This is what perseverance has found so far

Located north of the Martian equator, Jezero Crater was chosen as a target by NASA because it contains what appears to be an ancient river delta that formed at the bottom of a lake, so it could provide valuable data on exactly when the water flowed. The surface of Mars. As shown David Schusterof the University of California, Berkeley and one of the lead authors, rocks collected from the bottom of the crater by perseverance lie beneath delta sediments, so their ages would provide an upper bound on the age of delta formation.

According to Shuster, the main surprise was that the rocks collected from four different locations in Jezero hole They turn out to be igneous rocks, that is, they were formed by cooling molten magma, and are the best ones to establish an accurate chronology once the samples return to Earth. These rocks also show evidence that they were altered by water.

“From a sampling perspective, this is huge,” Schuster explains. “The fact that we have evidence of a water change in igneous rocks, are the components that get people excited, because it helps to understand the environmental conditions that could have supported life at some point.” These igneous rocks, in fact, retain accurate information about when exactly a lake was located in Jezero.

“We know that the lake existed after the igneous rocks formed,” he says. Kenneth Farley, another of the authors. This will allow us to address some important questions: When was the climate of Mars suitable for the lakes and rivers on the planet’s surface? And when did it change to the cold and dry weather we see today? «.

Prior to the mission, geologists expected the crater floor to be filled with sediment or lava, molten rock that spilled to the surface and cooled quickly. But in two places known as Séítah, (the Navajo word means “in the middle of the sand”), the rocks appear to have formed underground and then slowly cooled. Of course, everything that covered it has been eroded in the past 2.5 to 3.5 billion years.

It’s igneous rocks

“Literally, for the first nine months, when we were driving the rover across the crater floor, we were debating whether the rocks we were seeing were sediments deposited in a lake or igneous rocks. And they really are igneous rocks. And the shape of those igneous rocks is really amazing,” Farley explains. , because it doesn’t look like simple igneous rocks flowing into the crater. Instead, it looks like something that formed in the depths, then gradually cooled in a larger magma chamber.

The crystal structure of the igneous rock, similar to Sierra Nevada granite, but with a different composition and finer grains, showed millimeter-sized olive grains interspersed with pyroxene that could only have formed by slow cooling. The rough olivine is similar to that seen in some meteorites that are believed to have originated on Mars and eventually crashed to Earth. Data supporting this idea come from multispectral imaging and X-ray fluorescence analysis performed with the instruments onboard the persistence and is detailed in second scientific articleIts main author is YangliuPlanetary geologist at JPL.

According to Shuster, the data collected so far by Perseverance allows for two different scenarios to explain igneous rocks: “Either the rocks cooled underground and somehow emerged from the surface, or there was something like a lake of magma that filled the hole.” It gradually cools down.

The samples obtained by the rover at another nearby site called Máaz (Mars in Navajo) are also igneous samples, but of a different composition. Since this layer covers the exposed igneous rock layer in Sitah, Moaz rock may be the upper layer of the magma lake. In lakes of magma on Earth, the densest minerals settle to the bottom when they crystallize, forming layers of different compositions. These types of igneous formations are called accumulative, which means that they were formed by the deposition of olivine enriched with iron and magnesium and the subsequent multi-stage cooling of a thick magma body.

But there is also the possibility that the igneous rocks in Maaz were the result of a subsequent volcanic eruption. In any case, says Schuster, the top layer that was partially eroded could be hundreds of meters thick.

changed by water

However, both the slow-cooling rocks in Sitah and the faster-cooling rocks in Moaz showed a common feature: both were altered by the action of water, albeit in different ways. The Mezze rock contains pockets of minerals that may have condensed from a brine solution, while the Sitta rock has reacted with the carbonated water, according to chemical analyzes aboard the rover.

The exact times at which these various strata formed will only be revealed through laboratory analysis on Earth, as the geochemical tools needed for dating are too large to fit aboard the persistence.

“There’s a whole variety of different geochemical observations that we can do on these rocks when we bring them back to Earth,” Chester says. This will give us all kinds of information about that fiery environment. We’ll be able to tell when the rock crystallizes, which is one of the things that excites me the most. But it will also give us information about when volcanic activity occurs inside the planet. Combined with satellite imagery, we’ll be able to relate this to some of the broader, more regional volcanic activity.”

Schuster noted that duplicate rock samples were taken at each of the four sites visited, and they will all be stored within a year along with other duplicate samples at an emergency site near the delta, for use only if the initial samples were removed on board, as it is not possible to Reaching perseverance due to mechanical failure. Recently collected sediment samples from the delta itself will also be included, details of which are being prepared for a future scientific paper.