MAP – Mercury Space Weathering Maps
PDS Bundle: urn:nasa:pds:trang2017_mercury_space_weathering
PDS Collection: urn:nasa:pds:trang2017_mercury_space_weathering:data
For more information about MAP products, see the Mercury Space Weathering Maps Description (PDF).
The Mercury space weathering maps represent the abundance in weight percent (wt%) of four different particle types, nanophase native iron (shortened to “iron” or “Fe”) and amorphous carbon (shortened to “carbon” or “C”) and microphase native iron and amorphous carbon. Nanophase and microphase particles are roughly defined as particles with diameters of 10–100 nm and >100 nm, respectively. The submicroscopic particle maps represent the sum of the nanophase and microphase abundances for each respective phase (i.e., native iron and amorphous carbon). The maps cover the entire surface of Mercury (-180–180°E longitude and -90–90°N latitude) at 2 pixels per degree (0.5 degrees per pixel or 21290.4 m/pixel). The space weathering maps were derived using the radiative transfer model with the Visible Infrared Spectrograph (VIRS) data from the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission. The space weathering maps include interpolations over missing pixels, especially over the poles. The six maps are in equirectangular projection with a longitude of central meridian at 0°.
The derivation of the space weathering maps with the radiative transfer model is thoroughly described in Trang et al. (2017). The space weathering maps are based upon the models of Hapke (2001) and Lucey and Riner (2011), where we use the radiative transfer technique to model the MESSENGER VIRS. The modeling only includes wavelengths between 0.3–0.85 μm. Longer wavelengths are excluded because the data were noisy due to elevated temperatures (Izenberg et al., 2014).
The radiative transfer technique is a model that can reproduce a visible to near-infrared spectrum using physical principles. The radiative transfer model is based upon the work of Hapke (1981; 1993), where the model was modified to describe nanophase (Hapke, 2001) and microphase particles (Lucey and Riner, 2011). To use this model, a few assumptions about the regolith on Mercury was made, such as
The regolith consists of transparent silicates where the density of each particle is 3.0 g/cm3. The average grain size of these silicates is 20 μm (Warell et al., 2010).
The optical properties of this silicate regolith include a real index of refraction of 1.4 and a reflectance of 80% at all visible wavelengths.
These silicate particles contain varying amounts of nanophase and microphase native iron and amorphous carbon where the microphase particles are ~1 μm in size and the nanophase particles are smaller than the wavelength of visible light.
Included with these maps are a count map and error maps (one for each particle type). The count map represents the number of records for each pixel that was included in the median calculation. The nanophase and microphase native iron and amorphous carbon error maps show the L1 scale of the median—or 1.4826 times the median absolute difference.
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Hapke, B. 2001, Space weathering from Mercury to the asteroid belt, J. Geophys. Res., 106(E5), 10,039-010,073, doi:10.1029/2000JE001338.
Izenberg, N.R., Klima, R.L., Murchie, S.L., Blewett, D.T., Holsclaw, G.M., McClintock, W.E., Malaret, E., Mauceri, C., Vilas, F., Sprague, A.L., Helbert, J., Domingue, D.L., Head, J.W., Goudge, T.A., Solomon, S.C., Hibbitts, C.A., Dyar, M.D., 2014. The low-iron, reduced surface of Mercury as seen in spectral reflectance by MESSENGER. Icarus 228, 364–374.
Lucey, P.G., Riner, M.A., 2011, The optical effects of small iron particles that darken but do not redden: Evidence of intense space weathering on Mercury, Icarus, 212(2), 451–462, doi:10.1016/j.icarus.2011.01.022.
Trang, D., Lucey, P.G., Izenberg, N.R., 2017, Radiative transfer modeling of MESSENGER VIRS spectra: Detection and mapping of submicroscopic iron and carbon, Icarus, 293, 206–217, doi:10.1016/j.icarus.2017.04.026.
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