Searching for Life Across Space and Time Proceedings of a Workshop (2017) / Chapter Skim
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3 Exoplanets
3 Exoplanets
Pages 27-48
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From page 27... ...
EXTRASOLAR BIOSIGNATURES: DEVELOPING A COMPREHENSIVE FRAMEWORK FOR BIOSIGNATURE RECOGNITION Victoria Meadows of the University of Washington prefaced her talk on extrasolar biosignatures by explaining that she would essentially summarize the 2016 workshop hosted by the Nexus for Exoplanet System Science (NExSS) and the NASA Astrobiology Institute, called the "Exoplanet Biosignatures Workshop Without Walls." This workshop combined the expertise of NExSS, the NASA Astrobiology Institute, and the science and technology definition teams for exoplanet observation mission concepts to focus on the following three main questions: • What are the known remotely observable biosignatures, the processes that produce them, and their known non-biological sources?
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Barnes, 2015, Extreme water loss and abiotic O buildup on planets throughout the habitable zones of M dwarfs, 2 Astrobiology 15:119.
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Mason, ed.) , Chichester, U.K.: Praxis Publishing with permission from Springer; presented in Victoria Meadows, University of Washington/NASA Astrobiology Institute, "Extrasolar Biosignatures: Developing a Comprehensive Framework for Biosignature Recognition: Overview of the NExSS/NAI Biosignatures Workshop 2016," presentation to the Workshop on Searching for Life across Space and Time, December 5, 2016.
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The most general method would be to explore a large number of potential volatiles that may be biosignatures.30 However, without an example of a planet with life to analyze in context, this makes the risk of finding a false positive higher. Giving a preview of the material in the workshop report, she showed a figure demonstrating that having liquid water on the surface is a function of the star, the properties of the planetary system, and the properties of the planet itself.
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Pierrehumbert, 2014, Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets, The Astrophysical Journal Letters 785:20.
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He then continued along the path of long-term, geological trajectories, saying that, to him, the habitable zone is the region where feedbacks push the planet toward having liquid water as opposed to away from having liquid water. However, he said, once life begins, it then becomes part of the feedback loops.
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He then cautioned against thinking we know what an abiotic planet might look like, since we cannot explain the amount of water on Earth or know how much water a typical habitable zone rocky planet might contain. The final question directed toward Dr.
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However, careful consideration of false positives and false negatives is necessary. Type II Type II gases are produced by biomass capture.
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A workshop participant then brought up the topic of geochemical false positives, saying that one must take into account time. He gave hydrogen as an example.
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TECHNOLOGY NEEDS TO DISCOVER EARTH 2.0 Nick Siegler of the NASA Jet Propulsion Laboratory (JPL) began his talk by stating that the main goal of the Exoplanet Exploration Program technology effort is to enable future space missions to observe a planetary spectrum of a rocky planet in the habitable zone of its star and understand it in the context of potential life.
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. Further technological advancement would be required to observe rocky planets in the habitable zone of stars at a distance of 10 parsec (pc)
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masks are also shown. For consistency, the imaged planets discovered in the near-infrared are shown with vertical arrows pointing to the predicted contrast ratios at visible wavelengths; the Wide Field Infrared Survey Telescope (WFIRST)
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.43 He then brought up a slide showing past and future NASA and European Space Agency exoplanet missions, such as CHEOPS and PLATO. He requested that future planning think favorably of exoplanets, since we won't be able to analyze biosignatures and false positives or negatives unless we can directly image these exoplanets.
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Having a small planet orbiting a small star gives a higher planet-to-star contrast ratio than if the same planet orbited a larger star. This is true for measurements of the planet's transit depth, reflected light, and thermal emission.
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Planets orbiting close to their parent stars also acquire a very distinct Doppler signature due to their orbital motion. Brogi showed a figure demonstrating, with a toy model, the visibility of the planet signature with respect to the telluric lines from Earth's atmosphere (see Figure 3.4)
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Brogi's group tested the method already with VLT CRIRES on known directly imaged planets.59,60 He said that it worked because of two factors that help increase the signal-to-noise ratio. First, the signal-to-noise ratio increases with the square root of the number of lines analyzed.
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He then concluded by saying that this groundbased, high-resolution technique is capable of getting the masses, inclinations, rotations, and wind speeds for nontransiting hot Jupiters already, but if combined with high spatial resolution, it could allow the same thing for potentially habitable planets in the future. Audience Participation An audience member asked how many M dwarfs the next generation of extremely large telescopes will be able to survey.
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Moving to the outer solar system, another workshop participant brought up Cassini's discoveries on Enceladus. We now know that it has a liquid water ocean, and there is compelling evidence for hydrothermal vents as well.
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Continuing on this topic, another audience member referred to a debate on martian magnetofossils, which helped us become more skeptical and focus more on potential false positives. In the final comment about this topic, an audience member talked about what has not yet happened.
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A workshop participant then said that the questions of what is practical for remote detection and in situ detection are very different. He was confident that any form of life could be detected in situ, even if it did not use DNA as its genetic material.
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Continuing on that subject, a workshop participant said that Venus, Earth, and Mars all had liquid water in the past. Venus could have had liquid water for 2 billion years.
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Therefore, she thought that we needed to help each other out, particularly in avoiding false positives and false negatives. Then a workshop participant said that one discipline that is really needed is statistics.
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