Mars likely had a cold, icy past, new study finds

The question of whether Mars ever supported life has captured the imagination of scientists and the public for decades. The discovery hinges on a better understanding of the past climate of Earth’s neighbor: Was the planet warm and wet, with seas and rivers very similar to those found on our own planet? Or was it frigid and therefore potentially less likely to support life as we know it? A new study provides evidence for the latter hypothesis by identifying similarities between soils discovered on Mars and those of Newfoundland, Canada, a cold subarctic climate.

The study, published in Land and Environment Communications, They looked on Earth for soils containing materials comparable to those in Mars’ Gale Crater. Scientists often use soil to describe environmental history because the minerals present can tell the story of how the landscape has changed over time.

A better understanding of how these materials formed could help answer long-standing questions about the historical conditions of the Red Planet. The soils and rocks of Gale Crater provide a record of Mars’ climate 3 to 4 billion years ago, a time when water was relatively abundant on the planet, and the same time that life appeared on Earth.

“Gale Crater is a paleo-lake bed: there was obviously water. But what were the environmental conditions like when the water was there?” says Anthony Feldman, a soil scientist and geomorphologist now at DRI. “We’ll never find a direct analogue of the Martian surface, because the conditions are so different between Mars and Earth. But we can look at trends in Earth conditions and use those to try to extrapolate to Martian questions.”

NASA’s Curiosity rover has been studying Gale Crater since 2011 and has discovered a multitude of soil materials known as “X-ray amorphous materials.” These soil components lack the typical repeating atomic structure that defines minerals and therefore cannot be easily characterized using traditional techniques such as X-ray diffraction.

When X-rays are emitted from crystalline materials such as a diamond, for example, they scatter at characteristic angles based on the internal structure of the mineral. However, X-ray amorphous materials do not produce these characteristic “fingerprints.” This X-ray diffraction method was used by the Curiosity rover to demonstrate that X-ray amorphous materials made up between 15 and 73 percent of the soil and rock samples tested in Gale Crater.

“You can compare amorphous materials to jelly in X-rays,” Feldman says. “It’s a kind of soup of different elements and chemicals sliding around on top of each other.”

The Curiosity rover also performed chemical analyses on soil and rock samples, and found that the amorphous material was rich in iron and silica, but poor in aluminum. Beyond the limited chemical information, scientists don’t yet understand what the amorphous material is, or what its presence implies about Mars’ historical environment. Uncovering more information about how these enigmatic materials form and persist on Earth could help answer lingering questions about the Red Planet.

Feldman and his colleagues visited three sites looking for similar X-ray amorphous materials: the plateaus of Gros Morne National Park in Newfoundland, the Klamath Mountains of northern California, and western Nevada. All three sites had serpentine soils that the researchers expected to be chemically similar to the X-ray amorphous material in Gale Crater: rich in iron and silicon but lacking aluminum.

The three sites also provided a range of precipitation, snowfall and temperatures that could help better understand the type of environmental conditions that produce amorphous materials and promote their preservation.

At each site, the research team examined the soils using X-ray diffraction analysis and a transmission electron microscope, which allowed them to observe the soil materials at a more detailed level. Newfoundland’s subarctic conditions produced materials that were chemically similar to those found in Gale Crater, but lacked a crystalline structure. Soils produced in warmer climates such as California and Nevada did not.

“This shows that water is needed to form these materials,” Feldman says. “But you need the average annual temperature to be close to freezing to preserve the amorphous material in the soils.”

Amorphous material is often considered to be relatively unstable, meaning that at the atomic level, the atoms have not yet organized into their final, more crystalline forms.

“There’s something happening in the kinetics – or the reaction rate – that slows down the reaction rate, so that these materials can be preserved over geological time scales,” Feldman says. “What we’re suggesting is that very cold conditions, close to freezing, are a particular kinetic limiting factor that allows these materials to form and be preserved.”

“This study helps us better understand the climate of Mars,” Feldman adds. “The results suggest that the abundance of this material in Gale Crater corresponds to subarctic conditions, similar to those observed, for example, in Iceland.”