Mars likely had a cold and icy past, new research suggests

The question of whether life once existed on Mars has captivated the imaginations of scientists and the public for decades. Central to the discovery is understanding the past climate of Earth’s neighbor: Was the planet warm and wet, with seas and rivers much like those on our own planet? Or was it frigid and icy, and therefore potentially less conducive to life as we know it? A new study finds evidence to support the latter, identifying similarities between Martian soils and those of Canada’s Newfoundland, a cold subarctic climate.

The study, published in Communication Earth and Environment, searched for soils on Earth with similar materials to those of Gale Crater on Mars. Scientists often use soils to represent environmental history, because the minerals present can tell the story of how a landscape has evolved over time.

Understanding how these materials formed could help answer long-standing questions about historical conditions on the Red Planet. The soil and rocks of Gale Crater provide a record of the Martian climate between 3 and 4 billion years ago, during a relatively watery period on the planet, the same period when life first appeared on Earth.

“Gale Crater is a paleo-lake floor—there was clearly water there. But what were the environmental conditions when the water was there?” said Anthony Feldman, a soil scientist and geomorphologist now at DRI. “We’re never going to find a direct analog on the surface of Mars, because the conditions are so different between Mars and Earth. But we can look at trends under Earth conditions and use those to try to extrapolate to Mars questions.”

NASA’s Curiosity Rover has been exploring Gale Crater since 2011 and has found an abundance of soil materials known as “X-ray amorphous material.” These soil components lack the typical repeating atomic structure characteristic of minerals and therefore cannot be easily characterized using traditional techniques such as X-ray crystallography.

When X-rays are shot at crystalline materials such as diamond, the X-rays scatter at characteristic angles based on the internal structure of the mineral. However, X-ray amorphous material does not produce these characteristic “fingerprints.” This X-ray diffraction method was used by the Curiosity Rover to show 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 as Jello,” Feldman says. “It’s a soup of different elements and chemicals just sliding past each other.”

The Curiosity Rover also performed chemical analyses on the soil and rock samples, finding that the amorphous material was rich in iron and silica, but poor in aluminum. In addition to the limited chemical information, scientists don’t yet understand what the amorphous material is, or what its presence implies 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.

Feldman and his colleagues visited three locations 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 locations 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.

In addition, the three sites yielded variation in rainfall, snowfall, and temperatures, which can provide insight into the type of environmental conditions that produce amorphous material and promote its preservation.

At each site, the research team examined the soils using x-ray diffraction analysis and transmission electron microscopy, which allowed them to look at the soil materials at a more detailed level. The subarctic conditions of Newfoundland produced materials that were chemically similar to those in Gale Crater, but also lacked crystal structure. Soils produced in warmer climates such as California and Nevada did not.

“This shows that you need the water there to form these materials,” Feldman said. “But it has to be cold, with an average annual temperature near freezing, to maintain the amorphous material in the soil.”

Amorphous material is often considered relatively unstable. This means that the atoms are not yet organized at the atomic level 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 timescales,” Feldman said. “What we’re suggesting is that very cold, near-freezing conditions, is a specific kinetic limiting factor that allows these materials to form and be preserved.”

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