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The Almahata Sitta meteorite, whose preat-mospheric body was the asteroid 2008 TC3, fell on October 7, 2008 in the Nubian Desert in northern Sudan [e.g., 1, 2]. Numer-ous fragments have been recovered during several expeditions organized from December 2008 [2]. The meteorite was classified as an anomalous polymict ureilite with several different kinds of chondritic fragments [e.g., 3-5]. Noble gas studies performed on several fragments from the meteorite showed cosmic-ray expo-sure ages of about 20 My [e.g., 6-8], although slightly shorter ages were also reported in [9, 10]. Concentrations of trapped heavy noble gases are variable among the fragments of different lithologies [9, 10]. We report noble gas data on two samples from the #1 and #47 fragments [2], which were the same as those re-ported by Ott et al. [9]. Experimental Procedure: Weights of bulk samples #1 and #47 used in this work were 16.1 mg and 17.6 mg, respectively. Noble gases were extracted by stepwise heating at the tempera-tures of 800, 1200 and 1800˚C for #1 and 600, 800, 1000, 1200, 1400, 1600 and 1800˚C for #47. Concentrations and isotopic ra-tios of noble gases were measured with a modified-VG5400/MS-III at the Geochemical Research Center, University of Tokyo. Results and Discussion: Cosmogenic He and Ne are domi-nant in both #1 and #47, but trapped Ar, Kr and Xe concentra-tions are much higher in #47 than in #1, showing that noble gas compositions in #47 are similar to those of ureilites. 3He/21Ne and 22Ne/21Ne of cosmogenic He and Ne are 4.8 and 1.12 for #1 and 3.6 and 1.06 for #47, respectively, both of which plot on a Bern line [11]. This indicates negligible loss of cosmogenic 3He from #1 in our sample, unlike the low 3He/21Ne of 3.1 for #1 by Ott et al. [9]. Concentrations of cosmogenic 3He and 21Ne (10-8 cc/g) are 30 and 6.3 for #1 and 32 and 9.0 for #47, respectively, which are higher than those in [9] and give cosmic-ray exposure ages of ca. 20 My depending on assumed production rates. Rela-tive abundances of trapped 36Ar, 84Kr and 132Xe for #1 resemble those of Q-component, which is a dominant trapped noble gas component in chondrites. In contrast to #1, #47 plots below a trend for ureilites [12] as well as Q, which implies a partial loss of trapped 36Ar from the lithology of #47.

Regolith from C (and related) asteroid bodies are a focus of the current missions Dawn at Ceres, Hayabusa 2 and OSIRIS REx. An asteroid as large as Ceres is expected to be covered by a mature regolith, and as Hayabusa demonstrated, flat and therefore engineeringly-safe ponded deposits will probably be the sampling sites for both Hayabusa 2 and OSIRIS REx. Here we examine what we have learned about the mineralogy of fine-grained asteroid regolith from recent meteorite studies and the examination of the samples harvested from asteroid Itokawa by Hayabusa.

Differentiated and partially differentiated asteroids preserve a glimpse of planet formation frozen in time from the early solar system and thus are attractive targets for future exploration. Samples of such asteroids arrive to Earth in the form of achondrite meteorites. Many achondrites, particularly those thought to be most representative of asteroidal regolith, contain a diverse assortment of materials both indigenous and exogenous to the original igneous parent body intermixed at microscopic scales. Remote sensing spacecraft and landers would have difficulty deciphering individual components at these spatial scales, potentially leading to confusing results. Sample return would thus be much more informative than a robotic probe. In this and a companion abstract [1] we consider two regolithic achondrite types, howardites and (polymict) ureilites, in order to evaluate what materials might occur in samples returned from surfaces of differentiated asteroids and what sampling strategies might be prudent.

Analysis of samples returned to terrestrial laboratories enables more precise measurements and a wider range of techniques to be utilized than can be achieved with either remote sensing or rover instruments. Furthermore, returning samples to Earth allows them to be stored and re-examined with future technology. Following the success of the Hayabusa mission, returning samples from asteroids should be a high priority for understanding of early solar system evolution, planetary formation and differentiation. Meteorite falls provide us with materials and insight into asteroidal compositions. Almahata Sitta (AS) was the first meteorite fall from a tracked asteroid (2008 TC3) [1] providing a rare opportunity to compare direct geochemical observations with remote sensing data. Although AS is predominantly ureilitic, multiple chondritic fragments have been associated with this fall [2,3]. This is not unique, with chondritic fragments being found in many howardite samples (as described in a companion abstract [4]) and in brecciated ureilites, some of which are known to represent ureilitic regolith [5-7]. The heterogeneity of ureilite samples, which are thought to all originate from a single asteroidal ureilite parent body (UPB) [5], gives us information about both internal and external asteroidal variations. This has implications both for the planning of potential sample return missions and the interpretation of material returned to Earth. This abstract focuses on multiple fragments of two meteorites: Almahata Sitta (AS); and Dar al Gani (DaG) 1047 (a highly brecciated ureilite, likely representative of ureilite asteroidal regolith).

