Starship Asterisk*

http://lunar.gsfc.nasa.gov/lola/index.html wrote:
Van de Graaff Crater - The Lunar Figure 8

<<5.07.2010 - Van de Graaff Crater, located on the lunar far side north of South Pole-Aitken Basin (172.08, - 26.92), has an unusual figure 8 shape (~240 km x 140 km) that has long caught the eye of lunar scientists. Its shape suggests that it was formed by two separate impacts even though there is no crater wall separating its two halves. LOLA data indicate that the floor of the crater is relatively flat except for the presence of several smaller impact craters. Portions of its rim reach almost 1000 m above lunar mean elevation level, while its floor is near - 2100 m. Van de Graaff is a region of interest for robotic and human exploration of the Moon due to its location in a magnetically and geochemically anomalous region. The Moon does not have a global magnetic field like the Earth, thus the origin of its small, localized magnetic fields, such as the one near Van de Graaff, is of scientific interest. Van de Graaff and the surrounding region are also slightly enriched in thorium, an element found in lunar KREEP (potassium (K), rare earth elements (REE), and phosphorus (P)) terrain. Most of the Moon's KREEP-rich materials are found on the lunar near side, thus the presence of enhanced thorium in the Van de Graaff region is intriguing.>>

http://en.wikipedia.org/wiki/Shmoo wrote:
<<A shmoo (plural: shmoon, also shmoos) is a fictional cartoon creature. Created by Al Capp (1909 - 1979), they first appeared in his classic comic strip Li'l Abner on August 31, 1948, and quickly became a postwar national craze in the USA. A shmoo is shaped like a plump bowling pin with legs. It has smooth skin, eyebrows and sparse whiskers - but no arms, nose or ears. Its feet are short and round but dexterous, as the shmoo's comic book adventures make clear. It has a rich gamut of facial expressions, and often expresses love by exuding hearts over its head.

Cartoonist Al Capp ascribed to the shmoo the following curious characteristics:

• * They reproduce asexually and are very prolific. They require no sustenance other than air.
  
  * Naturally gentle, they require minimal care, and are ideal playmates for young children.
  
  * Shmoos are delicious to eat, and are eager to be eaten. If a human looks at one hungrily, it will happily immolate itself, either by jumping into a frying pan, after which they taste like chicken, or into a broiling pan, after which they taste like steak. When roasted they taste like pork, and when baked they taste like catfish. (Raw, they taste like oysters on the half-shell.)
  
  * They also produce eggs (neatly packaged), milk (bottled grade-A), and butter — no churning required. Their pelts make perfect bootleather or house timber, depending on how thick you slice it.
  
  * They have no bones, so there's absolutely no waste. Their eyes make the best suspender buttons, and their whiskers make perfect toothpicks. In short, they are simply the perfect ideal of a subsistence agricultural herd animal.
  
  * The frolicking of shmoon is so entertaining (such as their staged "shmoosical comedies") that people no longer feel the need to watch television or go to the movies.
  
  * Some of the more tasty varieties of shmoo are more difficult to catch. Usually shmoo hunters, now a sport in some parts of the country, utilize a paper bag, flashlight and stick to capture their shmoos. At night the light stuns them, then they can be whacked in the head with the stick and put in the bag for frying up later on.

Superficially, the Shmoo story concerns a cuddly creature that desires nothing more than to be a boon to mankind. Although initially Capp denied or avoided discussion of any satirical intentions, he was widely seen to be stalking bigger game subtextually. Shmoos are officially declared a menace, and systematically hunted down and slaughtered — because they were deemed "bad for business". The much-copied storyline was a parable that was interpreted in many different ways at the outset of the Cold War. Al Capp was even invited to go on a radio show to debate socialist Norman Thomas on the effect of the Shmoo on modern capitalism. "After it came out both the left and the right attacked the Shmoo", according to publisher Denis Kitchen. "Communists thought he was making fun of socialism and Marxism. The right wing thought he was making fun of capitalism and the American way. Capp caught flak from both sides. For him it was an apolitical morality tale about human nature… I think [the Shmoo] was one of those bursts of genius."

The actual origin of Capp's word "shmoo" has been the subject of debate by linguists for decades, leading to the misconception that the term was derived from "schmo" or "schmooze". However, "shmue" was a taboo Yiddish term for the female reproductive organ, the ultimate fertility symbol. It's one of many Yiddish slang variations that would find their way into Li'l Abner. Revealing an important key to the story, Al Capp himself wrote that the Shmoo metaphorically represented the limitless bounty of the earth in all its richness — in essence, Mother Nature herself.

