Carbon Cycle Instability for High-CO 2 Exoplanets: Implications for Habitability

The Astrophysical Journal American Astronomical Society 970:1 (2024) 32


RJ Graham, RT Pierrehumbert


Implicit in the definition of the classical circumstellar habitable zone (HZ) is the hypothesis that the carbonate-silicate cycle can maintain clement climates on exoplanets with land and surface water across a range of instellations by adjusting atmospheric CO2 partial pressure (pCO2). This hypothesis is made by analogy to the Earth system, but it is an open question whether silicate weathering can stabilize climate on planets in the outer reaches of the HZ, where instellations are lower than those received by even the Archean Earth and CO2 is thought likely to dominate atmospheres. Since weathering products are carried from land to ocean by the action of water, silicate weathering is intimately coupled to the hydrologic cycle, which intensifies with hotter temperatures under Earth-like conditions. Here, we use global climate model simulations to demonstrate that the hydrologic cycle responds counterintuitively to changes in climate on planets with CO2-H2O atmospheres at low instellations and high pCO2, with global evaporation and precipitation decreasing as pCO2 and temperatures increase at a given instellation. Within the Maher & Chamberlain (or MAC) weathering formulation, weathering then decreases with increasing pCO2 for a range of instellations and pCO2 typical of the outer reaches of the HZ, resulting in an unstable carbon cycle that may lead to either runaway CO2 accumulation or depletion of CO2 to colder (possibly snowball) conditions. While the behavior of the system has not been completely mapped out, the results suggest that silicate weathering could fail to maintain habitable conditions in the outer reaches of the nominal HZ.

Simultaneous retrieval of orbital phase resolved JWST/MIRI emission spectra of the hot Jupiter WASP-43b: Evidence of water, ammonia and carbon monoxide

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2024) stae1427


Jingxuan Yang, Mark Hammond, Anjali AA Piette, Jasmina Blecic, Taylor J Bell, Patrick GJ Irwin, Vivien Parmentier, Shang-Min Tsai, Joanna K Barstow, Nicolas Crouzet, Laura Kreidberg, João M Mendonça, Jake Taylor, Robin Baeyens, Kazumasa Ohno, Lucas Teinturier, Matthew C Nixon

nuance: Efficient Detection of Planets Transiting Active Stars

The Astronomical Journal American Astronomical Society 167:6 (2024) 284


Lionel J Garcia, Daniel Foreman-Mackey, Catriona A Murray, Suzanne Aigrain, Dax L Feliz, Francisco J Pozuelos

TOI-837 b is a young Saturn-sized exoplanet with a massive 70 M⊕ core

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2024) stae1344


Oscar Barragán, Haochuan Yu, Alix Violet Freckelton, Annabella Meech, Michael Cretignier, Annelies Mortier, Suzanne Aigrain, Baptiste Klein, Niamh K O’Sullivan, Edward Gillen, Louise Dyregaard Nielsen, Manuel Mallorquín, Norbert Zicher

Exploring the directly imaged HD 1160 system through spectroscopic characterisation and high-cadence variability monitoring

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2024) stae1315


Ben J Sutlieff, Jayne L Birkby, Jordan M Stone, Annelotte Derkink, Frank Backs, David S Doelman, Matthew A Kenworthy, Alexander J Bohn, Steve Ertel, Frans Snik, Charles E Woodward, Ilya Ilyin, Andrew J Skemer, Jarron M Leisenring, Klaus G Strassmeier, Ji Wang, David Charbonneau, Beth A Biller