An article published in the journal “Proceedings of the National Academy of Sciences (PNAS)” reports the results of an analysis of seismic data collected on the planet Mars by NASA’s InSight lander that concludes that the mid-crust of Mars could be filled with liquid water that saturates a layer of igneous rock. Vashan Wright and Matthias Morzfeld of the Scripps Institution of Oceanography and Michael Manga of the University of Berkeley used models similar to those used to map aquifers and oil fields to try to understand the composition of deep layers of the Martian subsurface.
The best explanation for the data collected by the InSight mission is that between 11.5 and 20 kilometers deep there’s a layer of igneous rock saturated with liquid water. The depth makes it impossible to reach it but if the entire mid-crust of Mars were made like this, there would be enough water to form an ocean between one and two kilometers deep on the surface.
The image (Courtesy James Tuttle Keane and Aaron Rodriquez, courtesy of Scripps Institution of Oceanography. All rights reserved) shows a cutout of the interior of Mars beneath NASA’s InSight lander with the dry upper crust and the mid-crust saturated with water.
The InSight lander reached Mars on November 26, 2018, and worked until 2022, detecting a lot of information about the interior of Mars. Even today there’s some seismic activity on the red planet, sometimes also generated by meteorite impacts, and InSight recorded it. All this data allowed deductions to be made about the thickness of the crust, the depth and composition of the core, and even some estimates of the temperature in the Martian mantle.
Previous studies had ruled out the presence of water in the upper layers of the crust, up to 5 kilometers deep. Now, however, this new study analyzed the data collected by InSight to understand what is at a greater depth with interesting results.
On Earth, models have been developed that interpret seismic readings to find and map aquifers and oil fields. An adapted version of those models was used to analyze seismic data collected by the InSight lander, and the best explanation for their characteristics is that between 11.5 and 20 kilometers deep there’s a layer of igneous rock, composed of cooled magma, saturated with liquid water.
When Mars was young, it was much more like Earth but is too small to maintain a spinning liquid core to generate a magnetic field. In essence, it lost its shield against the solar wind over three billion years ago, with the consequence that its atmosphere was slowly blown away.
Many researchers have previously suggested that much of the liquid water that once flowed on the surface of Mars ended up underground, but until now there have only been occasional discoveries. The InSight lander’s detections concern the area beneath it, but it’s possible that the mid-crust has similar characteristics across the planet. If this hypothesis were correct, it would contain enough water to form an ocean between one and two kilometers deep on the surface.
On Earth, drilling to depths greater than 10 kilometers is extremely complex, time-consuming, and therefore expensive. On Mars, such an undertaking is unthinkable, and it would be unthinkable even for a human expedition. This means that at least for the foreseeable future, it will not be possible to obtain any direct verification of the results of this study.
This study is interesting for understanding the history of Mars with regard to the water cycle and also for the geological processes that led to the formation of the mid-crust with water-saturated igneous rocks. All this is also linked to the assessments of the possible emergence and survival of life forms on Mars and the sources of water available for possible future crewed missions.
