exoplanet biosignaturesworkshop the workshop …...biosignature detection and general...

NancyY.Kiang,NASAGoddardInstituteforSpaceStudies,Nancy.Y.Kiang@nasa.govMaryNicole(“Niki”)Parenteau,NASAAmesResearchCenter,mary.n.parenteau@nasa.govShawnDomagal-Goldman,NASAGoddardSpaceFlightCenter,shawn.goldman@nasa.govhttp://nexss.info/community/workshops/exoplanet-biosignatures-workshop

The search for life beyond our Solar System motivates futureexoplanet missions to observe for biosignatures with global,potentially detectable, impacts on a planet. Biosignatures occur in anenvironmental context in which geological, atmospheric, stellarprocesses and interactions, and evolutionary history may work toenhance, suppress or mimic these biosignatures. Thus biosignaturescience is inherently interdisciplinary. Its advance is necessary toinform the design of the next flagship missions that will obtainspectra of habitable extrasolar planets.

NASA’s Nexus for Exoplanet System Science and the NASAAstrobiology Institute held a joint Exoplanet BiosignaturesWorkshop-Without-Walls in June-July 2016, which brought togetherthe astrobiology, exoplanet, and mission concept communities toreview, discuss, debate, and advance the science of biosignatures. Abroad range of experts were engaged, merging the interdisciplinaryreaches of NExSS, the NAI, NASA’s Exoplanet Exploration Program(ExEP), and international partners, such as the EuropeanAstrobiology Network Association (EANA) and Japan’s Earth LifeScience Institute (ELSI).

The workshop focused around three goals:1. State of the Science Review: What are known remotely-observable biosignatures, the processes that produce them, andtheir known non-biological sources?2. Advancing the Science of Biosignatures: How can we develop amore comprehensive conceptual framework for identifyingadditional biosignatures and their possible abiotic mimics?3. Confidence Standards for Biosignature Observation andInterpretation: What paradigm informed by both scientists andtechnologists could establish confidence standards forbiosignature detection?To ensure accessibility for contribution by as many of the

international community as possible, workshop activities included6 online videoconference sessions for interactive review of theState of the Science preliminary to an in-person meeting inSeattle, WA, including remote dial-in. Participants spannedastronomy, planetary science, Earth sciences, heliophysics,biology, instrument/mission development, and engineering fromaround the world.AlltalksandSeattlesessionsmaybestreamedonlineatthe

workshopwebsiteabove.

Theworkshopactivitieshaveculminatedinfivereviewpapersonthescienceandtechnologyofremotesearchesforsignsoflifeonexoplanets.Broadparticipationwassolicitedforthesepapers,whichwillserveasaninterdisciplinary,educational,stateoftheartreferenceforuseacrossawidecommunity.CommunitycommentsareinvitedinMay2017at:nexss.info.

ExoplanetBiosignatures:AReviewofRemotelyDetectableSignsofLifeContact: Edward Schwieterman, edward.schwieterman@ucr.eduThis paper provides an in-depth review of current

understanding of potential exoplanet biosignatures includinggaseous, surface, and temporal biosignatures. We focusparticularly on advances made since the review by Des Maraiset al. (2002). This paper does not propose new biosignaturesstrategies, but reviews currently existing literature to providea foundation for a path forward. We survey some biogenicspectral features that are well-known in the specialistliterature but not yet robustly vetted in the context ofexoplanet biosignatures. We also briefly review advances inassessing biosignature plausibility, including novel methods ofdetermining chemical disequilibrium and the minimumbiomass required for a given atmospheric signature.

Acknowledgments:MaryVoytek,NASANexusforExoplanetSystemSciencePennyBoston,CarlPiilcher,NASAAstrobiologyInstitute

ExoplanetBiosignatures:ObservationalProspectsContact:YukaFujii,yuka.fujii.ebihara@gmail.com

We provide an overview of the observational prospects forbiosignature detection and general characterization of temperateEarth-size planets. We summarize what kind of key planetaryproperties may become observable as the new facilities come on line,reviewing the planned space-based and ground-based projects as wellas the methodologies these projects will employ. We distinguishreasonable expectations for the first constraints on spectroscopicfeatures of atmospheres (and perhaps surfaces) of transiting and non-transiting planets obtainable before 2030, versus more detailedscrutinies and/or larger surveys to address statistical questions such asthe occurrence rate of habitable environments, to be planned beyond2030. The broad outlook which this paper presents is useful indeveloping the methodologies to assess the possibility of biospheresbased on what we can observe.

ExoplanetBiosignatures:FutureDirectionsContact:SaraWalker,sara.i.walker@asu.edu

We summarize novel concepts about planetary biosignaturesthat are just emerging in the literature, addressing the importanceof environmental context and biology that may be very differentfrom Earth. Topics include evaluating: the evolutionary trajectoryof coupled systems to identify high- vs. low-probability outcomes;classification of biosignatures from process-based, multi-disciplinary perspectives; laboratory and theoretical validationoutside of Earth-like conditions. We summarize the debates overthese novel ideas, proposals from the community for developingthem further, and consider modeling of observationaldiscriminatory power, and set the stage for future instrumentdevelopment requirements.

ExoplanetBiosignatures:AFrameworkforTheirAssessmentContact:DavidCatling,dcatling@uw.edu

We present a general scheme for observing potentialexoplanet biosignatures and gaining and expressingconfidence levels for positive detection of signs of life. Anappropriate framework uses models with data (in the formof exoplanetary system properties and spectral orphotometric data) to find the Bayesian likelihoods of thosedata occurring if the exoplanet has or does not have life.The latter includes the case of false positives, i.e., whereabiotic sources mimic biosignatures. Prior knowledge(including all factors that influence habitability and previousexoplanet observations) would be combined with thelikelihoods to arrive at the probability of life existing on agiven exoplanet given the observations.

ExoplanetBiosignatures:UnderstandingOxygenasaBiosignature intheContextofItsEnvironmentContact:VictoriaS.Meadow,vsm @astro.washington.edu

O2 remains our most robust biosignature. However,possibilities for false negatives exist, as on the early Earthwhen accumulation of biogenic O2 in the atmosphere wasdelayed by at least a billion years. Possibilities for falsepositives also have been uncovered through computermodeling of mechanisms for abundant O2 in the absence of abiosphere. We review past and current biosignature researchto detail the story of O2 as a specific example of how life is afunction of and modifies its planetary environment, and howwe would use remote-sensing observations to search forbiosignatures in the near term. In addition, we describecurrent knowledge of specific photometric, spectroscopic andtime-dependent observations of environmental context thatcould be made by future observatories to identify O2 as abiosignature, and discriminate it from potential falsepositives.

ExoplanetBiosignatures Workshop

Science

Models

Missions

Seager etal2016Parenteau 2015

SaraWalker

Wayetal.2016

Barnesetal.2016

https://ntrs.nasa.gov/search.jsp?R=20170004581 2020-04-20T10:08:21+00:00Z