Engineered collision spills new Moon secrets (w/ Video)

Oct 21, 2010
Peter Schultz and graduate student Brendan Hermalyn analyzed data from bits of the Moon’s surface kicked up by a NASA-engineered collision. They found unexpected complexity -- and traces of silver. Credit: Mike Cohea/Brown University

Scientists led by Brown University are offering the first detailed explanation of the crater formed when a NASA rocket slammed into the Moon last fall and information about the composition of the lunar soil at the poles that never has been sampled. The findings are published in a set of papers in Science stemming from the successful NASA mission, called LCROSS for Lunar CRater Observing and Sensing Satellite.

Mission control at Ames sent the emptied upper stage of a rocket crashing into the Cabeus crater near the Moon's south pole last October. A second spacecraft followed to analyze the ejected debris for signs of water and other constituents of the super-chilled lunar landscape.

In one of the papers, Brown planetary geologist Peter Schultz and graduate student Brendan Hermalyn, along with NASA scientists, write that the cloud kicked up by the rocket's impact showed the Moon's soil and subsurface is more complex than believed: Not only did the lunar regolith — the soil — contain water, it also harbored other compounds, such as hydroxyl, carbon monoxide, carbon dioxide, ammonia, free sodium, and, in a surprise, silver.

Combined, the assortment of volatiles — the chemical elements weakly attached to regolith grains — gives scientists clues where they came from and how they got to the polar craters, many of which haven't seen sunlight for billions of years and are among the coldest spots in the solar system.

Schultz, lead author on the Science paper detailing the impact crater and the ejecta cloud, thinks many of the volatiles originated with the billions of years-long fusillade of comets, asteroids and meteoroids that have pummeled the Moon. He thinks an assortment of elements and compounds, deposited in the regolith all over the Moon, could have been quickly liberated by later small impacts or could have been heated by the sun, supplying them with energy to escape and move around until they reached the poles, where they became trapped beneath shadows of the frigid craters.

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Peter Schultz and graduate student Brendan Hermalyn analyzed data from bits of the Moon’s surface kicked up by a NASA-engineered collision. They found unexpected complexity -- and traces of silver. Credit: Mike Cohea and Richard Lewis, Brown University

"This place looks like it's a treasure chest of elements, of compounds that have been released all over the Moon," Schultz said, "and they've been put in this bucket in the permanent shadows."

Schultz believes the variety of volatiles found in Cabeus crater's soil implies a kind of tug of war between what is being accumulated and what is being lost to the tenuous lunar atmosphere.

"There's a balance between delivery and removal," explained Schultz, who has been on the Brown faculty since 1984 and has been studying the Moon since the 1960s. "This suggests the delivery is winning. We're collecting material, not simply getting rid of it."

Astronauts sent as part of NASA's Apollo missions found trace amounts of silver, along with gold, on the near-side (Earth-facing side) of the Moon. The discovery of silver at Cabeus crater suggests that silver atoms throughout the migrated to the poles. Nevertheless, the concentration detected from Cabeus "doesn't mean we can go mining for it," Schultz said.

The crater formed by the rocket's impact within Cabeus produced a hole 70 to 100 feet in diameter and tossed up six-foot deep lunar material. The plume of debris kicked up by the impact reached more than a half-mile above the floor of Cabeus, high enough to rise into sunlight, where its properties could be measured for almost four minutes by a variety of spectroscopic instruments. The amount of ejecta measured was almost two tons, the scientists report. The scientists also noted there was a slight delay, lasting roughly one-third of a second, in the flash generated after the collision. This indicated to them that the surface struck may be different than the loose, almost crunchy surface trod by the Apollo astronauts.

"If it had been simply lunar dust, then it would have heated up immediately and brightened immediately," Schultz said. "But this didn't happen."

The scientists also noticed a one-half-mile, near-vertical column of ejecta still returning to the surface. Even better, the LCROSS was able to observe the plume as it followed on the heels of the crashing rocket. Schultz and Hermalyn had observed such a plume when conducting crater-impact experiments using hollow spheres (that mimicked the rocket that crashed into Cabeus) at the NASA Ames Vertical Gun Range in California before the LCROSS impact.

