Study finds water-altered soils throughout the southern highlands of Mars

  

 

Baton Rouge, La.— In a recently published collaborative study led by LSU Geology and Geophysics doctoral student Don Hood and his mentor, Suniti Karunatillake, associate professor of geology and geophysics, researchers were able to identify a key compositional irregularity in soils found on Mars, as it relates to soil hydration.

“Water is an important component in many geologic processes that produce minerals useful for human exploration of Mars,” said Hood. “By figuring out how much water was present, we can get a better idea of what to expect when we get there and what we will need to bring with us.”

Scientists studying Mars have identified and divided the planet into two separate regions: the northern lowlands and the southern highlands, which are separated by a planet-encircling change in elevation known as topographic dichotomy. However, the possibility of regionally distinct soil chemistries remains poorly understood.

The three-year, $360,000 project has been funded through the NASA Mars Data Analysis Program. The LSU researchers were joined by scientists across NASA-Ames; Institut de Recherche en Astrophysique et Planetologie, France; Rutgers University; University of Florida; Idaho State University; and Korea Institute of Geosciences and Mineral Resources, South Korea.

Hood and the group examined the chemistry of the soils throughout the mid-latitudes of Mars using nine chemical maps derived from Mars Odyssey Gamma-Ray Spectrometer data. Those data map the amounts and types of chemical elements at or near the planet’s surface by measuring the ways gamma photons are produced by the nuclear interactions between space radiation and soil to decimeter depths. The researchers found trends in spatial correlations among sulfur, chlorine, and hydrogen, distinct from other elements.

“In general, we expect that these three elements will vary together, collectively increasing and decreasing in abundance,” Hood said. “This is broadly true, but subtle shifts in that relationship—like the ones we detected—show that other processes, like small amounts of liquid water, have affected their distribution.”

The findings show that the processes by which water interacts with soils were likely active over larger areas in the southern highlands than previously realized, while such processes were negligible after the northern lowlands’ soils formed.

“The water must have been fairly widespread, though not in particularly large volumes throughout most of Mars’s southern highlands,” Hood said. “When combined with other findings about the presence of carbon in most soils, this may mean that almost all of the southern highlands were once habitable, making the chances of life emerging much higher.”

The researchers said their next step is to determine the minerals that carry the elements because the mineralogy of the subsurface “is difficult to constrain.”

“If we could determine not just how hydrogen, sulfur, and chlorine are varying, but what minerals they are found in, we would know even more about past processes,” Hood explained.

Equally important, the observed soil dichotomy motivates future work to determine underlying processes, such as apparently limited transport or mixing of soil across the dichotomy, and the role of hydrothermal processes in producing calcium or iron bearing salts that may hydrate Martian soils.

In turn, the outcomes advance prior works by this group on the possibility that hydrated-salt bearing soils first found in situ by the Spirit Rover, at Paso Robles in Gusev Crater, may be regionally significant.

Likewise, the group’s discovery provides broader geochemical context for the recent characterization of subsurface water ice at higher latitudes on Mars.

The group’s findings were published in the American Geophysical Union’s Geophysical Research Letters.