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Temporal and Spacial Variation of the Organic Particles in the Proto-Solar

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Temporal and Spacial Variation of the Organic Particles in the Proto-Solar 46th Lunar and Planetary Science Conference (2015) 2591.pdf TEMPORAL AND SPATIAL VARIATION OF THE ORGANIC PARTICLES IN THE PROTO-SOLAR DISK M. Numata1 and H. Nagahara1, 1Department of Earth and Planetary Science, the University of Tokyo Introduction: More than 80 distinct amino acids Model: We calculate evolution of a viscous disk are discovered in meteorites, which, in addition to their with special interests on the location of individual precursors, are suggested to be extraterrestrial origin particles-in order to know the chemical change of (e.g., [1-3]). Even the detection of glycine, the simplest organic materials. The disk evolution model and amino acid, has been claimed in samples from comet particle-tracking model by Ciesla [12, 13] were applied. 81P/Wild 2 returned by NASA’s Stardust spacecraft Disk temperature is determined by balancing vertical [4]. These discoveries suggest that interstellar energy flux assuming that all of the energy dissipation chemistry can produce such complex molecules. occurs at the midplane [14]. We use alpha-prescription Motivated by these studies, some observational search of Shakura & Sunyaev [15] for viscosity. for complex molecules in the interstellar medium The initial gas density is assumed to distribute as a reported to detect acetic acid [5], acetamide [6], self-similar solution [16] and particles containing aminoacetonitrile [7], and ethyl formate [8] in organic materials are released at each 10AU from 10A Sagittarius B2 molecular cloud. More recently, ALMA to 100AU at t = 0. Disk vertical temperature gradient is observation is expected to find more complexity of neglected. Particles are supposed to be small enough to such organic materials [9]. well couple with gas and they are thermally Organic materials in the asteroids and comets may equilibrated. The temperature that each particle be partially derived from molecular clouds and experienced is estimated on the basis of radial partially processed in proto-solar disk. It is one of the temperature distribution. critical problems whether organic materials in the The starting material is assumed to be “Greeberg interstellar dusts formed in molecular cloud could particle”, which consists of silicate core and organics survive and accreted to planetesimals. Interstellar dusts and ice mantle [17], and the chemical composition is in molecular clouds consist of silicates, organic taken from that for 297K of [11]. When heated, the C materials, ices, and carbonaceous particles [10]. and N composition of particles varies according to [11], Interstellar dusts were incorporated into the proto-solar but do not vary if temperature decreases; that is, the molecular cloud and were heated and evaporated in the organic grains keeps the composition for the highest proto solar nebula. Since the degree of evaporation of temperature they experienced. By summing up all the interstellar dusts depends on temperature and pressure grains with different thermal history located at every conditions of the solar nebula, the distribution and 1AU at a certain time, the local bulk chemical chemical compositions of the dusts in the solar nebula composition of organics in the disk is obtained. would vary from place to place and with time. Nakano Results and discussion: The temporal change of et al. [11] carried out evaporation experiments of mixture of molecular cloud and diffuse cloud organic gas density distribution, gas temperature and organic analogs, and showed that the C and N contents in particle distribution is shown in Fig. 1, which shows carbonaceous chondrites cannot be explained by the that particles initially located in the low-temperature heating of interstellar organic dusts before accretion to outer region drift inward, and that thermally parent bodies. In this study, we calculated when and unprocessed organic particles were present in the inner 6 where these molecular-cloud-organic materials region after 10 years because the