Detectability of life and photosynthesis on exoplanets
Atmospheric Beacons of Life from Exoplanets Around G and ..
Detectability of Life and Photosynthesis on Exoplanets.
Super-Earths are a class of planet not known in our Solar System but common among exoplanets. Can life survive there, and how would we detect it? I will present work exploring life on such worlds, especially Super-Earths with atmospheres that retain substantial amounts of hydrogen, and hence which will have surface chemistries substantially different from our own planet's. Surprisingly, the chemical inputs and outputs of life can be worked out from simple assumptions (or knowledge, when we have the knowledge) about planetary chemistry and environment, and the necessary properties of life. Some basic properties of the chemistry of life can be worked out from first principles: it must 'feed on' an energy source, it must be made of complex molecules which must therefore be of intermediate redox state. In the context of an hydrogen-rich super-Earth, I will discuss how these allow us to understand what biosignature gases such life could make. Gases can come from energy-generating reactions, and these are mostly constrained by the environment in which life grows. Gases can come from photosynthesis, which is also constrained by the environmental chemicals from which life builds its biomass. In both cases, we can not only identify the gases but also estimate the production rate, and hence whether it is plausible that life can make a detectable level of the gas. The third class of gases - those made by secondary metabolism - are harder to predict. Some modeling can be done, and I will touch on the issue of what chemicals to model. Lastly, I will mention the range of habitats, and hence of planetary environments, that such life might inhabit. Life on Super-Earth may actually be much more common than life on true Earth-analogues, but alas might also be much harder to detect.
The NASA Exoplanet Exploration Program (ExEP) is chartered by the NASA Astrophysics Division to implement the NASA space science goals of detecting and characterizing exoplanets and of searching for signs of life. The Program is responsible for space missions, concept studies, technology investments, and ground-based precursor and follow-up science that enables future missions and delivers mission Level-1 science. The ExEP includes the space science missions of Kepler, K2, and the proposed WFIRST/AFTA mission that includes both a microlensing survey for outer-exoplanet demographics and a coronagraph for direct imaging of gas- and ice-giant planets around nearby stars. Studies of probe-scale (medium class) missions for a coronagraph (internal occulter) and starshade (external occulter) explore the trades of cost and science and provide motivation for a technology investment program leading to the next decadal survey for NASA Astrophysics. Ground follow-up using the Keck Observatory contributes to the science yield of Kepler and K2, and mid-infrared observations of exo-zodiacal dust by the Large Binocular Telescope Interferometer help constrain the design and predicted science yield of the next generation of direct imaging missions. Technology development in high-contrast imaging for internal and external occulters enable the design of missions that fulfill the goal of detecting habitable worlds and looking for signs of life.
Detectability of life and photosynthesis on exoplanets.
The evolution of oxygenic photosynthesis and the resulting oxygenation of the atmosphere and oceans was arguably one of the most important events on the early Earth. In addition to setting the stage for the evolution of higher eukaryotic life forms, oxygen serves as a planetary-scale remotely detectable biosignature when searching for life on other planetary bodies. Cyanobacteria are the most evolutionarily ancient oxygenic phototrophs and use water as an electron donor for photosynthesis, producing oxygen as a waste product. However, it is thought that cyanobacteria didnt immediately acquire the ability to oxidize water. There is a large difference in the redox potentials between water and hydrogen and sulfide commonly used by the more ancient anoxygenic phototrophs. Members of our group have speculated that an intermediate reductant such as Fe(II) could have bridged the gap and acted as a transitional electron donor before water. The widespread abundance of Fe(II) in Archean and Neoproterozoic ferruginous oceans would have made it particularly suitable as an electron donor for photosynthesis. We have been searching for modern descendants of such an ancestral "missing link" cyanobacterium in the phototrophic mats at Chocolate Pots, a hot spring in Yellowstone National Park with a constant outflow of anoxic Fe(II)-rich thermal water. We present the results of our physiological ecology and complementary biosignature study, which revealed that the cyanobacteria grow anoxygenically using Fe(II) as an electron donor for photosynthesis in situ.
