Mars in the distant past turned out to be a much more complex and wetter world than previously thought. NASA’s Perseverance rover has discovered in Jezero Crater evidence of at least three different episodes of water interacting with rocks — from carbon dioxide-rich groundwater to hot hydrothermal flows.

Scientists studied an area called Margin Unit on the inner edge of the crater. Perseverance has been exploring it since 2023, and the observation results showed that the history of water here was far more complex than had been assumed from orbital images, according to Space.com.

Instead of an ancient shoreline — volcanic rocks

Before the rover’s arrival, scientists assumed that the Margin Unit consisted of sedimentary rocks formed along the shore of an ancient lake. Orbital observations pointed to this, particularly the carbonate minerals detected there.

However, Perseverance found not sedimentary but igneous rocks. They formed from molten material deep beneath the Martian surface or as a result of volcanic activity.

These rocks are exactly what preserved evidence of several subsequent episodes of water exposure. Using the SuperCam instrument, researchers examined more than 185 sections of bedrock and were able to reconstruct the sequence of processes that took place.

“Now we know that this place became a kind of crossroads for water systems,” said Candice Bedford, the study’s lead author and a researcher at Purdue University.

Water altered Martian rocks several times

The first episode occurred when carbon dioxide-rich groundwater reacted with olivine, a mineral formed during the slow cooling of magma. As a result, carbonate minerals appeared in cracks within the rocks.

Later, these rocks were apparently affected by water from the ancient Lake Jezero. Silica was found in some samples. It can form when olivine interacts with water and is especially characteristic of rocks that once lay below the lake level.

But then another episode occurred in the region — a much hotter one.

In the eastern part of the Margin Unit, scientists discovered mineral veins containing calcium sulfate and fluorite. Their presence indicates that hot water once circulated through the volcanic rocks.

Thus, the same area of Mars was successively exposed to different water systems: groundwater, the surface water of the ancient lake, and hot fluids moving through the rocks.

Hot water matters for the search for signs of life

On Earth, hydrothermal systems create conditions in which microorganisms can exist. That is why the discovery of similar processes on ancient Mars is especially interesting for scientists studying the planet’s potential habitability in the past.

At the same time, researchers still cannot determine the exact age of each of the discovered episodes. Their sequence is known, but it is still impossible to establish how much time passed between them.

However, the minerals themselves may become a kind of chronicle of changes in the Martian climate. Their composition and distribution make it possible to trace how different water sources and environmental conditions succeeded one another in a single region.

Mars turned out not to be what it looked like from orbit

The result is especially important because the Margin Unit was initially interpreted as part of an ancient shoreline. Actual surface observations revealed a much more complex picture.

Jezero Crater is located in one of the largest Martian regions rich in carbonates. Therefore, the data obtained may prove useful far beyond the specific site that Perseverance is currently exploring.

“If there’s one thing I’ve learned in 10 years of working with rovers on Mars, it’s that Mars constantly delivers surprises,” Bedford said.

The study was published on September 21 in the journal Communications Earth & Environment. Scientists hope that further study of the Margin Unit rocks will help reconstruct the history of water on Mars and understand when and where conditions suitable for life may have existed on the planet.