[HN Gopher] Dynamical origin of Theia, the last giant impactor o...
___________________________________________________________________
Dynamical origin of Theia, the last giant impactor on Earth
Author : bikenaga
Score : 56 points
Date : 2025-07-08 18:10 UTC (4 hours ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| echelon wrote:
| Imagine if life had evolved on Earth or Theia prior to impact.
| Imagine if it was intelligent and played witness to the giant
| cataclysm.
|
| Given that intelligence took an awfully long time to emerge from
| LUCA, that seems implausible. But it's fun to imagine pre-Theia
| "Silurians". That sort of impact would have scorched earth of any
| trace or remnant of their existence. It feels as though there
| must be sufficiently advanced civilizations out there witnessing
| this exact scenario play out without the necessary technology to
| stop it. Though that fate would be horrifying.
|
| Another thing to think about is that shortly after the Big Bang
| (if there was one, Lamda-CDM or similar models holding up), was
| that shortly after the Big Bang the temperature of the early
| universe was uniformly 0-100 degrees Celsius. It may have been
| possible for life to originated in this primordial interstellar
| medium without even so much as needing a host planet or star!
| Just life coalescing in space itself.
|
| That early primordial soup, if it existed, could have seeded the
| whole universe. Most aliens might have matching molecules and
| chirality if those decisions predate our galaxy.
| hbrav wrote:
| That second idea (cosmic primordial soup causing universal
| similarity / compatibility of life) could be a great component
| of a sci-fi story.
| MarkusQ wrote:
| That early warm interval would have been a soup of 75% H, 25%
| He, and 0.0000000% or so Li, with nothing heavier.
|
| Not much to start life with.
| belinder wrote:
| Temperature on its own wouldn't be enough for life would it?
| Isn't everything moving around way too fast after the Big bang
| and therefore too far apart for whatever life there would be to
| find food (or whatever equivalent source of energy)
| andrewflnr wrote:
| > It feels as though there must be sufficiently advanced
| civilizations out there witnessing this exact scenario play out
| without the necessary technology to stop it. Though that fate
| would be horrifying.
|
| I suspect this is not actually that common. Giant impacts are
| more common in early solar systems; things eventually settle
| into nice circular orbits like we have now. Whereas intelligent
| life does seem to take a while to evolve, so probably more
| common later in a solar system's life cycle.
| somanyphotons wrote:
| This animation makes it appear that proto-Earth was _very_
| comprehensibly torn apart, stunningly so
|
| https://en.wikipedia.org/wiki/Theia_(hypothetical_planet)#Co...
| shadowgovt wrote:
| I remember there being some modeling done to determine
| whether the Theia impact blew a chunk off Earth or basically
| re-liquified the planet. If I recall correctly, the resulting
| hypothesis was that the thermal load would have re-melted at
| least the crust (evidence for this was stacking of density in
| the moon, suggesting it formed out of a basically completely-
| liquified ball, which would have implied the crust was also
| liquified).
|
| There is some interesting evidence suggesting the deeper
| layers remained intact, in the form of a region under the
| Pacific that might be the impact scar. It's an inexplicably-
| dense zone that causes hot-spots at its corners resulting in
| increased surface volcanism, like how the edges of a leaf
| burn before the middle in a fire.
|
| ... but on the surface? Yeah, no hiding place.
| whycome wrote:
| Would oceans have remained at all?
| nntwozz wrote:
| The pre-Theia "Silurians" as you call them, depending on
| technological level could have left traces in the solar system
| like our Parker Solar Probe or something in the Lagrange
| points.
|
| Then again, how well do we know of stuff in these spaces today?
| It seems to me we barely have a clue of the space junk we
| ourselves sent up orbiting in our backyard.
| readthenotes1 wrote:
| The moon has 1.2% the mass of earth, so earth still got
| embiggened
| kridsdale1 wrote:
| What an epically cromulent day it was.
| shadowgovt wrote:
| So the boil-down on this is "Here's a theory that says about
| 5-10% of Earth's mass was mostly carbon and came all at once,
| like if Theia was mostly carbon and we got hit by it, so we did
| some simulation and the idea Theia was mostly carbon isn't ruled
| out by our current understanding of how our solar system might
| have formed?"
|
| If so, cool. It's a wise step to check the hypothesis to make
| sure it isn't immediately contradicting what we already
| understand.
___________________________________________________________________
(page generated 2025-07-08 23:00 UTC)