44 research outputs found
Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets
Recent studies have shown that ocean dynamics can have a significant warming
effect on the permanent night sides of 1 to 1 tidally locked terrestrial
exoplanets with Earth-like atmospheres and oceans in the middle of the
habitable zone. However, the impact of ocean dynamics on the habitable zone's
boundaries (inner edge and outer edge) is still unknown and represents a major
gap in our understanding of this type of planets. Here we use a coupled
atmosphere-ocean global climate model to show that planetary heat transport
from the day to night side is dominated by the ocean at lower stellar fluxes
and by the atmosphere near the inner edge of the habitable zone. This decrease
in oceanic heat transport (OHT) at high stellar fluxes is mainly due to
weakening of surface wind stress and a decrease in surface shortwave energy
deposition. We further show that ocean dynamics have almost no effect on the
observational thermal phase curves of planets near the inner edge of the
habitable zone. For planets in the habitable zone's middle range, ocean
dynamics moves the hottest spot on the surface eastward from the substellar
point. These results suggest that future studies of the inner edge may devote
computational resources to atmosphere-only processes such as clouds and
radiation. For studies of the middle range and outer edge of the habitable
zone, however, fully coupled ocean-atmosphere modeling will be necessary. Note
that due to computational resource limitations, only one rotation period (60
Earth days) has been systematically examined in this study; future work varying
rotation period as well as other parameters such as atmospheric mass and
composition is required.Comment: 34 pages, 13 figures, and 1 tabl
Super-Earth LHS3844b is tidally locked
Short period exoplanets on circular orbits are thought to be tidally locked
into synchronous rotation. If tidally locked, these planets must possess
permanent day- and nightsides, with extreme irradiation on the dayside and none
on the nightside. However, so far the tidal locking hypothesis for exoplanets
is supported by little to no empirical evidence. Previous work showed that the
super-Earth LHS 3844b likely has no atmosphere, which makes it ideal for
constraining the planet's rotation. Here we revisit the Spitzer phase curve of
LHS 3844b with a thermal model of an atmosphere-less planet and analyze the
impact of non-synchronous rotation, eccentricity, tidal dissipation, and
surface composition. Based on the lack of observed strong tidal heating we rule
out rapid non-synchronous rotation (including a Mercury-like 3:2 spin-orbit
resonance) and constrain the planet's eccentricity to less than 0.001 (more
circular than Io's orbit). In addition, LHS 3844b's phase curve implies that
the planet either still experiences weak tidal heating via a small-but-nonzero
eccentricity (requiring an undetected orbital companion), or that its surface
has been darkened by space weathering; of these two scenarios we consider space
weathering more likely. Our results thus support the hypothesis that short
period rocky exoplanets are tidally locked, and further show that space
weathering can significantly modify the surfaces of atmosphere-less exoplanets.Comment: Accepte
The dependence of transient climate sensitivity and radiative feedbacks on the spatial pattern of ocean heat uptake
The effect of ocean heat uptake (OHU) on transient global warming is studied in a multimodel framework. Simple heat sinks are prescribed in shallow aquaplanet ocean mixed layers underlying atmospheric general circulation models independently and combined with CO_2 forcing. Sinks are localized to either tropical or high latitudes, representing distinct modes of OHU found in coupled simulations. Tropical OHU produces modest cooling at all latitudes, offsetting only a fraction of CO_2 warming. High-latitude OHU produces three times more global mean cooling in a strongly polar-amplified pattern. Global sensitivities in each scenario are set primarily by large differences in local shortwave cloud feedbacks, robust across models. Differences in atmospheric energy transport set the pattern of temperature change. Results imply that global and regional warming rates depend sensitively on regional ocean processes setting the OHU pattern, and that equilibrium climate sensitivity cannot be reliably estimated from transient observations