What If Earth Had Rings?

Planetary rings are gorgeous, temporary structures created when a planet's gravity captures and tears apart smaller objects. Learn why Earth doesn't have rings (right now!) and what other planets' rings are like in today's episode of BrainStuff, based on these articles: https://science.howstuffworks.com/science-vs-myth/what-if/what-if-earth-had-rings.htm; https://science.howstuffworks.com/planets-with-rings.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to BrainStuff, a production of iHeartRadio. Hey BrainStuff, Lauren
Vogelbaum here. Earth's moon feels like an ever-present feature in
our skies, even if it's really only visible from any
given point on Earth about half the time. But what
if you looked skyward and saw not a moon, but

(00:23):
a ring, much like the ones that encircle our solar
system's gas giants? Saturn in particular is known for its
brilliant ring system, the most extensive we know of. But Jupiter, Uranus,
and Neptune have rings too. Today, let's talk about planetary rings,
and what it would be like if Earth boasted its own.

(00:45):
Scientists believe Earth did have a ring once, albeit a
few billion years ago. This ring would have appeared early
in the formation of Earth's moon. Our best hypothesis for
how the moon formed is what's called the giant impact hypothesis.
The idea is that about four and a half billion
years ago, while the Earth itself was still forming, a

(01:06):
large object or fellow proto-planet about the size of Mars
hit Earth at an angle. The impact threw debris into
space from Earth's crust and mantle. The impactor itself, which
we've named Theia, melted and merged with Earth's interior. Meanwhile,
some of the hot debris got caught in Earth's orbit

(01:29):
and eventually cooled and coalesced to form the moon. The
giant impact hypothesis would explain why moon rocks have a
composition similar to Earth's mantle and why they seem to
have been baked, and why the moon has no iron core,
because the iron in Earth's core and Theia's core remained
on Earth. But while the moon was coming together... all

(01:52):
of that debris would have been hovering in a ring
in Earth's orbit. Now, planetary rings are temporary structures. We
talked about this a while ago on the show, when,
back in 2018, researchers found that Saturn's glorious rings have
only been around for about 100 million years, and that
they'll be gone, having fallen into the gassy planet, and

(02:15):
100 million more. So, no matter what, this early ring
of Earth's wouldn't have lasted until today. But the reason
that this debris became a moon and not a ring
is that it existed outside of what's called the Roche limit.
The Roche limit is named for the French mathematician Edouard Roche, who,

(02:36):
in 1848, figured out that any given planet's gravitational pull
on a moon will be unequal across the surface of
that moon. That a planet exerts a greater gravitational force
on the side of the moon closest to the planet.
and a lesser gravitational force on the side facing away.
This means that if a moon or other object that

(02:59):
wanders into a planet's orbit is too close to the planet,
the unequal pull of the planet's gravity could tear it apart. Essentially,
the Roche limit is the minimum distance an object can
be from a planet and still hold itself together by
its own gravity. Inside the Roche Limit, any debris from
a giant impact, or any object that the planet attracts

(03:22):
with its gravitational pull, say smaller moons or asteroids, will
get torn apart again and again, eventually ground down to water, ice,
and dust particles, traveling along the planet's gravitational orbit like
water running down a drain, very slowly. Researchers estimate that
around Saturn, Ring material, to the amount of some 10

(03:45):
tons or 9,000 kilos, is falling into the planet every second.
Part of why our gas giants all have rings, but
our rocky inner planets don't, is that the outer planets
have masses large enough to attract ring material, and they
orbit far away enough from the sun for water ice
to stay frozen. Part of how we figured out that

(04:07):
Saturn's rings are so young is that they're predominantly made
of ice. If they were older, that ice would have
gotten contaminated over time with interplanetary debris, making them dull.
But they're still beautifully bright. Saturn has seven main rings,
each composed of thousands of tiny ringlets. They're massively wide,

(04:28):
extending up to 175,000 miles, or 280,000 kilometers, out into space.
But they're proportionally very thin, only about 30 feet or
10 meters thick. ranging up to a little over half
a mile or a kilometer at the thickest. They're made
up of chunks of water ice, rock, and other materials,

(04:49):
varying in size from specks to enormous house-sized pieces that
collide constantly, shattering the larger chunks. Scientists think the rings
formed when comets or asteroids collided with one or more
of the planet's moons. The fragments from the collisions spread
out around Saturn within the Roche limit. Saturn's two innermost

(05:12):
rings are very transparent. The next two out are the
brightest and largest. The fifth ring is very narrow and
held together by two moons, Pandora and Prometheus, that sit
on either side of the ring. The final two are
farther out, with the farthest made up of near-microscopic ice particles,
thought to have been ejected from the moon Enceladus, sprayed

(05:34):
out of volcanic geysers near its south pole. Saturn's rings
are named after the first seven letters of the alphabet,
in the order that they were discovered. So, from innermost
to outermost, that's D, C, B, A, F, G, and E.
The rings aren't perfect circles, but instead have bends in
them caused by the pull of gravity from nearby moons.

