Comparing the reflectivity of ungrouped carbonaceous chondrites with those of short-period comets like 2P/Encke

Abstract

Aims. The existence of asteroid complexes produced by the disruption of these comets suggests that evolved comets could also produce high-strength materials able to survive as meteorites. We chose as an example comet 2P/Encke, one of the largest object of the so-called Taurid complex. We compare the reflectance spectrum of this comet with the laboratory spectra of some Antarctic ungrouped carbonaceous chondrites to investigate whether some of these meteorites could be associated with evolved comets. Methods. We compared the spectral behaviour of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different specimens of the common carbonaceous chondrite groups do not match the overall features and slope of the comet 2P/Encke. By testing anomalous carbonaceous chondrites, we found two meteorites: Meteorite Hills 01017 and Grosvenor Mountains 95551, which could be good proxies for the dark materials that formed this short-period comet. We hypothesise that these two meteorites could be rare surviving samples, either from the Taurid complex or another compositionally similar body. In any case, it is difficult to get rid of the effects of terrestrial weathering in these Antarctic finds, and further studies are needed. A future sample return from the so-called dormant comets could also be useful to establish a ground truth on the materials forming evolved short-period comets. Results. As a natural outcome, we think that identifying good proxies of 2P/Encke-forming materials might have interesting implications for future sample-return missions to evolved, potentially dormant, or extinct comets. Understanding the compositional nature of evolved comets is particularly relevant in the context of the future mitigation of impact hazard from these dark and dangerous projectiles.

The polymict carbonaceous breccia Aguas Zarcas: A potential analog to samples being returned by the OSIRIS‐REx and Hayabusa2 missions

“…The chondrule size is consistent with that of CM chondrites (Rubin and Wasson 1986). The previous oxygen and geochemical results indicate consistence with CM chondrites (Meteoritical Bulletin).…”

“…Several lithologies are mentioned in the initial classification (1) a chondrule‐poor clast‐type constituting of ~80 vol% of the broken surfaces of ~2 kg of material having about 10 vol% chondrules, (2) a chondrule‐rich lithology with about 40 vol% chondrules, and (3) clasts with even lower chondrule to matrix ratio (one 3 g half stone shows <1 vol% of chondrules). The dominant chondrule‐poor lithology shows scattered small chondrules (mean diameter of 275 μm, n = 40), with prominent fine‐grained rims (The Meteoritical Bulletin). The chondrule size is consistent with that of CM chondrites (Rubin and Wasson 1986).…”

Distant Formation and Differentiation of Outer Main Belt Asteroids and Carbonaceous Chondrite Parent Bodies

“…Paradoxically, despite the fact that Ceres is the largest asteroid and several other large asteroids exhibit similar spectral properties, ammoniated phyllosilicates have not been found in CCs, such that the 3.1 μm absorption is not seen (Figures 1c and 3). Though long‐term collisional evolution likely affected their mineralogy through gardening and mixing (Beitz et al., 2016; Bischoff et al., 2006; Nittler et al., 2019; Tanbakouei et al., 2020; Trigo‐Rodríguez, 2015) and, consequently, infrared reflectance spectra, the common ammoniated features on many large asteroids, that dominate the mass of the asteroid belt and are thought to be primitive remnants of planetesimal formation (Bottke et al., 2005, 2015), require an explanation for their differences with CCs from their original water‐rock reaction conditions, such as starting material composition, W/R, and T of alteration.…”

“…Cumulative impacts have affected Ceres surface composition, though endogenous NH 4 ‐bearing phyllosilicates still remain (Marchi et al., 2019; Stein et al., 2019). Such collisions are also responsible for compaction of these bodies and formation of a crust beneath the regolith layer (e.g., Beitz et al., 2016; Bischoff et al., 2006; Blum et al., 2006; A. E. Rubin, 2012; Tanbakouei et al., 2020; Trigo‐Rodriguez et al., 2006).…”

“…As secondary minerals are the products of water‐rock reactions in asteroid precursors (icy planetesimals), when their internal temperatures ( T ) are high enough to melt water ice, the difference in mineral assemblages should reflect that of water‐rock reaction conditions. Water‐rock reactions are also responsible for lithification of bodies initially accreted as porous aggregates by forming secondary aqueous alteration minerals (e.g., A. E. Rubin et al., 2007), in concert with compaction due to impacts (e.g., Beitz et al., 2016; Bischoff et al., 2006; Blum et al., 2006; A. E. Rubin, 2012; Tanbakouei et al., 2020; Trigo‐Rodriguez et al., 2006).…”