Exosphere Modeling of Proxima b: A Case Study of Photochemical Escape with a Venus-like Atmosphere

Exoplanets orbiting M dwarfs within habitable zones are exposed to stellar environments more extreme than that terrestrial planets experience in our solar system, which can significantly impact the atmospheres of the exoplanets and affect their habitability and sustainability. This study provides the first prediction of hot oxygen corona structure and the associated photochemical loss from a 1 bar CO2-dominated atmosphere of a Venus-like rocky exoplanet, where dissociative recombination of O2 + ions is assumed to be the major source reaction for the escape of neutral O atoms and formation of the hot O corona (or exospheres) as on Mars and Venus. We employ a 3D Monte Carlo code to simulate the exosphere of Proxima Centauri b (PCb) based on the ionosphere simulated by a 3D magnetohydrodynamic model. Our simulation results show that variability of the stellar wind dynamic pressure over one orbital period of PCb does not affect the overall spatial structure of the hot O corona but contributes to the change in the global hot O escape rate that varies by an order of magnitude. The escape increases dramatically when the planet possesses its intrinsic magnetic fields as the ionosphere becomes more extended with the presence of a global magnetic field. The extended hot O corona may lead to a more extended H exosphere through collisions between thermal H and hot O, which exemplifies the importance of considering nonthermal populations in exospheres to interpret future observations.

Occulter to earth: prospects for studying earth-like planets with the E-ELT and a space-based occulter

Direct detection and characterization of Earth-like planets around Sun-like stars is a core task for evaluating the prevalence of habitability and life in the Universe. Here, we discuss a promising option for achieving this goal, which is based on placing an occulter in orbit and having it project its shadow onto the E-ELT at the surface of Earth, thus providing a sufficient contrast for imaging and taking spectra of Earth-like planets in the habitable zones of Sun-like stars. Doing so at a sensible fuel budget will require tailored orbits, an occulter with a high area-to-mass ratio, and appropriate instrumentation at the E-ELT. In this White Paper, submitted in response to the ESA Voyage 2050 Call, we outline the fundamental aspects of the concept, and the most important technical developments that will be required to develop a full mission.

Mars based settlements

This paper explores some ideas of how efficient Mar-based settlementswould look like in a futuristic time. The main idea is micro-climatingzones, then building up on those previously established habitable zones.

Integration of Satellite Image Derived Temperature and Water Depth for Assessing Fish Habitability in Dam Controlled Flood Plain Wetland

The present study attempted to investigate the changes in temperature conducive to fish habitability during the summer months in a hydrologically modified wetland following damming over a river. Satellite image-driven temperature and depth data calibrated with field data were used to analyse fish habitability and the presence of thermally optimum habitable zones in some fishes such as Labeo Rohita, Cirrhinus mrigala, Tilapia fish, Small shrimp, and Cat fishes. The study was conducted both at the water's surface and at the optimum depth of survival. It is very obvious from the analysis that a larger part of wetland has become an area that destroyed aquatic habitat during the post-dam period and existing wetlands have suffered significant shallowing of water depth. This has resulted in a shrinking of the thermally optimum area of fish survival in relation to surface water temperature (from 100.09 km2 to 74.24 km2 before the dam to 93.97 km2 to 0 km2 after the dam) and an improvement in the optimum habitable condition in the comfortable depth niche of survival. In the post-dam period, it increased from 75.49 % to 99.765%. Since the damming effect causes a 30.53 to 100% depletion of the optimum depth niche, improving the thermal environment has no effect on fish habitability. More water must be released from dams for restoration. Image-driven depth and temperature data calibrated with field information has been successfully applied in data sparse conditions, and it is further recommended in future work.

Terrestrial planet accretion constrained by isotopes: Implications for Earth-like habitats

