Dar al Gani 872

from U. Wiechert, A. N. Halliday, D-C. Lee, Institut for Isotope Geology and Mineral Resources, Zurich, Switzerland.
G. A. Snyder, L. A. Taylor, Planetary Geosciences Institute, University of Tennessee.
D. Rumble, Geophysical Laboratory, Carnegie Institution of Washington
Robert N. Clayton, University of Chicago
Ian Franchi, Open University, UK

Ludolf Schultz, Abt. Kosmochemie, Max-Planck-Institut für Chemie, May 2001
(all values are concentrations given in e-8 ccSTP/g)

• 3-He: 21.2
• 4-He: 2560
• 20-Ne: 2.65
• 21-Ne: 2.69
• 22-Ne: 3.13
• 36-Ar: 2.01
• 38-Ar: 2.36
• 40-Ar: 1250
• 84-Kr: 0.015
• 132-Xe: 0.007

Discussion: Dar al Gani 872 eucrite (related to Vesta), lunar or new achondrite?

The Univ. of Arizona and the Pr. Paul Sipiera, in their poster presentation for the Lunar and Planetary Science conference 2002 present DaG 872 as a heavily shocked HED: "yet another eucrite, yet another lesson to learn?"
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1106.pdf

But with its particular oxygen isotope data this meteorite is clearly different from the HED clouds (see graph. 1 and 2). The University of Arizona attributes this fact to a terrestrial contamination (calcite veins) which could influence the isotopes obtained by the Univ. of Chicago (R. N. Clayton). But a complementary work of the Open University (Ian Franchi) on our ask, taking care of this terrestrial contamination and working on the three lithologies continues to show values different from the HED cloud.

Other hypotheses:

1) Wasson J. T. [1996, Icarus] estimates that at least 60 bodies are required to account for the iron meteorites that formed in cores, and that it is likely that all these bodies had basalts on their surface immediately after differentiation. In addition to those bodies that provided iron meteorites there must be a set similar in size that have not yet been fragmented and others that are fragmented but whose core fragments have not been introduced into resonant orbits during the last 10 m.y. Some of these basaltic surface regions have been destroyed by impacts, but modeling calculations [Davis D. R. et al., 1979, in Asteroids] indicate that roughly half the initial set of bodies with D > 40 km are still present today. Thus it seems improbable that Vesta is the only large asteroid inside 2.6 AU resonance that had basalt on its surface and that has surviving basaltic materials capable of providing meteorites to the Earth.

May be DaG 872 is one of these basalts?

2) One hypothesis concerning the formation of the moon and its particular composition is that a Mars size planet has impacted the proto-Earth. "Such a model requires that the impactor and proto-Earth were very similar in oxygen isotope composition and that the oxygen isotope composition of the feeding zones for the two planets was, on average, identical. Assuming that a major proportion (50%) of the Moon is derived from the impactor then the oxygen isotope composition of the impactor could only deviate < 0.06 permil from the terrestrial fractionation line. It is clear that no significant proportion of material from a Martian or HED like source can have been mixed into the Moon."
[U. Wiechert, A. N. Halliday, D-C. Lee, G. A. Snyder, L. A. Taylor, D. Rumble, LPSC XXXI, "Oxygen isotope homogeneity of the moon"]
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1669.pdf

If this theory is confirmed, then in the past, differentiated asteroids with Moon/Earth oxygen isotope signature existed, so the basaltic meteorites we receive on Earth are not necessary only related to Moon/SNC/HED and we should expect a wilder variety.

3) "Lunar escape velocity is 2.38 km/s (1.48 miles per second), only a few times the muzzle velocity of a rifle (0.7-1.0 km/s). Any rock accelerated by an impact on the lunar surface to lunar escape velocity or greater will leave the Moon’s gravitational influence. Some ejected material becomes captured by the Earth’s gravitational field and lands on Earth shortly after ejection from the Moon. Other ejected material, however, assumes an orbit around the Sun. Some of that material may eventually strike Earth. This can take a long time. The record holder, lunar meteorite Yamato-82192/82193/86032, remained in space for about 9 million years before landing in Antarctica."...
..."Paul Warren (1994) makes a persuasive case that lunar meteorites come from relatively small craters, those of only a few kilometers in diameter. "
[Randy L. Korotev, Department of Earth sciences, Washington Univ.]

The lunar meteorites contain solar wind gas. But the solar wind penetrates only few millimeters in the soil. On the moon, it's the mixing of surface fragments by numerous small impact of meteorites which permits to detect those gas up to a depth of 10 meters or more (results of Apollo missions). If lunar meteorites come from relatively small craters, those of only a few kilometers in diameter, then the depth of the center of these craters is 200 meters or more. So 90% of the fragments ejected will contain no solar wind.

Where are these lunar meteorites with no solar wind implanted? Why haven't we find any in our collections, or do we have misclassified them?

On request, samples of DaG 872 are available for laboratories who want to perform complementary analyses on this heavily shocked achondrite.