Astromineralogy of Protoplanetary Disks (and other astrophysical objects) Steve Desch Melissa Morris Arizona State University

Outline I.Mineral Opacities: all minerals emit infrared radiation with different dependendes on wavelength II.Basics of Radiative Transfer: emission from comets / dusty disks can be calculated III.Observations of Disks and Comets: different astrophysical systems have different spectra that tells us about their mineralogy IV.Implications for Solar System Formation

Astrophysical Context Protoplanetary Disk: young (< 3 Myr) disk around new protostar, about 98% H 2 and He gas, 1% H 2 O and 0.5 % dust. Total mass ~ 0.1 M sun

Astrophysical Context Debris Disk: somewhat older (~ Myr) disk around main- sequence star, made entirely of dust shed from asteroids / planetesimals / comets. Total Mass ~ M moon

Astrophysical Context Zodiacal Light / Exo-zody Disk: Much older (~ Gyr) disk around main-sequence star, made entirely of dust shed from asteroids / planetesimals / comets. Total mass << 1 M moon

Astrophysical Context Comets: dirty snowballs

Mineral Opacities Transitions between solid state vibrational and bending modes lead to emission / absorption of photons in the infrared, at wavelengths character- istic of the mineral. Silicates: 10 m, 18 m FeS: 23 m Al 2 O 3 : 13 m SiO 2 : 8.6 m, 20.5 m

Mineral Opacities Shape and peak wavelength of the feature can further diagnose the chemical composition and crystallinity of the mineral. From Laboratory Astrophysics Group, AIU Jena Crystalline Olivine

Mineral Opacities Shape and peak wavelength of the feature can further diagnose the chemical composition and crystallinity of the mineral. From Laboratory Astrophysics Group, AIU Jena Amorphous Olivine

Mineral Opacities Amorphous Olivine vs. Amorphous Pyroxene

Mineral Opacities Phyllosilicates

Basics of Radiative Transfer Emission from a silicate particle only departs from a blackbody if the particles are small. C abs = a 2 Q abs Q abs = 4 x Im [ (m 2 - 1) / (m 2 + 2) ] (x << 1) Q sca = (8 x 4 / 3) | (m 2 - 1) / (m 2 + 2) | 2 (x << 1) x = 2 a /, m = n + i k Emission can be predicted only if particle size, shape, and complex index of refraction known.

Basics of Radiative Transfer Emission from optically thin systems (debris disks, comets) straightforward if temperature known. I = B (T p ) [1 - e - ], = n p a 2 Q abs ( ) L Temperature determined by balance between absorption of starlight and emission of infrared. Q abs ( ) (L / 4 r 2 ) d = Q abs ( ) B (T p ) d Essential to have complex index of refraction in optical as well as infrared!

Basics of Radiative Transfer Emission from optically thick protoplanetary disks more complicated: sum of optically thick blackbody disk emission plus emission features from hotter, optically thin layer on disk surface. H ~ T 1/2 disk = dH/dr - H/r (L / 4 r 2 ) / 2 = T 4 disk Feedbacks between glancing angle and disk structure and temperature.

Protoplanetary Disks crystalline silicates optically thick disk emission optically thin, hot surface layer Spitzer data of HD

Protoplanetary Disks Spitzer data of HD One possible model fit to data, including 3% phyllosilicates Same model but replacing 3% phyllosilicates with amorphous olivine / pyroxene

Protoplanetary Disks Apai et al. 2005

Protoplanetary Disks Minerals already identified in T Tauri and Herbig Ae/Be disks: Amorphous silicates (olivine / pyroxene) Crystalline silicates (olivine / pyroxene) SiO 2 FeS (as well as nano-diamonds and PAHs) We expect that phyllosilicates will be discovered in debris disks in the near future...

Debris Disks Okamoto et al beta Pictoris (12 Myr) debris disk: dust concentrated into belts. Crystalline silicates only at center (< 6 AU)

Debris Disks spectrum of Solar System zodiacal dust (Reach et al. 2003) contains crystalline silicates possibly phyllosilicates ???

Cometary Spectra Hale-Bopp comet NEAT/Q4

Cometary Spectra Definitely crystalline silicates (but almost enitrely in long- period comets)

Cometary Spectra Probably crystalline silicates

Implications for Solar System Formation Interstellar dust < 0.2% crystalline (Kemper et al. 2004) Cometary / Protoplanetary Disk dust ~ 50% crystalline (see Wooden, Desch, Harker & Keller 2006, PP V) Silicate dust was annealed. Must have attained temperatures > 1000 K. (Hallenbeck et al. 2000). These temperatures typical only < 1 AU from star. Large-scale radial transport? (Bockelee-Morvan et al. 2002) Or transient heating in situ (e.g., by shocks)? (Harker and Desch 2002)

Conclusions Infrared spectra of protoplanetary disks, debris disks, zodiacal disks, comets, etc., can be used to characterize the mineralogy of dust in those objects. Laboratory measurements of optical constants of minerals (complex index of refraction, from visual to infrared) + radiative transfer modeling = size, shape, composition, crystallinity of dust grains. Interstellar medium amorphous, but protoplanetary disks and comets have crystalline silicates, implying that dust in protoplanetary disks is thermally processed. Astromineralogy is a growing field with lots of opportunity for progress!