The Almahata Sitta polymict breccia and the late accretion of asteroid 2008 TC3

Horstmann, M.; Bischoff, A.

doi:10.1016/j.chemer.2014.01.004

Cited by 72 publications

(167 citation statements)

References 112 publications

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“…These findings shed new light on some old meteorite finds, such as the Galim meteorite fall (LL+EH), Hajmah (ureilite+L), Gao-Guenie (H+CR), and Markovka (H+L) (Borovička, Spurný & Brown 2015). Therefore asteroids with mixed mineralogies might be more abundant than previously thought, but their formation mechanism(s) remain mysterious (Horstmann & Bischoff 2014). One possible solution is that the heterogeneous composition of some asteroids was inherited from a time when the asteroid belt was in a different dynamical state, most likely in the very early Solar System.…”

Section: Introductionmentioning

confidence: 89%

Survival of the impactor during hypervelocity collisions – I. An analogue for low porosity targets

Avdellidou¹,

Price²,

Delbò³

et al. 2015

Mon. Not. R. Astron. Soc.

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Recent observations of asteroidal surfaces indicate the presence of materials that do not match the bulk lithology of the body. A possible explanation for the presence of these exogenous materials is that they are products of inter-asteroid impacts in the Main Belt, and thus interest has increased in understanding the fate of the projectile during hypervelocity impacts. In order to gain insight into the fate of impactor we have carried out a laboratory programme, covering the velocity range of 0.38 -3.50 km/s, devoted to measuring the survivability, fragmentation and final state of the impactor. Forsterite olivine and synthetic basalt projectiles were fired onto low porosity (<10%) pure water-ice targets using the University of Kent's Light Gas Gun (LGG). We developed a novel method to identify impactor fragments which were found in ejecta and implanted into the target. We applied astronomical photometry techniques, using the SOURCE EXTRACTOR software, to automatically measure the dimensions of thousands of fragments. This procedure enabled us to estimate the implanted mass on the target body, which was found to be a few percent of the initial mass of the impactor. We calculated an order of magnitude difference in the energy density of catastrophic disruption, Q*, between peridot and basalt projectiles. However, we found very similar behaviour of the size frequency distributions for the hypervelocity shots (>1 km/s). After each shot, we examined the largest peridot fragments with Raman spectroscopy and no melt or alteration in the final state of the projectile was observed.

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Section: Introductionmentioning

confidence: 89%

Survival of the impactor during hypervelocity collisions – I. An analogue for low porosity targets

Avdellidou¹,

Price²,

Delbò³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…; Bischoff et al. ; Warren and Rubin ; Horstmann and Bischoff ). Furthermore, a range of ureilite samples show intermediate, although often variable, grain sizes of silicates (100–300 μm; Bischoff et al.…”

Section: Introductionmentioning

confidence: 99%

“…; Goodrich et al. ; see Horstmann and Bischoff for a review). The ureilites recovered exhibit an impressive range of both textures and chemical compositions.…”

Section: Introductionmentioning

confidence: 99%

Si‐bearing metal and niningerite in Almahata Sitta fine‐grained ureilites and insights into the diversity of metal on the ureilite parent body

Horstmann

Humayun

Fischer-Gödde

et al. 2014

Meteorit & Planetary Scien

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A detailed mineralogical and chemical study of Almahata Sitta fine-grained ureilites was performed to shed light on the origin of these lithologies and their sulfide and metal. The Almahata Sitta fine-grained ureilites (silicates <30 lm grain size) show textural and chemical evidence for severe impact smelting as described for other fine-grained ureilites. Highly reduced areas in Almahata Sitta finegrained ureilites show large (up to $ 1 mm) Si-bearing metal grains (up to $ 4.5 wt% Si) and niningerite [Mg >0.5, (Mn,Fe) <0.5 S] with some similarities to the mineralogy of enstatite (E) chondrites. Overall, metal grains show a large compositional variability in Ni and Si concentrations. Niningerite grains probably formed as a by-product of smelting via sulfidation. The large Si-Ni variation in fine-grained ureilite metal could be the result of variable degrees of reduction during impact smelting, inherited from coarsegrained ureilite precursors, or a combination of both. Large Si-bearing metal grains probably formed via coalescence of existing and newly formed metal during impact smelting. Bulk and in situ siderophile trace element abundances indicate three distinct populations of (1) metal crystallized from partial melts in MS-20, (2) metal resembling bulk chondritic compositions in MS-165, and (3) residual metal in MS-168. Almahata Sitta fine-grained ureilites developed their distinctive mineralogy due to severe reduction during smelting. Despite the presence of E chondrite and ureilite stones in the Almahata Sitta fall, a mixing relation of E chondrites or their constituents and ureilite material in Almahata Sitta can be ruled out based on isotopic, textural, and mineral-chemical reasons.

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“…For example, Almahata Sitta meteorite, which fell in October 2008 in Sudan, is a polymict ureilite consisting of centimeter-to decimeter-sized fragments of different types of ureilites and various chondrites (Jenniskens et al 2009;Zolensky et al 2010;Bischoff et al 2010). The detailed studies of Almahata Sitta lead to a scenario involving break-up of a large ureilite parent body whose original diameter was larger than 200 km and reaccumulation into smaller daughter bodies (e.g., Bischoff et al 2010;Herrin et al 2010;Mikouchi et al 2010;Zolensky et al 2010;Goodrich et al 2014;Horstmann and Bischoff 2014). The parent asteroid of Almahata Sitta, asteroid 2008 TC3, is considered to have been a smaller rubble-pile block of these daughter bodies in which fragments were loosely packed, as evidenced by the fact that no recovered stones consisted of more than one lithology.…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and crystallography of some Itokawa particles returned by the Hayabusa asteroidal sample return mission

et al. 2014

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We studied seven Itokawa particles provided by the Japan Aerospace Exploration Agency (JAXA) as first International Announcement of Opportunity (AO) study mainly using electron and synchrotron radiation X-ray beam techniques. All the analyzed particles were collected from the first-touchdown site and composed of olivine and plagioclase with traces of Ca phosphate and chromite, and do not contain pyroxenes. Optical microscopy of these particles shows minor undulatory extinction of olivine and plagioclase, suggesting minor shock metamorphism (shock stage: S2). The electron microprobe analysis shows that olivine is

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The Almahata Sitta polymict breccia and the late accretion of asteroid 2008 TC3

Cited by 72 publications

References 112 publications

Survival of the impactor during hypervelocity collisions – I. An analogue for low porosity targets

Survival of the impactor during hypervelocity collisions – I. An analogue for low porosity targets

Si‐bearing metal and niningerite in Almahata Sitta fine‐grained ureilites and insights into the diversity of metal on the ureilite parent body

Mineralogy and crystallography of some Itokawa particles returned by the Hayabusa asteroidal sample return mission

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