Laboratory Simulations of Space Weathering Effects Giovanni Strazzulla INAF Osservatorio Astrofisico di Catania, Italy

Transcription

1 Laboratory Simulations of Space Weathering Effects Giovanni Strazzulla INAF Osservatorio Astrofisico di Catania, Italy 1

2 NNNNNNNN kev-mev ions ELECTRONS IONS MOLECULES Silicates Carbons Ices PHOTONS (UV, X) Structural, morphological and chemical modifications Used techniques : -RAMAN - UV-Vis-IR Spectroscopies Spectral ranges (μm) In situ Ex situ Transmittance Reflectance (bidirectional) (diffuse) (bidirectional) 2

3 RAMAN IN SITU Laser Ar + (514,5 nm) Raman Spectrometer Sample in the vacuum chamber 3

4 Irradiated materials ICES: H 2 O, CO, CO 2, CH 3 OH, CH 4, NH 3, SO 2, CARBONS: graphite, amorphous carbons, diamond, fullerene, asphaltite SILICATES: olivine, piroxene, METEORITES: Murchison, Orgueil (carbonaceous) Epinal (ordinary condrite) COSMIC DUST: Stratospheric IDPs, Stardust 4

5 Overview - Solar System minor bodies show a great variety of spectral colors. - These objects are exposed to micrometeorite bombardment, and irradiation by solar wind and high energy cosmic ions. Laboratory experiments attempt to simulate weathering effects on reflectance spectra, by irradiating: 1. silicates 2. ices 3. organics 4. meteorites Applications: - Near-Earth Objects and Main Belt Asteroids - Trans-Neptunian Objects, Centaurs, Comets, icy satellites 5

6 Intensity (counts/sec) Raman shift (cm -1 ) Enstatite 1009 Epinal Meteorite micro-raman spectra samples provided by the Vatican Observatory Intensity (counts/sec) Low-Fe Olivine Raman shift (cm -1 ) 6

7 Irradiated silicates Timescale in the Inner Solar System ~ years [G. Strazzulla, E. Dotto, R. Binzel, R. Brunetto, M.A. Barucci, A. Blanco, V. Orofino, Icarus 174, 31] Energy lost by elastic collisions [R. Brunetto & G. Strazzulla, Icarus, 179] (Ordinary Chondrite, H5) Inner Solar System: space weathering processes progressively change the surfaces of minor bodies, whose reflectance spectra become redder and darker. 1 cm 7

8 Epinal & NEOs 1.6 d Comparing with NEOs Norm Bidirect Reflectance Wavelength (μm) a Ion irradiation, simulating solar wind ions: time ~ years Epinal Yamada et al a. as prepared d. after 1.7 x Ar ++ /cm 2 crosses: 1998 SF36 circles: 1953 RA squares: 1997 GH3 Nanosecond pulse laser irradiation, simulating micrometeorite bombardment: time ~ 10 8 years 8

9 CH 4, CH 3 OH, C 6 H 6 Ion irradiation of frozen hydrocarbons produces an organic residue, whose VIS-NIR spectrum is very red and dark. Do different ices produce different-colored residual refractories? Spectral reddening function of the total dose [R. Brunetto, M.A. Barucci, E. Dotto, G. Strazzulla, ApJ 644, 646] 9

10 Moroz et al Icarus,

11 Hudson, Palumbo, Strazzulla, Moore, Cooper, Sturner, 2008, Laboratory studies of the chemistry of TNO surface materials, in: The Solar System beyond Neptune, Barucci, et al. (editors), Univ Arizona Press, Tucson, Estimated radiation doses (ev / 16-amu molecule) for ice-processing environments Object Centaur Triton Pluto Charon TNO Oort cloud comet Ices Detected H 2 O, CH-containing ices (CH 3 OH?), silicates, organics ( tholin ) N 2, CH 4, CO, CO 2, H 2 O N 2, CH 4, CO (and H 2 O?) H 2 O, NH 3, NH 3 -hydrate H 2 O, CH 4, NH 3, NH 3 -hydrate? Gases f : H 2 O, CO, CO 2, CH 3 OH, CH 4, H 2 CO, NH 3, OCS, HCOOH, HCN, C 2 H 6, C 2 H 2 Distance (AU) Dose at 1-μm Depth b Dose at 100-μm Depth b Dose at 1-m Depth 100 c - 10,000 e 100 c -200 e 30 c 100 c c ,000 d 30,000 d c -50 d c 100 c 30 c <48 ~1000 ~40, , c 100 c 30 c 500,000 d 30,000 d 50 d 500,000 d 30,000 d 50 d a Doses in ev (16-amu molecule) 1 for 4.6 Gyr, with an ice density of 1.0 g cm 3. b Solar Minimum c Cooper et al. (2003) extended with GEANT d Cooper et al. (2006a) e J. F. Cooper et al., unpublished data, 2006 f The assumed origin of these gases is the comet's nucleus. 11

12 IR and Raman Spectroscopy kev He + /cm 2 T=12 K H 2 O:CH 4 :N kev He αc T= 12 K Intensity (c.p.s.) Si Si kev He + /cm 2 CH 4 CH 4 CH 4 N 2 0 H 2 O:CH 4 :N 2 as deposited CO 2 CO Raman shift (cm -1 ) H 2 O CH 4 CH 4 Palumbo et al

13 IR and Raman Spectroscopy T=300 K 1200 T=300 K αc 1000 Intensity (c.p.s.) 800 Si Si αc residue from H 2 O:CH 4 :N kev He + /cm wavelength (μm) Raman shift (cm -1 ) % transmittance (a. u.) O-H T=300 K C-H kev He + /cm 2 C N (a) (b) (c) (d) (e) (f) (g) Irradiation wavenumber (cm -1 ) 13

14 14

15 Residue left over after ion irradiation of asphaltite, a solid bitumen originally soluble in chloroform. The clip testifies for the unsoluble residue formed after ion irradiation. insol3.mpg 15

16 Conclusions & further investigation - Space Weathering produces: a. Darkening and reddening of silicate spectra b. Darkening and reddening of ice spectra c. Flattening of bitumen spectra d. Darkening and reddening of CC spectra - Application to the composition and exposure time of: i. Main-Belt and Near-Earth Asteroids ii. Trans-Neptunian Objects and Centaurs Open points: Optical constants of irradiated materials have to be calculated, in a wide spectral range. We still need to discriminate processing effects from composition effects. 16