Laboratory data and modeling of Pluto’s spectra

Laboratoire de Planétologie de Grenoble,

CNRS - Université J. Fourier

Bernard.Schmitt@obs.ujf-grenoble.fr

Bernard Schmitt

Eric Quirico, Sylvain Douté et Olivier Brissaud

Optical properties of ices

Schmitt et al., 1998, Solar System Ices, p.199

Mesurement of spectral properties (0,4 – 200 µm) of molecular solids

Study effects of:- Temperature- Phases- Composition- Compounds - UV irradiations

Infrared Spectrometer with an optical cryogenic system (10 - 300 K)

Solids : - Ices - Clathrates, Hydrates, - Organics, - Minerals, …

Ices, organics, …Near and mid-infrared

Nitrogen

2 phases

Transition : 35.6K

- 2 very weak bands

- Very sensitive to phase

- Sensitive to temperature

- Fundamental band sensitive to CO2, H2O

- Spectral shape

surface thermometer Grundy et al., 1993, Icarus, 105, 254

Schmitt et al., 1998, Solar System Ices, 199

Methane

Grundy et al., 2002, Icarus, 155, 486

-Very large number of bands of various intensities, down to the visible range

- Band shape sensitive to temperature

Vis Near-IR Mid-IR

Methane

CH4 – N2 mixtures

Schmitt et al., 1998, Solar System Ices, 199

- Spectra very sensitive on the way the molecular mixture is formed

- Crystal growth from the liquid under thermodynamic equilibrium best represent the surface of Pluton and Triton !

Diluted CH4 – N2 mixturesCH4 spectrum sensitive to :

- Pure vs diluted

- N2 phase and temperature

- CH4 abundance (> 2%)

Quirico & Schmitt 1997a Icarus, 127, 354

Schmitt et al., 1998, Solar System Ices, 199

Spectrum = combination of the spectra of the saturated N2:CH4 solutions

Rich CH4 – N2 mixtures

Quirico et al; 1996 PSS, 44, 973

Water ice

Schmitt et al., 1998, Solar System Ices, 199

Amorphous phase :

Spectrum slightly depend on temperature

- Similar to high temperature crystalline

Crystalline phase :

Strong dependence with temperature, especially @ 1.65 µm band

H2O ice thermometer

Water ice : Phase and temperature

Grundy et al., 1998, JGR E, 103, 25809

Ammonia

Schmitt et al., 1998, Solar System Ices, 199

Pure ammonia :

- Several phases

Ammonia hydrates:

- 3 hydrate types + several phases

Complex spectra and not yet well studied (in course …)

Simple hydrocarbons

Quirico & Schmitt 1997a Icarus, 127, 354

Carbon monoxyde

Quirico & Schmitt 1997a Icarus, 127, 354

Quirico & Schmitt 1997a Icarus, 128, 181

Carbon dioxyde

Quirico & Schmitt 1997a Icarus, 127, 354

- Weakly sensitive to temperature

Methanol, nitriles, oxydes, …Many molecules measured or under study :

CH3OH, HC3N, C3H4, C2H5CN, C6H6, C3N3H3, …

Mesure de la réflectance spectrale (0,3 – 4,8 µm) bidirectionnelle des surfaces granulaires

Etude effets de la :

- Composition,

- Taille et forme des grains,

- Rugosité de surface,

- Indices optiques, …

Mesure spectres et fonctions de diffusion :

- Glaces, minéraux,

- Organiques,

- Matériaux géophysiques,

Applications :

Spectro-imagerie spatiale

• Visible slope and near-IR band strength sensitive to composition and structure of the macromolecular solid

yellow tholins

poly-HCN

black tholins

samples from LISA

C-H-N compounds

Wavelength (nm)

Ref

lect

ance

Bernard et al. 2006, Icarus 185, 301

surfaces par spectro-imagerie

• Composition– Identification de molécules– Etat physique– Modes de coexistence– Abondances – Distribution spatiale– Variations temporelles

• Origine - Evolutions– Origine chimique des molécules

– Complexité de la matière organique– Microphysique échanges surface/atmosphère – Transports (cycles jour, saison, climat, …)– Liens avec géologie, topographie, …

Molecules identification

Quirico et al. 1999 Icarus, 139, 159

Physical state

Quirico et al. 1999 Icarus, 139, 159

Distribution, abundance, grain size

Different ways of mixing :

- Molecular

- Compounds

- Granular

- Spatial

- Stratigraphy

(tholins)

Douté et al. 1999 Icarus, 142, 421

Complete modeling

• Comparison between objects

New-Horizon : spatial distribution

Quirico et al. 1999 Icarus, 139, 159