The dry rock outcrops on the martian plains of Meridiani Planum are thought to have as soon as been bathed in and formed by acidic waters, primarily based on proof collected by NASA’s Alternative rover in its seven years on the pink planet.
How these historical waters turned so acidic, nevertheless, has been an open query. A brand new research means that these acid waters had been created when iron-rich floor water rose to the floor of Mars and underwent chemical reactions — altering the state of the iron and boosting the acidity of the waters.
As Alternative has explored the Meridiani Planum space, it has analyzed sedimentary rocks thought to have been deposited about 3.7 billion years in the past. The minerals current within the rocks recommend that they shaped in a local weather that was arid however that skilled periodic floor water upwelling. Sure telltale minerals, significantly one known as jarosite, recommend that the waters that washed over the floor and shaped the rocks had been acidic.
Some scientists suppose that the water that formed this space of the martian floor got here from under the bottom, periodically welling up. However the rock this floor water would have been surrounded by is basalt, and the chemistry of such a system would have seemingly made for neutral-pH water.
So simply how did impartial water grow to be acidic sufficient (with a pH estimated between 2 and 4, or across the acidity of lemon juice or orange juice) to go away that attribute mineral signature?
Joel Hurowitz, an Alternative staff member at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues used chemical fashions and Alternative’s observations to recommend a mechanism that might reply that query.
If the groundwater was wealthy in a selected type of iron, that iron might need undergone a chemical transformation when the water reached the floor and was uncovered to the environment, leading to acidic waters. The iron within the water may have been oxidized — the place a molecule or atom loses an electron — both by ultraviolet mild or by response with dissolved oxygen. This course of would have left the water with an acidic pH, and the iron would have come out of the water resolution to finally type the rocks that Alternative noticed.
Hurowitz and his colleagues crunched the numbers to see if this mechanism may produce sufficient acid to clarify the circumstances at Meridiani. The outcomes appeared to match what Alternative’s observations instructed very intently, and “we had been form of pleasantly stunned by that,” Hurowitz stated.
Earlier strategies for a way the waters turned acidic embrace the concept atmospheric sulfur compounds — presumably generated by volcanic eruptions — may have fallen as acid rain, very similar to can occur in polluted air on Earth. However Hurowitz thinks the iron oxidation clarification higher suits the noticed chemistry of Meridiani and doesn’t require the onset of acid water movement to “completely coincide with volcanic exhalations and sulfur coming in from an exterior supply on your acidity.”
One key query left, which Hurowitz and his colleagues are already investigating, is “whether or not or not you’re in a position to decide up sufficient iron alongside these groundwater movement paths and produce them to the floor and have all this acid chemistry happen,” Hurowitz stated.