Mars has been the target of many planetary science missions involving flybys, orbiters, landers, and rovers that have focused on surface and atmospheric remote sensing as well as surface geochemistry and mineralogy.NASA’s InSight mission is the first to specifically target the subsurface using seismic methods, deploying a very broad-band seismometer: SEIS.
SEIS operates continuously with the primary goal to detect Mars quakes to quantify Martian seismicity and to infer the interior structure of Mars at all scales. In the study, Dr. Schmelzbach and co-authors used SEIS data to examine the shallow subsurface of Elysium Planitia, a flat-smooth plain just north of the Martian equator.
Right beneath the surface, they discovered a regolith layer of dominantly sandy material approximately 3 m (9.8 feet) thick above a 15-m (49-foot) layer of coarse blocky ejecta — rocky blocks that were ejected after a meteorite impact and fell back to the surface.They identified around 150 m of basaltic rocks, i.e., cooled and solidified lava flows, broadly consistent with the expected subsurface structure.
However, between these lava flows, starting at a depth of about 30 m, the researchers identified an additional layer 30 to 40 m thick with low seismic velocity, suggesting it contains soft sedimentary materials relative to the stronger basalt layers.They found 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 cold, hyper-arid conditions, which began approximately 3 billion years ago.