In a new study, planetary scientists have found strong similarities between the soil of Gale Crater on Mars and that of the cold, sub-Arctic climate of Newfoundland, Canada.
X-ray amorphous material comprises 15-73% by weight of the sedimentary rocks and eolian deposits in Gale Crater. This material is siliceous and high in iron and low in aluminum. The presence of volatiles is consistent with the presence of early weathering products. To better understand the impact of this material on past water conditions on Mars, Feldman and others used bulk and selective dissolution techniques, X-ray diffraction, and transmission electron microscopy to investigate the formation and lifetime of X-ray amorphous material in terrestrial iron-rich soils of different ages and environmental conditions. Image courtesy of M. Kornmesser / ESO.
Scientists often use soil to portray environmental history, as the minerals it contains can tell the story of a 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 soil and rocks in Gale Crater are a record of a climate that existed 3 to 4 billion years ago, when Mars was relatively water-rich, coinciding with the time when life first emerged on Earth.
“Gale Crater is an ancient lake bed and clearly water was present, but what were the environmental conditions like when the water was there?” said Dr Anthony Feldman, a soil scientist and geomorphologist at the Desert Institute.
“We'll never find a direct analogue on the Martian surface because conditions on Mars and Earth are so different, but we can look at trends under Earth conditions and apply them to problems on Mars.”
NASA's Curiosity rover has been exploring Gale Crater since 2011 and has found large amounts of soil material known as X-ray amorphous material.
These components of soil lack the typical repeating atomic structure that characterizes minerals and therefore cannot be easily characterized using traditional techniques such as X-ray diffraction.
For example, when a crystalline material like diamond is hit with X-rays, the rays scatter at characteristic angles based on the mineral's internal structure.
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 soil and rock samples tested in Gale Crater consisted of 15-73% X-ray amorphous material.
“Think of X-ray amorphous material as being like jelly, which is a soup of different elements and chemicals that slide around one another,” Dr. Feldman said.
Curiosity also conducted chemical analysis of soil and rock samples and found that the amorphous material was rich in iron and silica and deficient in aluminum.
Beyond limited chemical information, scientists don't yet understand what this amorphous material is or what its presence means about Mars' historical environment.
Uncovering more information about how these enigmatic materials formed and persist on Earth could help answer long-standing questions about the Red Planet.
Dr. Feldman and his colleagues visited three locations in their search for similar X-ray amorphous material: the Tablelands of Gros Morne National Park in Newfoundland, the Klamath Mountains in Northern California, and western Nevada.
All three sites contain serpentinite soils that the researchers predicted would be chemically similar to the X-ray amorphous material in Gale Crater, meaning it would be rich in iron and silicon but poor in aluminum.
The three locations also recorded ranges of rainfall, snowfall and temperatures, which could help provide insight into the types of environmental conditions that produce amorphous material and promote its preservation.
At each site, the team examined the soil using X-ray diffraction analysis and transmission electron microscopy, allowing them to see the soil material at a more detailed level.
The subarctic climate of Newfoundland produced materials chemically similar to those found at Gale Crater, but lacked the crystalline structure, whereas soils produced in warmer climates such as California and Nevada did not produce the crystalline structure.
“This tells us that you need water there to form these materials,” Dr. Feldman said.
“But to preserve the amorphous material in the soil, the average annual temperature needs to be cold, close to freezing.”
Amorphous materials are often considered to be relatively unstable, meaning that at the atomic level, the atoms have not yet organized into a final crystalline form.
“Something is happening in the rates, or kinetics, of the reactions that slows them down so that these materials are preserved over geological timescales,” Dr Feldman said.
“What we're suggesting is that very cold conditions, close to freezing, are the specific kinetic limiting factors that allow these materials to form and be preserved.”
“This research improves our understanding of the Martian climate.”
“The results suggest that the abundance of this material in Gale Crater is consistent with subarctic conditions similar to those found in Iceland, for example.”
Team work Published in a journal Communication Earth and the Environment.
_____
A.D. Feldman othersIn 2024, iron-rich X-ray amorphous material will record Mars' past climate and the persistence of water. Community Global Environment 5, 364; doi: 10.1038/s43247-024-01495-4
This article is based on a press release from the Desert Research Institute.
