53 research outputs found
The three regimes of atmospheric evaporation for super-Earths and sub-Neptunes
A significant fraction of super-Earths and sub-Neptunes are thought to
experience an extreme loss of volatiles because of atmospheric evaporation in
the early stages of their life. Though the mechanisms behind the extreme mass
loss are not fully understood, two contenders have been widely discussed:
photoevaporation from X-ray and ultraviolet irradiation and core powered mass
loss. Here, it is shown that both mechanisms occur but with different
timescales, and that atmospheric loss can take place over three regimes. In the
first regime, a planet has very high internal temperatures arising from its
high-energy formation processes. These high temperatures give rise to a fully
convecting atmosphere that efficiently loses mass without much internal
cooling. The second regime applies to planets with lower internal temperatures,
so a radiative region forms but the photosphere still remains outside the Bondi
radius. Hence, mass loss continues to depend only on the internal temperatures.
Planets with the lowest internal temperatures are in the third regime, when the
photosphere forms below the Bondi radius and mass is lost primarily because of
X-ray and ultraviolet irradiation. This paper provides the first unifying
framework for modeling atmospheric evaporation through the lifespan of a
planet.Comment: 37 pages, 13 figures, 2023 ApJ 943 1
RAPOC : the Rosseland and Planck opacity converter. A user-friendly and fast opacity program for Python
RAPOC (Rosseland and Planck Opacity Converter) is a Python 3 code that
calculates Rosseland and Planck mean opacities (RPMs) from wavelength-dependent
opacities for a given temperature, pressure, and wavelength range. In addition
to being user-friendly and rapid, RAPOC can interpolate between discrete data
points, making it flexible and widely applicable to the astrophysical and
Earth-sciences fields, as well as in engineering. For the input data, RAPOC can
use ExoMol and DACE data, or any user-defined data, provided that it is in a
readable format. In this paper, we present the RAPOC code and compare its
calculated Rosseland and Planck mean opacities with other values found in the
literature. The RAPOC code is open-source and available on Pypi and GitHub.Comment: 15 pages, 6 figures, 3 tables; Accepted for Publication in Exp.
Astro
Hot Super-Earths with Hydrogen Atmospheres: A Model Explaining Their Paradoxical Existence
In this paper we propose a new mechanism that could explain the survival of
hydrogen atmospheres on some hot super-Earths. We argue that on close-orbiting
tidally-locked super-Earths the tidal forces with the orbital and rotational
centrifugal forces can partially confine the atmosphere on the nightside.
Assuming a super terran body with an atmosphere dominated by volcanic species
and a large hydrogen component, the heavier molecules can be shown to be
confined within latitudes of whilst the volatile hydrogen
is not. Because of this disparity the hydrogen has to slowly diffuse out into
the dayside where XUV irradiation destroys it. For this mechanism to take
effect it is necessary for the exoplanet to become tidally locked before losing
the totality of its hydrogen envelop. Consequently, for super-Earths with this
proposed configuration it is possible to solve the tidal-locking and mass-loss
timescales in order to constrain their formation `birth' masses. Our model
predicts that 55 Cancri e formed with a day-length between approximately
hours and an initial mass less than hence
allowing it to become tidally locked before the complete destruction of its
atmosphere. For comparison, CoRoT-7b, an exoplanet with very similar properties
to 55 Cancri e but lacking an atmosphere, formed with a day-length
significantly different from hours whilst also having an initial
mass smaller than Comment: 20 pages, 15 figure
Exploring Super-Earth Surfaces: Albedo of Near-Airless Magma Ocean Planets and Topography
In this paper we propose an analytic function for the spherical albedo values
of airless and near-airless magma ocean planets (AMOPs). We generated 2-D
fractal surfaces with varying compositions onto which we individually threw
10,000 light rays. Using an approximate form of the Fresnel equations we
measured how much of the incident light was reflected. Having repeated this
algorithm on varying surface roughnesses we find the spherical albedo as a
function of the Hurst exponent, the geochemical composition of the magma, and
the wavelength. As a proof of concept, we used our model on Kepler-10b to
demonstrate the applicability of our approach. We present the spherical albedo
values produced from different lava compositions and multiple tests that can be
applied to observational data in order to determine their characteristics.
