<blockquote>
<p>Was Theia not a Kuiper Belt Object?</p>
</blockquote>
<p>Almost certainly not. The most widely accepted hypothesis is that Theia formed close to the proto-Earth, such as near one of the proto-Earth's L4 or L5 Lagrange points. If not there, it almost certainly formed somewhere in the inner solar system.</p>
<p>Where the Earth got its water remains a bit of a mystery.</p>

CC BY-SA 4.0
2023-02-23T12:39:35.293Z
Is it correct to assume most water gets lost during the formation of terrestrial planets in the habitable zone, because it's mostly in vapor form as the planet is incandescent, and the magnetic field is not formed yet?
Mark Besser
CC BY-SA 4.0
2023-02-23T12:56:25.293Z
@MarkBesser We do not know where the Earth got its water. This remains a highly contested topic. We do not know whether the existence of a magnetic field (or lack thereof) is critical. This too remains a highly contested topic. Both of these are scientific questions for future generations of scientists to address. That science still has unanswered questions might be disappointing to some, but it shouldn't be. If science had the answer to every question, there would be no motivation for people endeavor to be scientists.
David Hammen
CC BY-SA 4.0
2023-02-23T13:04:35.830Z
@MarkBesser Some scientists claim the Earth's water is primordial; that it was there as the Earth formed. Others claim that the Earth's water arrived with the Late Heavy Bombardment, long after the collision with Theia. Yet others claim that it arrived with the collision with Theia. My recommendation is to take each of these claims with huge grains of salt until the scientific community agrees that one explanation is unequivocally correct. Note well: There remain skeptics in the scientific community whether the collision with Theia occurred, or whether the Late Heavy Bombardment occurred.
David Hammen
CC BY-SA 4.0
2023-02-23T20:04:50.217Z
@MarkBesser - many minerals (rocks) contain water just fine as hydrates. There is lots of water in the mantle. See, for example, https://ssec.si.edu/stemvisions-blog/there-ocean-below-your-feet#:~:text=The%20finding%2C%20published%20in%20Science,surface%2C%20is%20trapped%20inside%20rocks.
Jon Custer
CC BY-SA 4.0
2023-02-25T15:04:17.573Z
@DavidHammen Thank you. So Theia as source of Earth's water is not that foolish a question. How would you rank the three hypotheses in percentage likelihood? Do you think perhaps Late Bombardment Objects still had abundant volatiles, as today only beyond-ice-line objects do? Maybe the ice line was closer too, the sun a bit less bright?
Mark Besser
CC BY-SA 4.0
2023-02-27T16:49:36.730Z
@MarkBesser There's no shortage of water in space. After H & He, oxygen is the most abundant element in the galaxy, followed by carbon. See https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe Of course, that doesn't tell us where the water & hydrates are located.
PM 2Ring
CC BY-SA 4.0
2023-03-05T16:34:59.407Z
“ We do not know where the Earth got its water. ” The origin of Earth’s water is ‘almost a closed issue’, to paraphrase a geochemist’s review paper (don’t have ref in front of me just now).  “ This remains a highly contested topic. ” You can’t speak for us.  “ Both of these are scientific questions for future generations of scientists to address.” Please stop speaking for us.
caInstrument
CC BY-SA 4.0
2023-03-05T18:08:41.833Z
@caInstrument Every peer reviewed paper says that the authors have solved the problem at hand. I can find paper upon paper that say that the Earth's waters came primarily from the Late Heavy Bombardment, but on the other hand I can find paper upon paper that say that the Earth's waters are primordial. They are all recent. Review papers can be problematic when the authors already have a particular point of view. The origin of the Earth's waters is anything but a closed issue. This is one of those areas where geochemists and geophysicists agree to disagree.
David Hammen
CC BY-SA 4.0
2023-03-08T21:30:35.330Z
My god, determinism? In geochemistry? DETERMINISM?!?! We won’t ask you about stellar physics (fusion, and general helio), genomics, or nutrition, either (biochemically OR ag markets). You wave away an entire class of inquiry- inverse problems- because you’re too squeamish for nuanced results. I recall Hume said: someone with goalposts moved as far as you would soon starve. I suppose you’re too squeamish for Viking results- the NASA missions AND the SSC mission.
caInstrument
CC BY-SA 4.0
2023-03-08T22:25:36.850Z
I do not understand the reason for the overly snarky comments, the personal attacks, or for the complete misinterpretation of what I wrote. I never once used the word "determinism". Where you inferred that is a complete mystery. Personally, I like areas where different branches of science currently agree to disagree. If all scientific problems were solved problems, why would we need future scientists? That there are open questions is why we do need them.
David Hammen
CC BY-SA 4.0
2023-02-22T14:26:32.817Z
2023-02-22T14:26:32.817Z
David Hammen
<p>Was Theia not a Kuiper Belt Object?</p>
<p>I assume most water is lost during formation of terrestrial planets in the habitable zone, and is subsequently replenished with comets or (if you're lucky) KBO/ice moons. Is this accurate?</p>
<p>So Theia was a KBO, right? <a href="https://indianapublicmedia.org/amomentofscience/did-theia-bring-water-to-the-earth.php" rel="nofollow noreferrer">https://indianapublicmedia.org/amomentofscience/did-theia-bring-water-to-the-earth.php</a>  Is this a mainstream notion already?</p>
<p>Edit - not sure I understand any grounds for snark, if the origin of Earth's abundant water is still an open question.</p>

