NASA’s Mars roving lander just made a shocking discovery as part of it’s “InSight” mission. “An additional layer 30 to 40 meters thick.” It’s the sort of thing that’s only exciting to geologists but now we know a lot more about Elysium Planitia and it will help plot where to lay the roadways once we set a base up.
Hidden secret on Mars
It’s amazing how much cool gear NASA engineers were able to pack on the Mars lander. They pinged signals into the crust and turned the echoes into a detailed map of what lies under the Martian surface, at least for the landing spot. InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport.
Seismic data collected in Elysium Planitia, which is the planet’s second largest volcanic region, suggests “the presence of a shallow sedimentary layer sandwiched between lava flows beneath the planet’s surface.”
The team wrote up their findings in a paper titled “The shallow structure of Mars at the InSight landing site from inversion of ambient vibrations.”
The international team of experts “examined the shallow subsurface to around 200 meters in depth.” Most of the results were expected but some of what they found surprised them.
Right beneath the surface of planet Mars, they discovered “a regolith layer of dominantly sandy material approximately three meters thick above a 15 meter layer of coarse blocky ejecta.” Those are big chunks blasted out of the crust by meteorite impact that fell back down.
“Below these top layers, they identified around 150 meters of basaltic rocks.” That means ancient lava flows, “which was largely consistent with the expected subsurface structure.” Then the data threw them a curve. There were two sets of flows, with mud sandwiched in between.
Between the lava flows
However, the scientists write, “between these lava flows, starting at a depth of about 30 meters,” they found “an additional layer 30 to 40 meters thick with low seismic velocity, suggesting it contains weak sedimentary materials relative to the stronger basalt layers.” The next step was to start dating everything.
To do that, they counted craters. On Mars, “surfaces with many impact craters from meteorites are older than ones with fewer craters. Also, craters with larger diameters extend into the lower layer, allowing the scientists to date the deep rock, while smaller ones allow them to date the shallower rock layers.”
After making some educated guesses, the team determined that the “shallower lava flows are approximately 1.7 billion years old, forming during the Amazonian period – a geological era on Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyper-arid conditions, which began approximately 3 billion years ago.”
The deeper, much older lava flow below the sediments formed “approximately 3.6 billion years ago during the Hesperian period, which was characterized by widespread volcanic activity.”
As well as they can figure out, “the intermediate layer with low volcanic velocities could be composed of sedimentary deposits sandwiched between the Hesperian and Amazonian basalts, or within the Amazonian basalts themselves.” They really aren’t sure but the findings “provide the first opportunity to compare seismic ground-truth measurements of the shallow subsurface to prior predictions based on orbital geological mapping.”
While the layer remains a mystery, the team is a lot closer to planning where to put the roads for a Mars colony. “Knowledge of the properties of the shallow subsurface is required to assess, for example, its load-bearing capacity and trafficability for rovers. Besides, details on the layering in the shallow subsurface help to understand where it might still contain ground water or ice.”