Scientific Information From The Mars Exploration Rover Mission - Water Hypothesis

Water Hypothesis

On March 2, 2004, NASA announced that "Opportunity has landed in an area of Mars where liquid water once drenched the surface". Associate administrator Ed Weiler told reporters that the area "would have been good habitable environment", although no traces of life have been found.

This statement was made during a press conference, where mission scientists listed a number of observations that strongly support this view:

• Distributions of spherules

Hypothesis: Spherules are concretions created in water as a solvent.

Competing hypothesis: Spherules are rehardened molten rock droplets, created by volcanoes or meteor strikes.

Supporting data: Location of spherules in the rock matrix is random and evenly spread.

Quote from Steve Squyres: "The little spherules like blueberries in a muffin are embedded in this rock and weathering out of it. Three ideas, lapilli, little volcanic hailstones, one possibility. Two, droplets of volcanic glass or impact. We've looked at these things very carefully. Probably concretions. If so, it's pointing towards water."

Detailed analysis of environmental, chemical, and mineralogical data taken from the Opportunity rover led to the elimination of the competing hypotheses, and the confirmation of the conclusion that the spherules were formed in place as post-depositional sedimentary concretions from an aqueous source

• Vugs

Hypothesis: Rock was formed in water, for instance by precipitation.

Competing hypothesis: Rock were formed by ash deposits.

Supporting data: Voids found in bedrock resemble "vugs" which are left by eroded away disk-shaped crystals, possible dissolved in a watery environment.

Quote from Steve Squyres: Second piece of evidence is that when we looked at it close-up, it was shot through with tabular holes. Familiar forms. When crystals grow within rocks, precipitated from water. If they're tabular, as they grow you can get tabular crystals and water chem changes and they go away or they weather away."

• Sulfates and jarosite

Hypothesis: Water created tell-tale salt chemicals in the rock.

Competing hypothesis: Chemistry of rocks is determined by volcanic processes.

Supporting data: Sulfate salts and jarosite mineral were found in the rock. On Earth they are made in standing water (possibly during evaporation).

Quote from Steve Squyres: "Next piece of evidence comes from APXS. We found it looked like a lot of sulfur. That was the outside of the rock. We brought with us a grinding tool, the RAT and we ground away 2-4 mm and found even more sulfur. Too much to explain by other than that this rock is full of sulfate salts. That's a telltale sign of liquid water. Mini-TES also found evidence of sulfate salts. Most compelling of all, the Mössbauer spectrometer in the RATted space showed compelling evidence of jarosite, an iron-(III) sulfate basic hydrate. Fairly rare, found on Earth and had been predicted that it might be found on Mars some day. This is a mineral that you got to have water around to make."

On March 23, 2004, NASA announced that they believe that Opportunity had not landed in a location merely "drenched in water", but on what was once a coastal area. "We think Opportunity is parked on what was once the shoreline of a salty sea on Mars," said Dr. Steve Squyres of Cornell University.

The announcement was based on evidence of sedimentary rocks that are consistent with those formed by water and not wind. "Bedding patterns in some finely layered rocks indicate the sand-sized grains of sediment that eventually bonded together were shaped into ripples by water at least five centimeters (two inches) deep, possibly much deeper, and flowing at a speed of 10 to 50 centimeters (four to 20 inches) per second," said Dr. John Grotzinger, from MIT. The landing site was likely a salt flat on the edge of a large body of water that was covered by shallow water.

Other evidence includes findings of chlorine and bromine in the rocks which indicates the rocks had at least soaked in mineral-rich water, possibly from underground sources, after they formed. Increased assurance of the bromine findings strengthens the case that rock-forming particles precipitated from surface water as salt concentrations climbed past saturation while water was evaporating.

The evidence for water was published in a series of scientific papers, with the initial results appearing in the journal Science and then with a detailed discussion of the sedimentary geology of the landing site appearing in a special issue of the journal Earth and Planetary Science Letters