CC BY-SA 4.0
2023-02-22T13:02:11.377Z
If it was, how do you explain the Moon & why doesn't Mars have a similar moon?
Fred
CC BY-SA 4.0
2023-02-22T13:08:48.917Z
It is fairly certain by now from geochemical analyses, that Theia must have been an asteroid. Not sure where you get this KBO-idea from. A random link from some non-science media site will usually not know the full research literature and hence present a biased/nonsensical picture.
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-02-22T21:32:53.160Z
There's some info about planet formation and axis tilts here: https://astronomy.stackexchange.com/q/26561/16685
PM 2Ring
CC BY-SA 4.0
2023-02-23T12:42:39.740Z
– @AtmosphericPrisonEscape Where did all the water come from?
Mark Besser
CC BY-SA 4.0
2023-02-24T13:18:38.350Z
@MarkBesser: Which "all the water"? You know that geochemically, Earth is a very dry place, right? Build Earth up from chondritic material, and you should get around ~60 Earth oceans worth of water content in the planet, whereas we have currently ~2-3 (1 on the surface, and 1-2 estimated deep in the rocks.). Even ignoring this, one giant impactor does not have to be delivering everything you want in one go? Late veneer from the nearby asteroid belt does the job perfectly well.
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-02-25T15:00:39.093Z
@AtmosphericPrisonEscape Could you point me to a humid asteroid? The only objects with abundant volatiles I see around are beyond the ice line.
Mark Besser
CC BY-SA 4.0
2023-02-25T15:10:27.513Z
@AtmosphericPrisonEscape  2) What are the current natural processes that process chondritic material into free water?
Mark Besser
CC BY-SA 4.0
2023-02-25T16:23:26.940Z
@MarkBesser Baking the water out (aka heat) is hypothesized by some to eventually do a nice job. (That's the essence of the hypothesis that water is primordial.) The keyword is eventually, but the Earth had hundreds of millions of years to do so. The first oceans formed about half a billion years after the Earth formed. As AtmosphericPrisonEscape noted, chondrites contain quite a bit of water in the form of hydrated minerals.
David Hammen
CC BY-SA 4.0
2023-02-27T01:46:27.610Z
@MarkBesser We don't know with 100% certainty what the composition is of asteroids - as we see only their surfaces - but those which fall onto Earth as meteorites we can characterize, see Fig. 2 in https://ui.adsabs.harvard.edu/abs/2004Icar..168....1R/abstract - essentially you can make Earth even with the dry enstatites - note that for this, they have reconstructed the positions of parent bodies in the main belt, the 'ground truth' data is only how much water sits in minerals per meteorite class.
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-02-27T12:02:34.247Z
@AtmosphericPrisonEscape  Thanks, this is the paper I was looking for. Formation beyond the ice line (of asteroids if not of ice moons) which then contribute to the planet is still key, and objects forming within the ice line will indeed be dry.
Mark Besser
CC BY-SA 4.0
2023-02-27T12:02:38.153Z
@DavidHammen This is nice, it makes the likelihood of non-dry exoplanets more likely.
Mark Besser
CC BY-SA 4.0
2023-02-27T16:16:39.713Z
@MarkBesser "nd objects forming within the ice line will indeed be dry" that's not what the paper is concluding. It's what it is assuming. Further note that since that article, research has moved on significantly.
AtmosphericPrisonEscape
<theia>
Was Theia not a Kuiper Belt Object?
Mark Besser
# Was Theia not a Kuiper Belt Object?