(05:58):
There's also a mysterious phenomenon among the rings, referred to
as spokes. These are features that rotate along with the rings,
but appear and disappear in ways that we haven't entirely
been able to explain yet. They look like spokes on
the wheels of the rings, and researchers think that they
may be formed by seasonal interactions between solar wind and

(06:20):
Saturn's magnetic field, creating some kind of static electricity that
pulls fine dust particles into different shapes. Saturn's rings are
bright enough that Galileo observed them way back in 1610,
though he didn't know what he was looking at. Their
extension from the sides of Saturn reminded him of ears,
and he wrote about them being two smaller stars, or

(06:43):
perhaps two large moons. It wasn't until 1655 that Dutch
scientist Christian Huygens identified them as rings. The other gas giants'
rings went undetected for over 300 years. Uranuses were the
first to be discovered in 1977. They run parallel to
its tilted equator, which is nearly at a right angle

(07:06):
to its orbit, so the rings appear to go up
and over the planet. It has two sets, nine inner
rings that are narrow and gray, and then two outer rings,
one reddish and one blue. Jupiter's rings weren't discovered until
Voyager 1's initial flyby in 1979. They're very faint. and
they're thought to have been created by meteoroid impacts on

(07:29):
small nearby moons. They have four components, an inner halo
of dust, a bright, thin main ring, and then two wide,
dim outer rings called the gossamer rings. Neptune's rings weren't
definitively detected until 1989, when Voyager 2 captured images of
them on its flyby. It has five main rings and

(07:52):
four prominent ring arcs, which are smaller rings that are
formed by faint, thin collections of micrometer-sized dust that's shepherded
around the ring system by Neptune's four small moons. But
back to Earth. It's unlikely that our planet will form
its own ring system anytime soon. In order to break

(08:13):
apart properly, an asteroid or a bunch of space rubble
would need to enter our orbit at around 9,000 kilometers,
which is in low-to-mid-medium Earth orbit. But what would it
be like if Earth did have rings? Okay, any rings
would most likely form parallel to the equator, and thus
would arc across the sky from east to west. And

(08:37):
your view of them would depend on your latitude away
from the equator. Near the equator, the rings would be
like thin slices of light erupting from the distant horizons
and stretching up into the sky as far as the
eye could see. The farther north or south you were,
the more the appearance of the rings would change. They'd
become markedly wider and more visible, and would, from some

(08:59):
vantage points, appear close enough to the horizon to reach
out and touch. Just as the moon currently does, the
rings would reflect sunlight back to Earth and appear to glow,
especially at night. Depending on exactly what they were made of,
the rings could reflect so much sunlight that the planet
would never fully plunge into darkness, but remain in a

(09:20):
gentle twilight, even in the depth of night. Even daylight
might be brighter because of them. Rings around Earth would
have significant climatic implications. These vast sheets of debris could
act as a shield in some regions, potentially preventing some
of the sun's rays from reaching Earth's surface. This could

(09:40):
lead to cooler temperatures in some areas, especially those beneath
the densest parts of the ring. Conversely, the reflected sunlight
from the rings could cause a warming effect in other regions.
Climate models would need to account for these new variables,
making our understanding of global weather patterns even more complex.
Planetary rings would also pose challenges to our current satellite infrastructure.

(10:05):
After all, we have stuff in our medium Earth orbit.
Just a bit farther out than a ring would sit,
we've placed a lot of telecommunications and GPS equipment, and
above that, a lot of weather platforms. rings could interfere
with the trajectories of nearby platforms or with communication from
the ground to anything orbiting above them. The presence of

(10:28):
a dense ring could also present navigational hazards for space
missions leaving or entering Earth's atmosphere. If material from the
rings should rain down onto the planet the way that
Saturn's ring material does, it could also pose a hazard
to the equipment in low Earth orbit, like the International
Space Station. Space agencies and other satellite constructors would need

(10:50):
to recalibrate and perhaps even redesign spacecraft to safely navigate
in or through such an environment. On the flip side,
falling ring material might create some spectacular meteor showers. And
just think of all the new sayings we'd have to
come up with. Perhaps we'd no longer shoot for the moon,

(11:10):
but aim for the rings instead. It's not completely out
of the realm of possibility. We're still learning about planetary rings.
Just in 2023, an international team of astronomers published a
study in the journal Nature about a new ring system
they discovered in the far reaches of our solar system.
The rings are around Quawar, a dwarf planet that's about

(11:34):
as wide as Texas and orbits beyond Neptune. The rings
are too faint to see directly from Earth, the team
discovered them by observing an oculation, meaning that they watched
the light from a background star, as Quawar blocked it
by passing between us and the star during its orbit.
What makes this ring system especially interesting is that it's

(11:55):
twice as far out from the surface of the dwarf
planet as scientists previously thought was possible according to the
Roche limit. So who knows? Maybe rings are in Earth's
future after all. Today's episode is based on the articles
Does Earth Have Rings? by Laurie L. Dove and The

(12:17):
Four Planets with Rings Might Surprise You by Mitch Ryan,
both on HowStuffWorks.com. BrainStuff is a production of iHeartRadio in
partnership with HowStuffWorks.com and is produced by Tyler Klang. For
more shows from iHeart Podcasts, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.