Asteroid 2008 TC₃—Almahata Sitta: A spectacular breccia containing many different ureilitic and chondritic lithologies

Abstract

Abstract-Asteroid 2008 TC 3 impacted Earth in northern Sudan on October 7, 2008. The meteorite named Almahata Sitta was classified as a polymict ureilite. In this study, 40 small pieces from different fragments collected in the Almahata Sitta strewn field were investigated and a large number of different lithologies were found. Some of these fragments are ureilitic in origin, whereas others are clearly chondritic. As all are relatively fresh (W0-W0 ⁄ 1) and as short-lived cosmogenic radioisotopes were detected within two of the chondritic fragments, there is strong evidence that most, if not all belong to the Almahata Sitta meteorite fall. The fragments can roughly be subdivided into achondritic (ureilitic; 23 samples) and chondritic lithologies (17 samples). Among the ureilitic rocks are at least 10 different lithologies. A similar number of different chondritic lithologies also exist. Most chondritic fragments belong to at least seven different E-chondrite rock types (EH3, EL3 ⁄ 4, EL6, EL breccias, several different types of EL and EH impact melt rocks and impact melt breccias; some of the latter are shock-darkened). In addition, two H-group ordinary chondrite lithologies were identified, and one sample of a chondrite type that is so far unique. The latter has some affinities to R chondrites. Oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the Almahata Sitta meteorite. Based on the findings presented in this study, the reflectance spectrum of asteroid 2008 TC 3 has to be evaluated in a new light.

Trachyandesitic volcanism in the early Solar System

“…2) falls in the field of the ureilites and feldspathic clasts from polymict ureilites (3,20,21); (ii) the feldspar mineralogy is very similar to the rare feldspathic clasts found in some polymict ureilites, which are considered as remnants of UPB melts (5); and (iii) it is most likely part of asteroid 2008 TC 3 , which was shown to be a fragment of an asteroid dominated by ureilitic lithologies (10,11).…”

“…2) were constrained to δ 18 O = 8.1 ‰, δ 17 O = 3.2 ‰, Δ 17 O = −1.06 ‰ and δ 18 O = 8.0 ‰, δ 17 O = 3.2 ‰, Δ 17 O = −1.04 ‰ (for details, see SI Appendix). They fall in the range of other ureilites, including those from Almahata Sitta (10,11,15,16), but at the 16 O-poor end of the range of oxygen isotopes in ureilites, which is the more common oxygen isotope composition found among ureilites.ALM-A ( Fig. 1; see SI Appendix, Tables S1− S3 and Figs.…”

“…A unique opportunity to gain new insights into ureilite petrogenesis was provided by the polymict asteroid 2008 TC 3 that impacted our planet October 7, 2008, in the Nubian Desert, Sudan, containing various ureilitic and ureilite-related fragments (10,11). Among its remnant fragments collected in the strewn field, collectively named the "Almahata Sitta" meteorites, the sample ALM-A (Almahata Sitta trachyandesitic meteorite) was recovered (12).…”

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

“…Such phenomena, which have been observed only relatively recently, are the source of the olivine and dark material deposits observed on Vesta (McCord et al 2012;Reddy et al 2012) and probably of the "Black Boulder" on (25143) Itokawa (Hirata & Ishiguro 2011). Mixing of asteroid material with different lithology through impacts is also necessary to explain the nature of the Near-Earth asteroid 2008 TC3, a multi-lithology body whose formation mechanism is still not completely understood (Jenniskens et al 2009;Bischoff et al 2010). 2008 TC3 impacted Earth's atmosphere on October 7, 2008 and it is estimated that it exploded approximately 37 km above the Nubian Desert in Sudan.…”

MarcoPolo-R: Near-Earth Asteroid sample return mission selected for the assessment study phase of the ESA program cosmic vision

“…This fall is the first instance where an object was observed astronomically as an asteroid and then was recovered as meteorite samples. It was identified as an F-class object, similar to C-class (bluer in the visible), but the meteorites are unexpectedly friable breccias of mostly ureilite and enstatite chondrite clasts [12,13]. The recovered meteorites represent only 0.005% of the initial mass [12], which demonstrates that mechanically weak material does exist in significant quantities within the inner Solar System and that the existing meteorite collection is significantly biased towards heavily processed material.…”