Habitable Snowballs: Temperate Land Conditions, Liquid Water, and Implications for CO₂ Weathering

Abstract

Habitable planets are commonly imagined to be temperate planets like Earth, with areas of open ocean and warm land. In contrast, planets in snowball states, where oceans are entirely ice covered, are believed to be inhospitable. However, we show using a general circulation model that terrestrial planets in the inner habitable zone are able to support large unfrozen areas of land while in a snowball state. Due to their lower albedo, these unfrozen regions reach summer temperatures in excess of 10 °C. Such conditions permit CO2 weathering, suggesting that continental weathering can provide a mechanism for trapping planets in stable snowball states. The presence of land areas with warm temperatures and liquid surface water motivates a more‐nuanced understanding of habitability during these snowball events.

Laboratory exploration of mineral precipitates from Europa's subsurface ocean

“…However, they will depend on the spectral type of the star, the rotational and orbital properties of the planet, and its geographical characteristics (e.g. Checlair et al, 2017Checlair et al, , 2019Foley, 2019;Paradise et al, 2019;Walsh et al, 2019;Yue & Yang, 2020), while the development and nature of a salt crust will depend on the details of the ocean composition. The abiotic origin of life is arguably the greatest unsolved scientific problem, but thus far has no standard model.…”

Thermodynamic and Energetic Limits on Continental Silicate Weathering Strongly Impact the Climate and Habitability of Wet, Rocky Worlds

“…This was appropriate for a first attempt at understanding the implications of the MAC formulation for planetary weathering behavior, but examination of our conclusions with higherdimensional models would be worthwhile. Previous threedimensional GCM global weathering studies have used the WHAK formulation (e.g., Donnadieu et al 2006;Edson et al 2012;Paradise & Menou 2017;Paradise et al 2020). Expanding beyond our zero-dimensional models would allow us to quantify the importance of things like continental configuration (e.g., Lewis et al 2018), atmospheric circulation (e.g., , clouds , and rotation rate (e.g., Yang et al 2014;Jansen et al 2019) for planetary precipitation, runoff, and weathering behavior.…”

“…Rocky exoplanet climate and habitability studies that include silicate weathering invariably use the WHAK model (e.g., Kite et al 2011;Abbot et al 2012;Edson et al 2012;Watanabe et al 2014;Foley 2015;Menou 2015;Abbot 2016;Batalha et al 2016;Haqq-Misra et al 2016;Paradise & Menou 2017;Ramirez 2018;Rushby et al 2018;Checlair et al 2019b;Paradise et al 2020). However, there are orders-of-magnitude discrepancies between the weathering rates predicted by laboratory silicate dissolution experiments and the weathering rates observed in field studies of silicate weathering (Velbel 1993;Malmström et al 2000;White & Brantley 2003;Maher et al 2006).…”

The Fundamental Connections between the Solar System and Exoplanetary Science

“…As liquid water and energy are both necessary ingredients for life, ocean planets represent prospective habitable environments beyond typical Earth‐like environments in the traditional HZ (Glaser et al., 2020). Indeed, even those such worlds that are mostly ice covered may have considerable regions of unfrozen land near their equators or small, equatorial regions of salt‐rich water where life could flourish (Del Genio et al., 2019; Olson et al., 2020; Paradise et al., 2019).…”