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Pages 324-351

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From page 324...
... 324 ORIGINS, WORLDS, AND LIFE Processes such as transport, flux, preservation, degradation, concentration, and dilution can modify and impact the distribution and activity of life in the subsurface, and habitable niches may be ephemeral or isolated (Lin et al. 2006; Lollar et al.
From page 325...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 325 FIGURE 12-7  Biosignature features and measurements ranging in strength of evidence and ease of measurement. Clockwise from top: Structural preferences in organic molecules (nonrandom and enhancing function)
From page 326...
... 326 ORIGINS, WORLDS, AND LIFE FIGURE 12-8  Decision tree describing the biosignature potential of a given environment (terrestrial or nonterran) in terms of measurable properties that might result in the environment being associated with detectable probable biosignatures that can be confidently ascribed to biology and have a high probability of preservation, along with those environmental properties that might result in a higher probability of false positive or false negative detections.
From page 327...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 327 In the coming decade, biosignature research needs to include a concerted effort to better understand abiosignatures (i.e., a signature of abiotic processes and phenomena) , in particular those that may mimic biosignatures (see also Question 11)
From page 328...
... 328 ORIGINS, WORLDS, AND LIFE Strategic Research for Q9.4 • Assess how the essential traits of Earth life, such as metabolism or bioenergetics, arose from the geochemical environment through theoretical, field, and laboratory studies of the connectivity and stoichiometry of metabolic networks, and the geological availability of exploitable redox gradients. • Develop a comprehensive framework for biosignature categories of Earth life to guide the understanding of what biosignatures will be prevalent in life through community-level dialog and consensus, supported by laboratory/experimental and modeling/theoretical research as well as field work on environmentally relevant biosignature classes as well as abiosignatures.
From page 329...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 329 TABLE 12-2  Biosignature Reliability, Detectability, and Preservation Vary with Time in the Geologic Record Biosignature Type Reported Geochemistry/ Organic Age (Ma) Isotope Mineralogy Morphology Carbon Lipid Forms Formation Type (location)
From page 330...
... 330 ORIGINS, WORLDS, AND LIFE Q9.5b Which Biosignatures Are Most Likely to Survive in the Environment, and at What Timescales of Preservation? The timescales and mechanisms of survivability make up a core research area that includes the survivability of a modern biosignature against processes that would act to destroy it as it forms; the survivability of a fossil biosignature against geological forces such as weathering, diagenesis, influx of brines or groundwaters; and metamorphism, and/or the survivability of abiosignatures (inherently the study of the relative rates of abiotic and biological, and potentially cryptic, processes)
From page 331...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 331 et al.
From page 332...
... 332 ORIGINS, WORLDS, AND LIFE Chan, M.A., N.W. Hinman, S.L.
From page 333...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 333 Furnes, H., K Muehlenbachs, T
From page 335...
... QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 335 NASEM (National Academies of Sciences, Engineering, and Medicine)
From page 336...
... 336 ORIGINS, WORLDS, AND LIFE Spinks, S.C., J Parnell, and S.A.
From page 338...
... Q10 PLATE: A composite image of Saturn's moons, Enceladus (foreground) and Titan (background)
From page 339...
... 13 Question 10: Dynamic Habitability Where in the solar system do potentially habitable environments exist, what processes led to their formation, and how do planetary environments and habitable conditions co-evolve over time? The past several decades of exploration of Earth's biosphere have expanded our knowledge of the range of environments with liquid water, nutrients, and energy sources that sustain life.1 Simultaneously, the past several decades of planetary exploration have revealed multiple ancient and modern potential habitable environments across the solar system.
From page 340...
... 340 ORIGINS, WORLDS, AND LIFE At present, with a single example of an inhabited world (Earth) , we lack the information to fully understand the conditions that lead to -- or prohibit -- the origin and sustenance of life on worlds in the solar system.
From page 341...
... QUESTION 10: DYNAMIC HABITABILITY 341 FIGURE 13-2  Question 10. Some of the major components of what constitutes a habitable environment.
From page 342...
... 342 ORIGINS, WORLDS, AND LIFE For example, any early ocean and atmosphere on Earth would have been sterilized by the Moon-forming impact. Subsequently, as Earth cooled and water oceans became reestablished, early Earth may have had a CO2- or a CH4-rich atmosphere akin to Titan today, depending on the balance of input from volcanism and impacts.
From page 343...
... QUESTION 10: DYNAMIC HABITABILITY 343 TABLE 13-1  Question 10. The Factors That Govern Planetary Habitability, and Whether Those Factors Are Present for Select Planetary Bodies Across the Solar System NOTE: Cells with a check and question mark signify likely/probable.
From page 344...
... 344 ORIGINS, WORLDS, AND LIFE exoplanetary systems (Question 12, Chapter 15)
From page 345...
... QUESTION 10: DYNAMIC HABITABILITY 345 around the giant planets. The habitable zone, as defined by the presence of liquid water (Q10.1)
From page 346...
... 346 ORIGINS, WORLDS, AND LIFE Q10.2c What Can Small Bodies Reveal About Habitability, and Are There Habitable Dwarf Planets Today? Results over the past decade by NASA's Dawn and New Horizons missions revolutionized our understanding of habitability related to small solar system bodies, such as asteroids, comets, and trans-neptunian objects (TNOs)
From page 347...
... QUESTION 10: DYNAMIC HABITABILITY 347 a contribution has been suggested for highly hydrated dust grains resulting from the interaction of the solar wind with planetesimals (Daly et al.
From page 348...
... 348 ORIGINS, WORLDS, AND LIFE The availability of liquid water at the surface of the terrestrial planets is determined in part by surface temperature, which itself is a function of distance from the Sun and atmospheric greenhouse warming. Although only small amounts of water are present in the clouds today, early Venus may have had a much more clement climate before a greenhouse effect drove liquid water into the atmosphere then away to space (Q6.2b)
From page 349...
... QUESTION 10: DYNAMIC HABITABILITY 349 antifreeze in the oceans themselves. Ammonia and salts can facilitate melting by freezing point lowering, but an interior heat source is still required.
From page 350...
... 350 ORIGINS, WORLDS, AND LIFE Mars, chondrite parent bodies, Ceres, Enceladus, Titan, Pluto, comets, the atmospheres of the giant planets, and possibly Venus (Table 13-1)
From page 351...
... QUESTION 10: DYNAMIC HABITABILITY 351 FIGURE 13-4  Question 10. Atmospheric chemistry leads to formation of complex organics on Titan.

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