157 research outputs found
Optical Properties of Organic Haze Analogues in Water-rich Exoplanet Atmospheres Observable with JWST
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
Laboratory Simulations of Haze Formation in the Atmospheres of super-Earths and mini-Neptunes: Particle Color and Size Distribution
Super-Earths and mini-Neptunes are the most abundant types of planets among
the ~3500 confirmed exoplanets, and are expected to exhibit a wide variety of
atmospheric compositions. 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. However, the compositions, size
distributions, and optical properties of these particles in exoplanet
atmospheres are poorly understood. Here, we present the results of experimental
laboratory investigations of photochemical haze formation within a range of
planetary atmospheric conditions, as well as observations of the color and size
of produced haze particles. We find that atmospheric temperature and
metallicity strongly affect particle color and size, thus altering the
particles' optical properties (e.g., absorptivity, scattering, etc.); on a
larger scale, this affects the atmospheric and surface temperature of the
exoplanets, and their potential habitability. Our results provide constraints
on haze formation and particle properties that can serve as critical inputs for
exoplanet atmosphere modeling, and guide future observations of super-Earths
and mini-Neptunes with the Transiting Exoplanet Survey Satellite (TESS), the
James Webb Space Telescope (JWST), and the Wide-Field Infrared Survey Telescope
(WFIRST).Comment: 19 pages, 4 figures and 1 tabl
Photochemical Haze Formation in the Atmospheres of Super-Earths and Mini-Neptunes
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)
Extinction risk and conservation of the world\u27s sharks and rays
The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world’s ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery
Multi-Messenger Astronomy with Extremely Large Telescopes
The field of time-domain astrophysics has entered the era of Multi-messenger
Astronomy (MMA). One key science goal for the next decade (and beyond) will be
to characterize gravitational wave (GW) and neutrino sources using the next
generation of Extremely Large Telescopes (ELTs). These studies will have a
broad impact across astrophysics, informing our knowledge of the production and
enrichment history of the heaviest chemical elements, constrain the dense
matter equation of state, provide independent constraints on cosmology,
increase our understanding of particle acceleration in shocks and jets, and
study the lives of black holes in the universe. Future GW detectors will
greatly improve their sensitivity during the coming decade, as will
near-infrared telescopes capable of independently finding kilonovae from
neutron star mergers. However, the electromagnetic counterparts to
high-frequency (LIGO/Virgo band) GW sources will be distant and faint and thus
demand ELT capabilities for characterization. ELTs will be important and
necessary contributors to an advanced and complete multi-messenger network.Comment: White paper submitted to the Astro2020 Decadal Surve
Impaired Mineral Ion Metabolism in a Mouse Model of Targeted Calcium-Sensing Receptor (CaSR) Deletion from Vascular Smooth Muscle Cells
Background Impaired mineral ion metabolism is a hallmark of CKD–metabolic bone disorder. It can lead to pathologic vascular calcification and is associated with an increased risk of cardiovascular mortality. Loss of calcium-sensing receptor (CaSR) expression in vascular smooth muscle cells exacerbates vascular calcification in vitro. Conversely, vascular calcification can be reduced by calcimimetics, which function as allosteric activators of CaSR.
Methods To determine the role of the CaSR in vascular calcification, we characterized mice with targeted Casr gene knockout in vascular smooth muscle cells (SM22αCaSRΔflox/Δflox).
Results Vascular smooth muscle cells cultured from the knockout (KO) mice calcified more readily than those from control (wild-type) mice in vitro. However, mice did not show ectopic calcifications in vivo but they did display a profound mineral ion imbalance. Specifically, KO mice exhibited hypercalcemia, hypercalciuria, hyperphosphaturia, and osteopenia, with elevated circulating fibroblast growth factor 23 (FGF23), calcitriol (1,25-D3), and parathyroid hormone levels. Renal tubular α-Klotho protein expression was increased in KO mice but vascular α-Klotho protein expression was not. Altered CaSR expression in the kidney or the parathyroid glands could not account for the observed phenotype of the KO mice.
Conclusions These results suggest that, in addition to CaSR’s established role in the parathyroid-kidney-bone axis, expression of CaSR in vascular smooth muscle cells directly contributes to total body mineral ion homeostasis
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
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