39 research outputs found
Impact of stellar flares on the chemical composition and transmission spectra of gaseous exoplanets orbiting M dwarfs
Stellar flares of active M dwarfs can affect the atmospheric composition of
close-orbiting gas giants, and can result in time-dependent transmission
spectra. We aim to examine the impact of a variety of flares, differing in
energy, duration, and occurrence frequency, on the composition and spectra of
close-orbiting, tidally locked gaseous planets with climates dominated by
equatorial superrotation. We used a series of pseudo-2D photo- and
thermochemical kinetics models, which take advection by the equatorial jet
stream into account, to simulate the neutral molecular composition of a gaseous
planet (effective temperature 800 K) that orbits a flaring M dwarf. We then
computed transmission spectra for the evening and morning limb. We find that
the upper regions of the dayside and evening limb are heavily depleted in CH4
and NH3 up to several days after a flare with a total radiative energy of erg. Molar fractions of C2H2 and HCN are enhanced up to a
factor three on the nightside and morning limb after day-to-nightside advection
of photodissociated species. CH4 depletion reduces transit depths by 100-300
parts per million (ppm) on the evening limb and C2H2 production increases the
14 micron feature up to 350 ppm on the morning limb. We find that repeated
flaring drives the atmosphere to a composition that differs from its pre-flare
distribution and that this translates to a permanent modification of the
transmission spectrum. We show that single high-energy flares can affect the
atmospheres of close-orbiting gas giants up to several days after the flare
event, during which their transmission spectra are altered by several hundred
ppm. Repeated flaring has important implications for future retrieval analyses
of exoplanets around active stars, as the atmospheric composition and resulting
spectral signatures substantially differ from models that do not include
flaring.Comment: 27 pages, 21 figures, accepted for publication in A&
Grid of pseudo-2D chemistry models for tidally locked exoplanets – II. The role of photochemistry
Funding: RB acknowledges funding from a PhD fellowship of the Research Foundation – Flanders (FWO). OV acknowledges support from the Agence Nationale de la Recherche (ANR), through the project EXACT (ANR-21-CE49-0008-0) and from the CNRS/INSU Programme National de Planétologie (PNP). This work was supported by CNES, focused on the EXACT project and Ariel. LC acknowledges support from the DFG Priority Programme SP1833 Grant CA 1795/3 and the UK Royal Society Grant URF R1 211718. LD acknowledges support from the FWO research grant G086217N. RB, TK, and LD acknowledge support from the KU Leuven IDN/19/028 grant ESCHER.Photochemistry is expected to change the chemical composition of the upper atmospheres of irradiated exoplanets through the dissociation of species, such as methane and ammonia, and the association of others, such as hydrogen cyanide. Although primarily the high altitude day side should be affected by photochemistry, it is still unclear how dynamical processes transport photochemical species throughout the atmosphere, and how these chemical disequilibrium effects scale with different parameters. In this work we investigate the influence of photochemistry in a two-dimensional context, by synthesizing a grid of photochemical models across a large range of temperatures. We find that photochemistry can strongly change the atmospheric composition, even up to depths of several bar in cool exoplanets. We further identify a sweet spot for the photochemical production of hydrogen cyanide and acetylene, two important haze precursors, between effective temperatures of 800 and 1400 K. The night sides of most cool planets (Teff < 1800 K) are shown to host photochemistry products, transported from the day side by horizontal advection. Synthetic transmission spectra are only marginally affected by photochemistry, but we suggest that observational studies probing higher altitudes, such as high-resolution spectroscopy, take photochemistry into account.Publisher PDFPeer reviewe
Photodissociation and induced chemical asymmetries on ultra-hot gas giants. A case study of HCN on WASP-76 b
Recent observations have resulted in the detection of chemical gradients on
ultra-hot gas giants. Notwithstanding their high temperature, chemical
reactions in ultra-hot atmospheres may occur in disequilibrium, due to vigorous
day-night circulation and intense UV radiation from their stellar hosts. The
goal of this work is to explore whether photochemistry is affecting the
composition of ultra-hot giant planets, and if it can introduce horizontal
chemical gradients. In particular, we focus on hydrogen cyanide (HCN) on
WASP-76 b, as it is a photochemically active molecule with a reported detection
on only one side of this planet. We use a pseudo-2D chemical kinetics code to
model the chemical composition of WASP-76 b along its equator. Our approach
improves on chemical equilibrium models by computing vertical mixing,
horizontal advection, and photochemistry. We find that production of HCN is
initiated through thermal and photochemical dissociation of CO and N2 on the
day side of WASP-76 b, which are subsequently transported to the night side via
the equatorial jet stream. This process results in an HCN gradient with a
maximal abundance on the planet's morning limb. We verified that photochemical
dissociation is a necessary condition for this mechanism, as thermal
dissociation alone proves insufficient. Other species produced via night-side
disequilibrium chemistry are SO2 and S2. Our model acts as a proof of concept
for chemical gradients on ultra-hot exoplanets. We demonstrate that even
ultra-hot planets can exhibit disequilibrium chemistry and recommend that
future studies do not neglect photochemistry in their analyses of ultra-hot
planets.Comment: 15 pages, 9 figure
