Last October, the announcement of the collaboration between SETI (specialised in the search for signs of extraterrestrial life) and the TESS satellite (specialised in the search for exoplanets) gave credibility to a new discipline, that of the search for life elsewhere than in our solar system. Scientists also believe that where there is water, there is life. And for good reason.
On Earth, so-called extremophilic organisms live in water, i.e. they can survive extreme conditions. They can persist in hot springs, acid fields, and salt lakes such as ice caps. They have therefore developed mechanisms to resist certain physical and chemical conditions. That is why the discovery of a large quantity of frozen water on Mars, for example, gives hope for finding traces of organisms on the Red Planet.
Indeed, if an organism can survive in such ruthless places, scientists believe they can extend their research to the less welcoming corners of other planets. But new evidence is somewhat challenging these expectations. According to researchers at the French National Centre for Scientific Research (CNRS), life is actually totally absent from some water points, under conditions that are far too extreme.
One of the most hostile places on the planet
To reach their conclusions, the scientists studied the geothermal sources of the Dallol volcano in the Danakil depression (Ethiopia). Its landscape is punctuated by lakes and craters, where the water is very warm, very salty and very acidic. The colours are flamboyant, with a palette of green, orange and brown. But don't get it wrong; the conditions of these places are considered to be the most extreme and inhospitable on the planet. Water points are the source of a toxic gas atmosphere, due to a volcano hidden under the surface. Yet scientists consider the region to be the warmest inhabited area in the world. And as a result, since 2016, they have been trying to find its inhabitants.
'It's an incredible but hostile place... Chlorine vapour has burned the airways,' said expedition leader Felipe Gómez of the Spanish Centre for Astrobiology, at the launch of the research. 'All the microorganisms living here will be extremophilic microbes of major interest to astrobiologists.' The first results, published only a few months ago, revealed the presence of microorganisms measuring only a few nanometers. According to the researchers, they were the first evidence of life in these hostile waters.
Two barriers preventing life
But a new study, carried out by another team and published in the Nature Ecology & Evolution journal at the end of October, challenges the relevance of this discovery. They analysed samples collected from four points on the site between 2016 and 2018. And their results suggest that the traces found are actually... 'Biological organism imposters:' silica-rich rice grains called 'biomorphs' that can be confused with cells. They also identified bacteria of human origin, probably introduced during 'intensive daily tourist visits to the site,' they wrote.
Moreover, they suggest that there is no natural microbial life in the Dallol lakes. 'We identify two major physicochemical barriers that prevent life from thriving in the presence of liquid water on Earth and potentially elsewhere,' they explained. However, they specify that the absence of proof is not proof of absence. But further research will be needed to demonstrate the presence of life in these inhospitable waters. For the time being, researchers remain convinced that colonisation is impossible.