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Victoria S Meadows, Christopher T Reinhard, Giada N Arney, Mary N Parenteau, Edward W Schwieterman, Shawn D Domagal-Goldman, Andrew P Lincowski, Karl R Stapelfeldt, Heike Rauer, Shiladitya DasSarma, Siddharth Hegde, Norio Narita, Russell Deitrick, Jacob Lustig-Yaeger, Timothy W Lyons, Nicholas Siegler, J Lee Grenfell
We describe how environmental context can help determine whether oxygen (O2 ) detected in extrasolar planetary observations is more likely to have a biological source. Here we provide an in-depth, interdisciplinary example of O2 biosignature identification and observation, which serves as the prototype for the development of a general framework for biosignature assessment. Photosynthetically generated O2 is a potentially strong biosignature, and at high abundance, it was originally thought to be an unambiguous indicator for life...
May 10, 2018: Astrobiology
Nancy Y Kiang, Shawn Domagal-Goldman, Mary N Parenteau, David C Catling, Yuka Fujii, Victoria S Meadows, Edward W Schwieterman, Sara I Walker
The rapid rate of discoveries of exoplanets has expanded the scope of the science possible for the remote detection of life beyond Earth. The Exoplanet Biosignatures Workshop Without Walls (EBWWW) held in 2016 engaged the international scientific community across diverse scientific disciplines, to assess the state of the science and technology in the search for life on exoplanets, and to identify paths for progress. The workshop activities resulted in five major review papers, which provide (1) an encyclopedic review of known and proposed biosignatures and models used to ascertain them (Schwieterman et al...
May 9, 2018: Astrobiology
N Nikolov, D K Sing, J J Fortney, J M Goyal, B Drummond, T M Evans, N P Gibson, E J W De Mooij, Z Rustamkulov, H R Wakeford, B Smalley, A J Burgasser, C Hellier, Ch Helling, N J Mayne, N Madhusudhan, T Kataria, J Baines, A L Carter, G E Ballester, J K Barstow, J McCleery, J J Spake
Broad absorption signatures from alkali metals, such as the sodium (Na I) and potassium (K I) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3 . However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6 . Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9 ...
May 7, 2018: Nature
Edward W Schwieterman, Nancy Y Kiang, Mary N Parenteau, Chester E Harman, Shiladitya DasSarma, Theresa M Fisher, Giada N Arney, Hilairy E Hartnett, Christopher T Reinhard, Stephanie L Olson, Victoria S Meadows, Charles S Cockell, Sara I Walker, John Lee Grenfell, Siddharth Hegde, Sarah Rugheimer, Renyu Hu, Timothy W Lyons
In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere...
May 4, 2018: Astrobiology
J J Spake, D K Sing, T M Evans, A Oklopčić, V Bourrier, L Kreidberg, B V Rackham, J Irwin, D Ehrenreich, A Wyttenbach, H R Wakeford, Y Zhou, K L Chubb, N Nikolov, J M Goyal, G W Henry, M H Williamson, S Blumenthal, D R Anderson, C Hellier, D Charbonneau, S Udry, N Madhusudhan
Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres 1 . Searches for helium, however, have hitherto been unsuccessful 2 . Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near-infrared transmission spectrum of the warm gas giant 3 WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms...
May 2018: Nature
Drake Deming
No abstract text is available yet for this article.
May 2018: Nature
Hirokazu Kadobayashi, Hisako Hirai, Hiroaki Ohfuji, Michika Ohtake, Yoshitaka Yamamoto
High-temperature and high-pressure experiments were performed under 2-55 GPa and 298-653 K using in situ Raman spectroscopy and X-ray diffraction combined with externally heated diamond anvil cells to investigate the stability of methane hydrate. Prior to in situ experiments, the typical C-H vibration modes of methane hydrate and their pressure dependence were measured at room temperature using Raman spectroscopy to make a clear discrimination between methane hydrate and solid methane which forms through the decomposition of methane hydrate at high temperature...
April 28, 2018: Journal of Chemical Physics
Nicolás Dubost, Nazim Ali Bharmal, Richard M Myers
The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. In order to achieve this, a high-sensitivity wavefront sensor, the pupil-modulated point-diffraction interferometer (m-PDI), is presented. This sensor modulates and retrieves both the phase and the amplitude of an incoming electric field. The theory behind the wavefront reconstruction, the visibility of fringes, chromatic effects and noise propagation are developed...
April 30, 2018: Optics Express
David C Catling, Joshua Krissansen-Totton, Nancy Y Kiang, David Crisp, Tyler D Robinson, Shiladitya DasSarma, Andrew J Rushby, Anthony Del Genio, William Bains, Shawn Domagal-Goldman
Finding life on exoplanets from telescopic observations is an ultimate goal of exoplanet science. Life produces gases and other substances, such as pigments, which can have distinct spectral or photometric signatures. Whether or not life is found with future data must be expressed with probabilities, requiring a framework of biosignature assessment. We present a framework in which we advocate using biogeochemical "Exo-Earth System" models to simulate potential biosignatures in spectra or photometry...
