196 research outputs found
Methane release on Early Mars by atmospheric collapse and atmospheric reinflation
A candidate explanation for Early Mars rivers is atmospheric warming due to
surface release of H or CH gas. However, it remains unknown how much
gas could be released in a single event. We model the CH release by one
mechanism for rapid release of CH from clathrate. By modeling how
CH-clathrate release is affected by changes in Mars' obliquity and
atmospheric composition, we find that a large fraction of total outgassing from
CH clathrate occurs following Mars' first prolonged atmospheric collapse.
This atmosphere-collapse-initiated CH-release mechanism has three stages.
(1) Rapid collapse of Early Mars' carbon dioxide atmosphere initiates a slower
shift of water ice from high ground to the poles. (2) Upon subsequent
CO-atmosphere re-inflation and CO-greenhouse warming, low-latitude
clathrate decomposes and releases methane gas. (3) Methane can then perturb
atmospheric chemistry and surface temperature, until photochemical processes
destroy the methane. Within our model, we find that under some circumstances a
Titan-like haze layer would be expected to form, consistent with transient
deposition of abundant complex abiotic organic matter on the Early Mars
surface. We also find that this CH-release mechanism can warm Early Mars,
but special circumstances are required in order to uncork 10 kg of
CH, the minimum needed for strong warming. Specifically, strong warming
only occurs when the fraction of the hydrate stability zone that is initially
occupied by clathrate exceeds 10%, and when Mars' first prolonged atmospheric
collapse occurs for atmospheric pressure > 1 bar.Comment: Accepted by Planetary and Space Scienc
First exploration of the runaway greenhouse transition with a GCM
Even if their detection is for now challenging, observation of small
terrestrial planets will be easier in a near future thanks to continuous
improvements of detection and characterisation instruments. In this quest,
climate modeling is a key step to understand their characteristics, atmospheric
composition and possible history. If a surface water reservoir is present on
such a terrestrial planet, an increase in insolation may lead to a dramatic
positive feedback induced by water evaporation: the runaway greenhouse. The
resulting rise of global surface temperature leads to the evaporation of the
entire water reservoir, separating two very different population of planets: 1)
temperate planets with a surface water ocean and 2) hot planets with a puffed
atmosphere dominated by water vapor. In this work we use a 3D General
Circulation Model (GCM), the Generic-PCM, to study the runaway greenhouse
transition, linking temperate and post-runaway states. Our simulations are made
of two steps. First, assuming initially a liquid surface ocean, an evaporation
phase which enriches the atmosphere in water vapor. Second, when the ocean is
considered entirely evaporated, a dry transition phase for which the surface
temperature increases dramatically. Finally, it converges on a hot and stable
post-runaway state. By describing in detail the evolution of the climate during
these two steps, we show a rapid transition of the cloud coverage and of the
wind circulation from the troposphere to the stratosphere. By comparing our
result to previous studies using 1D models, we discuss the effect of
intrinsically 3D processes such as the global dynamics and the clouds, keys to
understand the runaway greenhouse. We also explore the potential reversibility
of the runaway greenhouse, limited by its radiative unbalance.Comment: 15 pages, 17 figures, accepted for publication in A&
The CO2 âbroadened H2O continuum in the 100â1500 cm -1 region: Measurements, predictions and empirical model
Transmission spectra of H2O + CO2 mixtures have been recorded, at 296, 325 and 366 K, for various pres- sures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the âcontinuumâabsorption by the CO2 -broadened H2O line wings between 100 and 1500 cm-1 . The results are in good agreement with those, around 1300 cm-1 , of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors Ï calculated, almost thirty years ago, using a quasistatic approach and an input H2O âCO2 intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the con- tinuum over a spectral range where it varies by more than three orders of magnitude. An empirical cor- rection is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO2 rich planetary atmospheres
3D modelling of the climatic impact of outflow channel formation events on early Mars
Mars was characterized by cataclysmic groundwater-sourced surface flooding that formed large outflow channels and that may have altered the climate for extensive periods during the Hesperian era. In particular, it has been speculated that such events could have induced significant rainfall and caused the formation of late-stage valley networks.
We present the results of 3-D Global Climate Model simulations reproducing the short and long term climatic impact of a wide range of outflow channel formation events under cold ancient Mars conditions. We find that the most intense of these events (volumes of water up to 107km3 and released at temperatures up to 320 Kelvins) cannot trigger long-term greenhouse global warming, regardless of how favorable are the external conditions (e.g. obliquity and seasons). In any case, outflow channel formation events at any atmospheric pressure are unable to produce rainfall or significant snowmelt at latitudes below 40âN.