The final stages of the growth of a planet consist of violently energetic impacts, but new observations of the Moon and Mercury indicate that the energy of accretion does not remove all the water and carbon from the growing planet. Models demonstrate that rocky planets that accrete with as little as 0.01 wt% water produce a massive steam atmosphere that collapses into a water ocean upon cooling. The low water contents required indicate that rocky planets may be generally expected to produce water oceans through this process, and that an Earth-sized planet would cool to clement conditions in just a few to tens of millions of years. These results indicate that most rocky planets in our solar system and rocky exoplanets are likely to have been habitable early in their evolution, increasing the likelihood of life on the estimated 17 billion Earth-sized planets in the Milky Way.
How Extremely Large Telescopes will reveal exoplanets
What is the best strategy for finding signs of life beyond the Solar System? Until recent years this was a purely philosophical question, but today wehave the technical ability to search for signs of life on exoplanets around nearby stars, so the question is now a practical one. To start, we ask what kind of signs of life should we be looking for, and where should we be looking? Next we might ask about the methods we could use for such a search, and the kinds of evidence that we expect to obtain. Finally we can ask about the prospects for starting this search in the coming decade.
I am interested in using atmospheric models (photochemical and climatological) to recreate signals observed in the Archean rock record - a time period on Earth when there was life but no molecular oxygen (O2) in the atmosphere. This work will improve our understanding of the evolution of life on Earth, and inform our search for life on other planets as we learn more about the "most alien biosphere" we currently have data on.
This wo. Specifically, I'm working on the second task of that team, to "Characterize the Environment, Habitability and Biosignatures of the Earth Through Time." We want to uncover the history of biological metabolisms (e.g., methanogenesis, oxygenic photosynthesis, etc.) on the planet, and leverage that knowledge to simulate the biosignatures of the biosphere for different metabolic eras in the planet's history. This will give us a wider set of examples for the biospheres we can look for on extrasolar planets.
The reason to focus on early Earth as an example of an extrasolar biosphere is that we have a rock record with which to constrain our conceptual and numerical models. The data in the rock record I find most useful are isotopic proxies, which can deliver a tremendous depth and breadth of information about early Earth. My role in the interpretation of these proxies is to propose hypotheses that can explain as many data sets as possible, and use to test whether the hypotheses can explain the data given reasonable boundary conditions. Ideally, we also use model outputs to propose new geological proxies to look for in tests of the hypotheses.
Detecting Photosynthesis on Exoplanets - Centauri …
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'Is there life on exoplanets?'.
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There are also continuous observations of the Earth surface from near space satellites (e.g., NASA NEO). There are lots of spectral and some polarimetric data (e.g., POLDER mission) for various types of surface features, including grasses, different kinds of forestry, etc. The strongest life signature is “red edge” of plants on covering land masses. Signatures of algae in the ocean is very difficult to see. All these data we use for modeling possible signals from exoplanets.
A decade of Hα transits for HD 189733 b: ..
Sterzik agrees: “Using this technique [to observe exoplanets] is not within reach with current technology,” he says. For distant — and therefore exceedingly faint — targets, such measurements would require long exposures through much larger telescopes than are now available. Sterzik and his colleagues suggest that the next generation of telescopes — including instruments such as the European Extremely Large Telescope, which will have an aperture nearly 40 metres across and could be operational about a decade from now — could make observations that reveal that Earth is not the only planet hosting life.
22/06/2015 · Living color: life on ..
Again, we have to start from something . Earth is the only planet with life we know. Yes, we should be able to think broadly, so photosynthesis is not the only signature of life we look for. But it is one of the most prominent on our planet! And its general spectral characteristic, independently of the pigment – very broad and highly polarized absorption band near the maximum of the stellar flux. This is verified with plants (published), algae and bacteria (in prep.) and what we will search for on exoplanets, along with other biosignatures, such as water, oxygen, methane, or any other gases in disequilibrium.
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