Meridiani Planum
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Meridiani Planum is a plain located 2 degrees south of Mars' equator, in the westernmost portion of Sinus Meridiani. It hosts a rare occurrence of gray crystalline hematite. On Earth, hematite is often formed in hot springs or in standing pools of water; therefore, many scientists believe that the hematite at Meridiani Planum may be indicative of ancient hot springs or that the environment contained liquid water. The hematite is part of a layered sedimentary rock formation approximately 200 meters thick. Other features of Meridiani Planum include volcanic basalt and impact craters.
Mars rover Opportunity
In 2004, Meridiani Planum was the landing site for the second of NASA's two Mars Exploration Rovers, named Opportunity. It had also been the target landing site for Mars Surveyor 2001 Lander, which was cancelled after the failures of the Mars Climate Orbiter and Mars Polar Lander missions.
Preliminary results from Opportunity indicate that its landing site was once saturated for a long period of time with liquid water, possibly of high salinity and acidity. Features that suggest this include cross-bedded sediments, the presence of many small spherical pebbles that appear to be concretions, vugs inside rocks, and the presence of large amounts of magnesium sulfate and other sulfate-rich minerals such as jarosite.
In January 2005, the Opportunity rover discovered a pitted, boulder-like metallic object which was named Heat Shield Rock. Spectrometer analysis proved its identity as an iron-nickel meteorite.