"This was not your ordinary impact," Hermalyn said. "So in order to understand what we were going to see (with LCROSS) and maybe what effects that would have on the results, we had to do all these different experiments."

Even though the mission has been judged a success, Schultz said it posed at least as many questions as it answered.

"There's this archive of billions of years (in the Moon's permanently shadowed craters)," Schultz said. "There could be clues there to our Earth's history, our solar system, our galaxy. And it's all just sitting there, this hidden history, just begging us to go back."

Explore further: Computer simulation suggests early Earth bombarded by asteroids and comets

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GDM
5 / 5 (5) Oct 21, 2010
For those of you that missed the NASA audio feed on this, some highlights: LCROSS hit what is described as "dirt covered snow"; perhaps as much as 30% of the lunar surface (even in sun lit areas) are cold enough for frozen water to exist as "permafrost"; 11-12 gallons of water per ton of soil in Cabaeus crater, which could mean as much as a billion (1,000,000,000) gallons of water in Cabaeus alone; approx. 5.6% of the plume was water (1% was considered "useful"); lunar soil with these concentrations need only to be heated to "room temperature" to recover the water instead of "baking" the soild/rocks to 100's of degrees.
El_Nose
2 / 5 (2) Oct 21, 2010
question... with a spherical body that is revolving how does a crater have an area that never recieves sun light.

too those tempted to say the dark side of the moon -- please know that all sides of the moon recieve light as it rotates and the dark side of the moon means that because the rotational period is equal to its revolutionary period we only see one side illuminated by sunlight.
hypermach
5 / 5 (4) Oct 21, 2010
wow a question I can answer - the dark areas are in the bottom of a crater on the pole - its interesting that a mountain that is always in the sun is near a valley which is never lit
Doug_Huffman
1.7 / 5 (3) Oct 21, 2010
Hence the phrase "dark side of the moon'?
Graeme
4 / 5 (1) Oct 21, 2010
There should be some interesting chemistry in the moon crater with elemental sodium, water, ammonia and carbon dioxide. We could get sodium formate, urea, melamine, oxalate as well as sodium hydroxide. However what is the volatile silver substance that would lead to it migrating to the pole?
QuantumDelta
4 / 5 (1) Oct 22, 2010
The "Dark side of the moon" is a bit of an odd phrase, one would expect it to refer to the side of the moon that is currently facing away from the sun (*obviously, this changes as the moon orbits the earth), however in most instances in literature (fiction), it's used as an expression for the side of the moon that's facing away from the earth.
Although several craters on the moons poles never receive sunlight the poles on the whole do receive as much as the rest of the moon.
Anyone know if the moon wobbles? and ifso, to what degree? (I'd assume it'd have to be a tiny one compared to the earths for there to be permanently dark craters)...
Jimbaloid
4 / 5 (2) Oct 22, 2010
"dark side of the moon'?


Think about a total eclipse of the sun...
GDM
not rated yet Oct 22, 2010
"Dark Side of the Moon" - QD is correct - it is a 1950's term regarding the far side, which is always out of view from the Earth. By the way, there is an effort underway to preserve a specific crater about dead center on the far side as an electronic listening post/radio telescope site that would be virtually free from radio interference from Earth.
Also QD, yes, the moon does wobble very slightly. Not sure how much but it should be Google-able.
Graeme: The silver, as I understood from the NASA audio feed, is released in atomic form due to impacts and the atoms just "hop around" until they settle into a "cold sink" such as Cabeus crater, which has temperatures close to absolute zero. (Seriously! Some craters on the moon are the coldest known places in our solar system.) It isn't necessary that the craters be near the poles, although it helps. Some areas of the moon that receive a lot of sunlight can still have a lot of water trapped a few inches below the surface as permafrost.
Graeme
not rated yet Oct 31, 2010
After reading more on the topic, this article missed the major amount of mercury present, perhaps 5%, as much as the water ice.