(Asked by: username_0 on 2023-02-22)

Was Theia not a Kuiper Belt Object?

I assume most water is lost during formation of terrestrial planets in the habitable zone, and is subsequently replenished with comets or (if you're lucky) KBO/ice moons. Is this accurate?

So Theia was a KBO, right? <https://indianapublicmedia.org/amomentofscience/did-theia-bring-water-to-the-earth.php> Is this a mainstream notion already?

Edit - not sure I understand any grounds for snark, if the origin of Earth's abundant water is still an open question.

**Tags:** theia

> **Comments:**
> **username_1**: If it was, how do you explain the Moon & why doesn't Mars have a similar moon?  
> **username_2**: It is fairly certain by now from geochemical analyses, that Theia must have been an asteroid. Not sure where you get this KBO-idea from. A random link from some non-science media site will usually not know the full research literature and hence present a biased/nonsensical picture.  
> **username_3**: There's some info about planet formation and axis tilts here: https://astronomy.stackexchange.com/q/26561/16685  
> **username_0**: – @username_2 Where did all the water come from?  
> **username_2**: @MarkBesser: Which "all the water"? You know that geochemically, Earth is a very dry place, right? Build Earth up from chondritic material, and you should get around ~60 Earth oceans worth of water content in the planet, whereas we have currently ~2-3 (1 on the surface, and 1-2 estimated deep in the rocks.). Even ignoring this, one giant impactor does not have to be delivering everything you want in one go? Late veneer from the nearby asteroid belt does the job perfectly well.  
> **username_0**: @username_2 Could you point me to a humid asteroid? The only objects with abundant volatiles I see around are beyond the ice line.  
> **username_0**: @username_2  2) What are the current natural processes that process chondritic material into free water?  
> **username_4**: @MarkBesser Baking the water out (aka heat) is hypothesized by some to eventually do a nice job. (That's the essence of the hypothesis that water is primordial.) The keyword is eventually, but the Earth had hundreds of millions of years to do so. The first oceans formed about half a billion years after the Earth formed. As username_2 noted, chondrites contain quite a bit of water in the form of hydrated minerals.  
> **username_2**: @MarkBesser We don't know with 100% certainty what the composition is of asteroids - as we see only their surfaces - but those which fall onto Earth as meteorites we can characterize, see Fig. 2 in https://ui.adsabs.harvard.edu/abs/2004Icar..168....1R/abstract - essentially you can make Earth even with the dry enstatites - note that for this, they have reconstructed the positions of parent bodies in the main belt, the 'ground truth' data is only how much water sits in minerals per meteorite class.  
> **username_0**: @username_2  Thanks, this is the paper I was looking for. Formation beyond the ice line (of asteroids if not of ice moons) which then contribute to the planet is still key, and objects forming within the ice line will indeed be dry.  
> **username_0**: @DavidHammen This is nice, it makes the likelihood of non-dry exoplanets more likely.  
> **username_2**: @MarkBesser "nd objects forming within the ice line will indeed be dry" that's not what the paper is concluding. It's what it is assuming. Further note that since that article, research has moved on significantly.  

