What If Earth Picked Up a Second Moon?

Thanks to VertiPlay STEM Marble Run for supporting this episode of SciShow. Click the link in the description to see the more than 100 ways to play and learn some critical STEM skills! [♪ INTRO] We owe a lot to the Moon. Without it, our tides wouldn’t be as high, our seasons wouldn’t be as regular, and our days would be much shorter. But you know what? What we call “the Moon” isn’t the only moon the Earth has ever had. Once in a while, our planet’s gravity captures a tiny, rocky body, forcing it to make a few orbits around us before it continues its jaunt around the Sun. Because they’re so small, these objects usually go undetected. But what if Earth managed to capture something a lot bigger? Something much closer in mass to our current Moon? It might sound like a lot of fun, but once
you look at the consequences, you might start to hope this never happens. Now, not all of the consequences would be
catastrophic. For instance, if this second moon orbited
close to Earth, we would generally have more moonlight. And while that would affect nocturnal animals and make it easier for some predators to hunt, it likely wouldn’t destroy the food web. The light probably isn’t the thing we’d be most concerned about, though. We’d likely be thinking more about stuff
like tides. If we picked up another moon, its gravity would cause Earth’s tides to reach both higher highs and lower lows over the course of a month. That means a lot of people would probably have to move away from coastal areas, shifting the population of our planet. If the moons were orbiting at different distances from Earth, they’d also be traveling at
different speeds. And that would further mess up our tidal system, where we currently have a nice, regular spacing between high and low tides. The time between those tides would speed up, causing more shoreline erosion. And that would threaten not just aquatic life, but human infrastructure, which would get pummeled by waves all the more often. This extra force wouldn’t just pull on Earth’s
water, though: It would pull on everything on and underneath
the Earth’s surface, too. This would increase Earth’s volcanic activity, and the frequency of other natural disasters, like earthquakes and tsunamis. Which are rarely good for life – or for humans. On an even longer scale, this second moon would even affect how long our day is. Right now, our Moon is gradually slowing Earth’s rotation because it’s orbiting
around us more slowly than we’re spinning. Its gravity is tugging on Earth and creating a sort of drag. But a second satellite — especially one
close to the Moon’s size — would interfere with that process. Exactly how, though, would, of course, depend
on its orbit, but for the sake of simplicity, let’s say
it orbited in the same direction as our current Moon, and was located a bit closer to Earth. That satellite would help slow down our rotation, and our days would get longer. Which might sound kind of nice, because I
could use a couple extra minutes a day, until you realize that satellite would also gradually creep
outward because of some specific orbital mechanics. Eventually, it would smash into the Moon, which would almost definitely bring about some kind of Armageddon as debris rained down upon the Earth. Like I said… the moonlight probably isn’t the thing we should be most worried about. At the end of the day, of course the odds
of the Earth acquiring another Moon-like satellite
are very slim, but there is something to learn
here. These kinds of scenarios remind you of how important the specific conditions around our planet
are. Like, if our Moon had a different orbit or
mass, our world could be much different. So even though we usually take it for granted, maybe we should appreciate our Moon a little
bit more… look up there and say like – hey buddy, thanks, you’re really great. You’re always helping us out. Thanks for
being a friend. But don’t try and pick up a third friend.
Just us. Just the two of us. Building castles in the
sky. Understanding how a second moon would affect the Earth depends on an understanding of gravity and other physics. And if you’re looking to build up your STEM
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use promo code SCISHOW15. [♪ OUTRO]

Comments 100

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  • What did one Ocean say to the other Ocean?
    They just waved!

  • Want to go on a fun afternoon watching clips from great television? Look up Quite Interesting How Many Moons does the earth have?

  • The gravitational capture of the moon would also alter the Earth's solar orbit. It would probably add angular momentum, increasing the Earth's average orbital radius, lengthening the year, altering the seasons (by changing the time of year of the perihelion), and generally reducing solar heating, chilling the planet.

  • Then we have 24 moons year instead of 12

  • I'm always thankful for the moon. I love the nighttime for a reason 🙂

  • Secunda and Masser have entered the chat

  • Well welcome scihank

  • Casual games promo already in the beginning of video? Good choose for quality Sci guys… 🙁

  • what if the moon had a moon?…and, would that be called a moon or is there another name for a moon's moon?🤔

  • It doesn't have 2 moons. The Bible says that there was created a greater light to rule the day and a lesser light to rule the night. Don't know why scientists always want to come up with new ideas when they can't even get old ideas right. Remember they told people pluto was a planet for decades until recently they said no its not a planet. Let's demote it. They don't know as much as they claim they know. But they sure do make tons of mistakes

  • This set is dumb. The 2nd moon is not necessarily in the same space as the current moon.

  • surprised no one made any beast wars reference.

  • What will happen when we lose our moon?

  • Wait I thought it did
    Edit: smaller moon thing

  • I see hank I look sky I say thank

  • Tsunami tides…lesser astrophotography opportunities …longer days eventually…better tidal electricity generation…

  • Jackass!

