Near-surface thermal gradients and their effects on mid-infrared emission spectra of planetary surfaces

Details Near-surface thermal gradients and their effects on mid-infrared emission spectra of planetary surfaces Near-surface thermal gradients and their effects on mid-infrared emission spectra of planetary surfaces

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....9919063h&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. E9, p. 19,063-19,073

Astronomy and Astrophysics

Astronomy

28

Astronomical Models, Emission Spectra, Infrared Spectra, Planetary Surfaces, Radiative Heat Transfer, Solar Heating, Temperature Gradients, Thermal Emission, Astronomical Spectroscopy, Infrared Spectroscopy, Lunar Surface, Mars Surface, Mercury Surface, Opacity, Temperature Distribution, Thermal Conductivity

Scientific paper

We model the heat transfer by radiation and conduction in the top few millimeters of a planetary surface to determine the magnitude of near-surface (approximately 100 micrometers) thermal gradients and their effects on mid-infrared emission spectra for a number of planetary environments. The model is one-dimensional and uses a finite difference scheme for approximately 10 micrometers layers. Calculations are peformed for samples heated at the base and from above by sunlight. Our results indicate that near-surface radiative cooling creates significant thermal gradients in the top few hundred microns of surfaces in which radiation is an important heat transfer mechanism. The effect is maximized in evacuated, underdense particulate media with sufficiently high temperatures. Near-surface thermal gradients will be significant in fine-grained particulate surfaces on the Moon (40-60 K/100 micrometers) and Mercury (approximately 80 K/100 micrometers), increasing spectral contrast and creating emission maxima in the transparent regions of the spectra. They will be of lesser importance on the surface of Mars, with a maximum value of around 5 k/100 micrometers in areas of low thermal inertia, and will be negligible on planets with more substantial atmospheres (less than 1 K/100 micrometers). We conclude that the effects that thermal gradients have on mid-IR emission spectra are predictable and do not negate the utility of emission spectroscopy for remote determination of planetary surface composition.

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