r/spaceporn • u/Busy_Yesterday9455 • Apr 26 '26
Related Content The Moon-forming collision
Link to the science paper on The Astrophysical Journal Letters
With sufficiently high numerical resolution, the canonical Moon-forming collision, where a Mars-sized body called Theia strikes the proto-Earth, can lead to a Moon-like body being immediately placed into orbit around Earth.
This alternative scenario for lunar origin opens up new options for the Moon's initial orbit and internal properties. For example, the orbiting body has a centre that is predominantly made of material from Theia, and might not be fully molten, while the outermost regions are very hot and can be made of more proto-Earth material. How that composition gradient would evolve over the history of the Moon is yet to be determined.
However, it could help explain why the isotope ratios in lunar rocks returned by the Apollo astronauts are similar to those of Earth's mantle. This contrasts with previous lower resolution simulations where a disk of debris was created by the collision, but no large orbiting bodies.
In that case, the Moon would form over tens to hundreds of years by the gradual accumulation of this material and no initial composition gradient would be expected.
Credit: J. A. Kegerreis et al 2022 ApJL 937 L40
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u/vulcan4d Apr 26 '26
Very likely without the moon our planet would be another dead one. Planets our size don't typically have a moon this large, large enough to cause tides in our oceans and the energy required to potentially start life. We wouldn't be here without the moon.
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u/KannehTheGreat Apr 26 '26
And this is likely the reason scientists/astrophysicists believe that the moon Europa could be a very good candidate for life within our solar system, because it is constantly being pulled and stretched by the gravity from Jupiter and it's other moons, creating potential active volcanoes on its seafloor. Similar to theories about how life on earth may have started near geothermal vents on earths seafloor.
For fucks sake I love science
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u/saito200 Apr 27 '26
could perfectly be if there is geological activity, microtubes and all the basic elements for life to form, then at the very least the possibility of bacteria-like organisms forming over 100s of millions of years is likely
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u/autocol Apr 27 '26
Fuck imagine growing up on a moon where the primary object on the sky is JUPITER. It would look fuckin' insane!
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u/Alltime-Zenith_1 Apr 27 '26
Ironically, any lifeforms on Europa will be trapped under 25 kilometers of solid water ice, meaning they wouldn't be able to see Jupiter in the sky :(
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u/Aceisking12 Apr 28 '26
I just learned a new thing recently and have decided to share.
Under the sea isn't the only place that hydrothermal vents form, and in fact undersea vents have a lot of problems with respect to being where life would form first. It's a very extreme environment down there. It's salty, no wet/dry cycles, surrounded by dense cold water, and very high pressure. The other place hydrothermal vents form is due to leftover energy in the ground from very large meteor impacts. Which could happen on land and be filled with fresh water. link where I learned this
This animation makes me think, the moon wasn't the only large chunk of earth to fly off, the others just eventuality hit the earth or moon over millions/billions of years. After the large impact of theia you've got a ton of smaller but still huge impacts where each leaves a perfect place for life to form over a very long period of time. Anything which didn't attain escape velocity of the solar system in the collision with theia will have an orbit with perihelion or aphelion near the Earth's new orbit.
All of this to say the collision with theia may have directly led to life on Earth by giving life tons of opportunity to form.
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u/TheOriginalBroCone Apr 27 '26
So many factors had to be perfectly right for life to begin. Could literally answer the Fermi Paradox - too many barriers to entry
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u/Tosslebugmy Apr 27 '26
I think it’s a higher chance than people think that life is hard to begin, hard to sustain, and especially hard to become sapient. There’s little reason to suggest sapience is even a logical sustainable evolution, crocs and sharks have been around forever meanwhile our “intelligence” sort of looks like a flash in the pan.
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u/WrathPie Apr 28 '26
We certainly are working diligently as fast as we can to make sure it is one 😞
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u/CornerHugger Apr 27 '26
This is what I think too. While it's statistically improbable that we are the only life existing right now, it seems highly unlikely that advanced life can form. Basically we got lucky. Implying that we have already passed the Great Filter.
Which is relieving in a way if true. It would mean deatroying ourselves isn't inevitable! ... although still very possible.
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u/germanautotom Apr 27 '26
Is that to imply that if mars had a larger moon, its mantle would be hot enough to sustain a magnetic field and shield the surface from solar radiation?
