Thursday, December 6, 2012

LPOD Lunar photo of the day FOR December 6, 2012


I was doing some more checks on the LPOD web site and today's  image was fitting with the announcement from GRAIL about the new lunar gravity map.
- LRK -

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December 6, 2012
image by NASA/JPL-Caltech/IPGP

A windfall of first result was presented yesterday by Maria Zuber and team members of the Grail spacecraft currently orbiting the Moon. Grail's tandem spacecraft, Ebb  and Flow, yield the most precise measurements ever made of lunar gravity. Combining the new gravity data with the unexcelled topography from LRO allows the calculation of crustal thickness, as shown in this map by Wieczorek and other Grail scientists. Red marks the thickest crust, up to about 60 km, and dark blue to purple is thinnest.

Remarkably, the crust in parts of Mare Crisium and Mare Moscoviense is only 1 km thick or less. On Earth the thinnest crust under ocean floors is about 10 km thick and attempts to drill through it to reach the Moho, the crust-mantle boundary, failed. In Crisium, a crater 5 km wide could penetrate the crust and reach the lunar mantle; such a crater would be an important sample return target. The average lunar crustal thickness is found to be about 34 km, with the thickest being about 60 km in the farside highlands, of course some of that is due to piles of ejecta from the South Pole-Aitken basin. The purple stars represent areas that data from the Japanese Kaguya spacecraft indicated to be olivine-rich. Olivine is a mineral that is thought to be associated with the mantle, and the distribution of rare olivine around basins is consistent with their excavation of mantle material (which otherwise is not indicated by geochemistry). The excess of olivine around Crisium and Moscoviense is said to be expected because of their very shallow crusts, but of course the basin-forming impact is why the crust is thin. 

Chuck Wood

Related Links
More than a dozen different maps are shown in the Grail image gallery.
The Moho Song
http://www.nasa.gov/mission_pages/grail/multimedia/gallery/gallery-index.html
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If by chance you have the time or inclination to look further into the LPOD Wikispaces you will find comments and files noted.  One PDF file for a August 2010 meeting about the morphology of the moon I found interesting.
- LRK -

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Pages and Files
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Workshop Document Briggs version 4
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Let me see if I can copy some snips from the conference agenda just to make us all feel bad that we couldn't have been there.  :-)
- LRK -

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A Lunar Morphology Workshop
Thursday, August 5, 2010

We are pleased to offer a pre-Stellafane workshop at the historic Hartness House Inn and Porter-Hartness Museum of Telescope Making located in Springfield, Vermont, cosponsored by the Antique telescope Society. Proceeds will go towards the purchase of a replacement furnace for the Museum, which is run by volunteers from the Springfield Telescope Makers. This year we have added an evening banquet and after-dinner speaker, Professor Peter Schultz from Brown University.
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3:00 – 3:45 William Sheehan A man in a far-away place with an idea far ahead of its time: A. C. Gifford and the Modern Impact Theory of Lunar Crater Formation
3:45 – 4:30 Richard Evans Lunar rock and mineral mapping using public-domain software with Clementine and Lunar Prospector data: The Geological Lunar Research Group (GLR) Experience
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7:15 – 8:15 Peter Schultz Secrets from the Shadows of the Moon: Results from LCROSS
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Bert Willard Russell W. Porter – His lunar drawings and crater Porter
While living in Port Clyde, Maine, Porter made some fanciful drawings of the moon using his 16-inch polar telescope. Having spent many years above the Arctic Circle, he likened the lunar landscape to that of the polar landscape. The drawings are from the prospective of a lunar probe about to land on the moon. These were published in Popular Astronomy magazine in 1916. They will be compared to modern photographs taken by a member of the Springfield Telescope Makers.

Chuck Wood Introduction to lunar morphology

Peter Schultz Making the man in the Moon: Observing the Moon in the context of its geological history

Tom Dobbins Transient Lunacy

William Sheehan A man in a far-away place with an idea far ahead of its time: A. C. Gifford and the Modern Impact Theory of Lunar Crater Formation
The craters of the Moon, discovered by Galileo with his small telescope, are the distinguishing feature of the lunar surface. From the first, every glance at the surface of the Moon called forth the question of the origin of these remarkable features. Perhaps in part because of the name, the craters were long believed by most astronomers to be volcanic, but after it was reliably established (by Chladni and others in the 18th century) that stones--meteorites--actually fell from the sky onto the surface of the Earth, early versions of a meteorite impact theory were proposed to explain the lunar craters. These theories assumed that the meteorites fell onto the lunar surface while it was still in a plastic state and--in order to account for the uniformly circular outlines of the lunar craters--they were supposed to have dropped nearly vertically onto the lunar surface. These ideas were not, however, regarded as plausible by most astronomers.

Even the pioneer of the modern impact theory, the geologist G.K. Gilbert, who in 1892 presented his analysis that the lunar maria were formed by impacts, assumed that these structures were formed by mechanical impacts like the holes formed in a target fired from a gun. In order to account for their circularity, he too assumed they resulted from nearly vertical falls--and introduced the ad hoc assumption that the Earth must once have been surrounded by a Saturn-like ring to account for the perpendicularity of their encounters with the Moon.

The great breakthrough in understanding the formation of lunar craters came from applying basic principles of physics. In 1915, just after the beginning of World War I, the eccentric New Zealand Professor A.W. Bickerton, author of the controversial "partial impact theory" to explain novae and a host of other astronomical phenomena, realized that meteors travel with sufficient speed to produce results like those being seen with the exploding shells of the battlefields of Flanders and the Somme. Bickerton, however, was a poor mathematician; and it was left to his
friend and colleague A. C. Gifford--who as a student had won the Herschel prize for mathematical astronomy at Cambridge--to demonstrate, in 1924, the physics of impact, and to show that a collision of a meteorite with the Moon would be explosive in nature, and produce features modeling in all respects the actual forms of the lunar craters. Because Gifford published only in obscure New Zealand journals, his work remained practically unknown. However, it is now clear that Gifford anticipated all of the major ideas of the modern impact theory later developed (independently) by Ralph B. Baldwin, Eugene M. Shoemaker and others a generation later, and that he deserves to be more widely appreciated as one of the most important figures in the modern study of the Moon.
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Reading again the paragraph above:
"Because Gifford published only in obscure New Zealand journals, his work remained practically unknown. However, it is now clear that Gifford anticipated all of the major ideas of the modern impact theory later developed (independently) by Ralph B. Baldwin, Eugene M. Shoemaker and others a generation later, and that he deserves to be more widely appreciated as one of the most important figures in the modern study of the Moon."

You do notice Ralph B. Baldwin, and Eugene M. Shoemaker.  Early on it was thought that it was volcanic action that scared the lunar surface.  How could meteors make round holes in the regolith? Much discussion there.  Hmm, best sit down and do some reading in "Measure of the Moon" by Ralph B. Baldwin.

And for you folks, this may be helpful.
-LRK -

Here is to looking up, maybe near, maybe far, maybe even a star.
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WHAT THE MIND CAN CONCEIVE, AND BELIEVE, IT WILL ACHIEVE - LRK -

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