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which took place during the Martian summer, was -
19.6
ı
C, while the coldest was
97.7
ı
C. So in this region, the temperature remained far below the freezing point
(0
ı
C) of water.
8.3.9.9
Mars Exploration Rovers
The Mars Exploration rovers, Spirit and Opportunity, found a great deal of evidence
for past water on Mars. The Spirit rover landed in what was thought to be a large
lake bed. The lake bed had been covered over with lava flows, so evidence of past
water was initially hard to detect. On March 5, 2004, NASA announced that Spirit
had found hints of water history on Mars in a rock dubbed “Humphrey.” Detailed
inspection of the rock revealed a bright material filling internal cracks. Such material
may have crystallized from water trickling through the volcanic rock. The amount
of Mars once covered by ancient water remains unknown, as both rovers landed in
regions thought likely to be once under water.
The Opportunity rover was directed to a site that had displayed large amounts
of hematite from the orbit. Hematite often forms from water. The rover indeed
found layered rocks and marble- or blueberry-like hematite concretions. Elsewhere
on its traverse, Opportunity investigated aeolian dune stratigraphy in Burns Cliff in
Endurance Crater. Its operators concluded that the preservation and cementation of
these outcrops had been controlled by flow of shallow groundwater. In its years of
continuous operation, Opportunity is still sending back evidence that this area on
Mars was soaked in liquid water in the past (Figs.
8.13
,
8.14
,
8.15
,and
8.16
).
As Spirit traveled in reverse in December 2007, pulling a seized wheel behind,
the wheel scraped off the upper layer of soil, uncovering a patch of white ground
rich in silica. It must have been produced in one of two ways: one, hot spring
deposits produced when water dissolved silica at one location and then carried it
to another (i.e., a geyser), two, acidic steam rising through cracks in rocks stripped
them of their mineral components, leaving silica behind. The Spirit rover also found
evidence for water in the Columbia Hills of Gusev Crater. In the Clovis group
of carbonate-rich rocks enriched in the elements phosphorus, sulfur, chlorine and
bromine, the Mössbauer spectrometer (MB) detected goethite, which forms only in
the presence of water. Goethite is a mineral with an iron oxyhydroxide with ferric
iron (Fe
3C
) '-FeO(OH). This means that various regions of the planet once harbored
stable liquid water.
The MER rovers had been finding evidence for ancient wet environments that
were very acidic. In fact, what Opportunity has mostly discovered, or found
evidence for, was sulfuric acid, a harsh chemical for life. But in May 17, 2013,
NASA announced that Opportunity found clay deposits that typically form in
wet environments that are of near-neutral acidity. This finding provides additional
evidence about a wet ancient environment possibly favorable for life.
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