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Martian surface
The study of surface characteristics (or surface properties and processes〔Kieffer, H.H. et al. (1992). ''Mars.'' University of Arizona Press: Tucson, Part IV.〕) is a broad category of Mars science that examines the nature of the materials making up the Martian surface. The study evolved from telescopic and remote-sensing techniques developed by astronomers to study planetary surfaces. However, it has increasingly become a subdiscipline of geology as automated spacecraft bring ever-improving resolution and instrument capabilities. By using characteristics such as color, albedo, and thermal inertia and analytical tools such as reflectance spectroscopy and radar, scientists are able to study the chemistry and physical makeup (e.g., grain sizes, surface roughness, and rock abundances) of the Martian surface. The resulting data help scientists understand the planet’s mineral composition and the nature of geological processes operating on the surface. Mars’ surface layer represents a tiny fraction of the total volume of the planet, yet plays a significant role in the planet’s geologic history.〔Christensen, P.K.; Moore, H.J. (1992). The Martian Surface Layer, in Kieffer, H.H. et al., Eds. ''Mars.'' University of Arizona Press: Tucson, p. 686.〕 Understanding physical surface properties is also very important in determining safe landing sites for spacecraft.〔Golombek, M.P.; McSween, H.Y. (2007). Mars: Landing site Geology Mineralogy and Geochemistry, in ''Encyclopedia of the Solar System, 2nd ed.,'' McFadden, L.-A. et al. Eds. Elsevier: San Diego, CA, p.333-334〕
==Albedo and Color==
Like all planets, Mars reflects a portion of the light it receives from the sun. The fraction of sunlight reflected is a quantity called albedo, which ranges from 0 for a body that reflects no sunlight to 1.0 for a body that reflects all sunlight. Different parts of a planet’s surface (and atmosphere) have different albedo values depending on the chemical and physical nature of the surface.
No topography is visible on Mars from Earth-based telescopes. The bright areas and dark markings on pre-spaceflight-era maps of Mars are all albedo features. (See Classical albedo features on Mars.) They have little relation to topography. Dark markings are most distinct in a broad belt from 0° to 40° S latitude. However, the most prominent dark marking, Syrtis Major Planum, is in the northern hemisphere, outside this belt.〔Carr, M.H. (2007) ''The Surface of Mars;'' Cambridge University Press: New York, p. 1.〕 The classical albedo feature Mare Acidalium (Acidalia Planitia) is another prominent dark area that lies north of the main belt. Bright areas, excluding the polar caps and transient clouds, include Hellas, Tharsis, and Arabia Terra. The bright areas are now known to be locations where fine dust covers the surface. The dark markings represent areas that the wind has swept clean of dust, leaving behind a lag of dark, rocky material. The dark color is consistent with the presence of mafic rocks, such as basalt.
The albedo of a surface usually varies with the wavelength of light hitting it. Mars reflects little light at the blue end of the spectrum but much at red and higher wavelengths. This is why Mars has the familiar reddish-orange color to the naked eye. But detailed observations reveal a subtle range of colors on Mars' surface. Color variations provide clues to the composition of surface materials. The bright areas are reddish-ochre in color, and the dark areas appear dark gray. A third type of area, intermediate in color and albedo, is also present and thought to represent regions containing a mixture of the material from the bright and dark areas.〔Arvidson, R.E. et al. (1989). Nature and Distribution of Surficial Deposits in Chryse Planitia and Vicinity, Mars. ''J. Geophys. Res.,'' 94(B2), 1573–1587.〕 The dark gray areas can be further subdivided into those that are more reddish and those less reddish in hue.〔Barlow, N.G. (2008) ''Mars: An Introduction to Its Interior, Surface, and Atmosphere;'' Cambridge University Press: Cambridge, UK, p. 73.〕
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