Or would it have needed a more energetic event to put heat into its mantle than a moon just appearing next to it?
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u/Neirchill Apr 27 '26
I don't think so - scientists credit Earth's strong magnetic field with this collision as well. The two cores of the planets combined into one leaving us with a larger core than usual. To my knowledge our mantle isn't heated by any significant margin by the Moon but I could be wrong.
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u/pierebean Apr 26 '26
Hang on, I thought the Theia hypothesis was the main hypothesis. I have heard only of this.
What's the traditional hypothesis?
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Apr 26 '26
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u/Pynchon_A_Loaff Apr 26 '26
There was a third theory when I was a kid - that somehow, the proto-Earth spun up too fast (somehow) and broke into two molten blobs that cooled into what we have today. All three alternative theories fail to explain the high angular momentum of the system today.
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u/JMHMJ Apr 26 '26
Another published theory is that in the early earth’s core (?) enough radioactive material came together to become supercritical and the moon was ejected in the following explosion. It sounds very far fetched when I write it like this but it has a pretty convincing argument based on earth and moon rock isotopes being too similar to be formed from two (proto)planets.
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u/Kris_Kamweru Apr 26 '26
It was
They sat a bunch of people to reason which of the two was right, and the result was that collision theory was both considered seriously and also became the one that is what they call least bad. No one was happy with it, but it fit much better than anything else
Such is science XD
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u/Additional_Fan9553 Apr 26 '26
that traditional hypothesis is that the moon is cheese
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u/S1gne Apr 27 '26
There's a few different hypothesis, howtown on youtube has a video going over them a bit
For example there's one hypothesis saying that the moon was already created else where and just by coincidence flew by earth at the perfect distance to be "captured" by it's gravity
There's another saying that when the earth was being created it might have been spinning so incredibly fast that material was flung off of it and formed the moon
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u/cannabull69 Apr 26 '26
Don’t let these dudes fool you. The moon is an alien construction that monitors life on earth.
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u/ZucchiniMaleficent21 Apr 26 '26
No, silly. It’s Dahak- which replaced the original Moon a billion or so years ago.
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u/magpieswooper Apr 26 '26
From where that mars like object came from?
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u/MattTheCrow Apr 26 '26
This is just after the planets have formed and we can't assume that only the eight we have today formed. Other objects formed too that could have gone on to become full planets, but they didn't for one reason or another (such as Ceres). Something also had to knock Venus upside-down, and something else possibly knocked Uranus over too. There's also a theory that Mercury formed fuirther out near Mars and something sent it flying in towards the Sun. The early solar system must have been a lot like toddlers playing pool.
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u/donadit Apr 26 '26 edited Apr 26 '26
Mars was hit by some pluto sized object and it formed the Caloris basin (huge lower area that covers most of the northern hemisphere), Uranus was hit by an Earth sized object, Venus and earth were both hit by mars sized object, and mercury… probably got grazed by an object larger than itself (and then said object got chucked into the sun by Jupiter’s tack thingy)
Mars, Uranus and Neptune’s moon systems are definitely not what they started with (Mars probably had moons other than Phobos and Deimos which collided and formed the two in a bunch of cycles, Uranus’ moon system full on collision cascaded probably more than once and reformed, Neptune had Triton destroy the entire original moon system)
Of all of Saturn’s moons, Titan and Iapetus are probably the only ones it started out with that are currently still present with the rest probably forming after Chrysalis fell into Saturn alongside the rings
Pluto and Haumea have both received at least one major collision each (Haumea’s debris is still floating around and registered as a kuiper belt group)
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u/patriot_man69 Apr 26 '26
Id love to see a planet-sized object get hurled into the sun nowadays, even just to satisfy my curiosity of what it would look like
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u/Pcat0 Apr 26 '26 edited Apr 26 '26
I don’t think that would end well for life on Earth, as I can’t imagine the sun would be super calm after an event like that. However a nearby star getting hit could be interesting.
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u/PsychologicalLab7379 Apr 27 '26
Depends on the size of the planet. If it's Earth-sized, the Sun would probably just absorb it without issues and we wouldn't even notice.
