Why are the signs of life on Mars so confusing? National Geographic

In 2012, a new era in Mars research began when NASA launched its six-wheeler Curiosity of in the Gale crater. Today, this crater, 155 kilometers in diameter, contains a large mountain composed of many layered sediments that geologically record Mars’ past. The main purpose of Curiosity of is to look for signs of a planet’s habitability, such as water, organic molecules, and energy sources—the necessary ingredients for life as we know it.

It was easy to find evidence of liquid water; Scientists already suspected that there was a deep lake in the crater. Curiosity of He was able to almost instantly identify an entire group of rocks that could only have formed in the presence of water.

But other tasks were less easy.

over the years Curiosity of Traces found in Jezero Crater indicate the presence of many organic molecules, the chemical building blocks of all carbon-based life. The rover also encountered the remains of ancient hydrothermal vents, where liquid water once mixed at high temperatures with a variety of chemicals and may have created energy resources.

In addition, it has Curiosity of The methane content of the air above the crater was found to fluctuate with the seasons, sometimes showing strong extremes. These measurements correlate with previous observations from Earth, which have not been properly explained for more than a decade. On Earth, such fluctuations in methane levels would be clear indicators of active metabolic processes.

However, none of these observations can be linked to biological processes yet. In addition, there is always the possibility that we are dealing with processes that we do not yet fully understand and that only He appears about signs of life.

“Most carbon processes on Earth’s surface are biological in nature, so it’s very difficult for us to change perspective and try to imagine a world that isn’t the case,” says astrobiologist Christopher House of Penn State University. “Once you get out of that perspective of Earth, you can start to think about the ways in which Mars behaves differently from Earth.”

foreign carbon compounds

Curiosity ofThe strangest and most interesting observation is very recent. In multiple rock samples taken from different locations in the crater, the rover found organic compounds with odd proportions of different carbon isotopes, atoms of the same element but different numbers of neutrons in their nuclei.

On Earth, organisms prefer to use lighter isotopes of carbon in their metabolism or photosynthesis, which has changed the ratio of isotopes in organic matter somewhat.

And that’s also what scientists found at five different locations in Gale Crater: rocks in which the content of the lighter isotopes was higher than in the heavier ones, compared to percentages previously found in the Martian atmosphere and in Martian meteorites. The observations are reminiscent of carbon traces measured in Australia’s Tumbiana Formation, a 2.7-billion-year-old rocky outcrop that contains carbon traces of ancient microbes that metabolized methane.

The decrease in the presence of heavy carbon isotopes is really remarkable. Exciting. On Earth, something like this only happens through biology,” says Williams.

But astrobiologist House, who led the analysis, thinks the results are by no means conclusive. He and his colleagues describe three possible scenarios that could explain the shift in ratio.

The first is that isotopic imprinting was actually caused by ancient microbes. The second possibility is that the solar system passed through an interstellar dust cloud long ago in which the ratio of carbon isotopes shifted in favor of lighter isotopes. These types of clouds are known to exist, so it is possible that this cloud may have left its mark on Mars. The third possibility is that carbon dioxide2 In the Martian atmosphere it interacted with ultraviolet radiation and caused a strange signal. “We don’t know the answer,” House says.

It can be organic or inorganic. All three scenarios are consistent with the available data.

fuzzy layers

Last year, the NASA rover arrived perseverance On Mars, that spacecraft was also looking for traces of ancient life.

He was seen on his journey through Jezero Crater perseverance Purple layers of high iron content over countless rocks. According to Bradley Garcinski of Purdue University, who has studied strata, such deposits have not been detected by rovers on Mars before, although rocks with other deposits have been spotted in several places on the Red Planet.

On Earth, these types of coatings are called “desert varnish” and are formed from deposits of microbes feeding on minerals from rocks.

“Varnixes like this are very exciting and would certainly be of biological interest on Earth. So if they are found on other worlds, they are of great astrobiology interest to us,” says Williams.

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