On Earth, mud flows because water, a major ingredient, often exists in its liquid state.
On Mars, however, the thin atmosphere causes liquid water to sublimate or freeze. This general lack of liquid makes it difficult to explain mounds that dot parts of the Red Planet—mounds that some scientists think are mud volcanoes.
A study published in Communications Earth and Environment suggests that a key to understanding how these features form is simple: add salt. By lowering the freezing point of water, salt allows mud to flow for longer periods of time and form structures that more closely resemble flows on Earth.
Because salt has been detected on Mars, it is likely that Martian mudflows are also salty, much like Earth’s mud volcanoes, which form when pressurized mud and gases are pushed to the surface, often forming a cone with a crater.
Terrestrial “mudflows are similar to lava flows, but they’re made of water, clay, and other materials,” explained geophysicist Ondřej Krýza of the Institute of Geophysics of the Czech Academy of Sciences and first author of the study.
In the laboratory, Krýza and his colleagues tested how different salts affect mud behavior under Mars-like conditions. They prepared separate mud samples containing magnesium sulfate, sodium chloride, sodium sulfate, or calcium sulfate. Inside the Large Mars Chamber, a mechanism poured 500 milliliters of mud onto an aluminum tray cooled to around −25°C (−5.8°F), mimicking temperatures that might be found on the Martian surface. The chamber itself simulated the planet’s low atmospheric pressure.
The experiments showed that a solution of 10% magnesium sulfate or 2.5% sodium chloride maximized mud propagation. Both salts have been identified on the Red Planet.
Exploration of Microbial Life
“The study presents a unique and fascinating approach that I have not encountered before,” Ryodo Hemmi, a planetary geologist at the Japan Aerospace Exploration Agency who was not involved in the research, said in an email.
Hemmi pointed out that though some Martian mounds resemble mud volcanoes on Earth, how they formed remains unclear. He emphasized that the new study is valuable for examining mound shapes but that more research is needed before drawing definitive conclusions. Current models, he said, don’t explain how material composition affects the size and form of Martian mounds, especially given their large scale compared to mud volcanoes on Earth.
“These salts are important because they can…affect the flow of water and other fluids, which is crucial for understanding the potential for microbial life.”
“I believe their study provides a valuable new perspective on the morphological analysis of both terrestrial and Martian mud volcanoes,” Hemmi said.
“Mud volcanoes on Earth act like natural exploration wells because they bring up sediments from many different layers beneath the surface,” explained Adriano Mazzini, a geologist at the University of Oslo in Norway and a coauthor of the study.
If the volcano-like structures on Mars are, indeed, made of salty mud, studying them could provide insights into Mars’s subsurface geology and could potentially reveal areas where liquid water once existed or may still be hidden.
“These salts are important because they can…affect the flow of water and other fluids, which is crucial for understanding the potential for microbial life,” Krýza said.
—Larissa G. Capella (@CapellaLarissa), Science Writer
