Peering further into the surface of the Earth and any other planet can reveal a lot about its history and geological make-up. Now, the InSight lander on Mars‘ surface has given us our first view of what lies beneath the surface of the red planet. The seismometer onboard InSight, known as SEIS (Seismic Experiment for Interior Structure), detects a shallow sedimentary layer sandwiched between cemented rocks formed by lava flows at a depth of roughly 200 meters (650 feet). This could reveal a great deal about how Mars was formed, how it changed over time, and what geological causes are still in play today. The lava flows, in particular, can be linked to what we know about the planet’s volcanic past.
InSight landed on Mars in November 2018 in the Elysium Planitia, a vast and flat plain. The lander’s instruments analyzed the subtle ambient ground vibrations created by winds blowing across the planet’s surface to figure out what was hidden beneath the surface. On Earth, a similar technique was used to determine the subsurface composition and seismic risk. The waves on were compatible with two solid layers of rocks, such as basalt, and a thinner, less dense layer of material in the center, most likely sedimentary.
The appearance of that middle layer, which is 30-40 meters deep (98-131 feet), caught the researchers off guard, and it’s unclear what it’s comprised of or how it evolved. There may be some mixing with the Amazonian basalts, although the precision of seismic observations declines as depth drops. This data is essential in determining whether life ever existed on Mars. Still, it also tells us more about Earth’s history and evolution — Earth, and have geological compositions that are very similar. Aside from ancient planetary history, knowing what’s beneath the surface of at different times helps scientists figure out the ideal locations for future landers, rovers, and (eventually) space stations.