---

## 1 answers

### Answer by username_4 on 2023-02-22. Score: 5

> Was Theia not a Kuiper Belt Object?

Almost certainly not. The most widely accepted hypothesis is that Theia formed close to the proto-Earth, such as near one of the proto-Earth's L4 or L5 Lagrange points. If not there, it almost certainly formed somewhere in the inner solar system.

Where the Earth got its water remains a bit of a mystery.

> **Comments:**
> **username_0**: Is it correct to assume most water gets lost during the formation of terrestrial planets in the habitable zone, because it's mostly in vapor form as the planet is incandescent, and the magnetic field is not formed yet?  
> **username_4**: @MarkBesser We do not know where the Earth got its water. This remains a highly contested topic. We do not know whether the existence of a magnetic field (or lack thereof) is critical. This too remains a highly contested topic. Both of these are scientific questions for future generations of scientists to address. That science still has unanswered questions might be disappointing to some, but it shouldn't be. If science had the answer to every question, there would be no motivation for people endeavor to be scientists.  
> **username_4**: @MarkBesser Some scientists claim the Earth's water is primordial; that it was there as the Earth formed. Others claim that the Earth's water arrived with the Late Heavy Bombardment, long after the collision with Theia. Yet others claim that it arrived with the collision with Theia. My recommendation is to take each of these claims with huge grains of salt until the scientific community agrees that one explanation is unequivocally correct. Note well: There remain skeptics in the scientific community whether the collision with Theia occurred, or whether the Late Heavy Bombardment occurred.  
> **username_5**: @MarkBesser - many minerals (rocks) contain water just fine as hydrates. There is lots of water in the mantle. See, for example, https://ssec.si.edu/stemvisions-blog/there-ocean-below-your-feet#:~:text=The%20finding%2C%20published%20in%20Science,surface%2C%20is%20trapped%20inside%20rocks.  
> **username_0**: @DavidHammen Thank you. So Theia as source of Earth's water is not that foolish a question. How would you rank the three hypotheses in percentage likelihood? Do you think perhaps Late Bombardment Objects still had abundant volatiles, as today only beyond-ice-line objects do? Maybe the ice line was closer too, the sun a bit less bright?  
> **username_3**: @MarkBesser There's no shortage of water in space. After H & He, oxygen is the most abundant element in the galaxy, followed by carbon. See https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe Of course, that doesn't tell us where the water & hydrates are located.  
> **username_6**: “ We do not know where the Earth got its water. ” The origin of Earth’s water is ‘almost a closed issue’, to paraphrase a geochemist’s review paper (don’t have ref in front of me just now).  “ This remains a highly contested topic. ” You can’t speak for us.  “ Both of these are scientific questions for future generations of scientists to address.” Please stop speaking for us.  
> **username_4**: @username_6 Every peer reviewed paper says that the authors have solved the problem at hand. I can find paper upon paper that say that the Earth's waters came primarily from the Late Heavy Bombardment, but on the other hand I can find paper upon paper that say that the Earth's waters are primordial. They are all recent. Review papers can be problematic when the authors already have a particular point of view. The origin of the Earth's waters is anything but a closed issue. This is one of those areas where geochemists and geophysicists agree to disagree.  
> **username_6**: My god, determinism? In geochemistry? DETERMINISM?!?! We won’t ask you about stellar physics (fusion, and general helio), genomics, or nutrition, either (biochemically OR ag markets). You wave away an entire class of inquiry- inverse problems- because you’re too squeamish for nuanced results. I recall Hume said: someone with goalposts moved as far as you would soon starve. I suppose you’re too squeamish for Viking results- the NASA missions AND the SSC mission.  
> **username_4**: I do not understand the reason for the overly snarky comments, the personal attacks, or for the complete misinterpretation of what I wrote. I never once used the word "determinism". Where you inferred that is a complete mystery. Personally, I like areas where different branches of science currently agree to disagree. If all scientific problems were solved problems, why would we need future scientists? That there are open questions is why we do need them.  

---

