually these wild elliptical orbits
become more circular, a process known as
collisional damping.
The circulating debris eventually
settles into a flat disk around the
equator for a specific reason.
You see, the Earth is not a perfect
sphere. It has a bulge in the middle,
making its equatorial diameter about 43
km wider than its polar diameter.
This creates an asymmetric gravitational
field and generates torque, or
rotational pull, on nearby debris.
Gradually, this torque draws the
material orbiting at an angle into
alignment with the equatorial orbital
plane. Kind of like a spinning top that
wobbles, but eventually settles into a
stable spin.
And this process wouldn't be unique to
Earth. In fact, modeling from a 2017
study suggests that once upon a time,
Mars had rings, too. Not from the
breakup of a nearby asteroid, but from
its very own moon.
Researchers Andrew Hesselbrock and David
Minton predicted that Phobos's orbit
will bring it within the Roche limit in
about 70 million years.
At this point, it will break up and form
a ring around the planet, [music]
which will eventually deposit about 80%
of its debris onto the Martian surface.
The remaining 20% will coalesce to form
a new generation of satellites around
the red planet.
Extrapolating backward, the pair
suggested this cycle has been going on
since Mars's birth.
According to them, Mars has gone through
three to seven ring satellite cycles,
and they postulate Phobos and Deimos
themselves might be the result of such a
process, accreted from ring dust of a
previous bigger moon.
Could a similar process be responsible
for our own moon?
Well, possibly.
We think our moon could be the result of
a violent collision of two protoplanets
some 4.5 billion years ago. One was a
newborn Earth, and the other was a
Mars-sized rock called Theia.
This impact sent debris flying into the
planet's orbit, where, thanks to
collision damping and the equatorial
bulge, it would have eventually settled
into rings.
Over time, these fragments would have
accreted to form bigger and bigger
moonlets until they eventually coalesced
into the moon we see today.
So, if Earth already went through one
ringed phase,
what's to say it didn't go through
another 466 million years ago?
Rings could certainly explain the
Ordovician impacts.
Over time, dust and rocky material from
Earth's rings would have slowly rained
down onto the surface of the planet,
dotting impacts all along the equator,
which is exactly what we see.
But, the rings would have had
consequences beyond the impacts
themselves. [music]
Tonkin speculates that they could
explain the Hirnantian Ice house, a 8 to
10° global cooling event that took place
463
to 444 million years ago.
The rings would have blocked sunlight,
potentially triggering the cooling
despite high atmospheric CO2.
This period of glaciation is largely
accepted as the leading cause of the
late Ordovician mass extinction, which
killed off 85% of marine life.
Still, even if Earth did have rings back
then,
how come it doesn't anymore? Where did
they go? And will they ever come back?
As glorious as they are to behold, no
planet's rings last forever.
Even Saturn's spectacular rings are only
predicted to last another 100 million
years.
And Earth's rings would have disappeared
far more rapidly.
The main culprit is orbital decay.
Any material orbiting closer than 35,800
km altitude is considered to be below
Earth's synchronous orbit.
We aren't sure exactly how far from
Earth's surface its rings would have
been, but they almost certainly would
have been closer than that.
In this case, the rings would orbit
around Earth faster than the Earth
rotates about its own axis. With every
swing past our planet, the rings would
transfer some of that orbital motion
energy to make the Earth spin a tiny bit
faster.
The Earth's slower rotation would act
like a brake, sapping energy from the
rings, causing their orbital radius,
period, and altitude to decrease [music]
until they fell into the planet.
Atmospheric drag from Earth's exosphere
would only accelerate this process.
Extending from 700 to 10,000 km above
the surface, this part of our atmosphere
is incredibly tenuous.
Although it's still dense enough to
create friction on orbiting particles.
Each pass through the exosphere would
slow the material down slightly. Over
thousands of orbits, this would pull
fragments into lower and lower
trajectories until they burn up in the
atmosphere or impact the planet below.
From the surface of the Ordovician
Earth, it would seem as though the sky
were literally falling.
Not always dramatically, the majority of
the ring material would tumble down as
dust.
But occasionally, when a larger fragment
deorbits, a brilliant fireball would
streak across the sky.
As it fell into Earth, it would grow
bigger and bigger until it slammed into
the ground somewhere along the equator.
Along with gravity,
our rings would also have the sun to
contend with.
Charged particles from our sun would
constantly bombard the ring material,
stripping off electrons.
The resulting positive particles would
then become trapped in Earth's magnetic
field lines and get funneled down toward
the poles and the equator.
Eventually, they'd slam into the upper
atmosphere, giving off a dull glow
before disappearing forever.
Looking up from an ancient Earth, you'd
see a dim curtain of light in the
high-altitude sky, kind of like a faint
localized aurora.
But this light show can't go on forever.
Every glowing speck represents material
lost from the rings.