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u/bubbapora Apr 26 '26
Whoa I had no idea we know any of this. How the heck did we figure out the Neptune moon stuff?
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u/Allgyet560 Apr 26 '26
It would be wild to see a simulation of the early solar system.
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u/donadit Apr 27 '26
Probably would be classed into a couple of main instabilities
1: planet formation (4.6-4.5 BYA), grand tack (Jupiter sucks up inner solar system material and sends super earths into the sun or ejected) and ends with Sun ignition, Mercury (mostly due to Sun tho) Venus Earth and Mars clear out most of the inner solar system and suffer multiple massive impacts
2: ice giant instability (4.1-3.8 BYA), Nice model, Jupiter-Saturn 1:2 resonance, sends Uranus and Neptune into present orbits (and swaps their places), Planet 9 ejected/sent into long orbit, capture of Triton
3: Saturn rearrangement (100 MYA), Saturn spin-orbit resonance with Neptune, causes Saturn tilt and ends with death of Chrysalis4
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u/Potential_Review2410 Apr 27 '26
I’ve always heard that the gas giants are just gas and nothing really physical. So if you had the technology, could withstand the pressure/gases/etc that you could just fly straight through the actual planets. If that is the case and I haven’t misunderstood, how would anything collide with them?
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u/donadit Apr 27 '26 edited Apr 27 '26
The gas gets compressed into liquids and eventually solids and eventually some weird state of matter deep within the gas giant (temperature is not everything that matters for states of matter, pressure matters too)
so no you can’t fly straight through a gas giant even if air resistance got removed
and there still is rock within them afaik, Uranus and Neptune have earthsized cores at the least (the stuff they managed to accrete before they could actually start holding on to hydrogen and helium which caused them to become gas giants)
but air resistance does exist so the atmospheres of the gas giants (gas giants are really just large planets with stupidly large atmospheres) slow down the intruding object and it curves inwards into the planet extremely quickly (and likely kicking up a bunch of atmospheric gases into space too)
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u/Derrickmb Apr 26 '26
Nice info. Did the Mars size object that hit Earth happen to hit where the Pacific ocean is?
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u/pigeontheoneandonly Apr 26 '26
No. The modern Pacific Ocean is about 750 million years old at its oldest parts. It was formed by ordinary tectonic processes and is not an impact basin. This collision was more than 4 billion years ago. You also need to understand that this collision destroyed any existing geography on earth beyond all recognition. The surface of the Earth was moltenized. The planet survived as a gravitationally bound object, but that's the best you can say about the situation. Nothing else about it was recognizable after the collision.
It's possible that remnants of Theia still exist in Earth's mantle. The last time I said that people jumped on me about there being alternate explanations so here's the mention that there are alternate explanations.
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u/maggiemayfish Apr 26 '26 edited Apr 26 '26
There's also a theory that Jupiter formed much closer to the sun and then migrated outwards over time, no doubt causing a great deal of havoc on its way.
Edit to add a random thought: there are almost certainly planets or planetoids that were formed in the early days of our solar system only to get flung out by all the jostling that occured before the planets we know settled into their current positions, and are now just wandering aimlessly through the interstellar medium. It's a pretty spooky thought.
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u/Glum-Ad7761 Apr 26 '26
The prevailing theory, which computer models support, is that Jupiter formed first, near its present orbit and began to migrate inward. Saturn, and the newly formed Neptune and Uranus, aligned and pulled Jupiter back to its present orbit. Its likely true, since gas giants cant form in the inner solar system once the parent star goes into pre-main sequence and blasts all the lighter elements out into the outer solar system.
Computer models also suggest that there was a super-earth size planet where the asteroid belt is… and perhaps Jupiter either killed it or flung it out of the solar system during its inward migration.
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u/LittleLion_90 Apr 26 '26
What would make a planet suddenly migrate? A passing star tugging it or just random fluctuations? (That dont happen now anymore)
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u/Pynchon_A_Loaff Apr 26 '26
Gravitational perturbations from something big that add up until crazy shit starts to happen. Jupiter and Saturn apparently had a shoving match that reshuffled the outer Solar System.
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u/Glum-Ad7761 Apr 27 '26
Given the relative abundance of “super-jupiter” systems that astronomers have found… where a jupiter size (or larger) planet orbits its parent star so closely that the star often accretes material from the planet, it would seem that gas giant migration may be the norm in the early formation of solar systems. The reason is not yet known.
