A new analysis of seismic data from NASA’s Mars InSight mission has revealed a couple of surprises.
The first surprise: the top 300 meters of the subsurface beneath the landing site near the Martian equator contains little or no ice.
“We find that Mars’ crust is weak and porous. The sediments are not well-cemented. And there’s no ice or not much ice filling the pore spaces,” said geophysicist Vashan Wright of Scripps Institution of Oceanography at the University of California San Diego. Wright and three co-authors published their analysis in Geophysical Research Letters.
“These findings don’t preclude that there could be grains of ice or small balls of ice that are not cementing other minerals together,” said Wright. “The question is how likely is ice to be present in that form?”
The second surprise contradicts a leading idea about what happened to the water on Mars. The red planet may have harbored oceans of water early in its history. Many experts suspected that much of the water became part of the minerals that make up underground cement.
“If you put water in contact with rocks, you produce a brand-new set of minerals, like clay, so the water’s not a liquid. It’s part of the mineral structure,” said study co-author Michael Manga of the University of California Berkeley. “There is some cement, but the rocks are not full of cement.”
“Water may also go into minerals that do not act as cement. But the uncemented subsurface removes one way to preserve a record of life or biological activity,” Wright said. Cements by their very nature hold rocks and sediments together, protecting them from destructive erosion.
The lack of cemented sediments suggests a water scarcity in the 300 meters below InSight’s landing site near the equator. The below-freezing average temperature at the Mars equator means that conditions would be cold enough to freeze water if it were there.
Many planetary scientists, including Manga, have long suspected that the Martian subsurface would be full of ice. Their suspicions have melted away. Still, big ice sheets and frozen ground ice remain at the Martian poles.