On the long term, for an obliquity of âŒ45â and atmospheric pressures > 80 mbar, we find that the lake ice (formed quickly after the outflow event) is transported progressively southward through the mechanisms of sublimation and adiabatic cooling. At the same time, and as long as the initial water reservoir is not entirely sublimated, ice deposits remain in the West Echus Chasma Plateau region where hints of hydrological activity contemporaneous with outflow channel formation events have been observed. However, because the high albedo of ice drives Mars to even colder temperatures, snowmelt produced by seasonal solar forcing is difficult to attain.Earth and Planetary Science
RISTRETTO: a pathfinder instrument for exoplanet atmosphere characterization
We introduce the RISTRETTO instrument for ESO VLT, an evolution from the
original idea of connecting the SPHERE high-contrast facility to the ESPRESSO
spectrograph (Lovis et al 2017). RISTRETTO is an independent, AO-fed
spectrograph proposed as a visitor instrument, with the goal of detecting
nearby exoplanets in reflected light for the first time. RISTRETTO aims at
characterizing the atmospheres of Proxima b and several other exoplanets using
the technique of high-contrast, high-resolution spectroscopy. The instrument is
composed of two parts: a front-end to be installed on VLT UT4 providing a
two-stage adaptive optics system using the AOF facility with coronagraphic
capability and a 7-fiber IFU, and a diffraction-limited R=135,000 spectrograph
in the 620-840 nm range. We present the requirements and the preliminary design
of the instrument
Unbiasing the density of TTV-characterised sub-Neptunes: Update of the mass-radius relationship of 34 Kepler planets
Transit Timing Variations (TTVs) can provide useful information on compact
multi-planetary systems observed by transits, by putting constraints on the
masses and eccentricities of the observed planets. This is especially helpful
when the host star is not bright enough for radial velocity follow-up. However,
in the past decades, numerous works have shown that TTV-characterised planets
tend to have a lower densities than RV-characterised planets. Re-analysing 34
Kepler planets in the super-Earth to sub-Neptunes range using the RIVERS
approach, we show that at least part of these discrepancies was due to the way
transit timings were extracted from the light curve, which had a tendency to
under-estimate the TTV amplitudes. We recover robust mass estimates (i.e. low
prior dependency) for 23 of the planets. We compare these planets the
RV-characterised population. A large fraction of these previously had a
surprisingly low density now occupy a place of the mass-radius diagram much
closer to the bulk of the known planets, although a slight shift toward lower
densities remains, which could indicate that the compact multi-planetary
systems characterised by TTVs are indeed composed of planets which are
different from the bulk of the RV-characterised population. These results are
especially important for obtaining an unbiased view of the compact
multi-planetary systems detected by Kepler, TESS, and the upcoming PLATO
mission
Sensitive Probing of Exoplanetary Oxygen via Mid Infrared Collisional Absorption
The collision-induced fundamental vibration-rotation band at 6.4 um is the
most significant absorption feature from O2 in the infrared (Timofeyev and
Tonkov, 1978; Rinslandet al., 1982, 1989), yet it has not been previously
incorporated into exoplanet spectral analyses for several reasons. Either CIAs
were not included or incomplete/obsolete CIA databases were used. Also, the
current version of HITRAN does not include CIAs at 6.4 um with other collision
partners (O2-X). We include O2-X CIA features in our transmission spectroscopy
simulations by parameterizing the 6.4 um O2-N2 CIA based on Rinsland et
al.(1989) and the O2-CO2 CIA based on Baranov et al. (2004). Here we report
that the O2-X CIA may be the most detectable O2 feature for transit
observations. For a potentialTRAPPIST-1e analogue system within 5 pc of the
Sun, it could be the only O2 detectable signature with JWST (using MIRI LRS)
for a modern Earth-like cloudy atmosphere with biological quantities of O2.
Also, we show that the 6.4 um O2-X CIA would be prominent for O2-rich
desiccated atmospheres (Luger and Barnes, 2015) and could be detectable with
JWST in just a few transits. For systems beyond 5 pc, this feature could
therefore be a powerful discriminator of uninhabited planets with
non-biological "false positive" O2 in their atmospheres - as they would only be
detectable at those higher O2 pressures.Comment: Published in Nature Astronom
Map Style Formalization: Rendering Techniques Extension for Cartography
International audienceCartographic design requires controllable methods and tools to produce maps that are adapted to users' needs and preferences. The formalized rules and constraints for cartographic representation come mainly from the conceptual framework of graphic semiology. Most current Geographical Information Systems (GIS) rely on the Styled Layer Descriptor and Semiology Encoding (SLD/SE) specifications which provide an XML schema describing the styling rules to be applied on geographic data to draw a map. Although this formalism is relevant for most usages in cartography, it fails to describe complex cartographic and artistic styles. In order to overcome these limitations, we propose an extension of the existing SLD/SE specifications to manage extended map stylizations, by the means of controllable expressive methods. Inspired by artistic and cartographic sources (Cassini maps, mountain maps, artistic movements, etc.), we propose to integrate into our system three main expressive methods: linear stylization, patch-based region filling and vector texture generation. We demonstrate how our pipeline allows to personalize map rendering with expressive methods in several examples
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