Eccentric orbits may enhance the habitability of Earth-like exoplanets

The detection and characterization of Earth-like planets around Sun-like
stars is a crucial goal of exoplanetary research, given their promise for
hosting potentially habitable conditions. Key orbital parameters, such as
eccentricity, can influence a planet's climate response and, as a
consequence, affect its potential habitability. Utilizing the Earth-system
model - the Whole Atmosphere Community Climate Model (WACCM6), we
simulated Earth-like exoplanets with two different orbital parameters: one
circular (e = 0) and another highly eccentric (e = 0.4), both with zero
obliquity but fixing the annual mean insolation. The highly eccentric case
exhibits a 1.9 K warmer surface temperature due to lower surface and cloud
albedo and a weaker longwave cloud forcing. Exploring the annual global
mean climate difference, we analyzed latitudinal and seasonal variations
in hydrological cycle variables, such as sea ice, land snow, and clouds.
Land habitability metrics based on temperature and precipitation reveal
that the e=0.4 case has over 25% more habitable land area for more than
80% of its orbit compared with the e=0 case. Additionally, the global
circulation pattern shifts from a three-cell to a two-cell system in the
e=0.4 case, expanding the Hadley cell to higher latitudes, enhancing
meridional latent heat transport, and improving land habitability at
higher latitudes. Our study suggests that Earth-like exoplanets with high
eccentricity orbiting Sun-like stars may have greater land habitability
than their circular counterparts.