Submillimeter Astronomy of the Solar System Glenn Orton Jet Propulsion Laboratory California Institute of Technology

Thanks for help from many! Mark Gurwell Cassini Composite Infrared Spectrometer Team Linda Brown ISO Long-Wavelength Spectrometer Solar-System Team Bryan Butler Herschel Calibration Workshop Team Todd Clancy Gary Davis Brigette Hesman Juan Pardo Gene Serabyn Linda Spilker

“Submillimeter” Rigorously: 0.1 – 1.0 mm 10 – 100 cm GHz But I won’t let rigor get in the way of good science!

ADVANTAGES OF SUBMILLIMETER IN SOLAR-SYSTEM EXPLORATION Plethora of molecular lines Insensitivity to optical influence of haze & dust Low continuum opacity: senses deep in atmospheres High line-center opacity: senses high in atmospheres High-resolution of line cores and wings provides simultaneous depth and temperature/abundance information Senses subsurface of rocky & icy bodies

Total Lunar eclipse of July 16 th, 2000 Expected behavior: Fastest temperature drop at shortest wavelengths due to less penetration. Pardo, J.R., Serabyn, E., Wiedner, M.C., Icarus, submitted.

Atmosphere of Venus

Pardo and Serabyn: observation of HCl and search for OCS lines in Venus

Venus: submm spectra of SO 2 and search for SO (observations from the JCMT, Clancy et al. – to be given at the Cambridge, UK, AAS/DPS meeting) [SO2] ~ 2 x [SO] < 1 x 10 -9

Venus: Dayside vs Nightside Mesosphere Temperature Structure ↑ temperature inversion in dayside upper atmosphere. rapid temperature falloff in the nightside upper atmosphere ↓

Surface and Atmosphere of Mars

ISO/LWS Spectroscopy of Martian H 2 O Burgdorf et al Icarus 145, 79. surface H 2 O vmr = 3 ± 1 x 10-4 saturates ~ 13 ± 2 km optical path = 12 ± 3.5 precip. µm

Mars Surface Emissivity Deduced from ISO/LWS Flux (Burgdorf et al Icarus 145, 79)

Mars Observations from SWAS Gurwell et al Astrophys. J. 539, L143. resolved lines allow determination of T and H 2 O vapor profiles simultaneously

ODIN Observations of Mars: H 2 O and mean T surface Biver et al. (2005) Astron & Astrophys. 435, 765. resolved lines allow determination of T and H 2 O vapor profiles simultaneously

dust-free model

First SMA Image with all 8 Antennas: Mars can be used to map both T(p) and T surf Ho et al. (2004) Astrophys J. 616, 61.

Retrieved easterly zonal flow of Mars southern solstice circulation is stronger and deeper than in dynamical models, although retrieved meridional winds (not shown) are similar. Mars zonal winds derived from JCMT observations of 12 CO and 13 CO Doppler line shifts (Clancy et al. 2005).

Detection of H 2 O 2 in Mars ( JCMT) Initial detection of Mars atmospheric H 2 O 2, from JCMT during the favorable Mars opposition of late summer H 2 O 2 is the most abundant species of the key catalytic HO x family, which effectively controls both the photochemical stability and trace chemical makeup of the global Mars atmosphere (Clancy et al. 2004). Clancy et al. (2004) Icarus 168, 116.

Atmosphere of Jupiter

JUPITER < NH  H2--- 

Calibration of spectral continuum to lunar flux (Pardo and Serabyn, ongoing work)

Observation of low-frequency wing of NH 3 line

Cassini Composite Infrared Spectrometer (CIRS) at Jupiter

Upper limits for hydrogen halides in Jupiter Fouchet et al. (2001). Icarus 170, 237. [HF]<2.7× [HCl]<2.3×10 -9 [HBr]<1.0×10 -9 [HI]<7.6×10 -9

Refit to data of Weisstein, E. W. and E. Serabyn (1996) Icarus , 23. (a more detailed analysis by Mark Allen and students, Caltech, to come)

SWAS Observations of H 2 O Vapor in Jupiter Bergin et al Astrophys. J. 539, L147.

Atmosphere of Saturn

CH 4 VMR = 3.9 ± 0.9 x CH 4 /H 2 = 4.3 ± 1.0 x (for 88.1% H 2 ) C/H is 6 ± 2 times solar abundance This is consistent with an accreting core of M Earth (Mizuno 1980; Owen & Encrenaz 2003, 2005)

Orton, Serabyn and Lee (2000) Icarus 146, 48; (2001) Icarus 149, 489. Reanalysis of data of Weisstein and Serabyn (1994) Icarus 109, 367. Weisstein and Serabyn (1996) Icarus 123, 23.

SWAS Observations of H 2 O Vapor in Saturn Bergin et al Astrophys. J. 539, L147. Best fit: 2x nom H 2 O profile of Moses et al (2000) photochemical models

Atmosphere of Uranus

from Griffin and Orton (1993) Icarus 105, 537.

Atmosphere of Neptune

Neptune’s Submm Spectrum from Griffin and Orton (1993) Icarus 105, 537.

Observations of CO in Neptune Hesman et al. (2005) Submitted to I carus. Gurwell (2005) In progress.

