Incorporation of a Late-Forming Chondrule Into Comet Wild 2

Abstract

We report the petrology, O isotopic composition, and Al-Mg isotope systematics of a chondrule fragment from the Jupiter-family comet Wild 2, returned to Earth by NASA's Stardust mission. This object shows characteristics of a type II chondrule that formed from an evolved oxygen isotopic reservoir. No evidence for extinct 26 Al was found, with ( 26 Al/ 27 Al) 0 < 3.0×10 −6 . Assuming homogenous distribution of 26 Al in the solar nebula, this particle crystallized at least 3 Myr after the earliest solar system objects-relatively late compared to most chondrules in meteorites. We interpret the presence of this object in a Kuiper Belt body as evidence of late, large-scale transport of small objects between the inner and outer solar nebula. Our observations constrain the formation of Jupiter (a barrier to outward transport if it formed further from the Sun than this cometary chondrule) to be more than 3 Myr after calcium-aluminum-rich inclusions.

Nanoscale infrared spectroscopy as a non-destructive probe of extraterrestrial samples

“…This same region of Iris was also imaged with EDS as shown in Fig. 6c, indicating clear correspondence between the mesostasis region identified previously 33 (Z. Gainsforth et al, manuscript in preparation) and the elemental EDS map. We acquired a nanoFTIR line scan 7 mm in length along the dotted line indicated in Fig.…”

“…We also demonstrate that nanoscale IR spectroscopy can sense elemental concentration gradients at the level of a few percent caused by rapid cooling, identify sub-micron intergrowths at the confluence of distinct lattice structures, providing evidence for shock within a chondrule, and directly reveal juxtaposed crystalline and amorphous silicates in the Iris cometary grain. NanoFTIR measurements of Iris are consistent with mounting evidence 3,33,34 (Z. Gainsforth et al, manuscript in preparation) that igneous materials formed at high temperatures deep in the solar nebula were incorporated into cometary bodies, advancing a surprising scenario whereby planetary materials must have been mixed over the grandest scales into the outer solar system 1 .…”

“…We next applied nanoFTIR to a cometary particle returned from Comet 81P/Wild 2 by the NASA's Stardust recovery mission, a sample for which the non-destructive nature of our probe is of paramount importance. The cometary grain C2052,12,74 ('Iris') was first characterized by synchrotron X-ray, electron, and ion microscopies, as well as secondary ion mass spectroscopy 33 . On a surface of Iris exposed by ultramicrotomy, we first utilized our nanoFTIR system to acquire a broadband integrated image of the particle (Fig.…”

Cometary Isotopic Measurements

“…-Another interesting observation on Wild 2 material is the occurrence of CAIs as mentioned above. In the refractory minerals that were analyzed for Mg isotopes, no trace of the extinct 26 Al radioactivity (T 1/2 = 0.7 Myr) could be found (Matzel et al 2010;Ogliore et al 2012;Nakashima et al 2015), in contrast to the case of most of CAIs of primitive meteorites. The latter incorporated live 26 Al with an initial, "canonical" 26 Al/ 27 Al of 5 × 10 −5 , indicating early and fast (T < 1 Myr) formation of these high temperature condensates.…”

Coordinated Microanalyses of Seven Particles of Probable Interstellar Origin from the Stardust Mission.

“…Reliable techniques have been developed for the extraction of these particles from aerogel. Coordinated analyses are also relatively straightforward, often beginning with synchrotron-based x-ray fluorescence (S-XRF), X-ray Absorption Near-Edge Spectroscopy (XANES) and x-ray diffraction (S-XRD) analyses of particles while still embedded in small extracted wedges of aerogel called -keystones‖, followed by ultramicrotomy and TEM, Scanning Transmission X-ray Microscopy (STXM) and ion microprobe analyses (e.g., [1]). Impacts in foils can be readily analyzed by SEM-EDX, and TEM analysis after FIB liftout sample preparation.…”