Free Astronomy Magazine January-February 2021

7 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING P erseverance rover landing ellipse in Jezero Crater, on the flat floor of the crater, just east of a dramatic ancient river delta. [ESA/DLR/FU Berlin/Emily Lakdawalla] plication experiments were of con- sequence for also finding no trace of life – despite our knowledge of mi- crobial life existing in this region. The Azua-Bustos team only needed to dig up to 30 cm deep to discover a layer rich in smectite with a humidity of 78% (a phenomenon never ob- served before in that region), isola- tion from various external agents and, above all, inhabitation by at least 30 species of metabolically ac- tive microorganisms (bacteria and ar- chaea). It is very unlikely that any- thing like this could exist on Mars, as its surface became barren billions of years earlier than the Atacama De- sert. But it cannot be ruled out that the subsoil has retained evidence of the metabolism of microorganisms that proliferated during the Noachian era (between 4.1 and about 3.7 bil- lion years ago). If so, the biomarkers identified by Azua-Bustos and col- leagues in Yungay’s smectite can pro- vide detailed guidance on what to look for with Martian rovers. Overall, the discovery made in the At- acama Desert authorizes some opti- mism, but the very restricted location of the habitats of those same micro- organisms suggests that the search for similar scenarios on Mars could be extremely long and difficult. According to another team of re- searchers, coordinated by Carolina Gil-Lozano (Centro de Astrobiología, CSIC-INTA, Madrid), discovering bio- markers in the Martian smectite lay- ers could be impossible. This second team, which has members in com- mon with the first team (quite bi- zarre, given the opposite conclusions of the research), conducted simula- tions with clay and amino acids to verify the possible degradation of bi- ological material on Mars. If it is true that the sub-surface clay soils of that planet may have included and pro- tected colonies of microorganisms, it is also true that any contact of those clays with acidic fluids may have thwarted any ability of those clays to retain traces of vital presences. Previous studies had shown that the Martian surface of the distant past was affected by acidic fluids, proba- bly waters rich in corrosive substances and with high salinity, residue of the evaporation of primordial seas. The new laboratory experiments con- ducted by the Gil-Lozano team use glycine (the simplest and most pene- trating of the 20 ordinary amino acids) as a “lab rat” embedded in the clay to study what happens upon ex- posure. The team has shown that if this clay matrix is exposed to acidic fluids, the interlayer space is erased, transforming into a gel-like silica. The optimism authorized by the first research is therefore reduced, as you can guess from a statement of Al- berto Fairén (Centro de Astrobi- ología, CSIC-INTA, Madrid), second signatory of both researches: “ When clays are exposed to acidic fluids, lay- ers collapse and organic matter can- not be preserved. Our results explain why the search for organic com- pounds on Mars is so difficult.” !