Enhanced Habitability on High Obliquity Bodies near the Outer Edge of the Habitable Zone of Sun-like Stars. (arXiv:1905.09398v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Colose_C/0/1/0/all/0/1">Christopher M. Colose</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Genio_A/0/1/0/all/0/1">Anthony D. Del Genio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Way_M/0/1/0/all/0/1">Michael J. Way</a>
High obliquity planets represent potentially extreme limits of terrestrial
climate, as they exhibit large seasonality, a reversed annual-mean
pole-to-equator gradient of stellar heating, and novel cryospheres. A suite of
3-D global climate model simulations with a dynamic ocean is performed with
Earthlike atmospheres for low and high obliquity planets with various stellar
fluxes, CO2 concentrations, and initial conditions to explore the propensity
for high obliquity climates approaching the outer edge of the Habitable Zone to
undergo global glaciation. We also simulate planets with thick CO2 or H2
atmospheres, such as those expected to develop near or beyond the outer edge of
the Habitable Zone.
We show that high obliquity planets are hotter than their low obliquity
counterparts due to ice-albedo feedbacks for cold climates, and water vapor in
warm climates. We suggest that the water vapor greenhouse trapping is greater
on high obliquity bodies due to the different dynamical regimes that occur
between the two states.
While equatorial ice-belts are stable at high obliquity in some climate
regimes, it is harder to achieve global glaciation than for a low obliquity
planet. Temperate polar conditions can be present at high obliquity at forcings
for which low obliquity planets would be in a hard snowball state. We suggest
the conditions on high obliquity planets are likely to be more favorable for a
robust biosphere to develop approaching the outer edge of the HZ. However, the
influence of obliquity diminishes for dense atmospheres, in agreement with
calculations from 1-D Energy Balance Models.
High obliquity planets represent potentially extreme limits of terrestrial
climate, as they exhibit large seasonality, a reversed annual-mean
pole-to-equator gradient of stellar heating, and novel cryospheres. A suite of
3-D global climate model simulations with a dynamic ocean is performed with
Earthlike atmospheres for low and high obliquity planets with various stellar
fluxes, CO2 concentrations, and initial conditions to explore the propensity
for high obliquity climates approaching the outer edge of the Habitable Zone to
undergo global glaciation. We also simulate planets with thick CO2 or H2
atmospheres, such as those expected to develop near or beyond the outer edge of
the Habitable Zone.
We show that high obliquity planets are hotter than their low obliquity
counterparts due to ice-albedo feedbacks for cold climates, and water vapor in
warm climates. We suggest that the water vapor greenhouse trapping is greater
on high obliquity bodies due to the different dynamical regimes that occur
between the two states.
While equatorial ice-belts are stable at high obliquity in some climate
regimes, it is harder to achieve global glaciation than for a low obliquity
planet. Temperate polar conditions can be present at high obliquity at forcings
for which low obliquity planets would be in a hard snowball state. We suggest
the conditions on high obliquity planets are likely to be more favorable for a
robust biosphere to develop approaching the outer edge of the HZ. However, the
influence of obliquity diminishes for dense atmospheres, in agreement with
calculations from 1-D Energy Balance Models.
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