An artist's rendering of the Mars InSight lander. InSight, which stands for Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport, is designed to provide Mars its first full examination since its formation 4.5 billion years ago. Image Credit: NASA/JPL-Caltech 



Physics connects seismic data to properties of rock and sediments

A new analysis of seismic data from NASA's Mars InSight mission has revealed two major surprises.

The first surprise: there is little or no ice in the upper 300 meters (1000 feet) of the subsurface beneath the landing site near the Martian equator.

"We discovered that Mars' crust is weak and permeable." The sediments are uncementable. And there is no ice, or only a small quantity of ice, in the pore spaces," said Vashan Wright of the University of California, San Diego's Scripps Institution of Oceanography. Wright and three co-authors published their results in Geophysical Research Letters on August 9, 2022.

The second surprise contradicts a popular theory about what happened to Mars' water. It is thought that early in its existence, the red planet may have held oceans of water. Many specialists thought that much of that water was incorporated into the minerals that comprise underground cement.


On April 11, 2022, Sol 1199 of the InSight mission, NASA's InSight Mars lander captured this image of the area in front of the lander with its lander-mounted Instrument Context Camera (ICC). Image Credit: NASA/JPL-Caltech


Water may also pass through minerals that do not act as cement. However, the uncemented subsurface eliminates one method of preserving a record of life or biological activity, according to Wright. Cement, by nature, hold rocks and sediments together, preventing them from degrading.

The absence of cemented sediments suggests a lack of water 300 meters (1000 feet) below InSight's landing point near the equator. The average temperature near the Mars equator is below freezing, indicating that conditions would be cold enough to freeze water if it have existed.

Many planetary scientists, including Manga, have long suspected that the Martian subsurface is ice-covered. Their suspicions have dissipated. At the Martian poles, large ice sheets and frozen ground ice exist.

"We now have access to the most recent data and observations as scientists. And our models predicted that there would still be frozen ground with aquifers beneath at that latitude," said Manga, UC Berkeley professor and chair of Earth and planetary science,

The InSight spacecraft arrived on Elysium Planitia, a flat, smooth plain near Mars' equator, in 2018. Its instruments included a seismometer, which measures vibrations produced by marsquakes and meteorites crashing.

Researchers may link this data to a huge mass of knowledge about the surface, such as photographs of Martian landforms and temperature data. The surface data suggested that the subsurface could be made up of sedimentary rock and lava flows. However, the scientists had to account for uncertainty in subsurface properties such as porosity and mineral content.


Seismic waves from marsquakes provide information about the materials they travel through. Seismic velocities are affected by cementing minerals such as calcite, kaolinite, clay, and gypsum. The velocities acquired from the InSight data were interpreted by Wright's team at Scripps Oceanography using rock physics computer modeling.

"We ran our models 10,000 times each to include the uncertainties into our responses," said co-author Richard Kilburn, a graduate student in Wright's Scripps Tectonorockphysics Lab. The data was the best fit by simulations of a subsurface made mostly of uncemented material.

Scientists want to investigate the subsurface because if life exists on Mars, it would be there. Because there is no liquid water on the surface, underground life would be safe from radiation. Following a sample-return mission, the Mars Life Explorer mission concept is a NASA priority for the following decade. The plan is to dig two meters (6 feet) into the Martian crust at high latitude to search for life where ice, rock, and atmosphere meet.

The proposed international robotic Mars Ice Mapper Mission to assist NASA in identifying prospective science goals for the first human missions to Mars is already being considered. Scripps Oceanography assists in the preparation of new scientists to contribute to such missions.


The National Science Foundation, NASA, and the CIFAR Earth 4D program funded for this research.