1,230 research outputs found
Atmospheric studies of habitability in the Gliese 581 system
The M-type star Gliese 581 is orbited by at least one terrestrial planet
candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown
that additional planets inside the habitable zone of GL 581 would be
dynamically stable. Recently, two further planet candidates have been claimed,
one of them in the habitable zone.
In view of the ongoing search for planets around M stars which is expected to
result in numerous detections of potentially habitable Super-Earths, we take
the GL 581 system as an example to investigate such planets. In contrast to
previous studies of habitability in the GL 581 system, we use a consistent
atmospheric model to assess surface conditions and habitability. Furthermore,
we perform detailed atmospheric simulations for a much larger subset of
potential planetary and atmospheric scenarios than previously considered.
A 1D radiative-convective atmosphere model is used to calculate temperature
and pressure profiles of model atmospheres, which we assumed to be composed of
molecular nitrogen, water, and carbon dioxide. In these calculations, key
parameters such as surface pressure and CO2 concentration as well as orbital
distance and planetary mass are varied.
Results imply that surface temperatures above freezing could be obtained,
independent of the here considered atmospheric scenarios, at an orbital
distance of 0.117 AU. For an orbital distance of 0.146 AU, CO2 concentrations
as low as 10 times the present Earth's value are sufficient to warm the surface
above the freezing point of water. At 0.175 AU, only scenarios with CO2
concentrations of 5% and 95% were found to be habitable. Hence, an additional
Super-Earth planet in the GL 581 system in the previously determined dynamical
stability range would be considered a potentially habitable planet.Comment: 5 pages, 4 figures, accepted in Astronomy&Astrophysic
Clouds in the atmospheres of extrasolar planets. II. Thermal emission spectra of Earth-like planets influenced by low and high-level clouds
We study the impact of multi-layered clouds (low-level water and high-level
ice clouds) on the thermal emission spectra of Earth-like planets orbiting
different types of stars. Clouds have an important influence on such planetary
emission spectra due to their wavelength dependent absorption and scattering
properties. We also investigate the influence of clouds on the ability to
derive information about planetary surface temperatures from low-resolution
spectra.Comment: accepted for publication in A&
Spectral features of Earth-like planets and their detectability at different orbital distances around F, G, and K-type stars
We investigate the spectral appearance of Earth-like exoplanets in the HZ of
different main sequence stars at different orbital distances. We furthermore
discuss for which of these scenarios biomarker absorption bands may be detected
during primary or secondary transit with near-future telescopes and
instruments.We analyze the spectra taking into account different filter
bandpasses of two photometric instruments planned to be mounted to the JWST. We
analyze in which filters and for which scenarios molecular absorption bands are
detectable when using the space-borne JWST or the ground-based telescope E-ELT.
Absorption bands of CO2, H2O, CH4 and O3 are clearly visible in high-resolution
spectra as well as in the filters of photometric instruments. However, only
during primary eclipse bands of CO2, H2O and O3 are detectable for all
scenarios when using photometric instruments and an E-ELT telescope setup. CH4
is only detectable at the outer HZ of the K star since here the atmospheric
modeling results in very high abundances. Since the detectable CO2 and H2O
bands overlap, separate bands need to be observed to prove their existence in
the atmosphere. In order to detect H2O in a separate band, a S/N>7 needs to be
achieved for E-ELT observations, e.g. by co-adding at least 10 transit
observations. Using a spaceborne telescope like the JWST enables the detection
of CO2 at 4.3mu, which is not possible for ground-based observations due to the
Earth's atmospheric absorption. Hence combining observations of spaceborne and
groundbased telescopes might allow to detect the presence of the biomarker
molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere.
Other absorption bands using the JWST can only be detected for much higher
S/Ns, which is not achievable by just co-adding transit observations since this
would be far beyond the planned mission time of JWST.(abridged)Comment: 15 pages, 8 figure
Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology
We compare estimates of atmospheric precipitation during the Martian
Noachian-Hesperian boundary 3.8 Gyr ago as calculated in a radiative-convective
column model of the atmosphere with runoff values estimated from a
geomorphological analysis of dendritic valley network discharge rates. In the
atmospheric model, we assume CO2-H2O-N2 atmospheres with surface pressures
varying from 20 mb to 3 bar with input solar luminosity reduced to 75% the
modern value.
Results from the valley network analysis are of the order of a few mm d-1
liquid water precipitation (1.5-10.6 mm d-1, with a median of 3.1 mm d-1).
Atmospheric model results are much lower, from about 0.001-1 mm d-1 of snowfall
(depending on CO2 partial pressure). Hence, the atmospheric model predicts a
significantly lower amount of precipitated water than estimated from the
geomorphological analysis. Furthermore, global mean surface temperatures are
below freezing, i.e. runoff is most likely not directly linked to
precipitation. Therefore, our results strongly favor a cold early Mars with
episodic snowmelt as a source for runoff.
Our approach is challenged by mostly unconstrained parameters, e.g.
greenhouse gas abundance, global meteorology (for example, clouds) and
planetary parameters such as obliquity- which affect the atmospheric result -
as as well as by inherent problems in estimating discharge and runoff on
ancient Mars, such as a lack of knowledge on infiltration and evaporation rates
and on flooding timescales, which affect the geomorphological data.
Nevertheless, our work represents a first step in combining and interpreting
quantitative tools applied in early Mars atmospheric and geomorphological
studies.Comment: accepted in Planetary and Space Science, 37 pages, 14 figures, 2
table
Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star
Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to
high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in
earthlike atmospheres. We investigate to what extent this NOx may modify
biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as
related compounds such as water (H2O) (essential for life) and methane (CH4)
(which has both abiotic and biotic sources) . Our model results suggest that
such signals are robust, changing in the M-star world atmospheric column by up
to 20% due to the GCR NOx effects compared to an M-star run without GCR effects
and can therefore survive at least the effects of galactic cosmic rays. We have
not however investigated stellar cosmic rays here. CH4 levels are about 10
times higher than on the Earth related to a lowering in hydroxyl (OH) in
response to changes in UV. The increase is less than reported in previous
studies. This difference arose partly because we used different biogenic input.
For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike
on the Earth, relatively modest changes in these fluxes can lead to larger
changes in the concentrations of biomarker and related species on the M-star
world. We calculate a CH4 greenhouse heating effect of up to 4K. O3
photochemistry in terms of the smog mechanism and the catalytic loss cycles on
the M-star world differs considerably compared with the Earth
The extrasolar planet Gliese 581 d: a potentially habitable planet? (Corrigendum to arXiv:1009.5814)
We report here that the equation for H2O Rayleigh scattering was incorrectly
stated in the original paper [arXiv:1009.5814]. Instead of a quadratic
dependence on refractivity r, we accidentally quoted an r^4 dependence. Since
the correct form of the equation was implemented into the model, scientific
results are not affected.Comment: accepted to Astronomy&Astrophysic
Parameterization dependence of T matrix poles and eigenphases from a fit to piN elastic scattering data
We compare fits to piN elastic scattering data, based on a Chew-Mandelstam
K-matrix formalism. Resonances, characterized by T-matrix poles, are compared
in fits generated with and without explicit Chew-Mandelstam K-matrix poles.
Diagonalization of the S matrix yields the eigenphase representation. While the
eigenphases can vary significantly for the different parameterizations, the
locations of most T-matrix poles are relatively stable.Comment: 6 pages, 3 figures, 1 tabl
N2-associated surface warming on early Mars
Early Mars may have had a warmer and denser atmosphere allowing for the
presence of liquid water on the surface. However, climate model studies have
not been able to reproduce these conditions even with a CO2 atmosphere of
several bars. Recent 3D simulations of the early Mars climate show that mean
surface temperatures only slightly below 273K could be reached locally.
We want to investigate the effect of increased partial pressures of N2 on
early Mars' surface temperature by including pressure broadening of absorption
lines and collision-induced N2-N2 absorption.
A 1D radiative-convective cloud-free atmospheric model was used to calculate
temperature profiles and surface conditions. We performed a parameter study
varying the N2 partial pressures from 0 to 0.5bar at CO2 partial pressures
between 0.02bar and 3bar. These values are consistent with existing estimates
of the initial, pre-Noachian reservoir. Solar insolation was set to be
consistent with the late Noachian.
Our 1D global mean simulations clearly show that enhanced N2 content in the
Martian atmosphere could have increased surface temperatures. An additional
greenhouse warming of up to 13K was found at a high N2 partial pressure of
0.5bar. Still, even at this N2 partial pressure, global mean surface
temperatures remained below 273K, i.e. the freezing point of water. However,
given the magnitude of the N2-induced surface warming and the results of recent
3D studies which show that local mean surface temperatures are not much lower
than 273K, our results imply that the presence of atmospheric N2 could have led
to almost continously habitable mean surface conditions in some regions. In
addition, atmospheric water column amounts increased by up to a factor of 6 in
response to the surface warming, indicating that precipitation might also
increase upon increasing N2 partial pressure.Comment: 6 pages, 3 figures, accepted for publication in Planetary and Space
Scienc
Clouds in the atmospheres of extrasolar planets. I. Climatic effects of multi-layered clouds for Earth-like planets and implications for habitable zones
The effects of multi-layered clouds in the atmospheres of Earth-like planets
orbiting different types of stars are studied. The radiative effects of cloud
particles are directly correlated with their wavelength-dependent optical
properties. Therefore the incident stellar spectra may play an important role
for the climatic effect of clouds. We discuss the influence of clouds with mean
properties measured in the Earth's atmosphere on the surface temperatures and
Bond albedos of Earth-like planets orbiting different types of main sequence
dwarf stars.Comment: accepted for publication in A&
La construcción de la autoridad judicial: una comparación entre la Corte Constitucional italiana y el Tribunal Constitucional Federal alemán
Este artículo examina los fundamentos de la autoridad de la Corte Constitucional italiana comparándola con la del Tribunal Constitucional Federal alemán. En comparación con el Tribunal alemán, la Corte italiana ha construido su autoridad sobre una base particularmente débil. Sin embargo, ha tenido éxito en desarrollar una dinámica de “poder en la debilidad”, que explica importantes características de la Corte Constitucional italiana: su relación excepcionalmente cooperativa con los tribunales ordinarios, su estilo conciso de razonamiento, su deliberado bajo perfil frente a la opinión pública, su interacción activista con el legislador y su diálogo táctico con el Tribunal de Justicia de la Unión Europea
- …