Talk:Giant-impact hypothesis

Academic Language

Could we rewrite "...currently the favored hypothesis for lunar formation among the astronomy crowd." into a less informal style? Andypreston (talk) — Preceding undated comment added 15:14, 11 January 2024 (UTC)

Evidence for a magma ocean on earth

While true that we don’t have this, it’s immaterial. The earth is a dynamic planet. Nothing but a few specks of zircon remain from any Hadean crust. Earth likely could’ve had a magma ocean, but ongoing tectonics and convection homogenized it. Plus you aren’t going to get things like a global plagioclase flotation crust on earth because it isn’t less dense than hydrous magma.

So I don’t think the lack of evidence for one is relevant, at all, to the validity of the theory. We have no reason to expect direct evidence. — Preceding unsigned comment added by NewValeriInMixedStates (talk • contribs) 14:40, 20 March 2021 (UTC)

Immanuel Velikovsky

While Immanuel Velikovsky is hardly the flavour of the month, his 1950 book Worlds in Collision was one of the earlier giant-impact theories, and is still in print. Carl Sagan and many others have seen fit to evaluate it.

So, shouldn't it get a mention in this article, even if regarded as discredited? Andrewa (talk) 14:21, 12 January 2023 (UTC)

Mars-sized dwarf planet?

The article mentions the hypothesized "...collision between the early Earth and a Mars-sized dwarf planet". The quick summary for dwarf planet defines a dwarf planet as "...small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right."

How would a Mars-sized planet be classified as a dwarf planet, when dwarf planets need to be smaller than any of the eight classical planets, which include Mars, and Mercury, which is even smaller than Mars? Should this segment be edited to "...Mars-sized planet"? 97.125.148.239 (talk) 20:28, 12 February 2023 (UTC)

Reversed chronology in statetment

In the HISTORY section, this sentence contradicts itself with reversed chronology, placing 1969 after 1974 due to sentence structure or date error:

"Little attention was paid to Professor Daly's challenge until a conference on satellites in 1974, during which the idea was reintroduced and later published and discussed in Icarus in 1969 by William K. Hartmann and Donald R. Davis." Isa.Alsup (talk) 17:43, 11 July 2023 (UTC)

Proposal to merge Theia (planet) into this article

The Theia (planet) article was merged into this article in 2009, but recreated in 2013. I think it should be merged back into this article. Theia as a hypothetical object is not really separable from the giant impact hypothesis, and it's also currently short enough to not really warrant a spinout. A major issue that the properties of Theia are still poorly defined, authors don't even agree on what the size of Theia (with estimates varying from 10% to 45% the current mass of Earth) or how different it was isotopically from the Earth. If little can be meaningfully said about the properties of Theia, it hardly seems warranted as a standalone article. These controversies and disputes are better discussed in this article. Hemiauchenia (talk) 03:01, 6 October 2024 (UTC)

Merge The Theia article gives undue weight to the character of the object. It's only significance is as an impactor. Johnjbarton (talk) 14:34, 6 October 2024 (UTC)

Oppose I understand the proposal, but I believe it makes sense to have a separate article for the object and for the impact event. The existence of a further planetary-mass body in the primordial Solar System is notable in itself, not only due to the impact. That its properties are still uncertain has quite little to do with encyclopedic coverage.--cyclopia^speak! 16:04, 6 October 2024 (UTC)

Do any of the refs discuss Theia in any context other than impact? Are those refs sufficient to make Theia as a planetary-mass bodies in the primordial Solar System a notable topic? Johnjbarton (talk) 16:17, 6 October 2024 (UTC)

We postulate Theia only because of the Moon-forming impact, so you will hardly find sources that do not discuss it. However, this paper for example uses what we know of the impact to investigate the possible composition of Theia:«Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner Solar System at the late stages of terrestrial planet formation.» - it seems Theia itself is the subject of study, and with respect to more general problems than the Moon formation. This estimates the zirconium abundance in Theia to help extrapolate the isotopic compositon of the inner Solar System; the paper concludes: «In general, all models agree with a Theian composition that is very similar to the Earth and provide evidence that both Theia and the protoEarth originated from within the inner solar system. The Zr isotope uniformity of the Earth, Moon, enstatite chondrites (and possibly Theia) reveal that a large part of the inner solar system exhibits a uniform Zr isotope composition.»; similar approach here. This is a specific encyclopedic entry about Theia that concludes: « Resolving the source region and the nature of the Theia impactor has implication far beyond the Moon origin but could also be important for determining the carrier of oceanic water on the telluric planets», emphasizing how knowledge of Theia has ramification beyond the Moon formation. It seems to me there is a case to keep the two articles separated. --cyclopia^speak! 21:45, 6 October 2024 (UTC)