In Li'l Abner's words, "Shmoos hain't make believe. The hull [whole] earth is one!!">>

wonderboy wrote:Sounds daft, but could that crater have been created by a really slow impact from a potato like asteroid?

neufer wrote:

wonderboy wrote:Sounds daft, but could that crater have been created by a really slow impact from a potato like asteroid (no jokes rob) or would the rate of travel of this hypothetical potato mean that it would have been captured by the shmoo that is the earth? possibly even eaten?

http://en.wikipedia.org/wiki/Van_de_Graaff_%28crater%29 wrote:
<<Van de Graaff is an unusual lunar formation that has the appearance of two merged craters, approximately in a figure-8 shape with no intervening rim separating the two halves. The crater is located on the far side of the Moon, on the northeast edge of Mare Ingenii.

Orbital studies of the Moon have demonstrated that there is a local magnetic field in the vicinity of this formation that is stronger than the natural lunar field. This is most likely an indication of volcanic rock underneath the surface. The crater also has a slightly higher concentration of radioactive materials than is typical for the lunar surface.

The crater walls in the vicinity of Van de Graaff display an unusual grooved texture. This region lies at the antipode of the Mare Imbrium impact site, and it is thought that powerful seismic waves from this event converged at this point. Most likely this energy created the grooved appearance as the tremors triggered landslides, although the grooves may also have been formed by deposited clumps of ejecta from the impact.>>

http://www.planetary.org/blog/article/00003013/ wrote:
The Moon is a KREEPy place
The Planetary Society Blog
By Emily Lakdawalla Apr. 27, 2011

<<If you go to a conference about lunar geology, sooner or later you'll hear the term "KREEP" bandied about. (And almost as soon as KREEP is mentioned, a bad pun will be made. It's inevitable.) Context will tell you it has something to do with a special kind of lunar rock, but that'll only get you so far. What is KREEP, and why is it important on the Moon?

The simple definition is that KREEP is an acronym for potassium (chemical symbol K), rare earth elements (the ones that are always cut out of the periodic table and drawn in two separate rows of their own, abbreviated REE), and phosphorus (chemical symbol P). Despite their name, the stable rare earths are actually not that uncommon in nature; a few are as common as copper and lead and all are more common than mercury and iodine and way more common than gold and iridium.

Potassium, rare earths, and phosphorus are lumped together in the term KREEP because they tend to occur together in the lunar crust. To explain why they tend to occur together, we have to back up the story to the beginning, when the Moon formed.

The molten moon had a bulk composition of rock; more specifically, its bulk composition is of a mafic rock, one that's rich in iron and magnesium. It had also lost most of its volatile elements like hydrogen and sulfur, which would have bubbled out of the melt as gases and been stripped away by the solar wind. When a melt with this particular composition cools, it begins to solidify, of course.

But the way it solidifies is a bit strange. The solid material that forms when a rock melt solidifies does not have the same composition as the melt. What happens is that a particular kind of crystal starts to form in the melt. This crystal is called olivine; it's made of iron and/or magnesium plus silicon and oxygen. So when olivine crystals start to form, pretty much the only elements that are being removed from the melt to make the solids are iron, magnesium, silicon, and oxygen. Other minerals that crystallize out of rock melts at high temperatures are pyroxene (similar to olivine, just a bit richer in silicon and oxygen) and anorthite (which is made of calcium, aluminum, silicon, and oxygen).

Occasionally, some other metal ions get incorporated into the olivine crystals, substituting for iron or magnesium. This is much more likely to happen if the metal ion in question is the same diameter and charge (in this case, +2) as iron or magnesium. Nickel, for instance, very happily substitutes for iron or magnesium in olivine crystals; its ions are similar in size to iron and magnesium, and they usually have a +2 charge.

Some elements just can't squeeze in to the crystal lattices. Potassium, for example, is a very common element whose ions are so puffily large that they just don't fit very well in crystal lattices that want nice little iron and magnesium ions, and they also have the wrong charge (+1). So potassium, and other elements that are incompatible with the crystals that form at high temperatures, don't get included in the growing crystals; they remain in the leftover melt that still hasn't solidified yet.

