Scientists May Have Discovered the Origin of Organic Matter on Mars!

On Earth, organic matter is everywhere. It is found in current soils, as well as in layers formed by ancient sedimentary rocks, often giving them a black color. This organic matter mainly comes from the decomposition of living organisms that have inhabited Earth for over three billion years. Organic matter presents itself in the form of various carbon compounds composed mainly of carbon and hydrogen molecules.

Organic Matter Found in Sediments of Gale Crater on Mars

Given the significance of terrestrial biomass, it is not surprising to find organic matter in all environments on Earth. However, finding organic matter on Mars is much more surprising, especially since no signs of life have been found there yet. Nevertheless, in this arid and dusty landscape, the Curiosity rover has indeed detected traces of organic matter. Not just anywhere, but in ancient sediments deposited at the bottom of Gale Crater when it was once filled with a lake about 3.8 billion years ago. This is precisely where researchers hope to one day discover evidence that life might have temporarily existed on the Red Planet! A discovery that reignites hope. What if these organic molecules originated from biological activity, just like on Earth?

A Different Isotopic Composition from Earth’s Organic Matter

A new study finally answers this question, unfortunately in the negative. The organic matter found on Mars is significantly different from that on Earth. Organic matter is characterized by a ratio between two carbon isotopes, 13C and 12C. While on Earth, the abundance of 13C (which is used in biological activity) is 1.04% in sediments and 1.07% in atmospheric CO2, on Mars, it is much lower, between 0.92% and 0.99%. This difference suggests that the organic matter on Mars may have a different origin. But what could it be?

An Atmospheric Origin

In an article published in the journal Nature Geoscience, a team of researchers shows that in the Martian atmosphere, 12CO2 preferentially absorbs UV radiation from the Sun!The sun causes molecules to dissociate into ^12CO. This phenomenon, which also occurs on Earth, would have resulted in leaving behind an atmosphere enriched in ^13CO2. In the reducing atmosphere of Mars, this ^12CO would have reacted to form simple organic compounds such as formaldehyde and carboxylic acids. These organic compounds would have dissolved in lake water and then become part of the sediment composition. Therefore, Martian organic matter would have an atmospheric origin rather than a biological one.

Curiosity has detected organic matter several times on the surface of Mars. But how did it get there? According to researchers, these ingredients that could be the origin of life likely come in large quantities from space.

Organic molecules have been detected by the Curiosity rover several times on Mars during its travels in the Gale crater and on the foothills of Mount Sharp. As for their origin – a major question that researchers are pondering – the main hypothesis remains that of interplanetary dust sprinkling the planet. These dust particles are solid particles, a mixture of asteroids crumbled by collisions, debris from comets scattered during their traverses of the inner Solar System, and even ashes of ancient stars trapped in the cocoon of the Sun. In essence, it is primitive matter that has a lot to tell astronomers about planetary formation and may have had an implication in the emergence of life on Earth (and perhaps even on Mars).

Life on Mars: Atacama Desert Gives Hope

Not entirely convinced that the organic matter on Mars comes solely from interplanetary dust, an international team has launched an investigation to identify other possible culprits. According to their research, asteroids and comets may also play a role.

Nearly 200 tons of organic matter are dumped on Mars each year

Based on their research, the equivalent of eight trucks of organic matter is dumped on Mars every year, about 192 tons. Interplanetary dust dominates, accounting for approximately 67%, or 129 tons. The remaining 26% (around 50 tons) of the carbonaceous material is believed to originate directly from asteroids, and 7% (13 tons) from comets.

The researchers did not obtain these results by collecting pinches of dust from the Red Planet. Instead, they inferred these quantities through simulations of celestial bodies’ impact rates on Mars. “For the first time, we have calculated the carbon flux from asteroid and comet impacts,” they write in their study to be published in the journal Icarus. They took into account celestial bodies circulating in the Solar System, some of which are richer in organic matter than others. Regarding Mars, a planet located near the main asteroid belt, a large number of asteroids that have crashed on its surface for hundreds of millions of years are believed to be of the dominant C-type family, meaning carbonaceous, representing 75% of asteroids.

For the researchers, it would be worth exploring the areas around impact craters, up to 150 kilometers around. This is where the ejecta of celestial bodies have scattered, and where the Martian rovers should find the largest quantities of organic matter.

