Biosignatures Search in Habitable Planets

Abstract

The search for life has had a new enthusiastic restart in the last two decades thanks to the large number of new worlds discovered. The about 4100 exoplanets found so far, show a large diversity of planets, from hot giants to rocky planets orbiting small and cold stars. Most of them are very different from those of the Solar System and one of the striking case is that of the super-Earths, rocky planets with masses ranging between 1 and 10 M ⊕ with dimensions up to twice those of Earth. In the right environment, these planets could be the cradle of alien life that could modify the chemical composition of their atmospheres. So, the search for life signatures requires as the first step the knowledge of planet atmospheres, the main objective of future exoplanetary space explorations. Indeed, the quest for the determination of the chemical composition of those planetary atmospheres rises also more general interest than that given by the mere directory of the atmospheric compounds. It opens out to the more general speculation on what such detection might tell us about the presence of life on those planets. As, for now, we have only one example of life in the universe, we are bound to study terrestrial organisms to assess possibilities of life on other planets and guide our search for possible extinct or extant life on other planetary bodies. In this review, we try to answer the three questions that also in this special search, mark the beginning of every research: what? where? how?

Life as the Only Reason for the Existence of N2–O2-Dominated Atmospheres

“…Furthermore, especially in a humid atmosphere, water vapor, CO2, and even CH4 overexpose N2O bands [139].…”

“…NO can also be considered as secondary biosignature [143], more precisely as secondary metabolic biosignature [139]. For instance, it can be detected by the MIRI spectrograph (James Webb Space Telescope) at 5.3 μm [121].…”

Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab

“…These results renew, with higher and more interdisciplinary efforts, the search for life as an astrophysical problem. In this framework, it is critical to determine the types of biosignatures (based on the so-far-recognized life signatures) for when designing the next generation of ground- and space-based instruments that will observe these planets at both high spectral and spatial resolutions (e.g., Reference [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]). Among all the biosignatures, oxygen seems to be the most prominent signature that can reveal the existence of life on other planets [ 14 ].…”

Biogenic Metal Nanoparticles: A New Approach to Detect Life on Mars?

“…Any detectable sign, matter, gas, or pattern that strongly suggests a biological origin and can thus be used as evidence indicating the existence, past or present, of living organisms is a biosignature [48,51]. By definition, they are objective, quantifiable characteristics of biological processes.…”

“…By definition, they are objective, quantifiable characteristics of biological processes. They can be atmospheric biosignatures if referring to the presence of one or several gas species, surface biosignatures if detectable by their light reflection characteristics which allows them to be detected by remote sensing, or bioindicators if they suggest a biological origin but can also be produced abiotically [51]. Biosignatures can be divided into three different categories (Table 4): substances, objects, and patterns [48].…”