Composition Trends in KBOs and Composition Trends in KBOs and CentaursCentaurs

C. M. Dalle Ore C. M. Dalle Ore (SETI/NASA Ames)(SETI/NASA Ames)

D. P. Cruikshank D. P. Cruikshank (NASA Ames)(NASA Ames)

J.EmeryJ.Emery(NASA Ames)(NASA Ames)

OutlineOutline

• Spectral modeling with the Shkuratov code: Spectral modeling with the Shkuratov code: input, mixing strategies, goals and constraints.input, mixing strategies, goals and constraints.

• Description of input materials and how they Description of input materials and how they affect the resulting spectrum.affect the resulting spectrum.

• My best models, so far, for Quaoar, 1999TC36 My best models, so far, for Quaoar, 1999TC36 and Varuna.and Varuna.

IntroductionIntroduction

In a previous study (Cruikshank and Dalle Ore In a previous study (Cruikshank and Dalle Ore Earth, Moon Earth, Moon & Planets 92& Planets 92, 315, 2003), 315, 2003) we found trends in KBOs we found trends in KBOs compositions: minerals+organics(+Hcompositions: minerals+organics(+H22O)O)

New Spitzer data at 3.6 and 4.5New Spitzer data at 3.6 and 4.5m=>extended modelsm=>extended modelsfor three objects from our previous sample: Quaoar, for three objects from our previous sample: Quaoar,

1999TC36, and 20000Varuna. 1999TC36, and 20000Varuna. Comparison of new and old models confirms the need for Comparison of new and old models confirms the need for

“reddening” materials + darkening agent. Possible “reddening” materials + darkening agent. Possible presence of methanol and/or water mixed in with presence of methanol and/or water mixed in with organics.organics.

Modeling GoalsModeling Goals

Use plausible materials and plausible mixing schemes.Use plausible materials and plausible mixing schemes.

Carry the same components for all data (when possible).Carry the same components for all data (when possible).

Because of the lack of discrete spectral features in our data, Because of the lack of discrete spectral features in our data, the albedo information contained in the data (Stansberry et the albedo information contained in the data (Stansberry et al., Ap.J. 643, 556, 2006) is essential in computing al., Ap.J. 643, 556, 2006) is essential in computing accurate abundances for each component.accurate abundances for each component.

Find the best fitting model with the smallest possible number Find the best fitting model with the smallest possible number of components. of components.

Adopted CodeAdopted CodeModeling of the observed reflectance was obtained by means Modeling of the observed reflectance was obtained by means of the Shkuratov radiative transfer code (Shkuratov et al. of the Shkuratov radiative transfer code (Shkuratov et al. Icarus Icarus 137137, 235, 1999)., 235, 1999).

Input ParametersInput Parameters

The Shkuratov code requires three input parameters:The Shkuratov code requires three input parameters:

- relative abundances of each material- relative abundances of each material

- grain size information- grain size information

- optical constants for each material.- optical constants for each material.

Scattering Geometries and Mixing on Scattering Geometries and Mixing on Planetary SurfacesPlanetary Surfaces

Spatial (areal) mixtures

Inclusions intransparent particles

Intra-Mixes,or MolecularMixtures in individualparticles

Adjacent small Particles of Different composition: Intimate Mixtures

Tholins are strongly coloredTholins are strongly colored

• Tholins impart strong Tholins impart strong color to a planetary color to a planetary surfacesurface

• The coloration is very The coloration is very effective when tholin effective when tholin inclusions occur in inclusions occur in transparent ice particles, transparent ice particles, even when << 1% even when << 1% concentrationconcentration

•Tholins are complex Tholins are complex Mixtures of C, H, and NMixtures of C, H, and N

Tholins (deposited on transparent substrates) made by H. Tholins (deposited on transparent substrates) made by H. Imanaka (Imanaka (Icarus 168Icarus 168, 344, 2004) by cold plasma irradiation , 344, 2004) by cold plasma irradiation

of a flowing gaseous mixture of Nof a flowing gaseous mixture of N22 : CH : CH44 (9:1) at various (9:1) at various pressures.pressures.

