Posts Tagged ‘moon’

The Early Moon Was Wet – Scientists Say

Posted: February 19, 2013 by phaedrap1 in Science
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MessageToEagle.com – Traces of water have been detected within the crystalline structure of mineral samples from the lunar highland upper crust obtained during the Apollo missions, according to a University of Michigan researcher and his colleagues.

The lunar highlands are thought to represent the original crust, crystallized from a magma ocean on a mostly molten early moon. The new findings indicate that the early moon was wet and that water there was not substantially lost during the moon’s formation.

The results seem to contradict the predominant lunar formation theory — that the moon was formed from debris generated during a giant impact between Earth and another planetary body, approximately the size of Mars, according to U-M’s Youxue Zhang and his colleagues.

 


Click on image to enlargeClose up view of Hadley Rille and the Apollo 15 traverse map. Credits: NASA

“Because these are some of the oldest rocks from the moon, the water is inferred to have been in the moon when it formed,” Zhang said. “That is somewhat difficult to explain with the current popular moon-formation model, in which the moon formed by collecting the hot ejecta as the result of a super-giant impact of a martian-size body with the proto-Earth.

“Under that model, the hot ejecta should have been degassed almost completely, eliminating all water,” Zhang said.

Over the last five years, spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the moon is bone-dry.

 


Click on image to enlargeCalled the “Genesis Rock,” this lunar sample of unbrecciated anorthosite collected during the Apollo 15 mission was thought to be a piece of the moon’s primordial crust. In a paper published online Feb. 17 in Nature Geoscience, a University of Michigan researcher and his colleagues report that traces of water were found in the rock. Photo courtesy of NASA/Johnson Space Cente

In 2008, laboratory measurement of Apollo lunar samples by ion microprobe detected indigenous hydrogen, inferred to be the water-related chemical species hydroxyl, in lunar volcanic glasses. In 2009, NASA’s Lunar Crater Observation and Sensing satellite, known as LCROSS, slammed into a permanently shadowed lunar crater and ejected a plume of material that was surprisingly rich in water ice.

Hydroxyls have also been detected in other volcanic rocks and in the lunar regolith, the layer of fine powder and rock fragments that coats the lunar surface. Hydroxyls, which consist of one atom of hydrogen and one of oxygen, were also detected in the lunar anorthosite study reported in Nature Geoscience.

 

In the latest work, Fourier-transform infrared spectroscopy was used to analyze the water content in grains of plagioclase feldspar from lunar anorthosites, highland rocks composed of more than 90 percent plagioclase.

The bright-colored highlands rocks are thought to have formed early in the moon’s history when plagioclase crystallized from a magma ocean and floated to the surface.

The infrared spectroscopy work, which was conducted at Zhang’s U-M lab and co-author Anne H. Peslier’s lab, detected about 6 parts per million of water in the lunar anorthosites.

 

“The surprise discovery of this work is that in lunar rocks, even in nominally water-free minerals such as plagioclase feldspar, the water content can be detected,” said Zhang, James R. O’Neil Collegiate Professor of Geological Sciences.

 

Lunar Ferroan Anorthosite 60025

At 4.5 billion years old, this anorthosite is approximately the same age as the Moon itself. Made mostly of plagioclase feldspar, it is thought to be a sample of the Moon\’s early feldspar crust. Collected by Apollo 16. Locality: Lunar Highlands, near Descartes Crater , NA. Credits: NASA
“It’s not ‘liquid’ water that was measured during these studies but hydroxyl groups distributed within the mineral grain,” said Notre Dame’s Hui. “We are able to detect those hydroxyl groups in the crystalline structure of the Apollo samples.”

The hydroxyl groups the team detected are evidence that the lunar interior contained significant water during the moon’s early molten state, before the crust solidified, and may have played a key role in the development of lunar basalts. “The presence of water,” said Hui, “could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous moon scenario suggests.”

The researchers analyzed grains from ferroan anorthosites 15415 and 60015, as well as troctolite 76535. Ferroan anorthosite 15415 is one the best known rocks of the Apollo collection and is popularly called the Genesis Rock because the astronauts thought they had a piece of the moon’s primordial crust. It was collected on the rim of Apur Crater during the Apollo 15 mission.

Rock 60015 is highly shocked ferroan anorthosite collected near the lunar module during the Apollo 16 mission. Troctolite 76535 is a coarse-grained plutonic rock collected during the Apollo 17 mission.

