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A new study finds critical clues that lie in the Red Planet’s soil.

Recent studies comparing soils from Earth and Mars suggests that the historical climate of Mars was cold and subarctic, much like Newfoundland. The study focuses on amorphous materials in Gale Crater’s soil, potentially preserved by near-freezing conditions, offering new insights into Martian environmental conditions and its potential for life.

Probing Mars’ past climate through Earth’s soils

The question of whether Mars ever supported life has captured the imagination of scientists and the public for decades. Central to the discovery is gaining insight into Earth’s neighbor’s past climate: Was the planet warm and humid, with seas and rivers similar to our own? Or was it cool and icy and therefore potentially less likely to support life as we know it?

A new study finds evidence to support the latter by identifying similarities between soils found on Mars and those of Canada’s Newfoundland, a cold subarctic climate.

The rim and floor of Gale Crater as seen by NASA’s Curiosity rover. Credit: NASA/JPL-Caltech

Insights from Gale Crater soil analysis

The study, published in Communications Earth and Environment on July 7, is looking for soils on Earth with materials comparable to Gale Crater on Mars. Scientists often use soil to depict the history of the environment because the minerals present can tell the story of the landscape’s evolution over time. Understanding more about how these materials formed could help answer long-standing questions about the red planet’s historical conditions. The soils and rocks of Gale Crater provide evidence of the Martian climate between 3 and 4 billion years ago, during a time when water was relatively abundant on the planet – and the same time period in which life first appeared on Earth.

“Gale Crater is a palaeo lakebed – obviously there was water. But what were the environmental conditions when the water was there?” says Anthony Feldman, soil scientist and geomorphologist at DRI. “We will 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 that to try to extrapolate to Mars issues.

The Newfoundland Tablelands Exploration Site. Credit: Anthony Feldman/DRI

Challenges in the Analysis of Martian Materials

NASA’s Curiosity Rover has been exploring Gale Crater since 2011 and has discovered numerous soil materials known as “X-ray amorphous material.” 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 fired at crystalline materials like diamond, for example, the X-rays are scattered at characteristic angles based on the internal structure of the mineral. However, X-ray amorphous material does not create these characteristic “fingerprints”. This X-ray diffraction method was used by the Curiosity Rover to demonstrate that X-ray amorphous material comprised between 15 and 73 percent of the soil and rock samples tested in Gale Crater.

“You can think of X-ray amorphous materials like Jello,” Feldman says. “It’s this soup of different elements and chemicals just sliding past each other.”

The Curiosity rover also performed chemical analyzes of the soil and rock samples, finding that the amorphous material is rich in iron and silica but deficient in aluminum. Beyond the limited chemical information, scientists still do not understand what the amorphous material is or what its presence suggests about the historical environment of Mars. Uncovering more information about how these enigmatic materials form and persist on Earth could help answer persistent questions about the red planet.

Field studies mimicking Martian conditions

Feldman and his colleagues visited three places in search of similar X-ray amorphous material: the Tablelands of Gros Morne National Park in Newfoundland, the Klamath Mountains in northern California, and western Nevada. These 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 in aluminum. The three locations also provided a range of precipitation, snowfall and temperature that could help provide insight into the type of environmental conditions that produced amorphous material and promoted its preservation.

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

“It shows that you need the water there to form these materials,” Feldman says. “But it would have to be cold, near-freezing mean annual temperature conditions to preserve the amorphous material in the soils.”

Amorphous material is often considered relatively unstable, meaning that at the atomic level the atoms are not yet organized into their final, more crystalline forms. “There’s something going on in the kinetics—or the rate of the reaction—that slows it down so that these materials can be preserved over geologic time scales,” Feldman says. “What we’re suggesting is that very cold, near-freezing conditions are one particular kinetic limiting factor that allows these materials to form and be preserved.”

“This study improves our understanding of the Martian climate,” says Feldman. “The results suggest that the abundance of this material in Gale Crater is consistent with subarctic conditions similar to what we would see in, for example, Iceland.”

Reference: “Iron-rich X-ray amorphous material records past climate and water resistance on Mars” by Anthony D. Feldman, Elizabeth M. Hausrath, Elizabeth B. Rampe, Valerie Tu, Tania S. Peretiajko, Christopher DeFelice, and Thomas Sharp, 7 July 2024, Communications Earth and Environment.
DOI: 10.1038/s43247-024-01495-4