temperature of disk evaporate and how they distribute, which were not decreases with time where particles from outer regions considered in [11]. move. Purpose: We calculated disk evolution and particle Figure 2 shows the temporal-spatial variation of motion simultaneously in order to investigate C and N contents and C/N ratio of organic particles, temperature change of individual particles as a which include all the particles from different initial function of time and space, which enables us to trace locations and different thermal histories due to 4 the change of average chemical composition of turbulent motion of the gas. At 10 years, organic organics. The results would give critical information materials do not exist within 4AU, and those at 4-7AU on the chemical composition of precursor of organics are partially evaporated to be poor in C and N because in chondrite parent bodies. The fundamental difference many of the grains have experienced high temperature from the chemical network reactions on the surface of (Fig. 1b), which have turned into simple silicate grains. solid materials at lower temperatures of molecular The increase of C/N ratio at 4-6AU shows the mixing clouds is that the reactions in this work are thermal of raw materials keeping the composition of diffuse processes at higher temperatures (T>297K). cloud origin transported from outer regions, which 46th Lunar and Planetary Science Conference (2015) 2591.pdf hardly evaporate until 450K. The decrease of C/N ratio 106 ] a at 6-7AU indicates partially evaporated molecular -2 4 0yr cloud materials in this region. The inner edge of 10 104yr 5 organic materials keeping the initial C and N contents 10 yr [g cm 100 6 tend to move to the inner region of the disk. At 106 Σ 10 yr 1 years, only particles at 1-3AU are partially evaporated. 2000 Conclusions: Silicate-organics complex grains b 0yr from a molecular cloud origin were partially [K] 1000 104yr evaporated to be poor in organic materials inside 5AU gas 5 T 10 yr at the early stage of the proto-solar disk. As 106yr temperature decreases with time, primitive grains are 0 104 transported inward and chemical composition of 104yr c 5 organic materials in the inner regions of the disk 10 yr 100 changed from fractionated to unfractionated 106yr composition with disk evolution. A small amount of 1 diffuse cloud organic materials survive at the most 1 10 100 inner region and partially evaporated molecular cloud Number of particles organic materials and diffuse cloud organic materials r [AU] 4 5 6 are mixed at C/N ratio-decreasing region. This result Fig. 1. a) Distribution of gas density at 10 , 10 and 10 4 5 shows that composition of organic materials accrete to years b) Gas temperature of the midplane at 10 , 10 6 4 5 a planetesimal depend on when the planetesimal is and 10 years c) Distribution of particles at 10 , 10 6 formed. and 10 years 100 297[K] (Nakano et al., 2003) References: [1] Ehrenfreund, P. et al. (2001) ApJ, 4 550, 95-99. [2] Bernstein, M. P. et al. (2002) Nature, 10 10 [yr] 5 416, 401. [3] Elsila, J. E. et al. (2007) ApJ, 660, 911. 10 [yr] 106[yr] [4] Elsila, J. E., et al. (2009) Proc Nat. Acad. Sci, 98 , C [wt%] 1 2138. [5] Mehringer, D. M. et al. (1997) ApJ, 480, L71. [6] Hollis, J. M. et al. (2006) ApJ, 643, L25. 0.1 [7] Belloche, A. et al. (2008) A&A, 482, 179. 10 [8] Belloche, A. et al. (2009) A&A, 499, 215. [9] Belloche, A. et al. (2013) A&A, 482, 179. 297[K] (Nakano et al., 2003) [10] Greenberg (1998) A&A, 330, 375. [11] Nakano, H. 1 104[yr] et al. (2003) ApJ, 592, 1252. [12] Ciesla, F. (2010) 5 N [wt%] 10 [yr] Icarus, 208, 455. [13] Ciesla, F. (2011) ApJ, 740, 9. 0.1 6 [14] Armitage, P. J. Astrophysics of Planet Formation, 10 [yr] (Cambridge University Press, 2013) [15] Shakura, N. I 0.01 and Sunyaev, R. A. (1973) A&A, 24, 337. [16] Lyndenbell & Pringle (1974) MNRAS, 168, L603 40 [17] Greenberg, J. M. (2000) Science American, 283f, 104[yr] 46 30 105[yr] 6 C/N 10 [yr] 20 10 0 5 10 15 20 r [AU] Fig. 2. a) Temporal-spatial variation of C and N contents [wt%] of a silicate-organics complex grain originated in a molecular cloud (“Greenberg grain”) b) variation of C/N ratio .
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