1,533 research outputs found

    Optical Properties of Organic Haze Analogues in Water-rich Exoplanet Atmospheres Observable with JWST

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    JWST has begun its scientific mission, which includes the atmospheric characterization of transiting exoplanets. Some of the first exoplanets to be observed by JWST have equilibrium temperatures below 1000 K, which is a regime where photochemical hazes are expected to form. The optical properties of these hazes, which controls how they interact with light, are critical for interpreting exoplanet observations, but relevant experimental data are not available. Here we measure the density and optical properties of organic haze analogues generated in water-rich exoplanet atmosphere experiments. We report optical constants (0.4 to 28.6 {\mu}m) of organic haze analogues for current and future observational and modeling efforts covering the entire wavelength range of JWST instrumentation and a large part of Hubble. We use these optical constants to generate hazy model atmospheric spectra. The synthetic spectra show that differences in haze optical constants have a detectable effect on the spectra, impacting our interpretation of exoplanet observations. This study emphasizes the need to investigate the optical properties of hazes formed in different exoplanet atmospheres, and establishes a practical procedure to determine such properties.Comment: 4 figures, 1 Table, Published in Nature Astronom

    Photochemical Haze Formation in the Atmospheres of Super-Earths and Mini-Neptunes

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    UV (ultraviolet) radiation can induce photochemical processes in the atmospheres of exoplanet and produce haze particles. Recent transmission spectra of super-Earths and mini-Neptunes have demonstrated the possibility that exoplanets have haze/cloud layers at high altitudes in their atmospheres. Haze particles play an important role in planetary atmospheres because they affect the chemistry, dynamics, and radiation flux in planetary atmospheres, and may provide a source of organic material to the surface which may impact the origin or evolution of life. However, very little information is known about photochemical processes in cool, high-metallicity exoplanetary atmospheres. We present here photochemical haze formation in laboratory simulation experiments with UV radiation; we explored temperatures ranging from 300 to 600 degrees Kelvin and a range of atmospheric metallicities (100 times, 1000 times, and 10000 times solar metallicity). We find that photochemical hazes are generated in all simulated atmospheres, but the haze production rates appear to be temperature dependent: the particles produced in each metallicity group decrease as the temperature increases. The images taken with an atomic force microscope (AFM) show that the particle size (15 nanometers to 190 nanometers) varies with temperature and metallicity. Our results provide useful laboratory data on the photochemical haze formation and particle properties, which can serve as critical inputs for exoplanet atmosphere modeling, and guide future observations of exoplanets with the Transiting Exoplanet Survey Satellite (TESS), the James Webb Space Telescope (JWST), and the Wide-Field Infrared Survey Telescope (WFIRST)

    Coming Back to Life: The Permeability of Past and Present, Mortality and Immortality, Death and Life in the Ancient Mediterranean

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    The lines between death and life were neither fixed nor finite to the peoples of the ancient Mediterranean. For most, death was a passageway into a new and uncertain existence. The dead were not so much extinguished as understood to be elsewhere, and many perceived the deceased to continue to exercise agency among the living. Even for those more skeptical of an afterlife, notions of coming back to life provided frameworks in which to conceptualize the on-going social, political, and cultural influence of the past. This collection of essays examines how notions of coming back to life shape practices and ideals throughout the ancient Mediterranean. All contributors focus on the common theme of coming back to life as a discursive and descriptive space in which antique peoples construct, maintain, and negotiate the porous boundaries between past and present, mortality and immortality, death and life
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