Icy ComponentsIcy Components

•Crystalline water ice or Crystalline water ice or methanol were introduced methanol were introduced for those objects that for those objects that suggest or don't exclude in suggest or don't exclude in their observed their observed reflectances the presence reflectances the presence of these components.of these components.

Wavelength

Mineral and Organic Mineral and Organic ComponentsComponents

Pxmg100 (Mg-rich pyroxene):Pxmg100 (Mg-rich pyroxene): sets albedo level for brighter sets albedo level for brighter objects. (Enstatite = Mgobjects. (Enstatite = Mg22SiSi22OO66) ) Serpentine:Serpentine: sets albedo level for sets albedo level for darker object with a convex darker object with a convex curvature.curvature.Triton tholinTriton tholin, and , and Titan Titan tholintholin: introduce a curvature in : introduce a curvature in certain parts of the albedo certain parts of the albedo spectrum. Triton tholin provides a spectrum. Triton tholin provides a steep monotonic red slope short steep monotonic red slope short of 2.5of 2.5μμm Titan tholin yields a m Titan tholin yields a convex slope whose curvature is convex slope whose curvature is centered around 1.4centered around 1.4μμm . Both m . Both also yield a quick rise at about also yield a quick rise at about 33m. m.

Best Best Models Models

for for QuaoarQuaoar

Intra-mixture of HIntra-mixture of H22O and Triton tholin, necessary for steep O and Triton tholin, necessary for steep slope. Pyx or Serpentine or ? darkens the water to yield the slope. Pyx or Serpentine or ? darkens the water to yield the right albedo level. Tholins in right combination yield the red right albedo level. Tholins in right combination yield the red slope shape. Triton provides the fairly rapid rise after 3slope shape. Triton provides the fairly rapid rise after 3m.m.

Jewitt and Luu, Nature 432, 731, 2004

Best Best Models for Models for 1999TC1999TC3636: : HH22O basedO based

Intra-mixture of HIntra-mixture of H22O and Triton tholin, necessary for steep O and Triton tholin, necessary for steep slope.Best fitted by serpentine at 1.5 and 2 slope.Best fitted by serpentine at 1.5 and 2 m regions.Triton m regions.Triton tholin brings the albedo up after 3 tholin brings the albedo up after 3 m, Titan tholin adds curvature m, Titan tholin adds curvature in the 1 in the 1 m region.m region.

Dotto et al. Icarus 162, 408, 2003

Best Best Models Models

for for 1999TC1999TC3636: :

CHCH33OH OH basedbased

Intra-mixture of CHIntra-mixture of CH33OH and Triton tholin, necessary for steep OH and Triton tholin, necessary for steep slope. Best fitted by serpentine at 1.5 and 2 slope. Best fitted by serpentine at 1.5 and 2 m regions.Triton m regions.Triton tholin brings the albedo up after 3 tholin brings the albedo up after 3 m, Titan tholin adds curvature m, Titan tholin adds curvature in the 1 in the 1 m region. Fit is good at 3.6 and 4.5 m region. Fit is good at 3.6 and 4.5 m.m.

Dotto et al. Icarus 162, 408, 2003

Best Best Models Models

for for Varuna: Varuna:

HH22O O basedbased

Intra-mixture of HIntra-mixture of H22O and Triton tholin, necessary for steep slope. O and Triton tholin, necessary for steep slope. Pyx is the better darkening agent based on the shape and Pyx is the better darkening agent based on the shape and albedo at 2.5 albedo at 2.5 m. Pyx is too dark at 4.5 m. Pyx is too dark at 4.5 m.m.

Serpentine is slightly better at 4.5 Serpentine is slightly better at 4.5 m, but drops at 2.4 m, but drops at 2.4 m.m.

Licandro et al. A&A 373, L29, 2001

Best Best Models Models

for for Varuna: Varuna: CHCH33OH OH basedbased

Intra-mixture of CHIntra-mixture of CH33OH and Triton tholin, necessary for steep slope. OH and Triton tholin, necessary for steep slope. Serpentine fits well the 2 Serpentine fits well the 2 m region, but drops at 2.4 m region, but drops at 2.4 m and is too m and is too dark hereafter.Pyx misses the 2 dark hereafter.Pyx misses the 2 m feature. Fits well at 3.6 m feature. Fits well at 3.6 m, m, misses again at 4.5 misses again at 4.5 m.m.