April 20, 2018: Astrobiology
Bob Henderson
No abstract text is available yet for this article.
April 17, 2018: Scientific American
Cristina Puzzarini, Alberto Baiardi, Julien Bloino, Vincenzo Barone, Thomas E Murphy, Dennis Drew, Ashraf Ali
To gain information on the abiotic synthesis of the building blocks of life from simple molecules, and their subsequent chemical evolution to biological systems, the starting point is the identification of target species in Titan-like planets, i.e., planets that resemble the primitive Earth, as well as in Earth-like planets in the habitable zone of their star, namely planets where life can be already originated. In this scenario, molecular spectroscopy plays a crucial role because spectroscopic signatures are at the basis of an unequivocal proof for the presence of these target molecules...
August 4, 2017: Astronomical Journal
Richard A Frazin
The sensitivity of the pyramid wavefront sensor (PyWFS) has made it a popular choice for astronomical adaptive optics (AAO) systems. The PyWFS is at its most sensitive when it is used without modulation of the input beam. In nonmodulated mode, the device is highly nonlinear. Hence, all PyWFS implementations on current AAO systems employ modulation to make the device more linear. The upcoming era of 30-m class telescopes and the demand for ultra-precise wavefront control stemming from science objectives that include direct imaging of exoplanets make using the PyWFS without modulation desirable...
April 1, 2018: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
Elizabeth Gibney
No abstract text is available yet for this article.
March 29, 2018: Nature
Victoria S Meadows, Giada N Arney, Edward W Schwieterman, Jacob Lustig-Yaeger, Andrew P Lincowski, Tyler Robinson, Shawn D Domagal-Goldman, Russell Deitrick, Rory K Barnes, David P Fleming, Rodrigo Luger, Peter E Driscoll, Thomas R Quinn, David Crisp
Proxima Centauri b provides an unprecedented opportunity to understand the evolution and nature of terrestrial planets orbiting M dwarfs. Although Proxima Cen b orbits within its star's habitable zone, multiple plausible evolutionary paths could have generated different environments that may or may not be habitable. Here, we use 1-D coupled climate-photochemical models to generate self-consistent atmospheres for several evolutionary scenarios, including high-O2 , high-CO2 , and more Earth-like atmospheres, with both oxic and anoxic compositions...
February 2018: Astrobiology
Anthony Harness, Stuart Shaklan, Webster Cash, Philip Dumont
Starshade external occulters are a leading technology that provide the starlight suppression needed to directly image and spectroscopically characterize Earth-sized exoplanets in the habitable zone of nearby stars. A high-priority technology area identified in need of development for a future starshade mission is the development and validation of high-fidelity optical models to predict the performance of a full-scale starshade. We present the generalization of an algorithm to formulate the Fresnel diffraction equation as a one-dimensional integral around the edge of an arbitrary binary diffraction screen...
February 1, 2018: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
Joshua Krissansen-Totton, Stephanie Olson, David C Catling
Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions...
January 2018: Science Advances
Joseph R Schmitt, Jon M Jenkins, Debra A Fischer
The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a "Swiss cheese"-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or "lost"). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this "Swiss cheesing" may have...
April 2017: Astronomical Journal
Engin Keles, John Lee Grenfell, Mareike Godolt, Barbara Stracke, Heike Rauer
Understanding the possible climatic conditions on rocky extrasolar planets, and thereby their potential habitability, is one of the major subjects of exoplanet research. Determining how the climate, as well as potential atmospheric biosignatures, changes under different conditions is a key aspect when studying Earth-like exoplanets. One important property is the atmospheric mass, hence pressure and its influence on the climatic conditions. Therefore, the aim of the present study is to understand the influence of atmospheric mass on climate, hence habitability, and the spectral appearance of planets with Earth-like, that is, N2 -O2 dominated, atmospheres orbiting the Sun at 1 AU...
February 2018: Astrobiology
Daniel Clery
No abstract text is available yet for this article.
January 19, 2018: Science
Javier Tiffenberg, Miguel Sofo-Haro, Alex Drlica-Wagner, Rouven Essig, Yann Guardincerri, Steve Holland, Tomer Volansky, Tien-Tien Yu
We have developed ultralow-noise electronics in combination with repetitive, nondestructive readout of a thick, fully depleted charge-coupled device (CCD) to achieve an unprecedented noise level of 0.068  e^{-} rms/pixel. This is the first time that discrete subelectron readout noise has been achieved reproducible over millions of pixels on a stable, large-area detector. This enables the contemporaneous, discrete, and quantized measurement of charge in pixels, irrespective of whether they contain zero electrons or thousands of electrons...
September 29, 2017: Physical Review Letters
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