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

The question of whether Mars ever supported life has captivated the imagination of scientists and the public for decades. Central to the discovery is gaining insight into the past climate of Earth’s neighbor: Was the planet warm and humid, with seas and rivers very similar to those found on our planet? Or was it cold 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 study, published in Earth and Environment Communications, looked for soils on Earth with materials comparable to those of Mars’ Gale Crater. Scientists often use soil to describe the history of the environment, as 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 historical conditions on the Red Planet. The soils and rocks of Gale Crater provide a record of the Martian climate between 3 and 4 billion years ago, during a time of relatively abundant water on the planet — and the same time period that first saw life on Earth.

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

NASA’s Curiosity Rover has been investigating Gale Crater since 2011 and has found an abundance of soil material known as “X-ray amorphous material”. These soil constituents 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 shot at crystalline materials like a diamond, for example, the X-rays are scattered at characteristic angles based on the mineral’s internal structure. However, X-ray amorphous material does not produce these characteristic “fingerprints”. This X-ray diffraction method was used by the Curiosity Rover to demonstrate that X-ray amorphous material makes up between 15 and 73% of soil and rock samples tested in Gale Crater.

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

The Curiosity Rover also performed chemical analyzes on soil and rock samples, revealing that the amorphous material was rich in iron and silica but deficient in aluminum. Beyond the limited chemical information, scientists do not yet understand what the amorphous material is, or what its presence implies for the historical environment of Mars. Discovering 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 X-ray-like amorphous material: Gros Morne National Park in Newfoundland, the Klamath Mountains of 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 deficient in aluminum.

The three sites also provided a range of precipitation, snow, and temperatures that could help provide insight into the type of environmental conditions that produce amorphous material and encourage its preservation.

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

“It shows that you need water there to form these materials,” Feldman says. “But it has to be cold, the average annual temperature near freezing, in order to preserve the amorphous material in the ground.”

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

“There’s something going on in the kinetics—or the rate of reaction—that’s slowing it down so that these materials can be preserved on geologic time scales,” Feldman says. “What we’re suggesting is that very cold, near freezing conditions, is a particular kinetic limiting factor that allows these materials to form and be preserved.”

“This study improves our understanding of the Martian climate,” adds 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.”