Viking Lander image analysis of Martian atmospheric dust

Abstract

We have reanalyzed three sets of Viking Lander 1 and 2 (VL1 and VL2) images of the Martian atmosphere to better evaluate the radiative properties of the atmospheric dust particles. The properties of interest are the first two moments of the size distribution, the single‐scattering albedo, the dust single‐scattering phase function, and the imaginary index of refraction. These properties provide a good definition of the influence that the atmospheric dust has on heating of the atmosphere. Our analysis represents a significant improvement over past analyses (Pollack et al. 1977, 1979) by deriving more accurate brightnesses closer to the sun, by carrying out more precise analyses of the data to acquire the quantities of interest, and by using a better representation of scattering by nonspherical particles. The improvements allow us to better define the diffraction peak and hence the size distribution of the particles. For a lognormal particle size distribution, the first two moments of the size distribution, weighted by the geometric cross section, are found. The geometric cross‐section weighted mean radius (reff) is found to be 1.85±0.3 μm at VL2 during northern summer when dust loading was low and 1.52±0.3 μm at VL1 during the first dust storm. In both cases the best cross‐section weighted mean variance (νeff) of the size distribution is equal to 0.5±0.2 μm. The changes in size distribution, and thus radiative properties, do not represent a substantial change in solar energy deposition in the atmosphere over the Pollack et al. (1977, 1979) estimates.

[Comment on “Martian soil simulant available for scientific, educational study”] Caution advised on suitability of a Mars soil simulant

“…Martian air borne dust particles are concluded to be on average <2 microns [Pollack et al, 1995] or < 3 microns [Bell and Ockert-Bell, 1998;Haberle, 1998]. Given the acknowledged chemical similarity of the soil everywhere analyzed [Rieder et al, 1997], it is thus wide ly believed that at least the bulk of the soil on Mars is formed from this dust.…”

The imager for Mars Pathfinder experiment

“…Measurements of the variation of the sky intensity with azimuth when the sun was low in the sky were used by Viking to constrain the mean effective dust particle radius [Pollack et al, 1995]. We will observe the solar aureole not only near sunrise and sunset, but at various other times of the day.…”

Experimental and theoretical simulation of sublimating dusty water ice with implications for D/H ratios of water ice on Comets and Mars

“…However, in order to obtain dust (e), a grain size representative of martian airfall dust, it was first necessary to process the sieved JSC Mars-1. The grain size of martian airfall dust comes from the 1.6 μm radius particle peak of the distribution of dust observed in the martian atmosphere from landed spacecraft, as determined by studies of the martian atmosphere [31][32][33]. This material was produced by taking raw JSC Mars-1 and crushing it using a mortar and pestle before pouring the resulting detritus into a 10 cm deep water settling tank for 30 minutes.…”