A new analysis of seismic data from NASA’s Mars InSightmission there is led to several revelations for water on Mars.
Mars, now a parched desert, was once full of water, with traces of past streams and rivers still visible all over the planet. A leading theory suggests that water on Mars became part of the minerals that make up the underground cement.
However, a new analysis of seismic data from NASA’s Mars InSightmission produced several revelations contradicting this idea. The analysis led by Scripps Institution of Oceanography at the University of California, San Diegofound a lack of cemented sediments, suggesting a lack of water.
The analysis was published in Geophysical Research Letters.
Discoveries about underground water on Mars
First, the upper 300 meters of the subsurface, below the landing site near the Martian equator, contains little or no ice.
“We find that the crust of Mars 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 Vasan Wright of the Scripps Institution of Oceanography at UC San Diego and a co-author of the analysis.
“These findings do not rule out the possibility that there are ice grains or small ice balls that do not cement other minerals together,” Wright said. “The question is, how likely is the ice to be present in that form?”
The second finding contradicts a leading idea about what happened to water on Mars. The Red Planet may have harbored oceans of water early in its history. Several experts suspected that much of the water had become part of the minerals that include underground cement.
“If you put water in contact with rocks, you produce a whole new set of minerals, like clay, so the water is not a liquid. It’s part of the structure of the mineral,” 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 can also enter minerals that do not act as cement. But the uncemented subsurface removes one way of preserving a record of life or biological activity,” Wright said. By its very nature, cement holds rocks and sediments together, protecting them from erosion.
The lack of cemented sediments suggests a lack of water 300 meters below the InSight landing site, near the equator. At average temperatures below freezing, the conditions would be suitable for water to freeze if it were there.
Manga and many other planetary scientists have long suspected that the Martian subsurface would be full of ice. With this new evidence, that doesn’t seem to be the case. However, large ice sheets and frozen ground ice remain at the poles of Mars.
“As scientists, we are now faced with the best data, the best observations. And our models predicted that there should still be frozen land at that latitude with aquifers underneath,” said Manga, professor and chair of Earth and Planetary Sciences at UC Berkeley.
For the InSight spacecraft
In 2018, the InSight spacecraft landed on Elysium Planitia, a flat, smooth plain near the Martian equator. Its instruments include a seismometer that measures vibrations caused by earthquakes and crashing meteorites.
Scientists can relate this information to a vast amount of knowledge about the surface, including images of Martian landforms and temperature data. Surface data suggest that the subsurface may consist of sedimentary rocks and lava flows. Still, the team had to account for uncertainties about subsurface properties such as porosity and mineral content.
Seismic waves from earthquakes indicate the nature of the materials they travel through. Possible cementing minerals, such as calcite, clay, kaolinite, and gypsum, affect seismic velocities. Wright’s team at Scripps Oceanography used computer modeling of rock physics to interpret the velocities obtained from the InSight data.
“We ran our models 10,000 times each to incorporate the uncertainties in our answers,” said co-author Richard Kilburn, a graduate student at ScrippsTectonorocphysics Laboratoryled by Wright. The simulations that best fit the data show a subsurface consisting primarily of uncemented material.
Scientists intend to explore the subsurface because that is where life on Mars would most likely exist. There is no liquid water on the surface of Mars and life below the surface would be shielded from radiation.
NASA’s priorities for the future
After a sample return mission, NASA’s priority for the next decade is the Mars Life Explorer mission concept. The goal is to drill two meters into the crust of Mars at a high latitude to search for life. Ice, rock and atmosphere come together here.
The proposed Mars Ice Mapper international robotic mission is now under consideration to help NASA identify potential science targets for the first human missions to Mars. Scripps Oceanography helps prepare young scientists to contribute to such missions.
“All my life, growing up, I’ve heard that the Earth could become uninhabitable,” said study co-author Jhardel Dasent, another graduate student in the lab that Wright leads. “I am now at an age where I can contribute to the creation of knowledge about another planet that can take us there.”
This research was funded by the National Science Foundation, NASA andCIFAR Earth 4D program.
