Comparative Planetology
Thermal infrared detection of cold-trapped volatiles at the poles of airless bodies
Elliot Sefton-Nash
Birkbeck, University of London
There is growing evidence that volatiles are cold-trapped in permanently shadowed regions (PSRs) at the poles of airless bodies.

Volatiles could originate as ejecta from impacting comets or be compounds formed by implanting of solar wind H+ ions. Detection techniques include mapping of neutron suppression, RADAR polarization or ultraviolet to far infrared radiometry/spectroscopy.

Despite detection of significant H2O in the plume ejected from the permanently shadowed Cabeus crater by the 2009 LCROSS impactor mission, it remains unclear whether volatile deposits exist in similar abundance at any other lunar polar locations. This is unlike Mercury, where NASA’s Messenger mission has detected substantial surface water ice.

We discuss thermal infrared observations by the Diviner Radiometer (aboard NASA’s Lunar Reconnaissance Orbiter) that might constrain the presence of volatiles in lunar regolith. The lunar regolith is very thermally insulating at the surface and short-term changes in illumination, e.g. eclipses or diurnal cycles, have negligible effect on the energy balance of PSRs.

Elucidating the thermal response of the upper few metres of regolith in PSRs requires observation of longer-term seasonal thermal waves that may penetrate to depth, where volatile deposits could remain stable over geologic time. Challenges to this approach lie in comparing the observed thermal response to thermal models.

In addition, transient surface water-frost could cause anomalous emissive properties that may be detectable by comparing modelled to observed angular emission functions. Laboratory measurements, modelling efforts and an ongoing off-nadir observation campaign by Diviner support this approach.
16:30 - 18:00