OK, getting back to our cooling molten Moon: now gravity becomes important. Olivine and pyroxene are both quite dense, denser than the remaining melt. Given enough time for gravity to operate -- and it would have had quite a while, because it takes a long time for a molten body as big as the Moon to solidify -- the olivine and pyroxene crystals will sink all the way to the bottom of the magma ocean. They built up in a thick pile, hundreds, even a thousand kilometers worth of olivine and pyroxene crystals. Meanwhile, anorthite is less dense than the melt. So the anorthite crystals floated to the top, becoming a scum on the surface of the lunar magma ocean. That scum of anorthite is what we see today as the lunar highlands, relatively light-colored rocks that are made almost entirely of anorthite. (A rock made mostly of anorthite crystals is called anorthosite.) This process of forming and removing crystals of different composition than the remaining melt is called "fractional crystallization."

In between the olivine-pyroxene mantle and the anorthite crust, the leftover melt became more and more and more enriched in the incompatible elements, including potassium, rare earths, and phosphorus, the members of KREEP. This material was the last to solidify. It may actually have remained molten for a very long time after everything else was solid, because among the incompatible elements are thorium and uranium, radioactive elements that generate a lot of heat on their own through their decay.

OK, so that's what KREEP is. Now, why is it important? Fast-forward from the formation of the Moon to the Apollo program. The Apollo astronauts collected lots of samples of rocks and dust, and KREEP-rich materials were returned from every one of the landing sites. Geologists concluded that that KREEP-rich late melt was present all over the Moon.

A map of the thorium content of the lunar surface based on Lunar Prospector data shows that a large area on the nearside of the Moon, including the Imbrium basin and Oceanus Procellarum, is enriched in thorium relative to the rest of the Moon. There is also an area of enriched thorium on the farside, within the South Pole-Aitken Basin, but it is less enriched than the area on the nearside. Credit: Data: NASA / JPL / Jeff Gillis; map by Paul Spudis

---

So the results of the Lunar Prospector mission's Gamma-Ray Spectrometer (GRS) came as quite a shock. The GRS detected gamma rays naturally emanating from the Moon. Most of these gamma rays come from neutrons banging into atoms in the lunar crust, but gamma rays of one specific energy (2.6 Megaelectronvolts, if you must know) almost all come from the radioactive decay of thorium-232. So by looking at gamma rays from the Moon at that specific energy, the GRS team could make a map of thorium abundance on the Moon. Thorium, being an incompatible element that is found with the rare earths, is a marker for KREEP. Based on the Apollo samples, the GRS team espected to find a spotty distribution of thorium, some here and some there, all over the Moon. What they got instead was this:

Thorium is concentrated mostly in one area of the lunar nearside, in the around the great big Imbrium basin. It's not nearly as abundant anywhere else. On the farside, there's a bit more in the South Pole-Aitken Basin than elsewhere, but the enrichment is slight. If Imbrium dug in to the KREEP-rich material at the base of the crust, South Pole-Aitken should really have dug a lot of it out onto the surface, but it didn't; and neither did many of the other big basins, like Orientale for instance. This suggests that the KREEP-rich late last melt was concentrated on the nearside for some unknown reason; the heat from its decaying thorium and uranium could help explain the late mare volcanism on the nearside, which is kind of neat.

The thorium map is interesting, but it's also disturbing. If the rocks from every single Apollo landing site included KREEP-rich material, that means that the Apollo samples aren't representative of the Moon as a whole, only of the part of the Moon that's rich in KREEP. In fact, there is a distinct possibility that a great many of the Apollo samples represent ejecta from a single impact, the one that produced the Imbrium basin, which was one of the last big basins to form on the Moon; its ejecta did very likely land everywhere that the Apollo astronauts gathered samples. That's bad news for people who rely on the ages meaured from Apollo rock samples and the absolute dates given to the cratering chronology derived from it.>>

Chris Peterson wrote:The slowest speed any two objects can come together is determined by their escape velocities. In the case of the Moon, the escape velocity is 2.4 km/s, and that is the slowest possible collision.

Sam wrote:

Chris Peterson wrote:
The slowest speed any two objects can come together is determined by their escape velocities.
In the case of the Moon, the escape velocity is 2.4 km/s, and that is the slowest possible collision.

Could you explain why this is?
The case of an apple falling gently on Newton's head argues against having the
slowest possible collision = velocity_escape.

What am I missing?