The Almahata Sitta (hereafter "AHS") meteorite was derived from an impact of asteroid 2008TC3 on Earth and is classified as an anomalous polymict ureilite. More than 600 meteorite fragments have been recovered from the strewnfield. Previous reports indicate that these fragments consist mainly of ureilitic materials with textures and compositions, while some fragments are found to be chondrites of a wide range of chemical classes. Bulk oxygen three isotope analyses of ureilitic fragments from AHS fall close to the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line similar to ureilites. In order to further compare AHS with known ureilites, we performed high precision SIMS (Secondary Ion Mass Spectrometer) oxygen isotope analyses of some AHS samples

Ureilites are ultramafic achondrites, predominantly composed of olivine and pyroxenes with accessory carbon, metal and sulfide. The majority of ureilites are believed to represent the mantle of the ureilite parent body (UPB) [1]. Although ureilites have lost much of their original metal [2], the metal that remains retains a record of the formative processes. Almahata Sitta is predominantly composed of unbrecciated ureilites with a wide range of silicate compositions [3,4]. As a fall it presents a rare opportunity to examine fresh ureilite metal in-situ, and analyzing their highly siderophile element (HSE) ratios gives clues to their formation. Bulk siderophile element analyses of Almahata Sitta fall within the range observed in other ureilites [5]. We have examined the metals in seven ureilitic samples of Almahata Sitta (AS) and one associated chondrite fragment (AS#25).

Prior to recovery the Almahata Sitta fall was observed as the asteroid 2008 TC3 on an Earth-bound trajectory, providing a unique link between spectral data and ureilite composition. The event has also provided insight into the nature of ureilitic objects in space. In particular, the large size (4 m3) and low density (2.2 g/cm3) of the object combined with near-complete disintegration upon entry suggest a porous and loosely-consolidated body [1]. Accordingly, recovered fragments are small in size (1.5-283g) and represent several different ureilite lithologies. Some recovered fragments appear brecciated while others do not. We use chemical and mineralogic data to dissect the thermal history of this new ureilite, then use this information to compare the inferred size of fragments within the asteroid to those initially dislodged from a common ureilite parent body (UPB).

Mineralogy & Petrography: Almahata Sitta, deriving from the asteroid 2008 TC3, is a coarse-grained- to porous, fine-grained, fragmental breccia with subrounded mineral fragments and olivine aggregates embedded in a cataclastic matrix of ureilitic material. Mineral fragments include polycrystalline olivine, low-calcium, pigeonite, and augite. Abundant carbonaceous aggregates containing graphite, microdiamonds and aliphatics. Kamacite, Cr-rich troilite, silica and schreibersite are abundant. The compositional range of the silicates is characteristic of the ureilites as a group, but unusually broad for an individual ureilite. The dense lithology is typical for ureilites, but the porous lithology is anomalous. In the porous lithology pore walls are largely coated by crystals of olivine. Classification: Almahata Sitta is an anomalous, polymict eucrite. Anomalous features include large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and fine-grained texture. Tomography reveals that the pores define thin, discontinuous "sheets" connected in three dimensions, suggesting that they outline grains that have been incompletely welded together. The crystals lining the pore walls are probably vapor phase deposits. Therefore Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature.

HCN is a minor constituent of the Earth atmosphere, with a typical volume mixing ratio around 10(exp -10) HCN per air molecule. At present, the main source of HCN in the lower atmosphere is expected to be biomass burning. The atmospheric HCN has been observed since 1981, first in the infrared, then at microwave radio frequencies. Globally, above 30 km, HCN measurements are in excess of model predictions based on standard photochemistry and biomass burning as the only HCN source. This excess has been explained by: 1) ion-catalyzed reactions in the entire stratosphere, involving CH.3CN as a precursor and/or 2) a high altitude source as a result of chemical production from the methyl radical CH3, or from injection or production by meteors. HCN is a minor constituent of cometary ices. HCN polymers or copolymers have been suggested as constituents of cometary refractory organic matter, and would thus be present in the incoming meteoroids, if these polymers survived their stay in interplanetary space after ejection. HCN may also be created from the CN radical decomposition product of organic carbon, after reaction with hydrogen-bearing molecules. To test the hypothesis of HCN input by meteoroids or the formation in the upper atmosphere from meteoric ablation products, we decided to monitor the HCN submillimeter lines around a major shower: the Leonids.