9 research outputs found
Identification of carbon dioxide in an exoplanet atmosphere
Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called âmetallicityâ), and thus the formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme. The data used in this study span 3.0â5.5âmicrometres in wavelength and show a prominent CO2 absorption feature at 4.3âmicrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiativeâconvectiveâthermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0âmicrometres that is not reproduced by these models
Uranus in Northern Mid-Spring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging
We present results from mid-infrared imaging of Uranus at wavelengths of 13.0
micron and 18.7 micron, sensing emission from the stratosphere and upper
troposphere, acquired using the VISIR instrument at the Very Large Telescope
(VLT), September 4-October 20, 2018. Using a combination of inverse and forward
modeling, we analyze these northern mid-spring (L_s~46) images and compare them
to archival data to assess seasonal changes since the 1986 southern solstice
and subsequent equinox. We find the data are consistent with little change (<
0.3 K) in the upper tropospheric temperature structure, extending the previous
conclusions of Orton et al (2015) well past equinox, with only a subtle
increase in temperature at the emerging north pole. Additionally,
spatial-temporal variations in 13 micron stratospheric emission are
investigated for the first time, revealing meridional variation and a
hemispheric asymmetry not predicted by models. Finally, we investigate the
nature of the stratospheric emission and demonstrate that the observed
distribution appears related and potentially coupled to the underlying
tropospheric emission six scale heights below. The observations are consistent
with either mid-latitude heating or an enhanced abundance of acetylene.
Considering potential mechanisms and additional observations, we favor a model
of acetylene enrichment at mid-latitudes resulting from an extension of the
upper-tropospheric circulation, which appears capable of transporting methane
from the troposphere, through the cold trap, and into the stratosphere for
subsequent photolysis to acetylene
Longitudinal variations in the stratosphere of Uranus from the Spitzer infrared spectrometer
NASA's Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5â37 ÎŒm) disc-averaged spectra of Uranus very near to its equinox in December 2007. A mean spectrum was constructed from observations of multiple central meridian longitudes, spaced equally around the planet, which has provided the opportunity for the most comprehensive globally-averaged characterisation of Uranus' temperature and composition ever obtained (Orton et al., 2014a,b). In this work we analyse the disc-averaged spectra at four separate central meridian longitudes to reveal significant longitudinal variability in thermal emission occurring in Uranus' stratosphere during the 2007 equinox. We detect a variability of up to 15% at wavelengths sensitive to stratospheric methane, ethane and acetylene at the ~0.1-mbar level. The tropospheric hydrogenâhelium continuum and deuterated methane absorption exhibit a negligible variation (less than 2%), constraining the phenomenon to the stratosphere. Building on the forward-modelling analysis of the global average study, we present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008) of the Uranus-2007 spectra at each longitude to distinguish between thermal and compositional variability. We found that the variations can be explained by a temperature change of less than 3 K in the stratosphere. Near-infrared observations from Keck II NIRC2 in December 2007 (Sromovsky et al., 2009; de Pater et al., 2011), and mid-infrared observations from VLT/VISIR in 2009 (Roman et al., 2020), help to localise the potential sources to either large scale uplift or stratospheric wave phenomena
Jupiter's MultiâYear Cycles of Temperature and Aerosol Variability From GroundâBased MidâInfrared Imaging
We use a longâterm record of groundâbased midâinfrared (7.9â24.5 Όm) observations, captured between 1984 and late 2019 from 3âm and 8âm class observatories (mainly NASA's Infrared Telescope Facility, ESO's Very Large Telescope, and the Subaru Telescope), to characterize the longâterm, multiâdecade variability of the thermal and aerosol structure in Jupiter's atmosphere. In this study, spectral cubes assembled from images in multiple filters are inverted to provide estimations of stratospheric and tropospheric temperatures and tropospheric aerosol opacity. We find evidence of nonâseasonal and quasiâseasonal variations of the stratospheric temperatures at 10 mbar, with a permanent hemispherical asymmetry at midâlatitudes, where the northern midâlatitudes are overall warmer than southern midâlatitudes. A correlation analysis between stratospheric and tropospheric temperature variations reveals a moderate anticorrelation between the 10âmbar and 330âmbar temperatures at the equator, revealing that upperâtropospheric equatorial temperatures are coupled to Jupiterâs Equatorial Stratospheric Oscillation. The North and South Equatorial Belts show temporal variability in their aerosol opacity and tropospheric temperatures that are in approximate antiphase with one another, with moderate negative correlations in the North Equatorial Belt and South Equatorial Belt changes between conjugate latitudes at 10°â16°. This longâterm anticorrelation between belts separated by âŒ15° is still not understood. Finally we characterize the lag between thermal and aerosol opacity changes at a number of latitudes, finding that aerosol variations tend to lag after thermal variations by around 6 months at multiple latitudes.</p
