Lunar and Planetary Science XXXVI (2005) 1846.pdf

ASSOCIATION OF PRESOLAR GRAINS WITH MOLECULAR CLOUD MATERIAL IN IDPS. S. Messenger1 and L. P. Keller1, , 1Robert Walker Laboratory for Space Science, NASA Johnson Space Center, Mail Code KR, 2101 NASA Parkway, Houston TX 77059, [email protected].

Introduction: Anhydrous interplanetary dust bullet and embedded in elemental sulfur for particles (IDPs) collected in the stratosphere appear microtomy. TEM and spectroscopic analyses show chemically, mineralogically, and texturally primitive in that the elevated D/H in D11 is hosted by comparison to meteorites [1]. Particles that escape hydrocarbons in the carbonaceous matrix of the IDP significant atmospheric entry heating have highly [11]. Both samples were analyzed with the unequilibrated mineralogy, are volatile element rich, Washington University NanoSIMS ion microprobe and, overall, appear to have escaped significant parent following detailed mineralogical mapping by TEM. body hydrothermal alteration [2]. These IDPs are For most samples we acquired 6-10 image layers of comprised of the building blocks of the solar system. 16,17,18O-, 24Mg16O-, and 28Si-, in multidetection, using a The strongest evidence that anhydrous IDPs are 2 pA, 50 nm Cs+ primary ion beam. For one slice of primitive is that they contain abundant stardust and B10 we instead acquired images of 16,18O-,12C14N- molecular cloud material. In particular, presolar ,12C15N-,and 32S-. silicates were first identified in IDPs and are present in Results: Supernova olivine: IDP L2011B10 was abundances (450 – 5,500 ppm) that are well above that found to contain an isotopically unusual (18O-rich, 17O- observed in primitive meteorites (<170 ppm); [3-7]. poor) presolar olivine grain that probably originated The most fragile (cluster) IDPs also commonly exhibit from a type II supernova [12]. Since this (500 nm) large H and N isotopic anomalies that likely originated grain appeared in several consecutive slices of the by isotopic fractionation during extremely low IDP, we were able to perform complementary O, Si, temperature chemical reactions in a presolar cold and N isotopic imaging of the particle. A TEM image molecular cloud [8]. The D/H ratios exceed that of of the IDP containing the grain is shown in Fig 1, most primitive meteorites, and in rare cases reach where the presolar grain is identified by the 18O-rich values directly observed from simple gas phase region (Fig 1B), while the adjacent GEMS and FeS molecules in cold molecular clouds [9]. The most grains are identified in an overlain 32S map acquired by extreme D- and 15N-enrichments are usually observed NanoSIMS (Fig 1C). The presolar olivine grain is at the finest spatial scales (0.5 – 2 µm) that can be partially rimmed with 15N-rich organic matter (Fig measured. 1D). These observations suggest that D and 15N Deuterium hotspot: The D/H ratio map of IDP D11 ‘hotspots’ are in fact preserved nuggets of molecular is shown in Fig 2A where the values range from 3 to at cloud material, and that the materials within them also least 10 x the terrestrial ratio. The prominent D hotspot have presolar origins [10]. The advanced capabilities is 3-4 µm in size. The hotspot contains mineral and of the NanoSIMS ion microprobe now enable us to test glassy grains embedded in a carbonaceous matrix. this hypothesis. Here, we report two recent examples Grains at least 200 nm in size were large enough for of presolar silicates found to be directly associated isotopic measurements, including 12 grains of with molecular cloud material. enstatite, 12 olivine, 3 anorthite, 5 diopside, and one Methods: The two samples discussed here each of pyrrhotite and chromite. In addition to the followed different experimental protocols. The first crystalline components, we observed 12 GEMS grains sample discussed (B10) is a 10 µm fragment of cluster and 2 aluminosilicate glass grains. The crystalline #6 from collection flag L2011, two other fragments of silicates have abundant solar flare tracks. All of the which are enriched in D and 15N [8]. This IDP was silicates within the primary D-hotspot are found to embedded in low viscosity epoxy and thin (40 – 70 have O isotopic compositions that are nm) sections were obtained by ultramicrotomy. Thin indistinguishable from solar within 100 ‰ or less. sections of this IDP were placed on TEM grids for However, a 17O-rich presolar silicate was found nearby both TEM and NanoSIMS analysis. The second in a small region of D-rich carbonaceous matter (Fig. sample (D11) was a 20 µm fragment of cluster 13 from 2D). collection flag L2009. This IDP was pressed into a Discussion: Interstellar dust grains accrete coatings gold substrate for analysis with the Washington of mixed H2O/organic ices in cold molecular clouds University IMS-3f ion microprobe. Following D/H (13), and these ices may undergo extensive chemical measurements, the IDP was extracted from the Au processing driven by UV photolysis (e.g. 14) to substrate by hand with a scalpel, attached to an epoxy become protective mantles of refractory organic matter Lunar and Planetary Science XXXVI (2005) 1846.pdf

(15). The 15N-rich organic coating observed on the References: [1] Bradley J.P. et al. (1988) in Meteorites supernova olivine grain B10A is a clear example of the ant the Early Solar System, 861-898. [2] Flynn G. J. et expected association of stardust with molecular cloud al. (1996) in Physics, Chemistry, and Dynamics of matter. These results reinforce the previously Interplanetary Dust (eds Bo A. S. Gustafson and M. S. observed general trend that presolar grains are most Hanner) ASP Conf. Proc 104, 291-296. [3] Messenger abundant in 15N-rich IDPs [4]. S. et al. 2003. Science 300, 105 [4] C. Floss, F. J. The D hotspot in IDP D11 is among the most Stadermann (2004), LPS 35, Abstract #1281 (2004) [5] A. deuterium rich objects ever studied in the laboratory. Nguyen, E. Zinner (2004), Science 303, 1496 [6] K. It is therefore surprising that most of the material Nagashima, A. N. Krot, H. Yurimoto (2004), Nature within it appears to be of solar system origin. This 428, 921. [7] S. Mostefaoui, P. Hoppe (2004) ApJ implies that dust grains in the outer solar nebula 613, L149. [8] S. Messenger (2000) Nature 404, 968 accreted volatile organic mantles similar to that of [9] S. Messenger, R. M. Walker, in Astrophysical grains in the interstellar medium. The grains within Implications of the Laboratory Study of Presolar the D hotspot include high temperature nebular Materials, T. J. Bernatowicz and E. Zinner, Eds. (AIP condensates that likely formed in the inner, warmer Conf. Proc. 402, American Inst. of Phys., Woodbury, regions of the disk. It is possible that this material was NY, 1998), pp. 545-564 [10] L.P. Keller, S. Messenger, J. ejected by the early active sun in a bipolar outflow or P. Bradley (2000), JGR 105, 10397 [11] Keller L. P. et al. that this material migrated outward in a turbulent (2004) GCA 68, 2577. [12] Messenger S. and Keller L. P. nebular disk [16]. All of this must have occurred prior (2004) Met Planet Sci 39, Abstract #5185 [13] E. L. Gibb et to the association of the presolar organic matter with al. (2000), Astrophys. J. 536, 347 [14] M. P. Bernstein the nebular grains. (2002), Astrophys. J. 576, 1115 [15] A. Li, J. M. Greenberg (1997), Astron. Astrophys. 323, 566 [16] van Boekel et al. (2004) Nature 432, 479.