The Lunar Geminids

Lunar impacts since Nov. 2005. Numbers 14-16 and 19-20 are Geminids. Number 18 is a probable Geminid. [NASA Meteoroid Environment Group]-Enlarge Image.

As observers pray for clear skies ahead of the 2009 Geminid Meteor Shower, this weekend, hoping with the dark sky afforded by a New Moon to detect as many as 100 or more meteors per hour as our planet passes through the long column of extinct 3200 Phaeton, I've finally hit upon an excuse I needed since the LCROSS impact on October 9 to use an illustration brought up in 2007 showing how frequently the Moon is struck with explosive force.

People have witnessed meteors at every opportunity from time immemorial, of course. Often deliberately, as many will this weekend or, as often happens, sometimes directly in their line of sight the instant after they happen to glance up on a starry night.. While we do have a record of these speedy darts here on Earth, and the stark testimony of crater saturation on the Moon's surface as witness to this regular feature of our place in the Cosmos, the Moon's surface is billions of years old. Reading the history of the inner solar system engraved on the Moon will require sustained exploration, and this is likely to require an extended human presence there. Before we return to the Moon for more lengthy stays, however, we're going to need to finally get a solid idea on the probability of small impacts, their frequency juxtaposed against their magnitude.

First observed (but unclassified) in the 1860's the Geminids have steadily increased each year since, until in our time they are well-known as the year's best. Investigators are keen to know if this year will be it's peak. On encountering the column of their orbit, clustered around the ancient orbit of extinct Near Earth Object 3200 Phaeton, whether a comet or asteroid is not certain, we appear to have gotten closer and closer to the main population of fragments. Presumably we will, at some point, arrive at the depreciating side.

Which brings me, for the second time since 2007, to the results of a sustained observation campaign sponsored by NASA to create a record of impacts on the Moon, which gave rise to the phenomena now known as "the Lunar Geminids."

"January 3, 2007: Another meteor shower, another bunch of lunar impacts..."

"On Dec. 14, 2006, we observed at least five Geminid meteors hitting the Moon," reports Bill Cooke of NASA's Meteoroid Environment Office in Huntsville, AL. Each impact caused an explosion ranging in power from 50 to 125 lbs of TNT and a flash of light as bright as a 7th-to-9th magnitude star.

"The explosions occurred while Earth and Moon were passing through a cloud of debris following near-Earth asteroid 3200 Phaethon. This happens every year in mid-December and gives rise to the annual Geminid meteor shower: Streaks of light fly across the sky as rocky chips of Phaethon hit Earth's atmosphere. It's a beautiful display.

"The same chips hit the Moon, of course, but on the Moon there is no atmosphere to intercept them. Instead, they hit the ground. "We saw about one explosion per hour," says Cooke."

Re-read the report HERE.

New Lunar Meteorite Found In Antarctica

Although last year's inclement weather resulted in fewer Antarctic meteorite recoveries than usual, scientists have recently discovered that one of the specimens is a rare breed -- a type of lunar meteorite seen only once before.

The new specimen was found by a field party from the U.S. Antarctic Search for Meteorites program (ANSMET) headquartered at Case Western Reserve University. The meteorite was discovered on Dec. 11, 2005, on an icefield in the Miller Range of the Transantarctic Mountains, roughly 750 km from the South Pole.

This 142.2 g black rock, slightly larger than a golfball and officially designated MIL 05035, was one of 238 meteorites collected by ANSMET during the 2005-2006 austral summer. Heavy snows limited search efforts during much of the remainder of the six-week field season, making this meteorite, discovered just 600 m from camp, a particularly welcome find.

Scientists involved in classification of Antarctic finds at NASA's Johnson Space Center and the Smithsonian Institution's National Museum of Natural History said the mineralogy and texture of the meteorite are unusual. The new specimen is a very coarse-grained gabbro, similar in bulk composition to the basaltic lavas that fill the lunar maria, but its very large crystals suggest slow cooling deep within the Moon's crust. In addition, the plagioclase feldspar has been completely converted to glass, or maskelynite, by extreme shock (presumably impact events). The new specimen most closely resembles another Antarctic meteorite, Asuka 881757, one of the oldest known lunar basalt samples.

Like the other lunar meteorites, MIL 05035 is a piece of the Moon that can be studied in detail in the laboratory, providing new specimens from a part of the lunar surface not sampled by the US Apollo program. Many researchers believe that Apollo visited some of the most unusual and geochemically anomalous regions of the Moon, and lunar meteorites, knocked off the surface of the Moon by random impacts, give us samples that are more representative of the Moon as a whole. The highly-shocked nature of MIL 05035 suggests an old age and may provide new constraints on the early intense bombardment of the Earth-Moon system, improving our understanding of the history of the Earth's nearest neighbor and aiding NASA's efforts toward a return to the Moon.

Following the existing protocols of the U.S. Antarctic meteorite program, scientists from around the world will be invited to request samples of the new specimen for their own detailed research. Details concerning initial characterization of the specimen and sample availability are available through the Antarctic Meteorite Newsletter, available on the Web and mailed to researchers worldwide.

Discovery of this meteorite occurred during the fourth full field season of a cooperative effort by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) to enhance recovery of rare meteorite types in Antarctica, in the hopes new martian samples would be found.

The US Antarctic Meteorite program is a cooperative effort jointly supported by NSF, NASA and the Smithsonian Institution. Antarctic field work is supported by grants from NSF and NASA to Case Western Reserve University; initial examination and curation of recovered Antarctic meteorites is supported by NASA at the Astromaterials Curation facilities at the Johnson Space Center in Houston, Texas; and initial characterization and long term curation of Antarctic meteorite samples is supported by NASA and the Smithsonian Institution's National Museum of Natural History in Washington, D.C.

Petrology and Geochemistry of Miller Range 05035: Lunar Gabbroic Meteorite

ABSTRACT: Miller Range (MIL) 05035 is a lunar gabbroic meteorite. The mineralogy, Fe/Mn ratios in olivine and pyroxene, bulk-rock chemical composition and the bulk oxygen isotope values (δ17O = 2.86–2.97‰ and δ18O = 5.47–5.71‰) are similar to those of other mare basalts, and are taken as supporting evidence for a lunar origin for this meteorite. The sample is dominated by pyroxene grains (54–61% by area mode of thin section) along with large plagioclase feldspar (25–36% by mode) and accessory quartz, ilmenite, spinel, apatite and troilite. The bulk-rock major element composition of MIL 05035 indicates that the sample has a very low-Ti (VLT) to low-Ti lunar heritage (we measure bulk TiO2 to be 0.9 Wt.%) and has low bulk incompatible trace element (ITE) concentrations, akin to samples from the VLT mare basalt suite. To account for these geochemical characteristics we hypothesize that MIL 05035’s parental melt was derived from a mantle region dominated by early cumulates of the magma ocean (comprised principally of olivine and orthopyroxene). MIL 05035 is likely launch paired with the Asuka-881757 and Yamato-793169 basaltic lunar meteorites and the basaltic regolith breccia MET 01210. This group of meteorites (Y/A/M/M) therefore may be a part of a stratigraphic column consisting of an upper regolith environment underlain by a coarsening downwards basalt lava flow.