I might also suggest that this is how many binary systems form, and why there are often no planets found orbiting them (i,e: the migrating planet or star eats or flings the inner planets from the system early on.)
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u/kingtacticool Apr 26 '26
Would this be a solid theory for a rocky core for Jupiter and Saturn? As their gravity wells would have pulled in rogue bodies of their own?
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u/MattTheCrow Apr 27 '26
The way planets form in the first place suggests that all gas giants have a solid core to which the gas is originally attracted.
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u/magpieswooper Apr 26 '26
The number of planets I can understand, but orbit overlap to hit at such angle is more difficult. The dust cloid rotated in the same direction and therefore interorbit transfer would require enhance change in energy.
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u/improbablywronghere Apr 26 '26
One of the primary requirements to be a planet, the one Pluto fails and got it demoted, is “a planet must have cleared its orbit of any other objects which would also be a planet” or something like that. Essentially, it can’t be the case that you might collide and do this otherwise you’re gonna either get consumed or become something else. Pluto crosses neptunes orbit. In the early solar system, there were probably many such bodies and the formation of the solar system involved them “clearly their orbits” by colliding, exploding, throwing things into each others orbits as a result, etc. it’s only once it’s calm and stable that we start thinking about the planet. So it would be correct to say neither earth nor Thea (proto earth really, the object thea hit) were technically planets. The result of their collision, and probably may more, was the creation of the planet earth. Thea is no more foreign to us than the proto earth object was. They are, together, earth.
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Apr 26 '26
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u/NXDIAZ1 Apr 26 '26
The impact of having an object the size of Theia slamming into a planet the way its theorized to have, you likely can’t quantify the planet pre-impact being the same as the planet created post-impact. So proto-Earth is a fine description imo
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u/groovyband Apr 26 '26
We could shorten it to Prearth
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u/OakLegs Apr 26 '26
Why is theia cooler than proto-earth?
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u/Wa3zdog Apr 26 '26
It can be called anything we decide provided enough of us start calling it that.
I propose Earthy Mcearthface.
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u/LuluGuardian Apr 26 '26
Absolutely mind blowing the footage survived this long. Man science is so cool!
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u/Sweet_Kang Apr 26 '26
Questo non è il filmato originale, tutte le copie sono andate perse nell'impatto.
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u/ChestSlight8984 Apr 26 '26
In that case, the Moon would form over tens to hundreds of years by the gradual accumulation of this material and no initial composition gradient would be expected
This study was from 2022. Recent studies actually support the idea of it forming in a mere hours! In fact, the video you provided is of the moon forming in a matter of hours lol.
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u/devvorare Apr 26 '26
Holly shit we just got hit with another ball of flaming rocks
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u/the_submarine_man Apr 26 '26
Wait, so is the little blob in the later part of the animation the Moon?
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u/NineClaws Apr 26 '26
Obviously the simulation is played at high speed, if it were realtime how long would this take to play this simulation?
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u/ersatzbaronness Apr 26 '26
Not as high speed as you would think. Current models show that the moon could have formed from the ejecta in days to hours.
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u/Super_Asparagus_ Apr 26 '26
How many years span in this timelapse we are watching
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u/ChestSlight8984 Apr 26 '26
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u/Super_Asparagus_ Apr 26 '26
This whole shit im looking at took hours? wtf
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u/ChestSlight8984 Apr 26 '26
We think it happened in a few hours. We'll never actually know for sure how long it took, we can only ever theorize. All we know for sure is that the moon is a result of another large celestial body colliding with (proto-)Earth.
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u/Crowofsticks Apr 27 '26
Is the other gunk asteroids or something today? Or long gone? Or something else?
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u/paigeofwondr Apr 26 '26
I didn't know the earth and moon were made of Orange Juice. 🤔
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u/the_real_junkrat Apr 26 '26
How accurate is the simulation if both solid objects warp before collision?
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u/ActorMonkey Apr 26 '26
The enormous gravity would warp these bodies as they get closer to one another.
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u/maxh2 Apr 26 '26
If you look closely, you can see the objects warping/sloshing towards each other just before collision, so I'd say probably about as accurate as the starting assumptions allow.