<p>Here we discuss terrestrial planet formation by using Earth and our knowledge from various isotope data such as <sup>182</sup>Hf-<sup>182</sup>W, U-Pb, lithophile-siderophile elements, atmospheric <sup>36</sup>Ar/<sup>38</sup>Ar, <sup>20</sup>Ne/<sup>22</sup>Ne, <sup>36</sup>Ar/<sup>22</sup>Ne isotope ratios, the expected solar <sup>3</sup>He abundance in Earth’s deep mantle and Earth’s D/H sea water ratios as an example. By analyzing the available isotopic data one finds that, the bulk of Earth’s mass most likely accreted within 10 to 30 million years after the formation of the solar system. Proto-Earth most likely accreted a mass of 0.5 to 0.6 <em>M</em><sub>Earth</sub> during the disk lifetime of 3 to 4.5 million years and the rest after the disk evaporated (see also Lammer et al. 2021; DOI: 10.1007/s11214-020-00778-4). We also show that particular accretion scenarios of involved planetary building blocks, large planetesimals and planetary embryos that lose also volatiles and moderate volatile rock-forming elements such as the radioactive decaying isotope <sup>40</sup>K determine if a terrestrial planet in a habitable zone of a Sun-like star later evolves to an Earth-like habitat or not. Our findings indicate that one can expect a large diversity of exoplanets with the size and mass of Earth inside habitable zones of their host stars but only a tiny number may have formed to the right conditions that they could potentially evolve to an Earth-like habitat. Finally, we also discuss how future ground- and space-based telescopes that can characterize atmospheres of terrestrial exoplanets can be used to validate this hypothesis.   </p>

ExoPhot: a new approach for the study of photosynthesis viability in exoplanetary systems.

<p>NASA and ESA are making plans for the next generation of space telescopes, which should be able to detect biomarkers in the atmospheres of exoplanets in the classical habitable zones around their stars (i.e., the range of separations at which water would be in liquid state on the exoplanet surface). The launch of <em>James Space Webb Telescope</em> is scheduled for October 2021. The main questions are related with the type of organisms producing such possible biomarkers and with the related metabolism? Will autotrophs be the base of the exoplanet ecological pyramid, as on Earth? Will they be phototroph or chemotroph? Will they be photosynthetic? Oxygenic or anoxygenic? Which will their photosynthetic pigments be? ESA’s <em>LIFE</em> or any other new concept for which scientific requirements have not been defined yet might be able to not only detect biomarkers, but to shed light on the actual biochemistry of exoplanet ecosystems. Therefore, investigating the potential variety of photosynthetic systems in exoplanets, either real or to be discovered, is actually very timely, as the requirements of new such telescope concepts are not set yet.</p> <p>The conversion of solar energy to chemical energy through photosynthesis is considered one of the first metabolic routes on planet Earth. Although a low percentage of the solar radiation from our Sun is captured by photosynthesis, this metabolic route provides the energy to drive all the life on Earth. Cyanobacteria are thought to be the first photosynthetic microorganisms on Earth. Subsequent photosynthetic organisms acquired photosynthesis via cyanobacteria endosymbionts, that evolved into chloroplasts in plants (Tomioka & Sugiura 1983).</p> <p>At the same time, photosynthesis modified the atmosphere of the early Earth by producing oxygen as a by-product. The concentration in this gas was increased in the primitive atmosphere, transforming the metabolic possibilities for the rest of organisms and, nowadays, oxygen supports the whole aerobic organisms on the planet. The only requirements that photosynthesis has are the exposure to optical radiation from the corresponding star and the availability of water and carbon dioxide (as a carbon source), making photosynthesis a putative imperative metabolism to be present in any particular radiative planetary system.</p> <p>To deepen into this idea, ExoPhot aims to study the relation between photosynthetic systems on exoplanets around different types of stars (i.e. stellar spectral types) from an astrobiological and multidisciplinary point of view, by focusing on two aspects:</p> <ul> <li>Assess the photosynthetic fitness of a variety of photopigments (either real or hypothetical) as a function of star, exoplanet and atmospheric scenario.</li> <li>Delineate a range of stellar, exoplanet and atmospheric parameters for which photosynthetic activity might be feasible.</li> </ul> <p>To accomplish these goals, we will use state-of-the-art planetary and stellar models to retrieve the radiation signatures at the planet surface for a wide range of exoplanet, atmosphere and host star parameters, and will carry out a quantification of the overlap (convolution) between those spectra with the absorption spectra of photosynthetic pigments, both terrestrial and hypothetical (our own developments on computer-simulated primordial pigments). Here, at the EPSC2021 conference, we present our preliminary results and future work to be developed.</p> <p> </p> <p><em>Bibliography:</em></p> <p>Tomioka, N. & Sugiura, M. The complete nucleotide sequence of a 16S ribosomal RNA gene from a blue-green alga, Anacystis nidulans. <em>Molecular and General Genetics, </em>1983<em>, 191</em>, 46–50. https://doi.org/10.1007/BF00330888</p> <p> </p>