  • 🌜I had no idea our current moon isn't the only one we've ever had!

  • Why is 90°F air hot but 90° water is just warm or 70° air comfortable but 70° water cold?

  • you did not plug Seveneves

  • 4:39 I thought he was going to say: "It will help you masturbate.".

  • https://youtu.be/TaDpafqPOyU

  • Minmas?

  • 3:43

    H I S T H R O N E

  • "Building castles in the sky" was a shout out to us oldies, wasn't it? Not many of us (I've seen your stat vids) but we do appreciate the odd bone. Thanks!

  • Pfffft, try living on Venus, where the planet will kill you 5 different ways before you die.

  • Me to Moon: I love you!!

    Moon: *Moves to another planet*

  • we would have another moon to go to in 2069 ( ͡° ͜ʖ ͡°)

  • We already got one.

  • So no Chibi Moon? Awe

  • “Building castles in the sky”

  • Two moons, as a result of a newly captured moon, would be crossing the streams bad. Name that film? 🙂

  • We currently have a second “moon” or captured asteroid, it just happens to be rather far out and will eventually leave us.

  • Women would be the dominant sex of our species…
    Two cycles per month?

  • out of interest has scishow ever done an episode on antimatter / antihydrogen? if not they should see if there's enough to warrant an episode, its kinda interesting

  • The presence of a moon of outlandish size is almost certainly a factor in the existence of life on Earth. There has been no other planet, rocky or otherwise, found having a moon with a similar mass ratio to it's planetary host. The lack of such a moon would prevent large scale, quotidian ocean tides, potentially reducing the likelihood of life developing at all and severely inhibiting the subsequent occurrence of eukaryotes and multi-cellular organisms.

    The Fermi paradox may have a partial explanation in this unusual Earth/moon relationship and the apparent lack of similar pairings visible in the cosmos.

  • yeah…. but think about the epic surf, dude

  • Capturing one would be so much better than being hit by one.

  • "How important the specific conditions around our planet are"

    Also, how specific those important conditions are.

  • Was… was that an Umbrella Academy reference Hank?

  • Hank I'd just like you to know I thoroughly appreciated that "building castles in the sky" comment and now have Just The Two Of Us stuck in my head.

  • Gotta gather up all that extra energy, tides washing in and out is a massive energy system

  • According to BBC's Q.i. The earth does have two moons but it's really a "companion" on sorta the same orbit. The other one is called Cruithne (not pronounced the way it is spelt)

  • Our moon is unusually large as moons go. The biggest in the solar system in comparison to the planet it is orbiting, according to tv scientists.

  • The most dangerous thing about the second moon is that it will affect the Earth's precession that will affect our seasons. Which will be very bad and can lead to all kinds of nasty effects like unpredictable weather patterns, hurricanes, and global ice ages. In other words, it will break the stability of our climate. Which is not good.

  • I thought the marble set they were showing was a video game…

  • I Master Basic all the time. I'm a true professional Master Basicer

  • I'm Honestly not seeing any Downsides to these consequences.
    MuWa HA HA HA Ha!!!!!
    Look up QI and the Moon and you will see interesting facts about us already having other moons.

  • Having one, its called moon. Having two, its called moooon

  • There are currently 2 moons now…THATS EXACTLY WHY YOU CAN SEE A MOON OUT IN THE DAY…AND THAT SAME NIGHT, SEE ANOTHER MOON. Unless the earth has quit spinning…and since the other side of the earth hasn't reported not seeing the moon on their side…THEN THERE HAS TO BE TWO OF THEM.

  • This gives Wings of Fire a whole new meaning…

  • If Earth picked up a moon in a lagrange point we might not notice changes on Earth.


  • I'm surprised you didn't mention that the additional mass added to the Earth-Moon system would alter our orbit around the sun, almost certainly making it more elliptical and changing the amount of solar radiation we receive over the course of a year. It could potentially cause a global climate catastrophe long before the two moons collided.

  • What if we lost the moon?

  • What if my aunt had balls? She'd be my uncle.😜

  • Study the "Time before the moon" that so many ancient people speak of.
    Suffice-if-to-say you will find that our necessity for having a moon has been largely overhyped.

  • Apothis might become our second moon. Mother Shipton predicted "Six times the dragon will cross the sky before mankind will die." At the very least Apothis isn't going anywhere.

  • Would be a good idea to compare with other twin Moon systems in the solar system.

    There’s apparently like 100 moons or something according to Sandi Toksvig…

  • Moon debris raining down to annihilate live on earth was depicted in a recent novel called Seveneves.

  • Fake! The moon doesn't exist or something.

  • “Thats no moon…”

  • I think the likelihood of getting a second moon large enough to meaningfully affect earth is so so so so so small. Like, where would it even come from? Does ceres just one day decide to migrate to earth? Also, any smaller object that we can potentially capture would probably be ejected by Luna anyway.

