Interesting lunar abstracts from recent conferences Options

[Guest_BruceMoomaw_*]

Once again, my subjective judgement as to what the rest of you are likely to find interesting. Proceed at your own risk:

LPSC 2006:
#1408 -- New Arecibo studies if Shackleton Crater fail to show any high radar reflectivity that would indicate thick patches of ice: "These new data support the hypothesis that the south-polar hydrogen enhancement measured by the Lunar Prospector spacecraft reflects a widely disseminated component of the lunar regolith, rather than any localized concentration of water ice." (About 1.5% of the regolith by weight.)

#1593: A lunar-sample zircon shows the same excess of oxygen-18 that Stephen Mojzsis has interpreted, in Australian zircons dating all the way back to 4.4 billion years ago (the oldest surviving material on Earth), as evidence of large amounts of liquid water on Earth that early. Nemchin et al take this as evidence that the connection is thus a lot shakier than Mojzsis thinks.

#2454, 1153 and 1930: The debate over what caused the great difference between the Moon's nearside and farside -- the much thinner crust and extensive maria of the former -- continues. P.S. Mohit, at last year's LPSC ( http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2063.pdf ) went for internal processes as the cause: "These results, combined with the dearth of mare volcanism on the farside and the high concentration
of radiogenic elements in the PKT [Procellarum KREEP Terrane], suggest that the farside cooled faster than the nearside. This thermal asymmetry might have occurred as a consequence of the crustal thickness asymmetry. Once the magma ocean had mostly cooled, the remaining liquid would tend to pool beneath the thin crust of the nearside, bringing with it the majority of the heat-producing elements. Further cooling would then have sequestered the dregs into the PKT." J.J. Gillis-Davis goes for the same explanation at this year's conference -- but Charles Byrne and P.E. Clark (#1930 and 1153) say that an analysis of the distribution of nearside topographic altitudes shows evidence for an utterly gigantic ancient impact basin covering most of the Moon's nearside, with most of its ejecta thrown onto the farside to thicken the crust there.

EGU 2006:
http://www.cosis.net/abstracts/EGU06/05133/EGU06-J-05133.pdf : Ray Burgess says that age-dating of lunar meteorites, interestingly, shows "multiple major impact events occurring between <1.0-3.9 Ga. These ages do not cluster at 3.8-3.9 Ga, the dominant impact event recorded by Apollo impact melts, but there is a notable lack of impact ages older than 3.9 Ga, representing the period before most of the major lunar basins were formed." Does this work for or against the Terminal Bombardment theory?

http://www.cosis.net/abstracts/EGU06/00888...6-J-00888-1.pdf : T. Prettyman says that Lunar Prospector's gamma-ray spectral maps provide "confirmation that SPA [South Pole-Aitken Basin] does not expose mantle material at the resolution of the measurements", but merely exposes deep crustal material -- something hinted at in some earlier LPSC abstracts. If so, this weakens -- but by no means wrecks -- the case for the New Frontiers Aitken Basin sampling mission.

COSPAR 2006:
http://www.cosis.net/abstracts/COSPAR2006/...006-A-00154.pdf : Always the dissenters... E.J. Griv et al oppose the giant-impact theory of the Moon's origin, and argue instead for simultaneous accretion of the Earth and the Moon out of the "preplanetary disk" that formed the Earth. However, their argument is based on their belief that "the megaimpact hypothesis belongs to a rare class of catastrophic hypotheses that are based on low-probability random events" -- but some analyses suggest that such glancing giant impacts may actually be quite common in the inner parts of forming planetary systems.

Coming up next: my idea of interesting new Venus abstracts.

[Guest_BruceMoomaw_*]

One especially interesting abstract from last year's LPSC: http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1613.pdf , in which Joshua Neubert provides a very detailed rundown of what we currently know, don't know, and suspect about the lunar polar ice deposits -- including the still not-closed question of whether they really are ice.

One rather bloodcurdling passage: "If the solar wind is a large source of the hydrogen seen by Lunar Prospector, a significant amount of C, N, and H ions could be delivered as well. These ions provide the reactants necessary for even more complex reactions. Or, if cometary gases are deposited they will be trapped in amorphous ice. If significant amounts of ice exist, the products of these reactions with the solar wind or cometary impact should exist as well, such as amorphous ice with relatively high concentrations of trapped gases. If there are enough trapped gases from these reactions it could produce an explosive effect if a small amount of thermal energy were applied, such as that of a landed spacecraft or a small impact."