There is already overwhelming evidence that rivers and lakes once existed on Mars and now, a recent study has given a new twist on the idea.
Previous observations of soil observed along crater slopes on the Red Planet showed a significant amount of perchlorate salts, which tend to be associated with brines with a moderate pH level.
However, researchers have stepped back to look at the bigger picture through data collected from the 2001: Mars Odyssey, named in reference to the science fiction novel by Arthur C. Clarke, '2001: A Space Odyssey,' and found that a different chemical on Mars may be key.
The researchers found that the bulk soil on Mars, across regional scales the size of the U.S. or larger, likely contains iron sulfates bearing chemically bound water, which typically result in acidic brines. This new observation suggests that iron sulfates may play a major role in hydrating martian soil.
This finding was made from data collected by the 2001: Mars Odyssey Gamma Ray Spectrometer, or GRS, which is sensitive enough to detect the composition of Mars soil up to one-half meter deep. This is generally deeper than other missions either on the ground or in orbit, and it informs the nature of bulk soil on Mars.
"This is exciting because it's contributing to the story of water on Mars, which we've used as a path for our search for life on Mars," said co-author Nicole Button.
The study revealed that the older ancient southern hemisphere is more likely to contain chemically bound water while the sulfates and any chemically bound water are unlikely to be associated in the northerly regions of Mars.
The researchers considered several existing hypotheses in the context of their overall observations, which suggest a meaningful presence of iron-sulfate rich soils, which are wet compared to Mars' typically desiccated soil.
Among these hypotheses, the researchers identify acid fog and hydrothermal processes as more consistent with their observations than efflorescence, even though the sensitivity of GRS to elements, but not minerals, prevents a decisive inference. Hydrothermal sites, in particular, are increasingly recognized as important places where the exchange between the surface and deep parts of Earth's biosphere are possible. This hypothesis is significant to the question of martian habitability.
"Our story narrows it to two hypotheses, but emphasizes the significance of all of them," said lead author Suniti Karunatillake. "The depth and breadth of these observation methods tell us about global significance, which can inform the big question of what happened to the hydrologic cycle on Mars."
This research is published in the Journal of Geophysical Research: Planets.
