title: Exoplanet dynamics. Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars.
abstract: Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets' rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar mass. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere.
authors.affiliation: Canadian Institute for Theoretical Astrophysics, 60 St George Street, University of Toronto, Toronto, ON M5S3H8, Canada. Center for Planetary Sciences, Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada. Laboratoire de Météorologie Dynamique, Institut Pierre Simon Laplace, 4 Place Jussieu, BP 99, 75252 Paris, France. jleconte@cita.utoronto.ca.
authors.forename: Jérémy
authors.initials: J
authors.lastname: Leconte
authors.affiliation: Canadian Institute for Theoretical Astrophysics, 60 St George Street, University of Toronto, Toronto, ON M5S3H8, Canada. Department of Physics, University of Toronto, 60 St George Street, Toronto, ON M5S 1A7, Canada.
authors.forename: Hanbo
authors.initials: H
authors.lastname: Wu
authors.affiliation: Center for Planetary Sciences, Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada. Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada.
authors.forename: Kristen
authors.initials: K
authors.lastname: Menou
authors.affiliation: Canadian Institute for Theoretical Astrophysics, 60 St George Street, University of Toronto, Toronto, ON M5S3H8, Canada. Department of Physics, University of Toronto, 60 St George Street, Toronto, ON M5S 1A7, Canada.
authors.forename: Norman
authors.initials: N
authors.lastname: Murray