Biosignature False Positives

Harman, Chester E.; Domagal-Goldman, Shawn

doi:10.1007/978-3-319-30648-3_71-1

Cited by 3 publications

(3 citation statements)

References 121 publications

(138 reference statements)

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“…While this may be self-evident at present, this fact can be used as an argument for sample collection based on unique empirical observations on the mm-or meter-scale in martian (e.g., stromatolite-type features, evaporite mineral pigments) or europan/enceladen ice features (e.g., ambiguous cell motility, unique/patterned ice layering). Distinguishing between false positives in terrestrial samples (Cady et al, 2003;Cady and Noffke, 2009;Emerson et al, 2017;Reinhard et al, 2017;Harman and Domagal-Goldman, 2018;Neveu et al, 2018; continues to be necessary for planetary analogues.…”

Section: Caveats and False Positivesmentioning

confidence: 99%

A Proposed Geobiology-Driven Nomenclature for AstrobiologicalIn SituObservations and Sample Analyses

et al. 2021

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As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterrestrial/non-Earth biology, biogenic structures, and chemical processes generated from biological processes. The fact that Earth is our single data point for all life, diversity, and evolution means that there is an inherent bias toward life as we know it through our own planet's history. The search for life ''as we don't know it'' then brings this bias forward to decision-making regarding mission instruments and payloads. Understandably, this leads to several top-level scientific, theoretical, and philosophical questions regarding the definition of life and what it means for future life detection missions. How can we decide on how and where to detect known and unknown signs of life with a single biased data point? What features could act as universal biosignatures that support Darwinian evolution in the geological context of nonterrestrial time lines? The purpose of this article is to generate an improved nomenclature for terrestrial features that have mineral/microbial interactions within structures and to confirm which features can only exist from life (biotic), features that are modified by biological processes (biogenic), features that life does not affect (abiotic), and properties that can exist or not regardless of the presence of biology (abiogenic). These four categories are critical in understanding and deciphering future returned samples from Mars, signs of potential extinct/ancient and extant life on Mars, and in situ analyses from ocean worlds to distinguish and separate what physical structures and chemical patterns are due to life and which are not. Moreover, we discuss hypothetical detection and preservation environments for extant and extinct life, respectively. These proposed environments will take into account independent active and ancient in situ detection prospects by using previous planetary exploration studies and discuss the geobiological implications within an astrobiological context.

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Section: Caveats and False Positivesmentioning

confidence: 99%

A Proposed Geobiology-Driven Nomenclature for AstrobiologicalIn SituObservations and Sample Analyses

et al. 2021

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“…[28,29] Similarly, isotopic fractionation and morphological patterns resulted in the false positive detection claims associated with the Allan Hills meteorite. [30] Conversely, features such as structurally complex molecules [31] ; heredity, replication, and diversification [32] ; and technosignatures cannot exist in abiotic systems. [33] Features F I G U R E 1 Different underlying planetary processes can lead to the same atmospheric observables, which means that a specific observation of an atmosphere cannot unambiguously identify the surface processes, including biological ones.…”

Section: Earth 20 Is Not Life Detectionmentioning

confidence: 99%

“…[ 28,29 ] Similarly, isotopic fractionation and morphological patterns resulted in the false positive detection claims associated with the Allan Hills meteorite. [ 30 ] Conversely, features such as structurally complex molecules [ 31 ] ; heredity, replication, and diversification [ 32 ] ; and technosignatures cannot exist in abiotic systems. [ 33 ] Features which cannot exist in abiotic systems constitute a different class of biosignatures that are not subjected to false positives because they are only associated with life in all known situations.…”

Section: Introduction: What Are We Looking For When We Look For Life?mentioning

confidence: 99%

Life detection in a universe of false positives

Smith,

Mathis

2023

BioEssays

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Astrobiology aims to determine the distribution and diversity of life in the universe. But as the word “biosignature” suggests, what will be detected is not life itself, but an observation implicating living systems. Our limited access to other worlds suggests this observation is more likely to reflect out‐of‐equilibrium gasses than a writhing octopus. Yet, anything short of a writhing octopus will raise skepticism about what has been detected. Resolving that skepticism requires a theory to delineate processes due to life and those due to abiotic mechanisms. This poses an existential question for life detection: How do astrobiologists plan to detect life on exoplanets via features shared between non‐living and living systems? We argue that you cannot without an underlying theory of life. We illustrate this by analyzing the hypothetical detection of an “Earth 2.0” exoplanet. Without a theory of life, we argue the community should focus on identifying unambiguous features of life via four areas: examining life on Earth, building life in the lab, probing the solar system, and searching for technosignatures. Ultimately, we ask, what exactly do astrobiologists hope to learn by searching for life?

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Disruption of a Planetary Nitrogen Cycle as Evidence of Extraterrestrial Agriculture

Haqq-Misra¹,

Fauchez²,

Schwieterman³

et al. 2022

ApJL

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Agriculture is one of the oldest forms of technology on Earth. The cultivation of plants requires a terrestrial planet with active hydrological and carbon cycles and depends on the availability of nitrogen in soil. The technological innovation of agriculture is the active management of this nitrogen cycle by applying fertilizer to soil, at first through the production of manure excesses but later by the Haber–Bosch industrial process. The use of such fertilizers has increased the atmospheric abundance of nitrogen-containing species such as NH3 and N2O as agricultural productivity intensifies in many parts of the world. Both NH3 and N2O are effective greenhouse gases, and the combined presence of these gases in the atmosphere of a habitable planet could serve as a remotely detectable spectral signature of technology. Here we use a synthetic spectral generator to assess the detectability of NH3 and N2O that would arise from present-day and future global-scale agriculture. We show that present-day Earth abundances of NH3 and N2O would be difficult to detect, but hypothetical scenarios involving a planet with 30–100 billion people could show a change in transmittance of about 50%–70% compared to preagricultural Earth. These calculations suggest the possibility of considering the simultaneous detection of NH3 and N2O in an atmosphere that also contains H2O, O2, and CO2 as a technosignature for extraterrestrial agriculture. The technology of agriculture is one that could be sustainable across geologic timescales, so the spectral signature of such an “ExoFarm” is worth considering in the search for technosignatures.

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Biosignature False Positives

Cited by 3 publications

References 121 publications

A Proposed Geobiology-Driven Nomenclature for AstrobiologicalIn SituObservations and Sample Analyses

A Proposed Geobiology-Driven Nomenclature for AstrobiologicalIn SituObservations and Sample Analyses

Life detection in a universe of false positives

Disruption of a Planetary Nitrogen Cycle as Evidence of Extraterrestrial Agriculture

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