5 research outputs found
THOR 2.0: Major Improvements to the Open-Source General Circulation Model
THOR is the first open-source general circulation model (GCM) developed from
scratch to study the atmospheres and climates of exoplanets, free from Earth-
or Solar System-centric tunings. It solves the general non-hydrostatic Euler
equations (instead of the primitive equations) on a sphere using the
icosahedral grid. In the current study, we report major upgrades to THOR,
building upon the work of Mendon\c{c}a et al. (2016). First, while the
Horizontally Explicit Vertically Implicit (HEVI) integration scheme is the same
as that described in Mendon\c{c}a et al. (2016), we provide a clearer
description of the scheme and improved its implementation in the code. The
differences in implementation between the hydrostatic shallow (HSS),
quasi-hydrostatic deep (QHD) and non-hydrostatic deep (NHD) treatments are
fully detailed. Second, standard physics modules are added: two-stream,
double-gray radiative transfer and dry convective adjustment. Third, THOR is
tested on additional benchmarks: tidally-locked Earth, deep hot Jupiter,
acoustic wave, and gravity wave. Fourth, we report that differences between the
hydrostatic and non-hydrostatic simulations are negligible in the Earth case,
but pronounced in the hot Jupiter case. Finally, the effects of the so-called
"sponge layer", a form of drag implemented in most GCMs to provide numerical
stability, are examined. Overall, these upgrades have improved the flexibility,
user-friendliness, and stability of THOR.Comment: 57 pages, 31 figures, revised, accepted for publication in ApJ
The THOR+HELIOS general circulation model: multi-wavelength radiative transfer with accurate scattering by clouds/hazes
General circulation models (GCMs) provide context for interpreting
multi-wavelength, multi-phase data of the atmospheres of tidally locked
exoplanets. In the current study, the non-hydrostatic THOR GCM is coupled with
the HELIOS radiative transfer solver for the first time, supported by an
equilibrium chemistry solver (FastChem), opacity calculator (HELIOS-K) and Mie
scattering code (LX-MIE). To accurately treat the scattering of radiation by
medium-sized to large aerosols/condensates, improved two-stream radiative
transfer is implemented within a GCM for the first time. Multiple scattering is
implemented using a Thomas algorithm formulation of the two-stream flux
solutions, which decreases the computational time by about 2 orders of
magnitude compared to the iterative method used in past versions of HELIOS. As
a case study, we present four GCMs of the hot Jupiter WASP-43b, where we
compare the temperature, velocity, entropy, and streamfunction, as well as the
synthetic spectra and phase curves, of runs using regular versus improved
two-stream radiative transfer and isothermal versus non-isothermal layers.
While the global climate is qualitatively robust, the synthetic spectra and
phase curves are sensitive to these details. A THOR+HELIOS WASP-43b GCM
(horizontal resolution of about 4 degrees on the sphere and with 40 radial
points) with multi-wavelength radiative transfer (30 k-table bins) running for
3000 Earth days (864,000 time steps) takes about 19-26 days to complete
depending on the type of GPU.Comment: 31 pages, 24 figures, accepted for publication at MNRA
The THOR + HELIOS general circulation model: multiwavelength radiative transfer with accurate scattering by clouds/hazes
General circulation models (GCMs) provide context for interpreting multiwavelength, multiphase data of the atmospheres of tidally locked exoplanets. In the current study, the non-hydrostatic THOR GCM is coupled with the HELIOS radiative transfer solver for the first time, supported by an equilibrium chemistry solver (FastChem), opacity calculator (HELIOS-K), and Mie scattering code (LX-MIE). To accurately treat the scattering of radiation by medium-sized to large aerosols/condensates, improved two-stream radiative transfer is implemented within a GCM for the first time. Multiple scattering is implemented using a Thomas algorithm formulation of the two-stream flux solutions, which decreases the computational time by about 2 orders of magnitude compared to the iterative method used in past versions of HELIOS. As a case study, we present four GCMs of the hot Jupiter WASP-43b, where we compare the temperature, velocity, entropy, and streamfunction, as well as the synthetic spectra and phase curves, of runs using regular versus improved two-stream radiative transfer and isothermal versus non-isothermal layers. While the global climate is qualitatively robust, the synthetic spectra and phase curves are sensitive to these details. A THOR + HELIOS WASP-43b GCM (horizontal resolution of about 4 deg on the sphere and with 40 radial points) with multiwavelength radiative transfer (30 k-table bins) running for 3000 Earth days (864 000 time-steps) takes about 19–26 d to complete depending on the type of GPU
Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3
Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project’s detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet’s high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy