Transition from eyeball to snowball driven by sea-ice drift on tidally locked terrestrial planets

Abstract

Tidally locked terrestrial planets around low-mass stars are the prime targets for future atmospheric characterizations of potentially habitable systems 1 , especially the three nearby ones-Proxima b 2 , TRAPPIST-1e 3 , and LHS 1140b 4 . Previous studies suggest that if these planets have surface ocean they would be in an eyeball-like climate state 5-10 : ice-free in the vicinity of the substellar point and ice-covered in the rest regions. However, an important component of the climate system-sea ice dynamics has not been well studied in previous studies. A fundamental question is: would the open ocean be stable against a globally ice-covered snowball state? Here we show that sea-ice drift cools the ocean's surface when the ice flows to the warmer substellar region and melts through absorbing heat from the ocean and the overlying air. As a result, the open ocean shrinks and can even disappear when atmospheric greenhouse gases are not much more abundant than on Earth, turning the planet into a snowball state. This occurs for both synchronous rotation and spinorbit resonances (such as 3:2). These results suggest that sea-ice drift strongly reduces the open ocean area and can significantly impact the habitability of tidally locked planets.

Planetary system LHS 1140 revisited with ESPRESSO and TESS

“…The habitable-zone planet LHS 1140 b is now known to contain a significant amount of water with a relatively high probability. Previous works have studied the actual state of water layers on the surface of this planet by analyzing the possible eyeball, lobster, or snowball scenarios (Yang et al 2020). Future atmospheric studies with the James Webb Space Telescope and extremely large telescopes will be able to distinguish among these scenarios.…”

Detectability of biosignatures on LHS 1140 b

“…Assuming an Earth-like atmosphere with updated sea-ice paramerization the 3D model study of Yang et al (2020) suggested a reduced surface ocean on LHS 1140 b (from 12% to 3% surface coverage). Diamond-Lowe et al (2020) observed two transits of LHS 1140 b with the twin Magellan Telescopes but their analysis suggested that a precision increased by a factor of about 4 was needed for the detection of e.g.…”

Role of Surface Gravity Waves in Aquaplanet Ocean Climates

“…SGW interactions with sea ice, particularly in the Arctic Ocean, are an important mechanism within large‐scale climate variability and change on Earth (Squire, 2020). Moreover, sea‐ice dynamics have been shown to be of great significance for ocean‐covered exoplanet climate (Yang et al., 2020). Unfortunately, the simulations presented do not have the sea‐ice model dynamically coupled to the SGW model.…”

“…Moreover, sea-ice dynamics have been shown to be of great significance for ocean-covered exoplanet climate (Yang et al, 2020). Unfortunately, the simulations presented do not have the…”

“…However, dynamical aquaplanet ocean models have been applied to study significant climate problems, particularly poleward heat transport (Enderton & Marshall, 2009; Marshall et al., 2007; Salameh et al., 2018; Smith et al., 2006). Most widely they are used to study exoplanet habitability and ocean dynamics (Checlair et al., 2019; Cullum et al., 2016; Del Genio et al., 2019; Ferreira et al., 2014; Fujii et al., 2017; Hu & Yang, 2014; Kane et al., 2018; Salazar et al., 2020; Yang et al., 2019, 2020; Yue & Yang, 2020). We propose that SGWs are relevant to exoplanet ocean dynamics as they are on Earth.…”