The Moon may have formed from the same synestia (spinning donut shape) as Earth rather than through a collision between the early Earth and the hypothetical protoplanet Theia:
Making the moon: Study details new story for how the moon formed
A graduate student in Harvard's Department of Earth and Planetary Sciences, [Simon] Lock is the lead author of a study that suggests the Moon - rather than being spun out of the aftermath of a collision - emerged from a massive, donut-shaped cloud of vaporized rock called a synestia. Along with Lock, the study, published February 28 in Journal of Geophysical Research: Planets, is co-authored by Sarah Stewart (UC Davis), Michail Petaev (Harvard), Zoë Leinhardt (Bristol), Mia Mace (Bristol), Stein Jacobsen (Harvard), and Matija Ćuk (SETI).
"The commonly accepted theory as to how the Moon was formed is that a Mars sized body collided with the proto-Earth and spun material into orbit," Lock said. "That mass settled into a disk and later accreted to form the moon. The body that was left after the impact was the Earth. This has been the canonical model for about 20 years." It's a compelling story, Lock said, and it's also probably not correct. "Getting enough mass into orbit in the canonical scenario is actually very difficult, and there's a very narrow range of collisions that might be able to do it," he said. "There's only a couple of degree window of impact angles and a very narrow range of sizes...and even then some impacts still don't work."
"This new work explains features of the Moon that are hard to resolve with current ideas," said Stewart, a professor of Earth and Planetary Sciences at UC Davis. "This is the first model that can match the pattern of the Moon's composition."
The origin of the Moon within a terrestrial synestia (DOI: 10.1002/2017JE005333) (DX)
Previously: "Synestia" Phase of Planetary Formation Simulated
(Score: 2) by bzipitidoo on Friday March 02 2018, @04:05PM (2 children)
I'm trying to visualize this. The article that isn't behind a paywall is a bit sketchy on the details.
Reading about Haumea gives this progression for the deformation of a planet under increasing amounts of rotation:
sphere.
oblate spheroid.
triaxial ellipsoid.
dumbbell. And split into 2 bodies?
synestia (donut)
A rapidly spinning dumbbell in transition to becoming 2 separate bodies might fling a lot of material off the ends.
I wonder if instead of a triaxial ellipsoid, the mass could flatten into a spinning disk shape that thins at the center until a hole opens. I suspect that can't happen without the disk flying apart first. Maybe liquid magma rather than rock could do that?
(Score: 3, Informative) by takyon on Friday March 02 2018, @04:48PM
http://www.skyandtelescope.com/astronomy-news/could-a-giant-impact-have-vaporized-earth-to-create-the-moon/ [skyandtelescope.com]
pix
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by All Your Lawn Are Belong To Us on Friday March 02 2018, @09:40PM
I think the order is more like:
Synestia with center of mass at-or-near where the Earth will become.
A separate mass center forms inside the "hole", but far from gravitational center of the mass. I'm assuming it forms (or will form) a circular orbit inside the toroid but far from the center of mass. It might just be a dense spot on the deep edge of the toroid, dunno.
That mass attracts matter from the synestia (nonpay article calls a "rain" of rock) and forms its own spheroid. This becomes the Moon.
Remainder of the mass is pulled to the center of the hole, forming the spheroid that becomes the Earth.
Gravitational dance between the now two mass centers, Earth and Moon.
The nonpay article, if I follow it, suggests that this process allows for the similar isotopic properties of Earth and Moon, being the same "stuff". It doesn't explain why the actual elemental compositions are different - which the impactor theory does explain but fails to explain the isotopic similarity.
This sig for rent.