  • Made me think of 1Q84

  • Sci I. Sci show stands for scientism. The religions cult that worships the sun. If you dony know what I'm talking g about you and you believe this channel than you are completely brainwashed. This channel is a disgrace and fraud.

  • We like the Moon
    'Cause it is close to us
    We like the
    But not as much as a spoon
    'Cause that's more use for eating soup
    And a fork isn't very useful for that unless it has got many vegetables
    And then you might be better off with a chopstick
    Unlike the moon
    It is up in the sky
    It's up there very high
    But not as high as
    maybe dirigibles
    and zeppelins
    and lightbulbs
    and maybe clouds
    And puffins also
    I think maybe they go quite high too
    Maybe not as high as the moon
    'Cause the moon is very high
    We like the moon
    The moon is very useful, everyone
    Everybody like the moon
    Because it light up the sky at night
    and it lovely and it makes the tides go
    and we like it
    But not as much as cheese
    We really like cheese
    We like zeppelins
    We really like them
    and we like kelp and we like moose
    and we like deer and we like marmots
    and we like all the fluffy animals
    We really like the moon

  • If we had a second equal sized moon, say good by to Venice, Amsterdam, New York, Chicago, New Orleans, to name a few.

  • So, who was the first person to discover the Moon anyways?

  • I’m so glad that the moon is the way it is. This was a super interesting video. And so cool to see my video featured at 4:17!!

  • Hey Moon, are you really made of cheese?

  • Note: tides do not occur by the Moon or Sun directly pulling on the water that's at high tide. They work by the Moon or Sun squeezing the water at the sides of the Earth (where the low tides are).

  • You know, three is a crowd.

  • And where would we find such a body in our solar system?

  • Thanks Moon.

  • Thank you

  • a second moon? then earth will then have 2 testicles and will be able to have babies with mars….. wait….

  • Dreams in sorbet

  • A jean jacket?

  • Could an orbital resonance between our moon and another moon keep them from colliding in the future? Maybe a 2 to 1 resonance?

  • you should learn ASL…

  • Oh hey! I just finished reading Dr. Comins' book about this!

    It's the first cited source for this episode: "What If the Earth Had Two Moons?", and it's really interesting and covers a bunch of different moon-related what-if scenarios.

  • yes and already has 3

  • Plus it would change world religions, and wreak havoc on the human reproductive cycle. No joke; the 28 day lunar cycle is responsible for controlling OTHER 28 day cycles. So… 2 moons = your girlfriend being twice as irritable.

  • It would be a cool sight if the moon picked up a moon of it’s own. Not something really big, just big enough so we could clearly see it orbiting the moon.

  • So is the moon spun on its axis close to earths spin what effects wld that have?

  • Ummm YouTube decided I didn't need all notifications anymore and it flipped to "personalized". Just thought I'd let you know.
    I have been subbed for years and have been watching every video sense the bells existed. I just think it's weird that it changed. Not only channel thats happened to either. Super super weird.

  • when he described the moons colliding all i could think of was sonic adventure 2 and then "YOU HAVE 24 HOURS BEFORE THE PISS DRRRRRRROPPLETS HIT THE EARTH"

  • what if you picked up your dirty dishes once in a while?

  • I have already seen the documentary the 5th element. We get a new moonand Bruce Willis gets laid

  • What if Our "moon" is by Sciences own description….not "Like" any other "Moon" and therefore "Defies" basing it as the definition of a "Captured" body and is not in any way the same. Wake up Science , is it your illusion that we are being led to believe , Or is it your purpose to deceive us? There's something very disturbing about your ignorance.

  • I have a question, why do farts smell worse in the bath?

  • Oh you mean Minmus?

  • Years ago, I had a dream of some large body headed straight for earth. Of course, in the dream, there were the doomsday preppers of various sorts. Instead, what happened was this body was captured as another moon. It was neat to see, people gasped in awe of having 2 moons in the sky and could make for a good scifi book with the story more developed, and (of course) in the dream I didn't consider all of the scientific ramifications of having a second moon.

    Although, technically, we have thousands of artificial moons, all cataloged by NASA, from screws to rocket stages. This debris can cause problems if they reach the ground instead of completely burning up in the atmosphere. That's a more likely fear.

    The thing about the earth/moon being in such a relationship of "don't pick up a second 'friend'", sounds like mother earth and the man in the moon are committed to monogamy. That too, could be the basis for a scifi/fantasy story – especially if one of them decided to have "an affair".

  • Kerbin gets along just fine with two moons.

  • Our current moon will become jealous and leave, and then the new moon will reveal she was not looking for a long term relationship and move on, too.

    What would happen if the earth lost the moon? Darker nights and much reduced tides, yes, but would there be any more subtle effects?

  • QI has entered the chat

  • Sarcasm warning – the moon causes seas to rise and fall? Someone needs to alert the (fake) scientists who push the global warming narrative because they believe that only American vehicles and our awesome standard of living causes global warming, which controls the height of water. That is why they elected Obummer, peace be upon him, because he was their messiah who stated in a speech that he alone controlled the rising and receding of all of the world’s oceans.

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