We also can't forget the effects of the
moon's gravity.
Every time it passes overhead, the
moon's gravity would tug [music] on
nearby ring particles.
For particles at certain orbital
distances, this would happen repeatedly
at the same point in their orbit, a
phenomenon called orbital resonance.
The repeated gravitational kicks would
destabilize the rings' paths, ejecting
some particles outward into space and
nudging others inward, in this case
toward Earth.
Over millions of years, these resonances
would carve gaps through the rings,
accelerating their collapse.
We think Earth's rings disappeared after
about 40 million years because this is
when the L chondrite spike in the
geological record ends, no more asteroid
bombardment.
But Tompkins is confident we haven't
seen the last of our rocky companions,
saying, "This wasn't the first time
Earth had a ring, and it won't be the
last, most likely."
But, if Earth had rings today, how would
it affect us?
Would its satellites survive? How would
we get into space? Or, would we just end
up pulverized by a brutal impact from
infalling debris?
Let's assume Earth's hypothetical ring
sit somewhere between the thermosphere
and geostationary orbit, between 700 to
35,800
km up.
Commercial airplanes don't fly high
enough, so they wouldn't have to worry
about navigating the ring itself.
But, they still face danger from
infalling ring debris, burning up as
meteors on their way down.
Flight paths near the equator would need
constant monitoring for incoming
fragments.
A much bigger challenge is what to do
with satellites.
In low Earth's orbit, satellites travel
at 28,000 km/h.
At this speed, even the tiniest
particles can wreak havoc.
Satellites would need precise launch
windows to thread through the gaps in
the ring, or heavy shielding, which
would increase payload weight and lead
to higher fuel costs.
Maintenance would also be more
challenging. Failure rates would
increase, and the whole thing would
become much less reliable.
Back home on Earth, this would spell
disaster for our modern way of life.
We personally rely on satellites every
day for high-speed internet,
telecommunications, and GPS. But, we
also benefit from them in more indirect
ways. Aviation and shipping industries
need accurate GPS to keep operations
smooth and efficient, keeping the global
economy running. Weather predictions let
farmers manage their crops better,
keeping yields high and prices low.
Speaking of climate, a dense ring of
rocks surrounding the planet is bound to
affect it. The exact impact of rings on
Earth's weather patterns is hard to
pinpoint, but there are a few things we
are fairly sure of.
At the equator, the rings would block
some of the incoming light, casting a
shadow on equatorial regions like this.
As the Earth rotates through the
seasons, different equatorial regions
experience this shadow.
It hits the southern tropics in June,
July, and August, and the northern
tropics in December, January, and
February, making winters on both sides
much colder.
During equinoxes, when the Earth's axis
tilts [music] neither towards or away
from the Sun, the shadow would fall in a
thin line directly on the equator.
The cooling effect might only be a
degree or two, but that's enough to
shift weather patterns, alter growing
seasons, and stress [music] ecosystems
that depend on consistent sunlight, just
as it might have done during the late
Ordovician mass extinction I mentioned
earlier.
At the middle latitudes, the equinox
looks completely different. The planet
silhouette stretches across the rings,
casting the largest shadow of the year,
the smallest then arriving at the
solstice. Imagine the kind of folklore
that would arise from witnessing such
phenomena year after year.
But perhaps the most imminent threat to
civilization on a ringed Earth would be
the infall from the rings themselves.
Most would burn up as meteors, setting
the sky ablaze for those near enough the
equator to see it.
But every now and then, a larger
fragment would get past our atmospheric
defense and collide with the planet.
Now, we can't know how big the debris in
our ring system would have been, but a
fragment only has to be 50 m wide to
destroy an entire city. That doesn't
mean that those living closer to the
poles are safe from catastrophe.
A rock [music] just 1 km wide can spell
global devastation.
But perhaps my favorite difference in
this ringed world would be how we study
and understand our own cosmic backyard.
Mission launches would face the same
challenges as satellites.
And even if we could successfully pull
it off, the ring would interfere with
radio communication, scattering
transmissions, and creating dead zones.
>> [music]
>> Any probe we send to far-flung
destinations would ping back distorted
signals.
Radio astronomy, critical for studying
black holes, pulsars, and distant
galaxies, would get muddled with
interference, especially around the
equator.
Ground-based astronomy would also take a
hit. The light scattering off the rings
would make faint objects even harder to
detect. Our view outward into the
universe would be compromised.
The sky would be more awe-inspiring,
yes,
but it would be much harder to study.
Just because Earth doesn't currently
have rings, doesn't mean it never will
again.
Tompkins believes it's only a matter of
time before they return.
But when they do, humans will adapt, as
we always do.
You and I won't be there to see it.
But maybe that's what makes science so
powerful. It lets us witness the wonders
of the universe across time, painting
pictures of worlds we'll never touch,
but can still imagine and understand.
long-term, and every new member makes it
stronger.