Tiger Spots on Mars: Signs of Life or Chemistry in an Aqueous Environment?

The discovery of “leopard spots” in a Martian rock was recently heralded as evidence of “possible bio-structures.” But a more subtle reflection suggests that the spots could be the result of simple chemical reactions in a watery medium, without the need for life.

potential biostructures

Just like El Mundo immediately announcedOn July 25, NASA’s mission team launched the robotic rover perseverance It announced the discovery of strange sites on a Martian rock that could be “potential biostructures.” That is, the team suggested that these structures could be signs of past microbial life on the red planet. Let’s remember that Perseverance is NASA’s all-terrain vehicle that has already been traveling around Mars for three and a half years, collecting rocks and searching for signs of life.

This was not the first time this approach had been announced. It had only been a year since the team perseverance They found signs of organic molecules, thought to have come from microbes that were stuck to rocks in a 45-kilometre-wide impact crater near the Martian equator (Jezero Crater). The findings were published in the prestigious magazine nature But we were warned that before establishing a biological origin for these molecules, the research team must be able to rule out any other possible non-biological source, which is impossible based on the data.

Chiava waterfalls

We fear that we may now find ourselves in a somewhat similar situation. A year after the results obtained in the Jezero crater, perseverance It is located next to a 1 x 0.6 meter rock called Chiava Falls. This rock is made up of sediments deposited by a river that flowed through the area about 3.5 billion years ago, and emptied into the aforementioned crater (which was then a lake).

A team of researchers from perseverance He studied the rock of Chiava Falls in great detail. There are large white veins of calcium sulphate alternating with other red bands, probably containing hematite (a mineral consisting of iron oxide). In one of these bands appear small light spots of irregular shape and size of about a millimeter, surrounded by a dark outline, that is, they resemble the spots on a tiger’s skin.

After discovering these strange spots, the research team decided to use a drill. perseverance To dig around one of them, which results in a hole 6 cm wide. It was then proven that the leopard’s spots are not flat structures, but that the dark edges also extend deep, meaning that these spots are not just superficial, but three-dimensional structures.

aquatic medium

This type of staining is also observed in some terrestrial rocks with hematite. It is thought that the chemical reaction of hematite with water can cause the iron mineral to change color from red to white. So it is not impossible that this type of reaction also occurred on Mars when water flowed through that river that flowed into Jezero. Chemical reactions of this type can release iron and phosphate, and these materials can form the black rings that appear in the now famous leopard spots in Martian rocks.

It is true that on Earth, the energy released from these chemical reactions in an aqueous medium can be an important source of energy for microbes, and thus this type of stain is usually associated with the presence of microorganisms. But microbes are not required for these structures to form in hematite.

Therefore, we cannot at all rule out that the tiger-walk-shaped structures were formed by chemical reactions in an aquatic medium without the presence of life.

The scientists also identified small greenish olivine crystals alongside white veins of calcium sulfate. Olivine is a mineral that crystallizes from magma, and it’s a mystery how these crystals were brought to these locations by this ancient river. The team wonders whether olivine could have been introduced into the rocks at extremely high temperatures, and whether those conditions were favorable for the formation of leopard spots.

Bring rocks to earth

As we can see, current data do not allow us to link the Martian leopard spots to the presence of life. Team perseverance He has examined the Chiava Falls rock with every means at his disposal, drilling, laser scanning and X-raying it, but the small all-terrain vehicle carries only a limited set of tools.

What might be really desirable is to examine that rock with all the tools available in terrestrial laboratories, tools that are more modern, more versatile, and more powerful than those available on Earth. perseverance. That’s why NASA has been working for years with the European Space Agency (ESA) to design a mission capable of sending ships to Mars, collecting rock samples and bringing them back to Earth in a sealed package: this is the project. Mars sample return (Mrs).

The project is neither simple nor cheap. A review by an independent group of experts a few months ago concluded that if we were to get samples back on Earth by 2030, the budget would be about $13 billion (a sum far higher than the $8 billion initially projected). If the budget is not increased in this way, the mission’s timeline would have to be extended to 2040.

And let’s not forget that the Chinese space agency is also working on a similar project, but with shorter time frames (sample return between 2030 and 2031). For all these reasons, NASA and ESA are now reworking the design to make the MRS project cheaper, in an attempt to keep the schedule competitive with the Chinese mission.

The original announcement about the discovery of leopard spots on Mars can be read here. here.