Shaping the red planet’s surface

The surface and atmosphere of Mars have seen many changes over its 4.5-billion-year history. While the planet's current atmosphere is very thin (about 0.6% of Earth's), it was once thick enough to sustain liquid water.

According to new research published in Communications Earth & Environment, this ancient climate plays a key role in how we interpret sediment deposits imaged by orbiters and rovers.

To reach this conclusion, lead author and Assistant Professor Jacob Adler of Arizona State University's School of Earth and Space Exploration, alongside researchers from Georgia Institute of Technology, The Open University and Czech Academy of Sciences, conducted over 70 experiments in a Mars simulation chamber. They tested how flowing water-sediment mixtures would be affected by the varying pressures (5–1,000 mbar) and temperatures (−25 to 24 degrees Celsius) throughout the planet’s history.

"We found that studying sedimentary analogs on Earth didn't fully capture the physics occurring on Mars. On Mars, the deposit morphology of these water-sediment mixtures is greatly influenced by boiling or freezing," said Adler.

The experiments revealed that at higher atmospheric pressures (above 30 mbar), water and mud would have similar flow physics (rheology) as on Earth. This could indicate that some of the oldest sedimentary features on the surface (from the Noachian era, or 4.1–3.7 GaThe scientific abbreviation for giga-annum, which means one billion years. It is used primarily by geologists, paleontologists and cosmologists to describe events in the ancient past. ) should appear similar to Earth environments. In these scenarios, surface conditions may also have been more habitable for life.

On the other hand, as Mars started to lose most of its atmosphere (around 3.7 Ga), the dominant physics in sediment flow experiments changed to freezing and boiling. The team found that at the lower pressures Mars has experienced after the Noachian, the rheology and deposit shapes (morphology) were not at all Earth-like.

“At low present-day pressures, Mars mud would boil and levitate if the surface temperature was warm, or freeze and flow more like lava if the temperature was cold,” Adler shared. “And when we mapped out where on Mars, we would expect this different behavior, we found that this opposite behavior could happen at the same time at different locations on the planet. The small-scale climate variations across Mars’ topography are enough to see these opposing effects.”

The research suggests that studying the specific shapes of features like sediment flows, debris flows and mudflows could help scientists better estimate the former climate conditions. 

"By finding matching morphologies of what we see on Mars and what we see in these lab experiments," Adler shared, "we might be able to better time-stamp the paleo-climate record."

This discovery highlights how laboratory experiments are a critical part of planetary science activities, as they can help scientists better interpret remote sensing and modeling results.

"We’ve sent rover missions to Mars largely because we find compelling remote sensing evidence of deposits formed by water or mud that could indicate a habitable environment. We are often eager to compare what we find to Earth analogs, but these are not always suitable for comparison. This study shows there is still much we can learn about Mars by conducting experiments under Mars conditions.”

This work was supported by NASA.