The Ladder of Life Detection

Neveu, Marc; Hays, L. E.; Voytek, Mary A.; New, Michael H.; Schulte, Mitchell D.

doi:10.1089/ast.2017.1773

Cited by 206 publications

(173 citation statements)

References 191 publications

(326 reference statements)

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“…Perhaps more impactful would be the positive identification of uninhabited planets, which could inform the prior probability of abiogenesis (origin of life) and provide an abiotic fiducial for examining the role of biology in planetary processes on Earth-like planets (see Cockell 2011Cockell , 2014aCockell et al 2012Cockell et al , 2016. Antibiosignatures are also important to consider for solar system exploration (Neveu et al 2018), though this is beyond our scope here.…”

Section: Introductionmentioning

confidence: 99%

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Schwieterman

Reinhard

Olson

et al. 2019

ApJ

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Some atmospheric gases have been proposed as counter indicators to the presence of life on an exoplanet if remotely detectable at sufficient abundance (i.e., antibiosignatures), informing the search for biosignatures and potentially fingerprinting uninhabited habitats. However, the quantitative extent to which putative antibiosignatures could exist in the atmospheres of inhabited planets is not well understood. The most commonly referenced potential antibiosignature is CO, because it represents a source of free energy and reduced carbon that is readily exploited by life on Earth and is thus often assumed to accumulate only in the absence of life. Yet, biospheres actively produce CO through biomass burning, photooxidation processes, and release of gases that are photochemically converted into CO in the atmosphere. We demonstrate with a 1D ecosphere-atmosphere model that reducing biospheres can maintain CO levels of ∼100 ppmv even at low H 2 fluxes due to the impact of hybrid photosynthetic ecosystems. Additionally, we show that photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent. Since CH 4 buildup is also favored on these worlds, and because O 2 and O 3 are likely not detectable with the James Webb Space Telescope, the presence of high CO (>100 ppmv) may discriminate between oxygen-rich and reducing biospheres with near-future transmission observations. These results suggest that spectroscopic detection of CO can be compatible with the presence of life and that a comprehensive contextual assessment is required to validate the significance of potential antibiosignatures.

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Section: Introductionmentioning

confidence: 99%

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Schwieterman

Reinhard

Olson

et al. 2019

ApJ

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“…To avoid the uncertainty of Viking's findings, astrobiologist Marc Neveu of NASA headquarters in Washington, DC, and his colleagues used findings from the past 20 years of astrobiology research to develop the "Ladder of Life Detection," which they published in June. The ladder has 15 "rungs," each a measurable criterion that gets increasingly suggestive of evidence of life elsewhere-ranging from identifying habitability to detecting biomolecules to spotting metabolizing, evolving organisms-for researchers to use in their investigations (7).…”

Section: Of Mars and Microbesmentioning

confidence: 99%

Hunting for microbial life throughout the solar system

Mann¹

2018

Proc. Natl. Acad. Sci. U.S.A.

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“…This prediction is testable using the SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument on the Mars 2020 rover (Beegle et al 2015). Soots (complex abiotic organic matter) within ancient sediments are a potential life detection false positive (Sutter et al 2017, Neveu et al 2018, Eigenbrode et al 2018).…”

Section: Predictionsmentioning

confidence: 99%

Methane release on Early Mars by atmospheric collapse and atmospheric reinflation

Kite

Mischna

Yung

et al. 2020

Planetary and Space Science

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Please cite this article as: Kite, E.S., Mischna, M.A., Gao, P., Yung, Y.L., Turbet, M., Methane release on Early Mars by atmospheric collapse and atmospheric reinflation, Planetary and Space Science (2020), doi: https://doi. Abstract.A candidate explanation for Early Mars rivers is atmospheric warming due to surface release of H2 or CH4 gas. However, it remains unknown how much gas could be released in a single event. We model the CH4 release by one mechanism for rapid release of CH4 from clathrate. By modeling how CH4-clathrate release is affected by changes in Mars' obliquity and atmospheric composition, we find that a large fraction of total outgassing from CH4 clathrate occurs following Mars' first prolonged atmospheric collapse. This atmosphere-collapse-initiated CH4-release mechanism has three stages. (1) Rapid collapse of Early Mars' carbon dioxide atmosphere initiates a slower shift of water ice from high ground to the poles.(2) Upon subsequent CO2-atmosphere re-inflation and CO2-greenhouse warming, low-latitude clathrate decomposes and releases methane gas. (3) Methane can then perturb atmospheric chemistry and surface temperature, until photochemical processes destroy the methane.Within our model, we find that under some circumstances a Titan-like haze layer would be expected to form, consistent with transient deposition of abundant complex abiotic organic matter on the Early Mars surface. We also find that this CH4release mechanism can warm Early Mars, but special circumstances are required in order to uncork 10 17 kg of CH4, the minimum needed for strong warming. Specifically, strong warming only occurs when the fraction of the hydrate stability zone that is initially occupied by clathrate exceeds 10%, and when Mars' first prolonged atmospheric collapse occurs for atmospheric pressure > 1 bar.

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The Ladder of Life Detection

Cited by 206 publications

References 191 publications

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Hunting for microbial life throughout the solar system

Methane release on Early Mars by atmospheric collapse and atmospheric reinflation

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