Moon is younger and more Earth-like than thought

Geoff Heaps in New Zealand passed my an article written last December about how one might determine the age of the Moon.

Rocks brought back by the Astronauts have been looked at by scientists and from what is seen in their composition, have made some interesting observations about how old the Moon might be.

I hope we get a chance to get a better sampling from more areas of the Moon, both near and far side.

What the poles look like will certainly be of interest as well.

- LRK - Moon is younger and more Earth-like than thought20:13 19 December 2007 NewScientist.com news service Maggie McKee
(see more below)

Thanks for looking up with me.

And thanks even more to you who have woken me up from time to time. :-)

Larry KelloggWeb Site: http://lkellogg.vttoth.com/LarryRussellKellogg/
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Moon is younger and more Earth-like than thought
20:13 19 December 2007
NewScientist.com news service
Maggie McKee

It's a good thing the Moon doesn't have any feelings to hurt. New research suggests it is actually 30 million years younger than anyone had thought, and that it is merely a 'chip off the old block' of Earth rather than being made up of the remnants of a Mars-sized body that slammed into Earth billions of years ago.

That violent impact was thought to have taken place 30 million years after the solar system began to condense from a disc of gas and dust 4.567 billion years ago. The event was thought to have melted the Earth, generating a magma ocean that covered the planet and allowed iron and other metals to sink to its centre, forming a core.

At the same time, the Moon was thought to have coalesced from a disc of molten debris blasted off the Earth and the Mars-sized interloper.

But new research led by Mathieu Touboul of the Swiss Federal Institute of Technology in Zurich suggests that picture is not so simple. The researchers base their analysis on studies of an isotope of the metal tungsten in lunar rocks.

That isotope, tungsten-182, is produced by the decay of two other elements: hafnium-182, which has a half-life of 9 million years, and tantalum-182. Tantalum-182, however, is not an intrinsic component of the Moon – it forms when energetic charged particles from space, called cosmic rays, slam into the lunar surface.

Previous estimates of the Moon's age were based on tungsten measurements that did not subtract the effect of the decay of tantalum. "It is crucial to remove all the tungsten-182 coming from the cosmic-ray production," Touboul told New Scientist. "Otherwise, the age one gets is too old."

Lengthy formation
When Touboul's team accounted for tantalum, they found that the giant impact had to have occurred at least 50 million years after the solar system began to form, and that the Moon had completed its formation within the next 10 million years – about 30 million years later than thought.

The revised timing of the impact implies the terrestrial planets, such as the Earth and Mars, took longer to build up from the collision of smaller 'planetesimals' than previously thought. "The age of the Moon is also the age of Earth because the Moon-forming giant impact was the last major event in Earth's formation," says Touboul.

Alan Brandon, a scientist at NASA's Johnson Space Center in Houston, Texas, US, agrees. "It may mean that Earth and Mars took at least 50 million years, and possibly hundreds of millions of years, to reach their final mass," he comments.

The researchers also found that the composition of the Moon appears identical to that of the Earth's rocky mantle, "such that a major portion of the Moon must have been from proto-Earth", Brandon told New Scientist.

Similar makeup
He says this runs counter to some computer models showing that at least 80% of the Moon is made up of material from the Mars-sized world, which is expected to have a different makeup from the Earth. "I think the Moon-forming impact models will have to be redone to try to get an explanation for why the Earth and Moon are so compositionally similar," he says.

Intriguingly, the new work suggests the Moon formed at least 16 million years after the Earth's core formed. That raises questions about how the planet's iron-rich core could have coalesced in the absence of global magma oceans produced by the Moon-forming impact.

"It could be that there were several generations of magma oceans in Earth," Brandon says. "My guess is … that the Earth probably had a magma ocean at the time the Earth's core formed," he says, adding that the giant impact may have re-melted the material millions of years later.

Journal reference: Nature (vol 450, p 1169 and 1206)

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http://www.nature.com/nature/journal/v450/n7173/abs/nature06428.html
LetterNature 450, 1206-1209 (20 December 2007) doi:10.1038/nature06428; Received 12 July 2007; Accepted 24 October 2007
Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metalsM. Touboul1, T. Kleine1, B. Bourdon1, H. Palme2 & R. Wieler1Institute for Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, Eidgenössische Technische Hochschule Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland Institut für Mineralogie und Geochemie, Universität zu Köln, Zülpicherstrasse 49b, 50674 Köln, Germany Correspondence to: M. Touboul1 Correspondence and requests for materials should be addressed to M.T. (Email: touboul@erdw.ethz.ch).

The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth1 and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf–182W and 146Sm–142Nd chronometry2, 3, 4, but these methods have yielded contradicting results. In earlier studies3, 5, 6, 7, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first 60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface3, 7, compromising a reliable interpretation in terms of 182Hf–182W chronometry.
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http://www.spacedaily.com/news/lunar-01d.html
Boulder - August 15, 2001The "giant impact" theory, first proposed in the mid-1970s to explain how the Moon formed, has received a major boost as new results demonstrate for the first time that a single impact could yield the current Earth-Moon system. Simulations performed by researchers at Southwest Research Institute (SwRI) and the University of California at Santa Cruz (UCSC) show that a single impact by a Mars-sized object in the late stages of Earth's formation could account for an iron-depleted Moon and the masses and angular momentum of the Earth-Moon system
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http://spaceflightnow.com/news/n0108/15mooncreate/

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http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.htmlEarth-Asteroid Collision Formed Moon Later Than ThoughtRichard A. Lovettfor National Geographic News
December 19, 2007

The moon was formed from fragments of Earth after a collision with a giant asteroid relatively late in our planet's formation, new tests of moon rocks show.

The finding upends many of the prior theories for how the moon came to be, researchers say. Scientists have long believed that the moon was formed by a collision between our planet and a Mars-size object. Computer models have shown that in this scenario 80 percent of the moon's material should have come from the asteroid, with only 20 percent from Earth.

But the new study of moon rocks collected three decades ago by Apollo astronauts, however, found that Earth and the rocks were too similar for that to be the case. Earthly Material

The most likely explanation is that the moon was formed primarily of Earthly material, the authors say. Lead author Mathieu Touboul of the Swiss Federal Institute of Technology in Zurich said there is another theory that may explain its formation.

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http://news.nationalgeographic.com/news/2007/12/071219-moon-collision_2.html
Page 2 has more information. - LRK -

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http://www.psi.edu/projects/moon/moon.html
PSI's role:Two PSI senior scientists, Dr. William K. Hartmann and Dr. Donald R. Davis, were the first to suggest the leading modern hypothesis of the moon's origin, in a paper published in 1975 in the journal Icarus.
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How interesting, just finished reading Dr. Hartmann's book "Out Of The Cradle".-LRK -

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WHAT THE MIND CAN CONCEIVE, AND BELIEVE, IT WILL ACHIEVE - LRK

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