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Origin of the moon still shrouded in mystery

File:GRAIL's gravity map of the moon.jpg
gravity map of Moon/NASA

It might seem surprising that the exact origin of our moon is currently something of a mystery, but that’s the gist of a recent article in Nature:

Lunar-origin studies are in flux. No current impact model stands out as more compelling than the rest. Progress in several areas is needed to rule out some theories, support others or direct us to new ones.

We think something hit Earth 4.5 billion years ago, and the moon resulted, but after that the questions start.

It remains troubling that all of the current impact models invoke a process after the impact to effectively erase a primary outcome of the event — either by changing the disk’s composition through mixing for the canonical impact, or by changing Earth’s spin rate for the high-angular-momentum narratives.

Sequences of events do occur in nature, and yet we strive to avoid such complexity in our models. We seek the simplest possible solution, as a matter of scientific aesthetics and because simple solutions are often more probable. As the number of steps increases, the likelihood of a particular sequence decreases. Current impact models are more complex and seem less probable than the original giant-impact concept.

One solution, eagerly embraced by space buffs of course, would be a mission to Venus:

A clue may lie in Venus. The assumption that the Moon-forming impactor had a composition very different from that of Earth is largely based on what we know about Mars. We do not know the isotopic composition of Venus, the planet most similar to Earth in both mass and distance from the Sun. If Venus’s composition proves similar to that of Earth and the Moon, Mars would then seem to be an outlier, and an impactor composition akin to Earth’s would be more probable, removing many objections to the canonical impact.

Astronomers Discover Planet That Shouldn't Be There - Dec. 5, 2013 Excerpt: Weighing in at 11 times Jupiter's mass and orbiting its star at 650 times the average Earth-Sun distance, planet HD 106906 b is unlike anything in our own Solar System and throws a wrench in planet formation theories. "This system is especially fascinating because no model of either planet or star formation fully explains what we see," said Vanessa Bailey, who led the research. Bailey is a fifth-year graduate student in the UA's Department of Astronomy. http://www.sciencedaily.com/releases/2013/12/131205141629.htm bornagain77
ENV also comments: How the Moon Supports the Privileged Planet Hypothesis - December 5, 2013 Excerpt: Planetary scientists were optimistic that the Apollo missions would help decide among three leading hypotheses: capture, fission, and accretion. After Apollo, all three were rejected, leaving theorists without a theory until the "giant impact" hypothesis came along in the 1980s. Till recently, the scenario of a Mars-sized object striking the Earth at a glancing blow was hailed as accepted truth. TV documentaries animated the event handsomely, in vivid color. However, new observations have cast doubt on the (impact) idea. http://www.evolutionnews.org/2013/12/our_moon_still079861.html bornagain77
Mahuna, I have felt your comment to be important. I have headlined it as a part of the ID foundation series here, putting up links and three or so hours of viewing -- PP and a talk by GG. KF kairosfocus
Cue: Privileged Planet . . . kairosfocus
"As the number of steps increases, the likelihood of a particular sequence decreases." OK, so Earth is not merely "very improbable". It's very VERY very improbable. I don't see this as a problem for Earth, which I think we can prove actually exists. I do see it causing a problem for all those "Earth 2" exo-planets, of which we can subtract 99% (or something) based on the HIGHLY improbable repetition of the Earth-Moon formation. You MUST have a Moon to produce tides. And it MUST be a large Moon to act as a final shield against space debris that got past the Gas Giants. mahuna

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