<p>I was learning about the formation of Earth on <a href="https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/history-life-earth-tutorial/v/earth-formation" rel="nofollow noreferrer">Kahn Academy</a> where it was mentioned that a protoplanet named Theia had a glancing impact with the earth and formed the moon. It seems like there is also newer research (<a href="https://en.wikipedia.org/wiki/Theia_(planet)#cite_note-Nace2016-3" rel="nofollow noreferrer">Read on Wiki</a>) that suggests it was a head on collision. I'm curious if there is a current scientific consensus on this. </p>

<p>My understanding of this event is that a more direct hit is possible due to the identical nature of Earth and moon Oxygen isotopes. Suggesting a vigorous mixing and <a href="http://science.sciencemag.org/content/351/6272/493" rel="nofollow noreferrer">high-angular-momentum impact.</a> Meanwhile, this article suggests otherwise <a href="http://www.sciencedirect.com/science/article/pii/S0019103503002999" rel="nofollow noreferrer">"The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at infinity &lt;4 km/sec."
</a> I'm assuming that if the protolunar disk was lacking iron it means the hit would not have exposed the interiors of either protoplanet in the collision and would have been more of a glancing blow. </p>

CC BY-SA 3.0
2017-06-05T12:56:52.467Z
It might be easier for people to decide how to approach an answer if you showed whether you understood the difference between the theories or not. Typically, however, "recent research" should be a red flag for "not widely accepted".
Spencer
CC BY-SA 3.0
2017-06-05T15:39:52.260Z
I will look more into it and post what I understand. I am new to Earth science and was wondering if there was general consensus on this subject. Thanks!
Rhizoqueer
CC BY-SA 3.0
2017-06-07T23:58:06.973Z
By glancing they just mean not directly centered. your just seeing the limitation of imperfect language and hand drawn diagrams.
John
CC BY-SA 3.0
2017-06-08T00:52:52.010Z
There is also the argument that Earth has a larger core than what would be suspected. This suggests a head on collision where some of the iron core of Theia transferred to the Earth.
Jack R. Woods
CC BY-SA 3.0
2017-06-08T07:31:07.333Z
As far as I am aware there is no consensus. Lots of work still remains to be done on this.
bon
CC BY-SA 4.0
2023-02-12T09:43:21.827Z
These posts in Astro.SE should help: https://astronomy.stackexchange.com/questions/28911/what-was-earths-mass-before-the-collision-with-theia ... https://astronomy.stackexchange.com/questions/45368/if-theia-really-crashed-into-earth-did-it-impact-earths-axial-tilt ... https://astronomy.stackexchange.com/questions/47734/if-theia-did-collide-with-earth-would-it-have-produced-rings-if-so-would-we-e .. https://astronomy.stackexchange.com/questions/29507/what-is-earth-believed-to-have-looked-like-before-the-collision-with-theia
Nilay Ghosh
<earth-history><planetary-science><planetary-formation><astronomy>
Did Theia collide directly with proto-Earth?
Rhizoqueer
# Did Theia collide directly with proto-Earth?

(Asked by: username_0 on 2017-06-05)

I was learning about the formation of Earth on [Kahn Academy](https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/history-life-earth-tutorial/v/earth-formation) where it was mentioned that a protoplanet named Theia had a glancing impact with the earth and formed the moon. It seems like there is also newer research ([Read on Wiki](https://en.wikipedia.org/wiki/Theia_(planet)#cite_note-Nace2016-3)) that suggests it was a head on collision. I'm curious if there is a current scientific consensus on this.

My understanding of this event is that a more direct hit is possible due to the identical nature of Earth and moon Oxygen isotopes. Suggesting a vigorous mixing and [high-angular-momentum impact.](http://science.sciencemag.org/content/351/6272/493) Meanwhile, this article suggests otherwise ["The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at infinity <4 km/sec."](http://www.sciencedirect.com/science/article/pii/S0019103503002999) I'm assuming that if the protolunar disk was lacking iron it means the hit would not have exposed the interiors of either protoplanet in the collision and would have been more of a glancing blow.

**Tags:** earth-history, planetary-science, planetary-formation, astronomy

> **Comments:**
> **username_1**: It might be easier for people to decide how to approach an answer if you showed whether you understood the difference between the theories or not. Typically, however, "recent research" should be a red flag for "not widely accepted".  
> **username_0**: I will look more into it and post what I understand. I am new to Earth science and was wondering if there was general consensus on this subject. Thanks!  
> **username_2**: By glancing they just mean not directly centered. your just seeing the limitation of imperfect language and hand drawn diagrams.  
> **username_3**: There is also the argument that Earth has a larger core than what would be suspected. This suggests a head on collision where some of the iron core of Theia transferred to the Earth.  
> **username_4**: As far as I am aware there is no consensus. Lots of work still remains to be done on this.  
> **username_5**: These posts in Astro.SE should help: https://astronomy.stackexchange.com/questions/28911/what-was-earths-mass-before-the-collision-with-theia ... https://astronomy.stackexchange.com/questions/45368/if-theia-really-crashed-into-earth-did-it-impact-earths-axial-tilt ... https://astronomy.stackexchange.com/questions/47734/if-theia-did-collide-with-earth-would-it-have-produced-rings-if-so-would-we-e .. https://astronomy.stackexchange.com/questions/29507/what-is-earth-believed-to-have-looked-like-before-the-collision-with-theia  

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## 0 answers

