Olivine A Mars Surprise
The Mars Global Surveyor orbiter (in orbit now for six years) recently found the mineral silicate olivine in a 30,000 sq. km area of the Nili Fossae region of Mars. This finding was reported in Science magazine 302 (2003), 627-630. Now the Spirit rover has found olivine (plus iron 2 and iron 3) in the Martian dust at its landing site in the Gusev crater. This is significant because olivine is usually associated with volcanic eruptions. When exposed to water, olivine quickly transforms into other chemistry.
The presence of olivine may mean the soil at the Spirit site is finely ground lava void of water. This is supported by the returned photos showing wheel impressions in the soil despite fridge temperatures. The Gusev site is at least one hundred million plus years old based on the impact cratering. What lies directly under the surface soil will be examined to a short distance down by the rover.
Scientists believe the Nili Fossae region is a minimum of 3.6 billion years old dating back to the late bombardment period.
Complementing these findings are the carbonates findings of Global Surveyor also reported in the same issue of Science magazine. If water were present in the past atmosphere carbonates should be found. Carbonates form when carbon dioxide (the major component of the atmosphere) is exposed to water. Only 2-3% carbonates have been found in the atmospheric dust. This amount of carbonates could be accounted for by the rotational tilt of Mars to 60 degrees every million years or so. This tilt would melt the southern polar cap causing evaporation which would account for the carbonates that are there.
While these findings await Spirits further study, the Opportunity rover also have found olivine. Opportunity's Moessbauer spectrometer, an instrument on the rover's robotic arm designed to identify the types of iron- bearing minerals in a target, found a strong signal in a soil patch for olivine. A few days of analysis may be needed to discern this and whether fainter signals are from hematite.
For those supporting the life on Mars hypnosis, either microprobe or advanced, olivine
is bad news. These findings support the hypnosis that Mars has permanently been cold and dry and not warm and wet since the inner solar system late bombardment. This however does not mean there could not be near-surface ice below the Martian surface and of course at the poles. Near-surface ice or permafrost has been detected from orbit and could be forced to the surface in the case of large meter impacts which would release much energy including heat. Liquid water then could possibly exist underground in local areas near large craters for periods of time. Liquid water can not currently exist on or near the surface due to the very low atmospheric pressure and cold temperatures. Water ice on the surface would go directly to water vapor if heated, the same as dry ice does on Earth. Any triple point vaporization curve diagram for water will show this. For Mars to have had surface water in the past would have required a much thicker or heavier atmosphere then as present.
Scientists were puzzled by the discovery of olivine because it implies the soil consists at least partially of ground up rocks that have not been weathered or chemically altered. The black line in the following graph represents the original data; the three colored regions denote individual minerals and add up to equal the black line. Also spectrum analysis of the rock called Adirondack at Gusev crater indicates the probable presence of olivine.