Think of a very unpleasant smell. And now imagine even worse: something that can be found in a pile of penguin dung, or deep in a swamp; a scent that could be found inside the stomach of a badger or a fish. You will be thinking, without knowing it, about phosphane or phosphine.
It is a colorless, flammable gas that burns at only 38º C and whose smell reminds of garlic (but much worse). It is produced by some anaerobic bacteria (living in the absence of oxygen) when they degrade organic matter, but perhaps its most important characteristic is that it is extremely toxic, especially for aerobic living beings (which breathe oxygen).
Paradoxically, phosphine could be a clear trace of the presence of life. It is the main conclusion of an article recently published in the journal "Astrobiology" and which has been prepared by researchers from the prestigious Massachusetts Institute of Technology (USA). As they have concluded, the presence of phosphine in the atmosphere of a rocky world can only be explained by the activity of microorganisms little friendly to oxygen (anaerobes), so this molecule is a biomarker, a chemical trace of the presence of lifetime.
A visible footprint at 16 light years
Phosphine or phosphane is a very simple molecule: as indicated by the chemical formula PH3, it is composed of a phosphorus atom attached to three hydrogen atoms, which form a kind of stool. As the authors of this research have suggested, if this molecule were released into the atmosphere in the same amounts in which methane is released on Earth, this gas would generate a footprint that could be visible on a distant planet. Specifically, they have concluded that we could detect another planet's phosphine up to a distance of 16 light years, provided that we use the James Webb space telescope, which will be launched in 2021.
"Here on Earth, oxygen is an excellent biomarker," he said in a statement
Clara Sousa-Silva, MIT scientist and director of research. «But other things, apart from life, create oxygen. Therefore, it is important to take into account other stranger molecules that may not be so abundant, but which, if you find them, only have one explanation. If possible, extraterrestrial life.
Search for life near Earth
Currently, NASA's TESS telescope is looking for exoplanets and the Cheops telescope, recently launched by ESA, will help measure its mass. But after the launch of the James Webb telescope, and the coming into operation of the next giant terrestrial telescopes (such as the "Extremely Large Telescope") or future space observatories, scientists will feverishly analyze the atmospheres of the exoplanets. They will characterize hundreds of them, learn about their nature and diversity and identify in which there could be life as we know it.
For this reason, Sousa-Silva and the company have been trying for years to find out what the traces will be. At the moment, they have identified more than 16,000 candidates. However, in most cases, finding these molecules would not be an unequivocal sign of life, because those molecules could also be produced by geological or physicochemical causes.
Fortunately, it is not the case with phosphine. According to the study led by Sousa-Silva, the presence of phosphine on a rocky planet would be a solid mark of the existence of extraterrestrial life.
The pestilent phosphine, a trace of life
In the seventies, Voyager probes discovered phosphine or phosphane in the atmospheres of Jupiter and Saturn, from gigantic storms. At that time, Sousa-Silva set to work on the spectral footprint of this molecule, something like the "shadow" that would leave when a star's light filtered into an atmosphere. Later, it was decided to study in depth its chemical properties and to look for all the bibliographical references about it.
Thus, he discovered that phosphine is associated with anaerobic life: "It turns out that wherever there is no oxygen, such as marshes, marshes, sediments, intestines or windiness, there is phosphine," he explained.
To ensure that this molecule is a biomarker, they first ruled out that it could not be produced by mechanisms other than life. For this, the researchers carried out an exhaustive theoretical analysis of chemical routes to synthesize phosphine from phosphorus. They simulated their creation on planets like Jupiter or Saturn, where huge amounts of energy are needed to generate it, or on rocky planets.
Phosphine produced by lightning and meteorites
"In the end, we ended up investigating less and less plausible scenarios," Clara Sousa-Silva recalled. «For example, we wonder if two tectonic plates, sliding one over the other, could generate a plasma flash capable of producing phosphine. Or if it could be generated by lightning that fell somewhere with phosphorus or a meteorite laden with phosphorus when it hit Earth.
The results indicated, finally, that the finding of phosphine in a rocky world could only be explained by the presence of life.
Finally, they studied whether this information is useful and if this molecule could be detected through a telescope. To answer this question, they made simulations with oxygen-poor atmospheres (where phosphine-producing microorganisms would live), but rich in hydrogen or rich in carbon, and extrapolated what their light spectrum would be like. This is how they found out that yes, phosphine levels similar to methane levels produced on Earth could be detected, at a distance of 16 light years.
In the opinion of the research director, the study is not only relevant because it has identified a reliable biomarker. In addition, he believes that all the way traveled here is useful to learn to analyze other candidates for life markers. Everything indicates that it will be necessary to do it: in a matter of decades, extraterrestrial life could be found. . (tagsToTranslate) molecule (t) pestilent (t) aliens