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NASA astrobiologists say that we must recognize that life on Enceladus or other alien bodies may have originated by a process very different from the process by which life emerged on Earth. Alternatively, alien life may have originated in the same way as terran life but did not evolve as fast or as far as the terran biosphere. For example, if we accept the “RNA world” as part of a model for natural history on Earth, visits to the terran biosphere on early Earth would not have found encoded proteins, and possibly not straight-chain fatty acids.

The same might be so on Europa or Enceladus today, even if life there began in the same way as life on Earth, if the evolution of molecular structures in those alien biospheres has not progressed as fast or as far as the terran biosphere, or has progressed in different directions.

To the astrobiologist, Enceladus offers easy access to a potential subsurface biosphere via the intermediacy of a plume of water emerging directly into space. A direct question follows: If we were to collect a sample of this plume, what in that sample, through its presence or its absence, would suggest the presence and/or absence of life in this exotic locale?

Astrobiologist Steven Benner proposes a universal biosignature that could be used to detect the presence of a biological system that undergoes Darwinian evolution, such as might be found on Enceladus or other ocean worlds. He proposes a particular characteristic, based on the structure of the genetic material found in terrestrial life, that should be present in any genetic biopolymer regardless of underlying chemistry.




Instrumental in establishing the field of paleogenetics, Benner has worked with NASA to develop detectors for alien genetic materials, using the definition of life developed by the NASA Exobiology Discipline Working Group in 1992, “a self-sustaining chemical system capable of Darwinian evolution”.

To the astrobiologist, Enceladus offers a “gimmie,” a plume of water emerging from a subsurface salty, organics-laced ocean, in contact with a rocky core, on an alien object that requires no landing to collect. This makes especially pressing the question: What should we seek in this plume by way of molecules that might indicate whether that ocean contains life of some kind?

Alternatively, we might ask what molecules would, through their absence, suggest the presence or absence of life in Enceladus' ocean? These questions can be generalized to cover life in any aqueous environment, of which the Solar System is known to hold many [e.g. Europa and asteroids as well as Earth and likely Mars]. Extrasolar alien systems may also soon be known to hold many such lagoons.

More generally, we must be concerned, Benner writes, about the possibility that even if terran-similar proteins, nucleic acids, and lipids are found in the biosphere that we encounter on Enceladus, Europa, or any other extraterrestrial water lagoon, they might be built from components different from those found in the analogous biopolymers today on Earth. Several alternative sets of components for proteins and nucleic acids were recently propsoed by Rezzonico, together with the potential use of nanopore-based devices to detect them (Sarathy et al., 2017).

The most forthright answers to any or all these questions, of course, are “We do not know.” However, experiments in the area of synthetic biology over the past three decades offer some suggestions for how we might proceed.

The Daily Galaxy via LiebertPub.com 


Will an alien organism with a different biopolymer makeup be able to survive on Earth? Will they be able to ingest our vegetation and survive? Will be be able to ingest their plants and absorb the foreign hitherto unknown proteins? Or, will organisms from different solar systems with different biopolymer biologies and different amino acid chirality be able to survive at all in another potentially habitable planet that's similar to their own, but with plants and animals that have different amino acid chirality, nucleic acids, etc?

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