Jesús Martínez Frías
Planetary geologist and astrobiologist at the IGEO (CSIC-UCM). Academician of the Royal Academies of Sciences and Doctors of Spain. President of the Planetary Geology Commission of the Geological Society of Spain and of the Spanish Network of Planetology and Astrobiology.
This is research that approaches Martian habitability from a theoretical point of view, making high-quality theoretical models that are really interesting and novel, although, in my opinion, astrobiologically speculative. Considering an "ecological model" of Mars when there is still no evidence of life or its potential biomarkers is an interesting exercise, with valid conclusions in terms of what is suggested and the methodology used, but which would require more solidity and scientific rigour, beyond the purely theoretical.
So far there is no evidence of life or biomarkers of its past or present existence on Mars. Although this hypothesis, and others, cannot be ruled out, there is no evidence of the existence of methanogens either now or in the past. In fact, there is a very interesting open debate on the very existence (or not) of methane today. I think this point should have been addressed in more detail, as the evidence for methane is still the subject of scientific debate.
In my opinion, the authors have made an excellent theoretical approach, but limited only to what it is: a theoretical model.
Experimental data, both of the present-day geology, atmosphere, past geological record, mineralogy and geochemistry of Mars, including interpretations of palaeoenvironments and habitability based on all of the above parameters, are being provided by the ongoing Mars missions. I believe that it will be these detailed analyses that will confirm or disconfirm the validity and relevance of the proposed model in the future.