Comet Churyumov-Gerasimenko: Surprising Organic Matter in the Solar System

Of course, the contribution of these prebiotic ingredients raises questions about the emergence of life on Mars, especially when liquid water oceans covered its surface over 3.7 billion years ago, and the climate was warmer than it is today. This phenomenon is not just limited to the Red Planet, but also extends to other worlds beyond our Solar System, near other stars, where asteroids and comets, much like those in our own solar system, can saturate the surfaces.Exoplanets with carbon have been revealed by Kateryna Frantseva, who led this study. “And if, in addition to that, there is water, then you have the necessary ingredients for life. This increases the chances of someday discovering life elsewhere.”

Organic molecules have indeed been detected by Curiosity, as reported by Francis Rocard and François Poulet, but they are not the ones expected, and their quantities are insufficient to determine if life could have emerged on Mars long ago. The situation could evolve… In fact, in a few weeks, Curiosity should reach the clay layers of Gale Crater, which could have trapped these organic molecules. Explanations from these two specialists.

More than five years after its arrival on Mars, Curiosity reaches the clay layers of Gale Crater, its number one objective. It only has to cross Vera Rubin Ridge’s hematite ridge to reach this clay deposit, which indicates a period when liquid water remained stable for a fairly long time. At this ancient period in Martian history, the planet’s climate was temperate, as suggested by numerous studies. Life could have “found favorable conditions to appear,” explains Francis Rocard, a Mars specialist and head of planetary exploration programs at CNES.

Structured in stacked layers, these clays have the ability to trap “everything that exists at the time of their formation,” including organic molecules, if they existed at that time. In other words, these clays “could inform us about the remnants of an organic, even prebiotic, activity that is now extinct.” They may also host fossilized remnants of biological structures. “Their discovery would be a decisive step in the issue of the emergence of life on Mars in a very distant past.”

Curiosity has shown that the Gale Crater site was habitable in a distant past, measured in billions of years. Scientists would like to know more precisely at what time and especially for how long these favorable conditions persisted. However, only samples of these clays brought back to Earth can be dated in the laboratory. This is indeed the next step that will start in 2020 with the Mars2020 rover.NASA. On the other hand, Curiosity will help alleviate the disappointment of the “very glaring deficit of organic molecules” detected so far by the rover. While a few molecules have been discovered, such as methane, ethylene, and benzene, they are in tiny amounts measured in picomoles. Carbon dioxide, although abundant, is not very interesting for organic chemistry as it is extremely stable and not conducive to complex reactions that could lead to prebiotic chemistry.

If life could have emerged where these clays formed, there are “strong chances that organic molecules have been trapped there.” “Curiosity is fully capable of identifying and characterizing them,” says François Poulet, an astronomer at the Institute of Space Astrophysics and a member of the team that discovered phyllosilicate clays in the oldest terrains of the Noachian period (Mars Express, 2005).

The rover carries Chemin, a spectrometer with X-ray diffraction that accurately determines the mineralogical composition of a sample usually collected by drilling, and the suite of instruments SAM, which can determine the chemical, molecular, and isotopic composition of these samples. So far, it has not been possible to determine if these organic molecules are of biotic or abiotic origin, although certain isotopic ratios and chirality measurements that SAM could perform are recognized criteria. However, specific molecules in greater quantities are necessary for this determination.

Did You Know?

The Institute of Space Astrophysics has the most comprehensive database on clay deposits on the surface of Mars. It lists several thousand, including the one in Gale Crater. These can be classified into two very distinct categories: those formed deep underground in a very hot hydrothermal environment, and those formed in an open environment, on the surface, potentially in contact with the atmosphere.

Most of the identified deposits were formed underground and are located in the oldest terrains of the Noachian and Phyllosian periods, better preserved from erosion. Therefore, they do not necessarily indicate the Martian climate of that time. In contrast, clays formed on the surface are representative of the environment at the time but are more difficult to detect due to the erosion they have undergone over several billion years.

The Martian exploration conducted by the team at this Institute is partially funded by CNES.

From Martian orbit, the clays in Gale Crater appear rich in iron but have a less varied composition compared to other sites on Mars. “The spectral diversity constrained from orbital observations is low.” Furthermore, the geological context of these clay deposits remains uncertain, so it is still not known how they were formed. It is possible that these clay minerals “are older than Gale Crater, a more recent formation (between 3.5 and 3.8 billion years).” Some types of clays may have formed on the Martian surface rather than underground. In this case, this clay deposit may have come from the erosion of a nearby site and re-sedimented during more recent but brief fluvial episodes that did not generate significant amounts of new clays.