Characterizing Temperature and Aerosol Variability during Jupiter's 2006â07 Equatorial Zone Disturbance
We use groundâbased midâinfrared (8â20âÎŒm) data acquired by three different instruments between 2005 and 2008 to characterize the variability of tropospheric temperature and aerosol opacity during the 2006â2007 Equatorial Zone disturbance. This disturbance is part of a repeating pattern of cloudâclearing events at Jupiter's equator, observed as a significant brightening at 5âÎŒm (sensing the 2â to 7âbar region) and darkening at visible wavelengths (sensing the âŒ0.7âbar pressure level). The data reveal a brightness temperature increase of âŒ3.1âK between 2005 and February 2007 at 8.6âÎŒm sensing tropospheric aerosol opacity and temperature near 0.6â0.8âbar. At wavelengths sensing tropospheric ammonia and temperatures between 150 and 600âmbar, the brightness temperature remains largely invariant between 2005 and 2008. The tropospheric vertical temperature profile and the tropospheric aerosol opacity were derived from images captured in different filters on four different dates, one for each year. The retrieved aerosol opacity at âŒ0.6â0.8âbar shows a decrease at 2â5°S of âŒ45% in 2006 and âŒ65% in 2007, with respect to 2008. This is consistent with cloud clearing/thinning during the coloration of the Equatorial Zone at visible wavelengths. This brightening at 8.6âÎŒm started in 2005 and preceded the brightening at 5âÎŒm, which started in April 2006. The results also suggest that cloud clearing during the Equatorial Zone disturbances is not simply the result of tropospheric warming, at least at pâPlain Language SummaryJupiter's equatorial latitudes between âŒ7°, known as the Equatorial Zone (EZ), undergo dramatic planetaryâscale disturbances that completely alter its appearance at different altitudes of the troposphere between 0.7 and 4âbar. Here we characterize the last EZ disturbance, observed in 2006â2007, to investigate what atmospheric conditions vary during these disturbances. Retrieved aerosol opacity at âŒ0.6âbar shows a decrease at 2â5°S of âŒ45% in 2006 and âŒ65% in 2007, with respect to 2008, consistent with cloud clearing/thinning during these events. This removal of aerosol opacity is observed to start in 2005, a year before the deeper clouds are cleared. These results indicate that the EZ disturbance involves the clearing of both the ammonia ice cloud near 0.7âbar and the deeper NH4SH clouds with each cloud deck responding at different times. Results also suggest that cloud clearing during the EZ disturbances is not simply the result of tropospheric warming in the middleâtoâhigh troposphere. We propose that cloud clearing occurs due to a decrease in the ammonia gas upwelling from deeper levels.</div
The Temporal Brightening of Uranus' Northern Polar Hood From HST/WFC3 and HST/STIS Observations
AbstractHubble Space Telescope WideâField Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus' north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023, https://doi.org/10.1038/s41550-023-02047-0) (IRW23), consisting of a deep haze layer based at âŒ5 bar, a 1â2 bar haze layer, and an extended haze rising up from the 1â2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (STIS) (HST/STIS) observations (Sromovsky et al., 2014, 2019, https://doi.org/10.1016/j.icarus.2014.05.016, https://doi.org/10.1016/j.icarus.2018.06.026) revealing a reduction in cloudâtop CH4 volume mixing ratio (VMR) (i.e., above the deep âŒ5 bar haze) by an average of 0.0019 ± 0.0003 between 40â80âŠN (âŒ10% average reduction) from 2012 to 2015. A combination of latitudinal retrievals on the HST/WFC3 and HST/STIS data sets, again employing the IRW23 model, reveal a temporal thickening of the 1â2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase in integrated opacity of 1.09 ± 0.08 (âŒ33% increase) at 0.8 ”m north of âŒ45°N, concurrent with a decrease in the imaginary refractive index spectrum of the 1â2 bar haze layer north of âŒ40°N and longwards of âŒ0.7 ”m. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 ± 0.1 (58% increase) north of 45°N between 2012 and 2015, and from the aforementioned decrease in CH4 VMR. Our results are consistent with the slowing of a stratospheric meridional circulation, exhibiting subsidence at the poles
Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices With VLT/VISIR
Using images at multiple midâinfrared wavelengths, acquired in 2018 May using the Very Large Telescope Imager and Spectrometer (VISIR) instrument on ESO's Very Large Telescope (VLT), we study Jupiter's poleâtoâpole thermal, chemical and aerosol structure in the troposphere and stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones and warm cloudâfree cyclonic belts persists throughout the midâlatitudes, up to the polar boundaries, and evidence a strong correlation with the vertical maximum windshear and the locations of Jupiter's zonal jets. At high latitudes, VISIR images reveal a large region of midâinfrared cooling poleward âŒ64°N and âŒ67°S extending from the upper troposphere to the stratosphere, coâlocated with the reflective aerosols observed by JunoCam, and suggesting that aerosols play a key role in the radiative cooling at the poles. Comparison of zonalâmean thermal properties and highâresolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex. However, the southern stratospheric polar vortex is partly masked by a warm midâinfrared signature of the aurora. Coâlocated with the southern main auroral oval, this warming results from the auroral precipitation and/or joule heating which heat the atmosphere and thus cause a significant stratospheric emission. This high emission results from a large enhancement of both ethane and acetylene in the polar region, reinforcing the evidence of enhanced ionârelated chemistry in Jupiter's auroral regions.</p
Modelling the seasonal cycle of Uranusâs colour and magnitude, and comparison with Neptune
We present a quantitative analysis of the seasonal record of Uranusâs disc-averaged colour and photometric magnitude in Strömgren b and y filters (centred at 467 and 551ânm, respectively), recorded at the Lowell Observatory from 1950 to 2016, and supplemented with HST/WFC3 observations from 2016 to 2022. We find that the seasonal variations of magnitude can be explained by the lower abundance of methane at polar latitudes combined with a time-dependent increase of the reflectivity of the aerosol particles in layer near the methane condensation level at 1 â 2âbar. This increase in reflectivity is consistent with the addition of conservatively scattering particles to this layer, for which the modelled background haze particles are strongly absorbing at both blue and red wavelengths. We suggest that this additional component may come from a higher proportion of methane ice particles. We suggest that the increase in reflectivity of Uranus in both filters between the equinoxes in 1966 and 2007, noted by previous authors, might be related to Uranusâs distance from the Sun and the production rate of dark photochemical haze products. Finally, we find that although the visible colour of Uranus is less blue than Neptune, due to the increased aerosol thickness on Uranus, and this difference is greatest at Uranusâs solstices, it is much less significant than is commonly believed due to a long-standing misperception of Neptuneâs âtrueâ colour. We describe how filter-imaging observations, such as those from Voyager-2/ISS and HST/WFC3, should be processed to yield accurate true colour representations.</p
Temperature and Composition Disturbances in the Southern Auroral Region of Jupiter Revealed by JWST/MIRI
Jupiter's South Polar Region (SPR) was observed by James Webb Space Telescope/MidâInfrared Instrument in December 2022. We used the Medium Resolution Spectrometer mode to provide new information about Jupiter's South Polar stratosphere. The southern auroral region was visible and influenced the atmosphere in several ways: (a) In the interior of the southern auroral oval, we retrieved peak temperatures at two distinct pressure levels near 0.01 and 1 mbar, with warmer temperatures with respect to nonâauroral regions of 12 ± 2 K and 37 ± 4 K respectively. A cold polar vortex is centered at 65°S at 10 mbar. (b) We found that the homopause is elevated to km above the 1âbar pressure level inside the auroral oval compared to km at neighboring latitudes and with an upper altitude of 350 km in regions not affected by auroral precipitation. (c) The retrieved abundance of C2H2 shows an increase within the auroral oval, and it exhibits high abundances throughout the polar region. The retrieved abundance of C2H6 increases toward the pole, without being localized in the auroral oval, in contrast with previous analysis (Sinclair et al., 2018, https://doi.org/10.1016/j.icarus.2017.09.016). We determined that the warming at 0.01 mbar and the elevated homopause might be caused by the flux of charged particles depositing their energy in the SPR. The 1âmbar hotspot may arise from adiabatic heating resulting from auroralâdriven downwelling. The cold region at 10 mbar may be caused by radiative cooling by stratospheric aerosols. The differences in spatial distribution seem to indicate that the hydrocarbons analyzed are affected differently by auroral precipitation.</p