Licandro et al. A&A 373, L29, 2001

ConclusionsConclusions

• We confirm the need of “reddening” materials to We confirm the need of “reddening” materials to reproduce the red slope in the UV/vis part of the reproduce the red slope in the UV/vis part of the spectrum. Best results are achieved when the tholins spectrum. Best results are achieved when the tholins are mixed molecularly into an ice.are mixed molecularly into an ice.

• Pyx, serpentine or yet another mineral are good choices Pyx, serpentine or yet another mineral are good choices as darkening agents of the albedo levels.as darkening agents of the albedo levels.

• 4.54.5m data point can be challenging to fit: could a m data point can be challenging to fit: could a different organic material or mineral or ? yield a better different organic material or mineral or ? yield a better fit?fit?

Data SourcesData Sources

• 1999TC36: Dotto et al. Icarus 162, 408, 2003.1999TC36: Dotto et al. Icarus 162, 408, 2003.• Quaoar: Jewitt and Luu, Nature 432, 731, 2004.Quaoar: Jewitt and Luu, Nature 432, 731, 2004.• 20000Varuna: Licandro et al. A&A 373, L29, 20000Varuna: Licandro et al. A&A 373, L29,

20012001

Sources of the Optical ConstantsSources of the Optical ConstantsHH22OO: From Grundy from 0.96um on, spliced with:: From Grundy from 0.96um on, spliced with:

•0.3 - 0.88 0.3 - 0.88 μμm from S. Warren (m from S. Warren (Appl. Opt. 22Appl. Opt. 22, 1206, 1982), 1206, 1982)

•0.88 – 0.960.88 – 0.96 μμm from T. Roush (m from T. Roush (LPSC XXVIILPSC XXVII, 1107, 1996), 1107, 1996)

The adopted constants are for T=40K.The adopted constants are for T=40K.

CHCH33OH: From Brown (?). T=90K.OH: From Brown (?). T=90K.

Pmx100Pmx100: A Mg-rich pyroxene from Dorschner et al. : A Mg-rich pyroxene from Dorschner et al. A&A 300A&A 300, 503, 1995 , 503, 1995 (through Jena database) MgSiO3.(through Jena database) MgSiO3.

Triton tholinTriton tholin: Organic material from B. N. Khare et al. (: Organic material from B. N. Khare et al. (BAAS 26BAAS 26, 1176, 1994), 1176, 1994)

Titan tholinTitan tholin: Organic material from B. N. Khare, C. Sagan(: Organic material from B. N. Khare, C. Sagan(Icarus 60Icarus 60, 127, , 127, 1984)1984)

SerpentineSerpentine: From Roger Clark for lambda < 2.5 um and from Mooney & : From Roger Clark for lambda < 2.5 um and from Mooney & Knacke (1985, Icarus, v64, pp493-502) for lambda > 2.5 um.Knacke (1985, Icarus, v64, pp493-502) for lambda > 2.5 um.

Tholin Production Experiments

•Pressures : 0.26 hPa (0.2 torr), 1.6 hPa (1.2 torr)

•CH4/N2 : 10/90

•RF Power: 100 W

•Room Temperature

Pyrex Plate

RF Power Supply13.56 MHz

Plasma

Matching Networks

MFC

P

Pump

T

Substrates

Gas A

Thermocouple gauge

Pressure gauge

Water-cooled baseplate

MFC

Gas B

Adopted Mixing StrategiesAdopted Mixing StrategiesIntimate mixturesIntimate mixtures are those in are those in which the components are which the components are distributed in a salt and pepper distributed in a salt and pepper fashion. Their reflectance is fashion. Their reflectance is calculated from an average of the calculated from an average of the single-scattering albedo of each single-scattering albedo of each component.component.

Intra-mixturesIntra-mixtures are those in which are those in which one component mixes with the other one component mixes with the other at the molecular level yielding a new at the molecular level yielding a new component with new optical component with new optical properties, calculated as a weighted properties, calculated as a weighted mean of the original ones.mean of the original ones.