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79th Annual Meeting ofBORON the Meteoritical AND Society IN COMETARY (2016) PARTICLES: O. J. Stenzel and J. Paquette 6380.pdf

BORON AND OXYGEN IN COMETARY PARTICLES. Oliver J. Stenzel and J. Paquette and the COSIMA Team, Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany, [email protected].

Introduction: The cometary dust experiment COSIMA is a time of flight secondary ion mass spectrometer (ToF-SIMS) on board the Rosetta space craft. Since August 2014, COSIMA has been collecting dust from the inner coma of 67P/Churyumov-Gerasimenko [1], [2]. The particles have been analyzed for their size distribution, particle flux and morphology [3], [4]. [5] as well as [1] found high amounts of in the particles using the high resolution ToF-SIMS. In this work we present some of our results for and oxygen and compare with meteorite samples analyzed in the lab with the COSIMA reference model (RM). Varying degrees of oxygen isotopic fractionation have long been known in solar system solids such as the terrestrial planets, chondrules, and CAIs (-aluminum-rich inclusions) [6] and, more recently, in the sun [7]. A value has also been measured for the cometary gas from comet 67P [8]. Evidence for the presence of CAIs (which can have quite different oxygen isotopic content than the terrestrial value) has already been seen in this comet [9]. Thus a comparison of the isotopic ratio of a cometary dust particle may shed light on the history of Churyumov-Gerasimenko. Data and Methods: COSIMA produces high resolution mass spectra (1400 at 100 u). Individual spectra typically contain very few counts for B and 18O, so that they are indistiguable from noise. To be able to analyze these “rare” elements like boron and of oxygen we add up many hundred spectra, in case for the Boron more than 1300. The peaks from these summed spectra are fitted with Gaussian functions.

Figure 1: One slice of a summed spectrum of cometary particles in the range of the boron isotopes 10B and 11B in positive SIMS mode. Figure 2: Oxygen peak from spectra sampled on a single particle. SIMS in negative mode.

Results: Figure 1 shows the presence of both 10B and 11B. Some contribution of the surface contamination of the collecting target might contribute to this signal. The abundance and isotopic ratio of this element will be discussed. Figure 2 represents the peak at 16O for the sum of more than 1100 spectra. The peakshape is typical for on-particle spectra in the negative mode. The contribution of the cometary particle predominantly lies on the left hand side of the maximum peak. The average 18O/16O isotopic ratio of this particle is currently being estimated.

References: [1] M. Hilchenbach, J. Kissel, Y. Langevin, et al., Astrophys. J. Lett., vol. 816, no. 2, p. L32, 2016. [2] J. Kissel, K. Altwegg, B. C. Clark, et al., Space Sci. Rev., vol. 128, no. 1–4, pp. 823–867, Feb. 2007. [3] Y. Langevin, M. Hilchenbach, N. Ligier, et al., Icarus, vol. 271, pp. 76–97, Jun. 2016. [4] Merouane S., Y. Langevin, O. J. Stenzel, et al., Dust particle flux and size distribution in the coma of 67P/Churyumov-Gerasimenko measured in-situ by the COSIMA instrument on board Rosetta, in revision Astronomy&Astrophysics 2016. [5] R. Schulz, M. Hilchenbach, Y. Langevin, et al., Nature, vol. 518, no. 7538, pp. 216–218, Feb. 2015. [6] Clayton, R.N., L. Grossman and T. K. Mayeda, Science 182, 485-488, 1973. [7] McKeegan, K. D., A. P. A. Kallio, V. S. Heber, et al., Science 332, 1528-1532. [8] Altwegg K., H. Balsiger, A. Bar-Nun, et al., Science 347, 1261952-1-1261952-3. [9] Paquette, J.A., C. Engrand, O. Stenzel, M. Hilchenbach, J. Kissel, and the COSIMA Team, Meteoritics and Planetary Science, accepted, 2016.