Cassini CIRS Observations of Titan volume mixing ratios in stratosphere: CH 4 : 1.6 ± 0.5 x CO : 4.5 ± 1.5 x 10 -5

SMA Spectra of HC 3 N, HC 15 N, HCN in Titan, Gurwell

SMA: HC 15 N Distribution in Titan Gurwell et al. in progress

Comet C/1999 H1 (Lee): SWAS Observations Neufeld et al Astrophys. J. 539, L151. H 2 O line emission used to determine production rate vs time in the coma of Comet Lee; no evidence for periodicity

ODIN Observations of Comet Ikeya-Zhang 16 O/ 18 O ratio is nearly the same as for terrestrial oceans also consistent with the ratio in Comet Halley

Spectrum is largely consistent with predictions for a standard thermophysical model ISO LWS observations of Ceres

BB=simple blackbody, e FF =1.0 HC=high conductor, rapid rotator LC=low conductor, slow rotator From Redman et al. Astron. J. 116, 1478 high conducting, rapid rotating model does best.

From Burgdorf et al. (2000) in “ISO Beyond the Peaks”, 9 ISO/LWS Observations: mineral / ice absorption …or just stray light from Jupiter?

Issues: Absolute Radiance Calibration Spectroscopy

Solar-System Objects as Flux Calibrators Some Herschel instruments plan on using Uranus as a standard submillimeter flux calibrator, with Neptune and Mars as part of a calibration system.  How well-characterized are their fluxes?  How constant are their fluxes?

URANUS STANDARD MODEL SPECTRUM (Griffin and Orton 1993 Icarus 105, 537) Based on Voyager-1 IRIS spectra between 200 and 400 cm -1 Model used to extrapolate spectrum Temperature structure derived from 200 – 400 cm -1 spectrum Collision-induced H 2 -H 2, H 2 -He, H 2 -CH 4 absorption - Molar fraction He = ± (Conrath et al J. Geophys. Res. 92, 15003) - Molar fraction of CH 4 = 0.02 ± 0.01 (Orton et al Icarus 67, 289, Lindal et al J. Geophys. Res. 92, 14987) Uncertainty of radiance ~2% between 50 and 500 cm -1 Extrapolation to longer wavelengths is less certain.

Uranus Variability?

failure of Uranus standard model? (Gurwell)

Neptune’s Variability in the Near Infrared

Good correspondence between Rudy Mars thermophysical model and Pardo-Serabyn lunar-based calibration

Rudy et al. thermophysical model for Mars The model takes into account the viewing geometry and Martian season. Although it is a good model, there are some problems: -based fundamentally on cm scale (Baars et al.), since measurements were done at 2 & 6 cm at VLA (though some of it is independent of this); -no roughness; -no subsurface scattering; -no lateral heat transport; -uncertainties with extent and properties of surface CO 2 ice; -somewhat outdated surface albedo and emissivity information (based on old Viking information); -no atmosphere. Despite this, it is probably the state of the art for Mars thermophysical models - but is it good to 1 – 3% (Herschel desire)?

Improvements to the Rudy et al model: incorporate new (in the past 15 years!) spacecraft data. Wilkinson Microwave Anisotropy Probe observations of the absolute brightness temperature from GHz Cosmic Background Imager data (calibrated against Jupiter, but very accurate, from GHz) VLA observations of bulk dielectric from 5-44 GHz.

Herschel flux calibration strategy, adopted at Dec 2004 workshop: Full spectra of Mars and Uranus between 57 and 600 mm for one date (July, 1st, 2007) at 100 MHz resolution New workshop! Coordinated space- and ground-based observations (cm, mm, submm): Simulation of observations  Study of various effects (models, pointing, mirror accuracy, error beam) with output from e.g Mars LMD-Model (R.Moreno)

Current Public Spectroscopic Databases DatabaseWebsites ( cm -1 Num of Species Num of Transitions HITRAN 2004 cfa - (/hitran) terrestrial moleculeswww.harvard.edu 0.0 to ,734,469 GEISA 2003 ara.lmd.polytechnique.frmolecules planetary  terrestrial 0.0 to (98 iso) 1,668,371 JPL 2005spec.jpl.nasa.gov spec.jpl.nasa.gov molecules,radicals,atoms astrophysics  terrestrial 0.0 to 100. (1314.) (340)2,644,111 CMSD 2005 (Cologne) molecules,radicals,atoms astrophysics 0. to 300. (1134.) (300) 2 M?

Far-IR CH 4 Intensities for ground state transitions in HITRAN and GEISA low by 16%? HITRAN intensities for Far IR set by one “indirect method”, (calc.) [Hilico et al., J Mol Spec, 122, 381(1987)] with claim of accuracy of ± 30%. Cassam-Chenai, [JQSRT, 82,251(2003)] predicts ab initio Q branch based on Stark measurements [Ozier et al. Phys Rev Lett, 27,1329, (1971)]. The intensities are 16% higher than HITRAN values. Lab data (left) confirms a higher value for R branch manifolds. Lab Spectra of Far-IR CH4 (Wishnow) hitran fit from Orton

Low temperature spectrum of methane absorption coefficient= -ln(transmission)/(density^2 * path) First observation of R(3)-R(7) lines measurements at 0.24 and 0.06 cm-1 spectral resolution Centrifugal distortion dipole lines superposed on collision-induced spectrum. Dashed line: CH 4 Collision-Induced Absorption (CIA) from A. Borysow. Wishnow, Leung, Gush, Rev. Sci. Inst., 70, 23 (1999)

No public infrared database tailored for submm astronomy Astronomers often use their own private (undocumented) collections Basic molecular parameters (positions, intensities) available for dozens, not hundreds, of species Insufficient attention to line-by-line intensities Pressure broadening coefficients needed (models and meas.) CIA models need to be validated.