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Pages 352-381

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From page 352...
... 352 ORIGINS, WORLDS, AND LIFE FIGURE 13-5  Question 10. Oxidation and hydration of silicate rocks in reactions that produce iron-bearing phases, serpentine, and other phyllosilicates also generate hydrogen, which can serve as an energy source for life.
From page 353...
... QUESTION 10: DYNAMIC HABITABILITY 353 preservation in the presence of H2S. So far, the martian organics can all be explained by abiotic processes, although our understanding of organic compounds on Mars is nascent, and strategies are being developed to discriminate between abiotic and biotic organics (Question 11)
From page 354...
... 354 ORIGINS, WORLDS, AND LIFE H2O and H2S. Whether there is phosphorus in the Venus atmosphere remains unclear: P sourced from volcanic eruptions could exist as P4O6 in the lower atmosphere, before being lofted to middle- and upper atmospheric levels and converted to PH3; this latter phenomenon was recently tentatively observed.
From page 355...
... QUESTION 10: DYNAMIC HABITABILITY 355 of ice may transport oxidants to Europa's ocean (e.g., Hand et al.
From page 356...
... 356 ORIGINS, WORLDS, AND LIFE Q10.5c How and Why Have the Inventories, Forms, and Distribution of Life-Supporting Elements Changed Through Time? The availability of CHNOPS on a planet varies with time by mechanisms similar to those controlling the availability of water (Q10.3)
From page 357...
... QUESTION 10: DYNAMIC HABITABILITY 357 Q10.6a What Are the Available Energy Sources for Life? All life as we know it exploits energy via thermodynamic disequilibria.
From page 358...
... 358 ORIGINS, WORLDS, AND LIFE only sustain life in a dormant state against environmental stressors but to support metabolism, mobility, growth, and reproduction (Hoehler 2007)
From page 359...
... QUESTION 10: DYNAMIC HABITABILITY 359 hydrological parameters that control fluid circulation. In some cases, such processes might become transiently self-sustaining: for example, volumetric expansion associated with mineral hydration, as observed in serpentinization systems, can lead to fresh fracturing and, hence, further introduction of fluid.
From page 360...
... 360 ORIGINS, WORLDS, AND LIFE Q10.7b What Endogenous Factors Control the Continuity of Habitability? The duration of habitability may be most strongly affected by the processes associated with heat transfer and loss over time, which are themselves a function of planetary size and starting composition (e.g., Ehlmann et al.
From page 361...
... QUESTION 10: DYNAMIC HABITABILITY 361 • Develop technologies for in situ measurement of light and radiogenic isotopes that trace the fluxes of key CHNOPS species and geological evolution in absolute time by miniaturization and maturation of instruments for isotope measurement on landed missions to terrestrial and ocean worlds. • Increasingly high-fidelity analyses of organics and metal isotopes that determine abiogenic versus biogenic organic production as well as reservoirs and fluxes of key elements for biology by development of sample return technology for silicate, ice, and atmospheric samples and advanced facilities for returned sample analysis and curation.
From page 362...
... 362 ORIGINS, WORLDS, AND LIFE Glavin, D.P., C.M.O'D. Alexander, J.C.
From page 363...
... QUESTION 10: DYNAMIC HABITABILITY 363 NASEM (National Academies of Sciences, Engineering, and Medicine)
From page 364...
... 364 ORIGINS, WORLDS, AND LIFE Webster, C.R., P.R. Mahaffy, J
From page 366...
... Q11 PLATE: A true-color "selfie" of the Perseverance rover, accompanied by the Ingenuity helicopter, on the surface of Mars in 2021. SOURCE: Courtesy of NASA/JPL-Caltech/MSSS.
From page 367...
... 14 Question 11: Search for Life Elsewhere Is there evidence of past or present life in the solar system beyond Earth, and how do we detect it? Building on insights from terrestrial life and our understanding of the diversity of habitable environments elsewhere, as well as significant advancement in biosignature detection technologies, we are poised to conduct a rigorous, systematic search for life beyond Earth in the solar system.1 Four hundred years after Galileo revolutionized our understanding of our place in the universe, ours could realistically be the generation that triggers another scientific revolution, this time in biology.
From page 368...
... 368 ORIGINS, WORLDS, AND LIFE FIGURE 14-1  The search for life builds on previous discoveries that span body interiors and surfaces to atmospheres and dynamic habitability (vertical axis)
From page 369...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 369 Aerosols/hazes/ clouds Regolith/sediments/ ice/permafrost Deep aquifers/ice FIGURE 14-2 Target environments and possible architectures of missions to search for life on other planetary bodies of the solar system. Left: Mission architectures to rocky planets and bodies with an atmosphere include (but are not limited to)
From page 370...
... 370 ORIGINS, WORLDS, AND LIFE identified. Laboratory experiments designed to simulate the conditions and processes that occur in extraterrestrial material environments, such as cosmic ice irradiation and low-temperature photochemistry and geochemistry, are an important complement to the characterization of astromaterials (Hoehler et al.
From page 371...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 371 but incomplete (Q10.4)
From page 372...
... 372 ORIGINS, WORLDS, AND LIFE Q11.1c What Are the Relevant Chemical Pathways That Can Lead from Prebiotic Chemistry to Biochemistry, and How Does That Transition Depend on the Geochemical State of the Environment? Chemical pathways (i.e., links of chemical reactions)
From page 373...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 373 reliability, detectability, and survivability (Meadows 2017; Meadows et al.
From page 374...
... 374 ORIGINS, WORLDS, AND LIFE Q11.2b What Are the Relationships Between the Physical and Chemical Properties and Processes Operating in a Habitable Environment and the Potential Amount of Biomass That Might Be Present? How Might This Drive the Detectability of Any Biosignatures Present?
From page 375...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 375 produced it, and the environment(s) in which the signature(s)
From page 376...
... 376 ORIGINS, WORLDS, AND LIFE provide a more rigorous standard of proof. In addition, such frameworks can help identify sets of measurements that together discriminate between a biotic or abiotic origin for potential biosignatures with high statistical significance (NASEM 2019)
From page 377...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 377 FIGURE 14-4  The search for life has been revolutionized in the past decades by pivotal discoveries such as the identification of what is now recognized as a third branch in the tree of life (Archaea) and confirmation of subsurface liquid water oceans within several moons of Jupiter and Saturn.
From page 378...
... 378 ORIGINS, WORLDS, AND LIFE FIGURE 14-5  To provide evidence of life above the threshold established by abiotic processes in a given environment, multiple independent biosignatures (B) are needed, as well as a thorough understanding of the physicochemical setting (C)
From page 379...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 379 FIGURE 14-6  Examples of instruments that can be used to search for chemical/molecular biosignatures, organized by their range of detection limits and sample processing requirements. Note that sample preconcentration can improve detection limits for some instruments.
From page 380...
... 380 ORIGINS, WORLDS, AND LIFE metabolic biosignatures (which would indicate organisms that are alive today) may no longer be present, evidence of past life in the returned samples can be ascertained from chemical and morphological fingerprints left behind.
From page 381...
... QUESTION 11: SEARCH FOR LIFE ELSEWHERE 381 Q11.3d If We Do Not Find Evidence of Life in a Habitable Environment, What Would It Take to Convince Ourselves That There Truly Is or Was No Life Present There, Rather Than Possibly Not Having Detected It (a False Negative)

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