Why do signs of life on Mars seem so confusing? National Geographic

In 2012, a new era in Mars research began when NASA launched its six-wheeled vehicle Curiosity of In the crater of the volcano Gale. Today, this crater, 155 kilometers in diameter, contains a large mountain made up of many stratified sediments that record Mars’ geology past. The main purpose of Curiosity of It is the search for signs of the planet’s survival, such as water, organic molecules, and energy sources – ingredients that are essential to life as we know it.

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

But other tasks were less clear.

over the years, Curiosity of Traces in Jezero Crater indicate the presence of many organic molecules, the basic chemical building blocks of all carbon-based life. The rover also found the remains of ancient hydrothermal vents, sites where liquid water at high temperatures mixed with a variety of chemical compounds, potentially a source of energy.

In addition to, Curiosity of He found that the methane content in the air above the crater fluctuates with the seasons and sometimes shows strong outliers. These measurements are consistent with previous observations from Earth, which have not been properly explained for over ten years. On Earth, these fluctuations in methane levels may 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 are just He appears About the signs of life.

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

Weird carbon compounds

Curiosity ofThe most unusual and most interesting observation dates back to a very recent history. In multiple rock samples taken from different locations in the crater, the rover found organic compounds with odd ratios between different carbon isotopes, and atoms of the same element but with different numbers of neutrons in its core.

On Earth, living things prefer to use lighter isotopes of carbon in the process of metabolism or photosynthesis, so that the proportion of isotopes in organic matter changes slightly.

Here’s what scientists found at five different locations on Gale Crater: rocks in which the lighter isotopes were higher than the heavier ones, compared to the ratios they had previously found in the Martian atmosphere and in Martian meteorites. The observations are reminiscent of carbon traces measured in the Australian Tumbiana Formation, a 2.7 billion-year-old outcrop that contains carbon traces of ancient microbes that metabolized methane.

The reduction in the presence of heavy carbon isotopes is really cool. Exciting. On Earth, this only happens through biology, says Williams.

But astrobiologist House, who led the analysis, says the results aren’t entirely clear. He and his colleagues described three possible scenarios that could explain the changing ratio.

The first is that ancient microbes did indeed cause the isotope signature. The second possibility is that the Solar System passed so long ago through an interstellar dust cloud that the ratio of carbon isotopes has shifted in favor of lighter isotopes. Such clouds are known to exist, so it is possible that this cloud left its mark on Mars. The third possibility is that carbon dioxide2 In the Martian atmosphere, ultraviolet radiation interacted to produce a strange signal. “We don’t know the answer,” House says.

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

mysterious layers

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

On his journey through Jezero crater perseverance There are countless purple layers on the rocks that contain a high percentage of iron. According to Bradley Garcinsky of Purdue University, who studies the layers, these types of sediments have not been detected by spacecraft on Mars, although rocks with other deposits have been spotted in several places on the Red Planet.

On Earth, these types of layers are called “desert varnishes” and consist of deposits of microbes that feed on minerals from the rocks.

These types of varnishes are very interesting and would certainly be of biological interest on Earth. So if they are found on other worlds, they are of great astrobiological significance to us,” says Williams.

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