Barium in twilight zone suspended matter as a potential proxy for particulate organic carbon remineralization : results for the North Pacific
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1673-1683, doi:10.1016/j.dsr2.2008.04.020.This study focuses on the fate of exported organic carbon in the twilight zone at two
contrasting environments in the North Pacific: the oligotrophic ALOHA site (22°45'
N 158°W; Hawaii; studied during June–July 2004) and the mesotrophic Subarctic
Pacific K2 site (47°N, 161°W; studied during July-August 2005). Earlier work has
shown that non-lithogenic, excess particulate Ba (Baxs) in the mesopelagic water
column is a potential proxy of organic carbon remineralization. In general Baxs
contents were significantly larger at K2 than at ALOHA. At ALOHA the Baxs profiles
from repeated sampling (5 casts) showed remarkable consistency over a period of
three weeks, suggesting that the system was close to being at steady state. In contrast,
more variability was observed at K2 (6 casts sampled) reflecting the more dynamic
physical and biological conditions prevailing in this environment. While for both sites
Baxs concentrations increased with depth, at K2 a clear maximum was present
between the base of the mixed layer at around 50m and 500m, reflecting production
and release of Baxs. Larger mesopelagic Baxs contents and larger bacterial production
in the twilight zone at the K2 site indicate that more material was exported from the
upper mixed layer for bacterial degradation deeper, compared to the ALOHA site.
Furthermore, application of a published transfer function (Dehairs et al., 1997)
relating oxygen consumption to the observed Baxs data indicated that the latter were in
good agreement with bacterial respiration, calculated from bacterial production. These
results corroborate earlier findings highlighting the potential of Baxs as a proxy for
organic carbon remineralization.
The range of POC remineralization rates calculated from twilight zone excess
particulate Ba contents did also compare well with the depth dependent POC flux
decrease as recorded by neutrally buoyant sediment traps, except in 1 case (out of 4).
This discrepancy could indicate that differences in sinking velocities cause an
3
uncoupling of the processes occurring in the fine suspended particle pool from those
affecting the larger particle pool which sustains the vertical flux, thus rendering
comparison between both approaches risky.This research was supported by Federal Science Policy
Office, Brussels through contracts EV/03/7A, SD/CA/03A, the Research Foundation
Flanders through grant G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as
well as the US National Science Foundation programs in Chemical and Biological
Oceanography
Photochemically-produced SO in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that
regulates the atmospheric composition and stability. However, no unambiguous
photochemical products have been detected in exoplanet atmospheres to date.
Recent observations from the JWST Transiting Exoplanet Early Release Science
Program found a spectral absorption feature at 4.05 m arising from SO
in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass
(0.28 M) gas giant exoplanet orbiting a Sun-like star with an equilibrium
temperature of 1100 K. The most plausible way of generating SO in
such an atmosphere is through photochemical processes. Here we show that the
SO distribution computed by a suite of photochemical models robustly
explains the 4.05 m spectral feature identified by JWST transmission
observations with NIRSpec PRISM (2.7) and G395H (4.5). SO
is produced by successive oxidation of sulphur radicals freed when hydrogen
sulphide (HS) is destroyed. The sensitivity of the SO feature to the
enrichment of the atmosphere by heavy elements (metallicity) suggests that it
can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an
inferred metallicity of 10 solar. We further point out that
SO also shows observable features at ultraviolet and thermal infrared
wavelengths not available from the existing observations.Comment: 39 pages, 14 figures, accepted to be published in Natur
Photochemically produced SO2 in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO2) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 MJ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref. 4). The most plausible way of generating SO2 in such an atmosphere is through photochemical processes5,6. Here we show that the SO2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations7 with NIRSpec PRISM (2.7σ)8 and G395H (4.5σ)9. SO2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H2S) is destroyed. The sensitivity of the SO2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations
Recommended from our members
Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b
Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5 μm to 12 μm with the JWST’s Mid-Infrared Instrument. The spectra reveal a large day–night temperature contrast (with average brightness temperatures of 1,524 ± 35 K and 863 ± 23 K, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase-curve shape and emission spectra strongly suggest the presence of nightside clouds that become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1–6 ppm, depending on model assumptions). Our results provide strong evidence that the atmosphere of WASP-43b is shaped by disequilibrium processes and provide new insights into the properties of the planet’s nightside clouds. However, the remaining discrepancies between our observations and our predictive atmospheric models emphasize the importance of further exploring the effects of clouds and disequilibrium chemistry in numerical models.Peer reviewe
Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b
Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 μm with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524±35 and 863±23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1-6 parts per million, depending on model assumptions)