A paper titled “Water in lunar anorthosites and evidence for a wet early moon” was published online Feb. 17 in the journal Nature Geoscience.

Huge Moon-Forming Collision Theory Gets New Spin

Posted: October 18, 2012 by phaedrap1 in News, Science
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Moon Born in Violence
This artist’s conception of a planetary smashup whose debris was spotted by NASA’s Spitzer Space Telescope three years ago gives an impression of the carnage that would have been wrecked when a similar impact created Earth’s Moon. A team at Washington University in St. Louis has uncovered evidence of this impact that scientists have been trying to find for more than 30 years. Image released Oct. 17, 2012.
CREDIT: NASA/JPL-Caltech

The moon did indeed coalesce out of tiny bits of pulverized planet blasted into space by a catastrophic collision 4.5 billion years ago, two new studies suggest.

The new research potentially plugs a big hole in the giant impact theory, long the leading explanation for the moon’s formation. Previous versions of the theory held that the moon formed primarily from pieces of a mysterious Mars-size body that slammed into a proto-Earth — but that presented a problem, because scientists know that the moon and Earth are made of the same stuff.

The two studies both explain how Earth and the moon came to be geochemical twins. However, they offer differing versions of the enormous smashup that apparently created Earth’s natural satellite, giving scientists plenty to chew on going forward.

A fast-spinning Earth

One of the studies — by Matija Cuk of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, Calif., and Sarah Stewart of Harvard — suggests the answer lies in Earth’s rotation rate.

If Earth’s day had been just two to three hours long at the time of the impact, Cuk and Stewart calculate, the planet could well have thrown off enough material to form the moon (which is 1.2 percent as massive as Earth).

This rotational speed might sound incredible, and indeed it’s close to the threshold beyond which the planet would begin to fly apart. But researchers say the early solar system was a “shooting gallery” marked by many large impacts, which could have spun planets up to enormous speeds.

Cuk and Stewart’s study, which appears online today (Oct. 17) in the journal Science, also provides a mechanism by which Earth’s rotation rate could have slowed over time.

After the collision, a gravitational interaction between Earth’s orbit around the sun and the moon’s orbit around Earth could have put the brakes on the planet’s super-spin, eventually producing a 24-hour day, the scientists determined.

A Massive Collision Creates the Moon
Simulation of an off-center, low-velocity collision between two protoplanets containing 45 percent and 55 percent of Earth’s mass. Color scales with particle temperature in kelvin, with blue-to-red indicating temperatures from 2,000 K to in excess of 6,440 K. After the initial impact, the protoplanets re-collide, merge and form a rapidly spinning Earth-mass planet surrounded by an iron-poor protolunar disk containing about 3 lunar masses. The composition of the disk and the final planet’s mantle differ by less than 1 percent.
CREDIT: Southwest Research Institute

A bigger impactor

Cuk and Stewart’s version of the cosmic smashup posits a roughly Mars-size impactor — a body with 5 percent to 10 percent the mass of Earth. However, the other new study — being published in the same issue of Science today — envisions a collision between two planets in the same weight class.

“In this impact, the impactor and the target each contain about 50 percent of the [present] Earth’s mass,” Robin Canup, of the Southwest Research Institute in Boulder, Colo., told SPACE.com via email.

“This type of impact has not been advocated for the Earth-moon before (although a similar type of collision has been invoked for the origin of the Pluto-Charon pair),” Canup added, referring to the largest moon of Pluto.

In her computer models, the symmetry of this collision caused the resulting moon-forming debris disk to be nearly identical in composition to the mantle of the newly enlarged Earth.

Canup’s models further predict that such an impact would significantly increase Earth’s rotational speed. But that may not be a big issue, since Cuk and Stewart’s work explains how Earth’s spin could have slowed over time.

A third study, published today in the journal Nature, determined that huge amounts of water boiled away during the moon’s birth. The finding, made by examining moon rocks brought back to Earth by Apollo astronauts, further bolsters the broad outlines of the giant impact theory.

Though the gigantic smashup occurred 4.5 billion years ago, scientists may one day be able to piece together in detail how it all went down, Canup said.

“Models of terrestrial planet assembly should be able to evaluate the relative probability of, e.g., the collision I advocate vs. the one proposed by Cuk and Stewart,” she said.

 

by Mike Wall, SPACE.com Senior Writer

Date: 17 October 2012