“Ecological biosignatures” hold promise for revealing alien organisms that may dwell within icy...
The hottest spots in the search for alien life are a few frigid moons in the outer solar system, each known to harbor a liquid-water ocean beneath its icy exterior.
Each of these aquatic extraterrestrial locales might be the site of a "Second genesis," an emergence of life of the same sort that occurred on Earth billions of years ago.
Astrobiologists are now pursuing multiple interplanetary missions to learn whether any of these ocean-bearing moons actually possess more than mere water-namely, habitability, or the nuanced geochemical conditions required for life to arise and flourish.
As impressive as these missions are they are only preludes to future efforts that could more directly hunt for alien life itself.
Such ambiguities can lead to false positives, cases in which scientists think they see life where none exists.
At the same time, if organisms possess radically different biochemistry and physiology from that of terrestrial creatures, scientists could instead encounter false negatives, cases in which they do not recognize life despite having evidence for its presence.
These clues would be suitable for discovering life in its myriad possible forms-even if that life employed profoundly unearthly biochemistry.
If the regularity of chemical ratios within cells is a universal property of biological systems, here or anywhere else in the cosmos, then careful stoichiometry could be the key to eventually discovering life on an alien world.
The study's emphasis on such "Ecological biosignatures" is the latest in a slow-simmering, decades-long quest to link life not only to the fundamental limitations of physics and chemistry but also to the specific environments in which it appears.
Performing cytometry in an alien moon's subsurface ocean would be far more challenging than merely sending instrumentation there: Because of the paucity of available energy in those sunlight-starved abysses, scientists expect any life there to be single-celled, extremely small and relatively sparse.