Perseverance would not be able to detect biomolecules on the surface of Mars, according to a study
Perseverance, in search of life on Mars Perseverance, this is how NASA has decided to name the rover it will send to Mars in the summer of 2020. A rover from which researchers expect a lot. He will be the first to collect rock samples to be brought back to Earth. Objective: to find traces of microbial life.
This is one of the main missions of the Perseverance rover: to find traces of life in the rocks of the Martian soil or at least try. Because it is not fossils of organisms that Perseverance is looking for, but molecules, more or less complex, which would have been synthesized by biological processes. The Curiosity rover would have taken the first step by confirming the presence of organic molecules (methane and carbon compounds) on Mars. If Perseverance succeeded in finding more complex biomolecules, it could mean that the planet would have experienced the beginnings of even very rudimentary organic life. A rather exciting prospect!
This goal is also one of the next rover that should join Mars: Rosalind Franklin. This new rover from the ESA and Roscosmos ExoMars program will carry a suite of instruments on board with the aim of performing Raman spectroscopic measurements. Raman spectroscopy is a chemical analysis method that identifies the structure of molecules present in a sample. This type of instrument already equips the Perseverance rover. If this method is effective on Earth, and very widely used to detect biomolecules, things seem to be complicated on Mars.
Because there is a major difference between Mars and Earth: the atmosphere. If Mars does have one, it is however much thinner than that of Earth. However, the Earth’s atmosphere plays an essential role in the preservation of life: it stops a large part of ultraviolet radiation (UVR), which is harmful in high doses for living organisms.
Is this method of analysis best suited for Perseverance?
Could biomolecules remain stable under the fire of solar radiation impacting the Martian soil? Some studies prior to the mission have shown that while the rate of degradation is certainly very high in the first centimeters of the surface, the regolith nevertheless had the ability to protect certain biomolecules. Considering this hypothesis, however, there is another problem, linked to the method of analysis this time. Indeed, if the scientists showed that biomolecules could remain detectable despite the atmospheric conditions of Mars, these tests had not been carried out using Raman spectroscopy to carry out the analyses.
A team of researchers has therefore come to question the analytical capacity of this type of instrument under Martian conditions. A series of experiments (Biomex) was thus carried out on board the International Space Station. Seven different types of biomolecules were exposed to solar radiation outside the station for 469 days. They were mixed with analogues of Martian regolith in order to better simulate the environmental conditions prevailing on the Red Planet. The samples were then analyzed with Raman spectroscopy.
The regolith signal overlaps that of the biomolecules
The researchers then realized that, during the analyzes of the samples most exposed to UVR (simulating those of the Martian surface), the signal associated with the minerals of the regolith partially covered, or even completely masked the signal associated with the biomolecules. For example, the particularly strong signal of hematite, a mineral very present on Mars, falls in exactly the same range of values as that of chlorophyll, cellulose or other biomolecules, preventing their detection. Samples containing a lot of clay proved to be even more difficult to analyze. However, this mineral is considered to be the matrix most likely to have preserved organic molecules on Mars.
Drilling deep, Rosalind Franklin’s solution
All hopes therefore turn to the Rosalind Franklin rover, which will have the capacity to drill up to 2 meters deep to recover samples protected from UV rays.
A modification of the analysis technique by Raman spectroscopy also shows good results on Earth, but the equipment still needs to be miniaturized before it can be integrated into a potential Mars mission. In the meantime, a new data processing approach could nevertheless make it possible to extract certain information from the samples analyzed by Perseverance.
What if traces of life on Mars were just below the surface?
Mars is so hostile today that it seems unimaginable to find signs of ancient life on its surface. However, it would perhaps suffice to dig a few centimeters to detect, if they exist, traces still preserved.
While Perseverance continues to survey the area around the Jezero crater on Mars on its own, work continues a little closer to home to help it in its mission.
“The environment on Mars is very hostile, tells Numerama the main author Mickaël Baqué, of the German Aerospace Center in Berlin. Molecules are under a lot of stress from radiation, and we wanted to know how badly they were affected. The stakes are high, since Perseverance has two instruments, placed on its SuperCam camera and at the end of its SHERLOC arm, which are equipped with Raman spectrometers supposed to be able to detect them.
This technology has an advantage in this area: it does not damage the materials it has to analyze. Infrared spectroscopy (classic) makes molecules vibrate by heating them, in order to reveal the composition of an object, which sometimes amounts to destroying the most fragile molecules. Raman spectroscopy uses the frequency of light circulating in molecules to characterize them.
Doubts about the survival of molecules
The Raman instrument is one of the main novelties of Perseverance which distinguishes it from Curiosity, the other rover which did not have access to this technique. Even if it is not its only goal in this mission, all the instrumentation around the Raman was greeted with enthusiasm by the community of astrobiologists, as well as by the general public – inevitably eager to know if there was indeed of life on Mars.
But the doubt remains, and some studies had raised doubts about the ability of these possible molecules to survive on the surface of Mars. To find out, Mickaël Baqué and his team went looking for terrestrial organisms called extremophiles, capable of withstanding very difficult conditions. They survive in deserts, in Antarctica or at high altitudes, for example. Seven types of molecules (carotene, chlorophyllin or even cellulose) were thus selected to see if they could survive on Mars.
However, how to simulate the environment of the red planet with its fine atmosphere saturated with carbon dioxide, and especially its solar radiation much stronger than on the surface of the Earth? The answer is simple: you have to go into space. This is how the small team of molecules ended up on board the International Space Station, and more precisely in the Expose-R2 platform. This chest placed outside the station accommodates a number of organisms ranging from insects to fungi, including different types of bacteria.