Atmospheric Retrievals of the Phase-resolved Spectra of Irradiated Brown Dwarfs WD-0137B and EPIC-2122B

The Astrophysical Journal American Astronomical Society 968:2 (2024) 126

Authors:

Joshua D Lothringer, Yifan Zhou, Dániel Apai, Xianyu Tan, Vivien Parmentier, Sarah L Casewell

Does 'net zero' mean zero cows?

The Bulletin of the atomic scientists Taylor & Francis 80:3 (2024) 153-157

Authors:

John Lynch, Raymond Pierrehumbert

Abstract:

A significant share of anthropogenic global warming comes from livestock production. There is debate about whether there can be any role for livestock in a climatically sustainable future; the debate is particularly heated for cows and sheep, largely due to the methane they burp out. However, short-lived gases like methane affect climate in a fundamentally different way than long-lived gases like carbon dioxide. Consequently, climate stabilization does not require zeroing-out cattle herds. But this doesn't mean we can eat our beef and have it (a tolerable climate) too-livestock still contribute to global warming. Preventing or limiting future growth in livestock-related emissions can represent a sensible part of the portfolio of responses to the climate crisis, particularly when carbon dioxide emissions are not on track to reach net zero sufficiently quickly.

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

The Astrophysical Journal Letters American Astronomical Society 966:2 (2024) L24

Authors:

Shang-Min Tsai, Hamish Innes, Nicholas F Wogan, Edward W Schwieterman

Abstract:

Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (≳20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH4, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C2H4) and ethane (C2H6), in the mid-infrared between 9 and 13 μm.

Time-resolved Hubble Space Telescope Wide Field Camera 3 Spectrophotometry Reveals Inefficient Day-to-night Heat Redistribution in the Highly Irradiated Brown Dwarf SDSS 1557B

The Astrophysical Journal American Astronomical Society 966:1 (2024) 4

Authors:

Rachael C Amaro, Dániel Apai, Ben WP Lew, Yifan Zhou, Joshua D Lothringer, Sarah L Casewell, Xianyu Tan, Travis Barman, Mark S Marley, LC Mayorga, Vivien Parmentier

Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b

Nature Astronomy Nature Research 8:7 (2024) 879-898

Authors:

Taylor J Bell, Nicolas Crouzet, Patricio E Cubillos, Laura Kreidberg, Anjali AA Piette, Michael T Roman, Joanna K Barstow, Jasmina Blecic, Ludmila Carone, Louis-Philippe Coulombe, Elsa Ducrot, Mark Hammond, João M Mendonça, Julianne I Moses, Vivien Parmentier, Kevin B Stevenson, Lucas Teinturier, Michael Zhang, Natalie M Batalha, Jacob L Bean, Björn Benneke, Benjamin Charnay, Katy L Chubb, Brice-Olivier Demory, Xianyu Tan

Abstract:

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5 μm to 12 μm with the JWST’s Mid-Infrared Instrument. The spectra reveal a large day–night temperature contrast (with average brightness temperatures of 1,524 ± 35 K and 863 ± 23 K, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase-curve shape and emission spectra strongly suggest the presence of nightside clouds that become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1–6 ppm, depending on model assumptions). Our results provide strong evidence that the atmosphere of WASP-43b is shaped by disequilibrium processes and provide new insights into the properties of the planet’s nightside clouds. However, the remaining discrepancies between our observations and our predictive atmospheric models emphasize the importance of further exploring the effects of clouds and disequilibrium chemistry in numerical models.