A year and a half after NASA’s Perseverance rover landed on Mars, we are receiving new data and with it, several surprises. The rover has been touring and investigating Jezero Crater , located in the Martian northern hemisphere relatively close to the equator. This 45 kilometer – sized crater once housed a lake of liquid water , as shown by the channels that flow to and from it and the delta that can be seen in satellite imagery . This is why it was chosen for the site of the Perseverance mission, which has among its main objectives to search for traces of past life on the red planet.
As published in a recent scientific article, the rover has been studying the subsurface of the crater with its built-in radar and has observed that the layers located several meters deep are tilted . The slope, thickness, and shapes detected for these inclined strata suggest two possibilities for their formation: either they were created by slowly flowing lava flows, gradually cooling , or they were formed from the deposit of sediments carried there by the water that flowed through the crater billions of years ago.
Perseverance is currently traversing the delta that was formed where a river filled the lake formed inside Jezero Crater with water. All this information collected by the Perseverance rover will help us to know in detail the geological history of this region of Mars. From the information they could have gathered so far, the researchers expected to find horizontal layers. This discovery therefore indicates that the geological history of the region must have been more complex than previously thought.
Although the possibility that these layers formed as part of the delta that we do know occupied the region in the past might seem the most likely, the data that the rover has collected so far from the region suggests that the origin of their rocks is igneous . To obtain all this information, the rover has been using its radar instrument, with which it has sent pulses directly to the subsoil and, depending on how they were reflected, it has been able to reconstruct the appearance of the area studied . This study has been carried out along 3 kilometers and reaching a depth of about 15 meters . The information that we are obtaining could be compared to the stratigraphic cuts that we can sometimes observe on the sides of a highway, where the mountain has been cut vertically to make way for the road. Here we see different layers with different thicknesses, colors and textures . On Mars, these types of cuts are impossible, because we are not able to move the necessary machinery there, so we resort to radar study , which is also not as destructive.
All of this information will also give detailed context to the rock samples that Perseverance has been collecting and that will return to Earth on a future mission for analysis. These samples, collected at different points in the Jezero Crater, will give us information about the time when the crater contained a lake and will allow us to define a temporal range. Although in-depth analysis will have to wait for ground-based laboratories, the rover has already been able to deduce that four of the samples taken are igneous rock. From these samples comes the evidence that the tilted rock layers have this same origin. Perseverance has also observed that these igneous rocks show signs of being eroded by water and ultimately altered by the presence of liquid.
This of course has created high expectations, because it is precisely these environments where we would expect life to have proliferated if it ever existed on the surface of Mars. The collected samples are especially interesting because they are, again, not what the researchers expected to find, which were rocks that had been formed on the surface by rapidly cooling lava. The collected rocks, however, show a subsurface origin , which caused them to cool much more slowly . We know this because the size, shape and composition of the crystals that form tell us of a slow cooling, similar to that observed in similar formations on Earth. Since they were formed several billion years ago, what protected them from the elements has been eroded either by water at the time or by wind more recently.
These samples will be collected in a future mission that will take off in 2028 , will reach the red planet the following year and after a complicated process of recovering the Perseverance samples , it will take off from the Martian surface to return to Earth in 2033 .
Svein-Erik Hamran et al, 2022, Ground penetrating radar observations of subsurface structures in the floor of Jezero crater, Mars. Science Advances, DOI: 10.1126/sciadv.abp8564
KA Farley et al, 2022, Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars. Science, DOI: 10.1126/science.abo2196