Earth-like environment likely on ancient Mars

A research team using the ChemCam instrument onboard NASA's Curiosity rover discovered higher-than-usual amounts of manganese in lakebed rocks within Gale Crater on Mars, which indicates that the sediments were formed in a river, delta, or near the shoreline of an ancient lake. The results were published today in Journal of Geophysical Research: Planets.

"It is difficult for manganese oxide to form on the surface of Mars, so we didn't expect to find it in such high concentrations in a shoreline deposit," said Patrick Gasda, of Los Alamos National Laboratory's Space Science and Applications group and lead author on the study. "On Earth, these types of deposits happen all the time because of the high oxygen in our atmosphere produced by photosynthetic life, and from microbes that help catalyze those manganese oxidation reactions.

"On Mars, we don't have evidence for life, and the mechanism to produce oxygen in Mars's ancient atmosphere is unclear, so how the manganese oxide was formed and concentrated here is really puzzling. These findings point to larger processes occurring in the Martian atmosphere or surface water and shows that more work needs to be done to understand oxidation on Mars," Gasda added.

ChemCam, which was developed at Los Alamos and CNES (the French space agency), uses a laser to form a plasma on the surface of a rock, and collects that light in order to quantify elemental composition in rocks.

The sedimentary rocks explored by the rover are a mix of sands, silts, and muds. The sandy rocks are more porous, and groundwater can more easily pass through sands compared to the muds that make up most of the lakebed rocks in the Gale Crater. The research team looked at how manganese could have been enriched in these sands -- for example, by percolation of groundwater through the sands on the shore of a lake or mouth of a delta -- and what oxidant could be responsible for the precipitation of manganese in the rocks.

On Earth, manganese becomes enriched because of oxygen in the atmosphere, and this process is often sped up by the presence of microbes. Microbes on Earth can use the many oxidation states of manganese as energy for metabolism; if life was present on ancient Mars, the increased amounts of manganese in these rocks along the lake shore would have been a helpful energy source for life.

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Curiosity rover finds new evidence of ancient Mars rivers, a key signal for life

New analysis of data from the Curiosity rover reveals that much of the craters on Mars today could have once been habitable rivers.

"We're finding evidence that Mars was likely a planet of rivers," said Benjamin Cardenas, assistant professor of geosciences at Penn State and lead author on a new paper announcing the discovery. "We see signs of this all over the planet."

In a study published in Geophysical Research Letters, the researchers used numerical models to simulate erosion on Mars over millennia and found that common crater formations -- called bench-and-nose landforms -- are most likely remnants of ancient riverbeds.

The study was the first to map the erosion of ancient Martian soil by training a computer model on a combination of satellite data, Curiosity images and 3D scans of the stratigraphy -- or layers of rock, called strata, deposited over millions of years -- beneath the Gulf of Mexico seafloor. The analysis revealed a new interpretation for common Martian crater formations which, until now, have never been associated with eroded river deposits.

"We have everything to learn about Mars by better understanding how these river deposits can be interpreted stratigraphically, thinking about rocks today as layers of sediment deposited over time," Cardenas said. "This analysis is not snapshot, but a record of change. What we see on Mars today is the remnants of an active geologic history, not some landscape frozen in time."

Prior studies of satellite data from Mars had identified erosional landforms called fluvial ridges as being possible candidates for ancient river deposits. Using data collected by the Curiosity rover at Gale crater, the team found signs of river deposits that are not associated with fluvial ridges, but rather bench-and-nose landforms that have never been linked to ancient river deposits.

"This suggests that there could be undiscovered river deposits elsewhere on the planet, and that an even larger section of the Martian sedimentary record could have been built by rivers during a habitable period of Mars history," Cardenas said. "On Earth, river corridors are so important for life, chemical cycles, nutrient cycles and sediment cycles. Everything is pointing to these rivers behaving similarly on Mars."

In designing their computer model, Cardenas and his team found a new use for 25-year-old scans of Earth's stratigraphy. Collected by oil companies, the scans of beneath the Gulf of Mexico seafloor provided an ideal comparison to Mars, Cardenas explained.

The team simulated Mars-like erosion using the 3D scans of actual, recorded stratigraphy on Earth. When they ran the simulation, the model revealed erosional Martian landscapes that formed topographic benches and noses, rather than fluvial ridges, appearing almost identical to landforms observed by the Curiosity rover inside the Gale crater.

"Our research indicates that Mars could have had far more rivers than previously believed, which certainly paints a more optimistic view of ancient life on Mars," Cardenas said. "It offers a vision of Mars where most of the planet once had the right conditions for life."

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