Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Near-term studies of Venus-like atmospheres with <jats:italic>James Webb Space Telescope</jats:italic> (<jats:italic>JWST</jats:italic>) promise to advance our knowledge of terrestrial planet evolution. However, the remote study of Venus in the solar system and the ongoing efforts to characterize gaseous exoplanets both suggest that high altitude aerosols can limit observational studies of lower atmospheres, and potentially make it challenging to recognize exoplanets as “Venus-like.” To support practical approaches for exo-Venus characterization with <jats:italic>JWST</jats:italic>, we use Venus-like atmospheric models with self-consistent cloud formation of the seven TRAPPIST-1 exoplanets to investigate the atmospheric depth that can be probed using both transmission and emission spectroscopy. We find that <jats:italic>JWST</jats:italic>/Mid-IR Instrument Low Resolution Spectrometer secondary eclipse emission spectroscopy in the 6 <jats:italic>μ</jats:italic>m opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the subcloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semimajor axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolation—a convincing false positive for atmospheric escape and an empirical “cosmic shoreline.” However, developing observational and theoretical techniques to identify Venus-like exoplanets and discriminate them from stellar windswept worlds will enable advances in the emerging field of terrestrial comparative planetology.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Results from the <jats:italic>Kepler</jats:italic> mission indicate that the occurrence rate of small planets (&lt;3 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub>) in the habitable zone of nearby low-mass stars may be as high as 80%. Despite this abundance, probing the conditions and atmospheric properties on any habitable-zone planet is extremely difficult and has remained elusive to date. Here, we report the detection of water vapor and the likely presence of liquid and icy water clouds in the atmosphere of the 2.6 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub> habitable-zone planet K2-18b. The simultaneous detection of water vapor and clouds in the mid-atmosphere of K2-18b is particularly intriguing because K2-18b receives virtually the same amount of total insolation from its host star (<jats:inline-formula> <jats:tex-math> <?CDATA ${1368}_{-107}^{+114}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1368</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>107</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>114</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlab59dcieqn1.gif" xlink:type="simple" /> </jats:inline-formula> W m<jats:sup>−2</jats:sup>) as the Earth receives from the Sun (1361 W m<jats:sup>−2</jats:sup>), resulting in the right conditions for water vapor to condense and explain the detected clouds. In this study we observed nine transits of K2-18b using <jats:italic>Hubble Space Telescope</jats:italic>/WFC3 in order to achieve the necessary sensitivity to detect the water vapor, and we supplement this data set with <jats:italic>Spitzer</jats:italic> and <jats:italic>K2</jats:italic> observations to obtain a broader wavelength coverage. While the thick hydrogen-dominated envelope we detect on K2-18b means that the planet is not a true Earth analog, our observations demonstrate that low-mass habitable-zone planets with the right conditions for liquid water are accessible with state-of-the-art telescopes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Atmospheric compositions can provide powerful diagnostics of formation and migration histories of planetary systems. We investigate constraints on atmospheric abundances of H<jats:sub>2</jats:sub>O, Na, and K, in a sample of transiting exoplanets using the latest transmission spectra and new H<jats:sub>2</jats:sub> broadened opacities of Na and K. Our sample of 19 exoplanets spans from cool mini-Neptunes to hot Jupiters, with equilibrium temperatures between ∼300 and 2700 K. Using homogeneous Bayesian retrievals we report atmospheric abundances of Na, K, and H<jats:sub>2</jats:sub>O, and their detection significances, confirming 6 planets with strong Na detections, 6 with K, and 14 with H<jats:sub>2</jats:sub>O. We find a mass–metallicity trend of increasing H<jats:sub>2</jats:sub>O abundances with decreasing mass, spanning generally substellar values for gas giants and stellar/superstellar for Neptunes and mini-Neptunes. However, the overall trend in H<jats:sub>2</jats:sub>O abundances, from mini-Neptunes to hot Jupiters, is significantly lower than the mass–metallicity relation for carbon in the solar system giant planets and similar predictions for exoplanets. On the other hand, the Na and K abundances for the gas giants are stellar or superstellar, consistent with each other, and generally consistent with the solar system metallicity trend. The H<jats:sub>2</jats:sub>O abundances in hot gas giants are likely due to low oxygen abundances relative to other elements rather than low overall metallicities, and provide new constraints on their formation mechanisms. The differing trends in the abundances of species argue against the use of chemical equilibrium models with metallicity as one free parameter in atmospheric retrievals, as different elements can be differently enhanced.</jats:p>