Is olivine a sign of a perpetually cold, dry Mars or is it a sign of something else?

Here is a TES image of the surface of Mars between 45 degrees north and 45 degrees south. The upper image shows the albedo differences, the lower images uses false colors to indicate the presence or absence of certain minerals. The blue areas are thought to represent areas of olivine, an easily erodable mineral generally formed in the mantle.

Here is the USGS press release caption for the above image:

"(bottom). The reflected light view is similar to a black and white photo of Mars, which shows Mars is dominated by light and dark areas. In the upper left, several large volcanos are seen, labeled V1 to V4. The lower image is a color composite of reflected and thermal light, where red is reflected light (called albedo), a 7.27 micron spectral feature indicative of sulfates in green, and in blue are spectral features due to the green mineral olivine with some contribution from pyroxenes (both volcanic minerals). Small white areas are low iron olivine, for example at the area labeled N, and the rim of the crater Argyre, labeled A. The small magenta spots near the center of the image, labeled H, are coarse-grained iron oxide. The other magenta area at upper left, labeled C, is due to clouds. Yellow and green areas probably contain more sulfate. Note the small round red spots on the left side of the image: these are giant volcanos (V1-V4), relatively sulfate free. Ancient lava flows from some of these volcanos also show as red and are relatively sulfate free. The vast areas of blue indicate abundant olivine which weathers so easily that it implies there has been little water and weathering reactions on Mars. Olivine occurs predominantly in the darker materials in the southern hemisphere. It also occurs in the giant 3000-mile long canyon system, Valles Marineris (labeled VM)."



You can click on the picture to link with the press release

The Southern Highlands, a heavily cratered area thought to be ancient, appear to be widely covered with olivines, consistent with the observation that the surface has been repeatedly flooded with volcanic material. This extensive flooding appears to have come through surface cracks and rifts, rather than from volcanoes.

The Southern Highlands today are some 3-8km higher than in the Northern Plains in most places. Atmospheric pressure is considerably lower here than the 6mb often quoted. There is a tongue of blue, apparently olivine, seen in the upper left area of the false color image. This is Acidalia, part of the vast Northern Plains of Mars, believed by some to be the bed of a vanished ocean. Acidalia is peppered with craters, nearly all of which appear stark white against a dark background, and nearly all of which show evidence of significant fluid fill, probably the result of formation in water-ice rich terrain. This is inconsistent with the presence of olivine, if this area is old and was the bed of a sea.

Another tongue of blue, on the right in the false color image, is Syrtis Major, a Highland volcanic province, one of the first dark areas spotted by telescopic observers in the 17th century. Syrtis is relatively heavily cratered but shows few signs of weathering over most of its surface.

The light area between Acidalia and Syrtis is also a Highland province, called Arabia Terra, a region that shows extensive erosion. Much of this erosion is unique to Arabia, and seems to involve the actions of fluids. Extensive channeling is found on Arabia, as well as apparently collapsed and undermined ground. Some areas appear to be peeled away. The margins are split and fractured. Other areas of Arabia are heavily coated with layers of friable material and dust.

Olivines are not found in Arabia, which may be the result of the extensive, and poorly understood, erosive history of the province. Curiously, olivines are apparently found in the bed of the Valles Marineris and throughout the chaos regions adjacent to the canyons. Given the obvious erosion here and the absence of volcanic deposits, the presence of olivines in this region is not easy to understand. The other dark areas in the image also apparently are composed of olivines, at least according to the color key below the image. However, another look suggests that the blue in these areas, possibly as well as in Acidalia, is an artifact, the result of the color-coding process, as it applies to all dark regions on the planet.

The hematite areas, seen in pink, imply the action of water in the Sinus Meridiani region. There are also many whitish deposits in Meridiani, not shown here, that suggest the presence of carbonates as well, though no measurement has yet been able to confirm the indications. Meridiani was once proposed as a region where underground water (perhaps derived from a polar source) rose to the surface. That idea seems to have been lost, but it may be revived if carbonates are ever found on the surface of Mars.