Laboratory Simulations of Space Weathering Effects Giovanni Strazzulla INAF Osservatorio Astrofisico di Catania, Italy gianni@oact.inaf.it http://web.ct.astro.it/weblab/ 1
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 0.7-20 0.2-20 Reflectance 0.7-2.7 (bidirectional) 0.2-2.5 (diffuse) 2.27-20 (bidirectional) 2
RAMAN IN SITU Laser Ar + (514,5 nm) Raman Spectrometer Sample in the vacuum chamber 3
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
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
Intensity (counts/sec) 1.2 1.0 0.8 1.4 1.2 1.0 340 400 662 681 300 400 500 600 700 800 900 1000 Raman shift (cm -1 ) Enstatite 1009 Epinal Meteorite micro-raman spectra samples provided by the Vatican Observatory Intensity (counts/sec) 1.2 1.0 0.4 825 855 918 Low-Fe Olivine 700 750 800 850 900 950 1000 Raman shift (cm -1 ) 6
Irradiated silicates Timescale in the Inner Solar System ~ 10 4-10 6 years [G. Strazzulla, E. Dotto, R. Binzel, R. Brunetto, M.A. Barucci, A. Blanco, V. Orofino, 2005. Icarus 174, 31] Energy lost by elastic collisions [R. Brunetto & G. Strazzulla, 2005. 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
Epinal & NEOs 1.6 d Comparing with NEOs Norm Bidirect Reflectance 1.4 1.2 1.0 0.8 0.6 0.8 1.2 1.6 2.0 2.4 Wavelength (μm) a Ion irradiation, simulating solar wind ions: time ~ 10 4-10 6 years Epinal Yamada et al. 1999 a. as prepared d. after 1.7 x 10 16 Ar ++ /cm 2 crosses: 1998 SF36 circles: 1953 RA squares: 1997 GH3 Nanosecond pulse laser irradiation, simulating micrometeorite bombardment: time ~ 10 8 years 8
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, 2006. ApJ 644, 646] 9
Moroz et al Icarus, 2004 10
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, 507-523 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) 5-35 48-1000 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 - 100 c - 30 500,000 d 30,000 d c -50 d 30-40 100 c 100 c 30 c <48 ~1000 ~40,000-100,000 100 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
IR and Raman Spectroscopy 800 +1.5 10 16 30 kev He + /cm 2 T=12 K H 2 O:CH 4 :N 2 + 30 kev He + 600 αc T= 12 K Intensity (c.p.s.) 400 10 Si Si +3.2 10 16 30 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 500 1000 1500 2000 2500 3000 3500 Raman shift (cm -1 ) H 2 O CH 4 CH 4 Palumbo et al. 2004 12
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 2 +1.9 10 15 30 kev He + /cm 2 200 wavelength (μm) 3 3.5 4 4.5 5 500 1000 1500 2000 2500 3000 3500 Raman shift (cm -1 ) % transmittance (a. u.) 101 100 99 98 O-H T=300 K C-H +10 16 30 kev He + /cm 2 C N (a) (b) (c) (d) (e) (f) (g) Irradiation 3400 3200 3000 2800 2600 2400 2200 2000 wavenumber (cm -1 ) 13
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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
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