Currently, there is a strong degeneracy in the surface composition of AMOPs due
to the large uncertainties in their measured spherical albedos. In spite of
this, when applied to Kepler-10b we show that its high albedo could be caused
by a moderately wavy ocean that is rich in oxidised metallic species such as
FeO, , . This would imply that Kepler-10b is
a coreless or near-coreless body
GJ 357 b: A Super-Earth Orbiting an Extremely Inactive Host Star
In this paper we present a deep X-ray observation of the nearby M dwarf GJ
357 and use it to put constraints on the atmospheric evolution of its planet,
GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ
357 in order to see how they affect the perceived planetary properties. We
estimate the age of GJ 357 b by comparing the observed X-ray luminosity of its
host star, derived from a recent {\em XMM-Newton} observation {(), with age relations for M dwarfs. We
find that GJ 357 presents one of the lowest X-ray activity levels ever measured
for an M dwarf, and we put a lower limit on its age of \,Gyr.} Using this
age limit, we perform a backwards reconstruction of the original primordial
atmospheric reservoir. Furthermore, by considering the systematic errors in the
stellar parameters, we find a range of possible planetary masses, radii, and
densities. From the backwards reconstruction of GJ 357 b's irradiation history
we find that the upper limit of its initial primordial atmospheric mass is
. An initial atmospheric reservoir significantly larger
than this may have survived through the X-ray and ultraviolet irradiation
history, hence being inconsistent with current observations that suggest a
telluric composition. In spite of the unlikelihood of a currently existing
primordial envelope, volcanism and outgassing may have contributed to a
secondary atmosphere. Under this assumption, we present three different
synthetic infrared spectra for GJ 357 b that one might expect, consisting of
, , and , and .Comment: Accepted for publication in A&
Exploring the potential of using a text-based game to inform simulation models of risky migration decisions
Background:
In this paper, we explore the potential of games to collect empirical data for informing agent-based simulation models of migration. To examine the usefulness of game-based approaches, we conducted a simple, yet carefully designed psychological experiment.
Methods:
In a preregistered study, we used a novel, immersive experimental setting to investigate the risky migration decisions made by migrants and non-migrants. Participants (284 migrants and 284 non-migrants) played a choice-based interactive fiction game—a fully text-based game where players progress by selecting from a list of possible actions—that involved making three risky migration decisions. In one condition, participants were shown a non-linear progress bar and explicit acknowledgements of the choices they made to promote perceived agency: the feeling that one’s actions have a non-trivial impact on the game. In the other condition, the progress bar was linear, and the explicit acknowledgements were omitted.
Results:
Our experimental manipulation was successful; participants in the former condition self-reported higher perceived agency than participants in the latter condition, as did migrants compared to non-migrants. Nevertheless, condition and migrant status did not meaningfully affect the risky migration decisions participants made in the game.
Conclusion:
These findings indicate that the results of generic studies on risky migration decisions conducted on non-migrants can potentially inform simulation models of migration. However, these findings were obtained from a single experiment, and thus warrant replication and further research before definitive conclusions can be drawn. Furthermore, a simple text-based game may be too superficial to allow deep insights into the idiosyncrasies of migration decision-making. This suggests a possible trade-off between clear interpretability of the results and the usefulness for informing simulation models of complex social processes, such as migration
Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b
We performed a radial velocity (RV) monitoring of the 40 Myr old star DS Tuc
A with HARPS at the ESO-3.6m to determine the planetary mass of its 8.14-days
planet, first revealed by TESS. We also observed two planetary transits with
HARPS and ESPRESSO at ESO-VLT, to measure the Rossiter-McLaughlin (RM) effect
and characterise the planetary atmosphere. We measured the high-energy emission
of the host with XMM observations to investigate models for atmospheric
evaporation. We employed Gaussian Processes (GP) regression to model the high
level of the stellar activity, which is more than 40 times larger than the
expected RV planetary signal. We extracted the transmission spectrum of DS Tuc
A b from the ESPRESSO data and searched for atmospheric elements/molecules
either by single-line retrieval and by performing cross-correlation with a set
of theoretical templates. Through a set of simulations, we evaluated different
scenarios for the atmospheric photo-evaporation of the planet induced by the
strong XUV stellar irradiation. While the stellar activity prevented us from
obtaining a clear detection of the planetary signal from the RVs, we set a
robust mass upper limit of 14.4 M_e for DS Tuc A b. We also confirm that the
planetary system is almost (but not perfectly) aligned. The strong level of
stellar activity hampers the detection of any atmospheric compounds, in line
with other studies presented in the literature. The expected evolution of DS
Tuc A b from our grid of models indicates that the planetary radius after the
photo-evaporation phase will fall within the Fulton gap. The comparison of the
available parameters of known young transiting planets with the distribution of
their mature counterpart confirms that the former are characterised by a low
density, with DS Tuc A b being one of the less dense.Comment: 24 pages, 19 figures, Accepted for publication on Astronomy and
Astrophysic
ARES. III. Unveiling the Two Faces of KELT-7 b with HST WFC3*
We present the analysis of the hot-Jupiter KELT-7 b using transmission and emission spectroscopy from the Hubble Space Telescope, both taken with the Wide Field Camera 3. Our study uncovers a rich transmission spectrum that is consistent with a cloud-free atmosphere and suggests the presence of H_{2}O and H^{−}. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature–pressure profile, collision induced absorption, and H^{-}. KELT-7 b had also been studied with other space-based instruments and we explore the effects of introducing these additional data sets. Further observations with Hubble, or the next generation of space-based telescopes, are needed to allow for the optical opacity source in transmission to be confirmed and for molecular features to be disentangled in emission
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