Detection of polonium-210 on martian dust by Opportunity's APXS
Titre du congrès :Michigan Geophysical Union Conference
Ville du congrès :Ann Arbor
Date du congrès :02/05/2006
Introduction : Polonium-210 is a decay product of uranium-238, present in the martian atmosphere and on the martian surface owing to exhalation of radon-222 from the subsurface. The half-life of its parent lead-210 (22.3 years) is such that the measurement of 210Po provides an indirect way of estimating the radon exhalation rate on a global scale, integrated over time scales of a few decades. Coupled with measurements of radon and its progeny, it can give valuable insight into surficial and atmospheric processes, in particular the exchange of volatiles at the surface, the presence of outgassing vents, the atmospheric aerosol cycle and the soil water and uranium contents (Sabroux et al., 2003, 2004; Meslin et al., 2006). These isotopes have drawn much less attention on Mars than on the Moon, probably because their measurement on Mars is comparatively more challenging.
The alpha mode of the Alpha-Particle X-Ray Spectrometer (APXS) onboard MER rovers was primarily designed to measure the concentration of oxygen and carbon in martian rocks and soils by Rutheford Backscattering of alpha particles emitted by a 244Cm source. It turns out that the upper part of APXS spectra also encompasses emission lines from several natural alpha-emitting radionuclides. Thus, we have investigated into the possible contribution of natural radioactive sources to alpha spectra, namely of polonium-210 and radon-222.