Evidence for a Low Surface Temperature on Pluto from Millimeter-Wave Thermal Emission Measurements
S. Alan Stern 1,
David A. Weintraub 2, and
Michel C. Festou 3
1 Space Sciences Department, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238
2 Department of Physics and Astronmy, Vanderbilt University, Nashville, TN 37235
3 Observatoire Midi-Pyrénées, F-31400 Toulouse, France
Thermal continuum emission from the Pluto-Charon system has been detected at wavelents of 800 and 1300 micrometers, and significant upper limits have been obtained at 450 and 1100 micrometers. After the subtraction of emission from Charon, the deduced surface temperature of much of Pluto is between 30 and 44 kein, probably near 35 to 37 kelvin. This range is significantly cooler than what radiative equilibrium models have suged and cooler than the surface temperature derived by the Infrared Astronomy Satellite. The low temperature indicates that methane cannot be present at the microbar pressure levels indicated by the 1988 stellar occultation measurements and that the methane features in Pluto's spectrum are from solid, not gas-phase, absorptions. This result is evidence that Pluto's atmosphere is dominated by nitrogen or carbon monoxide rather than methane.
Submitted on May 10, 1993
Accepted on July 16, 1993
