Pluto's Thermal Lightcurve: Spitzer Mips and Irs Observations

Details Pluto's Thermal Lightcurve: Spitzer Mips and Irs Observations Pluto's Thermal Lightcurve: Spitzer Mips and Irs Observations

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.2104l&link_type=abstract

American Astronomical Society, DPS meeting #38, #21.04; Bulletin of the American Astronomical Society, Vol. 38, p.518

Astronomy and Astrophysics

Astronomy

Scientific paper

Previous observations with IRAS and ISO (at 60-200 micron) have indicated that the Pluto-Charon system exhibits a thermal lightcurve. We here report on observations of the system with the SPITZER MIPS and IRS instruments. Observations with MIPS were obtained at 24, 70 and 160 micron on Sept. 17-22, 2004, sampling eight orbital longitudes. The data clearly indicate a 24-micron lightcurve, with a 50 % amplitude, and a mean flux of about 7 mJy, roughly anticorrelated with the visible lightcurve, but with a 15-20° delay, indicative of thermal inertia. The 70-micron data also indicate a lightcurve with an amplitude of 30 %, less than observed by ISO at 60 micron. Finally, the noisier 160-micron data do not clearly exhibit a lightcurve but show fluxes that are typically twice lower than the ISO 150-micron fluxes. A preliminary analysis of the MIPS data in terms of thermophysical models of Pluto's surface, using multiple terrain models derived from visible and infrared spectroscopy and visible lightcurve information, indicates that (i) Pluto's surface thermal inertia is (3--5)x10^4 erg cm-2 s-1/2 K-1 (ii) Charon's surface temperature is in the range 54-59 K, suggesting that Charon also has a measureable thermal inertia, but probably lower than Pluto (iii) the spectral emissivity of Pluto's surface, and particularly the H2O-tholin regions, decreases from 24 to 160 micron.
SPITZER/IRS spectra, acquired on Aug. 27-Sept. 2, 2004 at 8 longitudes, indicate that the Pluto-Charon spectrum is featureless over 20-35 micron. Preliminary inspection of these spectra in terms of thermal lightcurve suggests a consistent behaviour with the MIPS photometric measurements. We will present a joint analysis of the MIPS and IRS data, with the hope of further refining the model parameters.

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