Other Opportunities to Find Organic Molecules on Mars

However, the size of this deposit is smaller than those at other sites. Some sites, in fact, show stacks of several tens or even hundreds of meters. Therefore, scientists believe that “these clays may not ultimately be representative of older clays.” This suspicion is reinforced by “the presence of sulfates nearby.”

Finally, if Curiosity does not discover organic molecules, scientists “will obviously be very disappointed,” emphasizes Francis Rocard, as these clays a priori present the “most favorable context for assessing the astrobiological potential of Mars,” adds François Poulet. That said, it is still “too early to assess this strategy,” the two researchers want to point out. They have high expectations for the ExoMars rover (2020) and its drill capable of “digging up to two meters to collect The material that has not been irradiated by cosmic radiation, which for billions of years has the effect of destroying organic molecules in the near subsurface,” explains Francis Rocard. Another highly anticipated instrument, SuperCam, which will be installed on NASA’s Mars2020 rover, differs from its predecessor currently in use on Curiosity. This instrument is specifically designed for the search for organic molecules using UV to infrared LIBS, passive infrared, and a Raman spectrometer.

As expected from reading between the lines of NASA’s statements on the analysis of Martian soil by Curiosity’s instruments, organic molecules have indeed been detected. However, it is very likely that they are not of Martian origin. The exact source of these molecules remains unknown. While NASA announced that no groundbreaking revelations about the existence or emergence of life on Mars would be made at an American Geophysical Union conference, many enthusiasts followed the conference broadcast live on Monday, December 3, 2012.

It was understood that no evidence of the presence of living organisms could be provided by Curiosity, since the rover does not have instruments for that, unlike its predecessors, the Viking probes. However, the robot is indeed capable of discovering and identifying organic molecules in the soil, rocks, or atmosphere of Mars. So far, no one has demonstrated the existence of organic molecules in the soil of Mars, although methane traces have been discovered in its atmosphere from space.

It was therefore thought that the detection of these molecules by the Sample Analysis at Mars instrument (SAM) had sparked enthusiasm from one of the mission’s leaders, John Grotzinger. He informally told a journalist that SAM had provided measurements “worthy of making it into the history books.”

Certainly, denials quickly arrived, including a clarification from NASA at the end of last week. But the American agency’s press release was peculiarly phrased. It did not mention the absence of evidence of organic matter on Mars, but rather the absence of incontrovertible evidence. During the public conference broadcast live on the web from San Francisco, researchers announced that organic molecules had indeed been detected by SAM, specifically chlorinated derivatives.

Are the molecules detected by Sam Martian?

The sample analyzed by Sam comes from a collection in a sandy and dusty soil at the bottom of Gale crater. This sample was placed in a small oven where it was heated to release gases. The operation went smoothly, and the analysis of these gases provided excellent results. Water vapor, carbon dioxide, sulfur dioxide, and perchlorate were detected, along with chlorinated derivatives of alkanes, which could be the result of chemical reactions between non-biological gases released during sample heating.

Undetermined origin for carbon atoms

While it was shown that chlorine atoms were of Martian origin, the same cannot be said for carbon atoms, which may have been brought from Earth despite measures taken to prevent such contaminations. There is no evidence that there were organic molecules in the Martian soil sample before heating or that these molecules do not come from Earth. However, it is certain that there are no large quantities of organic compounds in the soil sample. Even if such molecules were found, it is not clear if they are of biological origin or if they come from abiotic processes specific to Mars.

Samples with Curiosity, drilling with ExoMars

Complex organic molecules are known to exist abundantly in certain meteorites like those from Murchison and likely in comets as well. It was expected that Mars’ soil would be enriched with organic molecules of this kind from space. However, this does not seem to be the case at least where the rover is located. Mars is not shielded from

UltravioletsUltraviolets on Mars may be degraded by a thick atmosphere or cosmic rayscosmic rays by a magnetospheremagnetosphere like on Earth, which could lead to the rapid destruction of organic molecules on the surface of Mars.

These negative results should not be discouraging. The Curiosity mission, scheduled to last 2 years, is just getting started. Given the excellent performance of the instruments highlighted by NASA researchers, there is a good chance that exciting discoveries await us, even if they do not directly involve exobiology. The discovery of traces of life may only come through drilling conducted by the rover of the European ExoMars mission in a few years.

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