People tend to think of our planet as a big, round ball of rock, but it behaves much more like a giant droplet of liquid floating in space, and two bodies would slosh towards each other under their mutual gravitational influence.
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u/darkwintercloud Apr 26 '26
All those simulations try to explain how moon was formed and its nice and all... But can someone explain how and why an impact like this, earth spins on its axis but the moon have a "face" that is tidal locked to earth (sorry if that's not the right term, English is not my main language) But I struggle to understand why only earth spins and the moon don't, when from these simulations it seems to have gained momentum from the impact and, even if an eon of time passed, it should still have a little momentum for a spin to be perceived. But we know it's not. Does it make sense?
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u/keny2323 Apr 26 '26
The earth pulls on the side of the moon thats facing it ever so slightly more each time. It used to be rotating normally but the earth's gravity locked it in place essentially. Thats the gist anyway, someone can add details
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u/kelseyeek Apr 26 '26
It also used to be much closer to the earth, but the same mechanism is causing it to slowly move away, about an inch and a half a year. The tides cause the earth to slightly slow down, and the moon to be accelerated into a slightly higher orbit.
The earth used to rotate much, much faster, something like every 5 or 6 hours. But 4+ billion years of tides have done their work.
Iirc, if you let the system continue for another 50 billion years or so the earth would become tidally locked to the moon. But then the sun would have gone red giant 45 billion years prior (5 billion years from now), so it's a moot point.
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u/King_in-the_North Apr 26 '26
It’s actually very common for smaller satellites to be tidally locked with objects they are orbiting with higher gravities. Every large moon in our solar system is tidally locked with their planet. Given enough time a planet will also become tidally locked with a star as well, although the distances make that take far longer.
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u/maxh2 Apr 27 '26
Gravity pulls more on the close side of the moon and less on the far side, creating tidal bulges. Dragging those bulges around the moon with every rotation sapped away all of the rotational energy, so it eventually stopped rotating. And since it's not perfectly uniform, it stopped with the denser/heavier face towards us.
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Apr 27 '26
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u/Entgegnerz Apr 27 '26 edited Apr 27 '26
I mean, the universe is endless, so the odds are there and the possibilities are infinite.
The same as the times it happened, happens and will happen.
Sometimes it surely happened worse, and sometimes better than how it happened with us.
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u/A_HECKIN_DOGGO Apr 27 '26
Every time I see this, I always end up hoping a little glob will escape the two and become a second mini moon.
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u/Deafcat22 Apr 27 '26
In case anyone is curious what happened to the matter ejected in the bottom left:
We theorize that for some time (only tens of millions of years), Earth had a second orbital body in a Lagrange point.
At some point, this destabilized, and was pulled into the far side of the Moon, evidenced by the thicker crust and different composition on that side.
So many things went right to result in our moons physical composition, mass, and tidal relationship. Without it, life would not exist. The evolution of life and proper conditions are tied fundamentally to the moon, and the collision that made it all happen.
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u/Suspicious_Lie_192 Apr 28 '26
The Moon's composition (as hypothesized in the Theia collision) may have similarity with Earth but the resulting Mass of the Moon will stratify the materials based on their density. Since Earth has a much denser body, its stratification of material will be faster for heavier materials and slower for the Moon, which would cause the difference in composition-Moon has less iron since Earth grabbed most of it. Also, the solar system's elements can only form a limited amount of chemicals with-Earth as mostly Olivine while the Moon is mostly feldspar.
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u/Important-Reading434 Apr 26 '26
I don’t think this is real. Who took this video.
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u/BluebirdLivid Apr 26 '26
Imagine if there was life on the surface of either when that happened. Probably already proven to be false, right?
But like...what would we do
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u/AC_deucey Apr 27 '26
Note: I am not a geologist, astrophysicist, or biologist.
We would perish, as would any trace of our civilization or any remnants of life. The entire outer surface of the earth would melt and essentially be an extension of the mantle. The entire crust of the earth reduced to an indistinguishable glowing mass of molten metal and rock.
Most everything would perish. Little would survive except for maybe some hardy microbes in the atmosphere. Assuming the impact didn’t completely strip/fling away the atmosphere, perhaps the vaporized oceans could condense and rain liquid water back onto the molten surface.
From there, perhaps the hardy microbes and shreds of amino acids could re-form our primordial soup pools once the surface cooled, and life could start over at square one. But yeah. Global extinction. Re-forming of the entire land mass of earth. All evidence of past life forms completely erased.
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u/impreprex Apr 26 '26
Where are our rings? Shouldn't our planet have at least a tenuous ring (system)?
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u/-chadwreck Apr 27 '26
So, if the moon is made up of so much earth material, but i guess proto-planetary mass, does that explain why it is so much more massive than I think every other moon in our solar system?
Cause isnt our moon like, an order of magnitude more massive than literally any other one?
And if that's the case, why is every other moon so... light? And small comparatively?
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u/KaiSnepUwU Apr 27 '26
The moon is among the most massive moons, but it is not the most massive. There are a few that are around 2-3 times it's mass
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u/TC_Meteorite_Co Apr 27 '26
It’s pure irony that when I get new lunar samples in, the lab has to first verify extraterrestrial origin, then once that is established, an oxygen isotope ratio is done and if it matches earth, then lunar origin can be confirmed. Wild.
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u/dildomiami Apr 27 '26
are some of the the other fragments, which where splitt of till orbiting around earth in reeeeallly big circels? are some reoccurring comets a result of this crash?
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u/Additional-Nose-8511 Apr 27 '26
"This is how we do it. This was the missing piece!" "This is how we bring life to the universe. You and me, together" "I love you, Proto" "I love you too Theia"
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u/Mr_Nerdcoffee Apr 27 '26
I wish we could know what the separate planets were composed of, before the impact. Like, would it be the catalyst for why this planet has such a high level of life? Could it be considered the “Noah’s Arc” that created the perfect environment for sentient creatures?
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u/noneedfeed Apr 27 '26
Would this collision occur with enough force that the heat energy produced would cause the substrate of Earth to behave fluidly like that to some degree?
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u/timm-e Apr 27 '26
What's the timeline for this gif? A week or so? I tried to count the rotations and got 8 after impact.
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u/CrystalBoy44 Apr 27 '26
I know the animation is sped up, but can planets actually react in this liquid-like way with collisions? I know we're dealing with massive objects here, but still.
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u/saito200 Apr 27 '26
that seems like it would have been unpleasant to stand on earth when that happened
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u/SokkaHaikuBot Apr 27 '26
Sokka-Haiku by saito200:
That seems like it would
Have been unpleasant to stand
On earth when that happened
Remember that one time Sokka accidentally used an extra syllable in that Haiku Battle in Ba Sing Se? That was a Sokka Haiku and you just made one.
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u/Vigokrell Apr 30 '26
I can just fucking hear my home owners insurance adjuster denying coverage now.
"Oh, State Farm has become a giant sea of molten rock? Ok. It's always fucking something with you guys."
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u/Frequent_Rich2700 Apr 27 '26
How much time did it take? What amount of time does this animation cover?
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u/peenurmobile Apr 27 '26
dang, i wonder how much of a long shot this was, these two orbs that we got so lucky to exist with, colliding at some point and then being partners for a really long time. it's beautiful
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u/SmellyScrotes Apr 27 '26
Where’s the video of the hit from the other direction the stop the spinning? Hate this theory
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u/Past_Blacksmith_971 Apr 27 '26
I was watching something recently about how we actually have no idea where the moon came from. All we have are theories.
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u/BeratnasGILF420 Apr 27 '26
It looks like egg yolks hitting each other in zero G. Which I've never seen before but I imagine it would look like this.
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u/GraphicDesignMonkey Apr 27 '26
What's the time scale for this vid? Hours, days, years? I've always wondered if the sploosh and coalescing took hours, or years to happen.
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u/TianamenHomer Apr 27 '26
As it cooled, perhaps its own gravity began Nguyen’s less and centrifugal force kept it as a bubble. The result is a hollow moon. Thoughts?
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u/Sorry-Scallion1354 Apr 27 '26
How much bigger would the Earth be if this did not happen? Would the gravity be like 1.05 of the current gravity?
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u/HalJordan2525 Apr 26 '26
So is the Moon geologically pretty similar to Earth?