5 research outputs found
An intense narrow equatorial jet in Jupiterâs lower stratosphere observed by JWST
The atmosphere of Jupiter has eastâwest zonal jets that alternate as a function of latitude as tracked by cloud motions at tropospheric levels. Above and below the cold tropopause at ~100âmbar, the equatorial atmosphere is covered by hazes at levels where thermal infrared observations used to characterize the dynamics of the stratosphere lose part of their sensitivity. James Webb Space Telescope observations of Jupiter in July 2022 show these hazes in higher detail than ever before and reveal the presence of an intense (140âmâsâ1) equatorial jet at 100â200âmbar (70âmâsâ1 faster than the zonal winds at the cloud level) that is confined to ±3° of the equator and is located below stratospheric thermal oscillations that extend at least from 0.1 to 40âmbar and repeat in multiyear cycles. This suggests that the new jet is a deep part of Jupiterâs Equatorial Stratospheric Oscillation and may therefore vary in strength over time.JWST-ERS-01373, NASA/ESA Hubble Space Telescope programmes no. 16913, 15502 and 16790, PID2019-109467GB-I00 funded by MCIN/AEI/10.13039/501100011033/, Grupos Gobierno Vasco IT1742-22. I.d.; European Research Council Consolidator Grant (under the European Unionâs Horizon 2020 research and innovation programme, grant agreement no. 723890), STFC PhD Studentship, NASA grants 80NSSC21K1418 and 80NSSC19K0894
JWST MIRI flight performance: The Medium-Resolution Spectrometer
The Medium-Resolution Spectrometer (MRS) provides one of the four operating
modes of the Mid-Infrared Instrument (MIRI) on board the James Webb Space
Telescope (JWST). The MRS is an integral field spectrometer, measuring the
spatial and spectral distributions of light across the 5-28 wavelength
range with a spectral resolving power between 3700-1300. We present the MRS's
optical, spectral, and spectro-photometric performance, as achieved in flight,
and we report on the effects that limit the instrument's ultimate sensitivity.
The MRS flight performance has been quantified using observations of stars,
planetary nebulae, and planets in our Solar System. The precision and accuracy
of this calibration was checked against celestial calibrators with well-known
flux levels and spectral features. We find that the MRS geometric calibration
has a distortion solution accuracy relative to the commanded position of 8 mas
at 5 and 23 mas at 28 . The wavelength calibration is accurate
to within 9 km/sec at 5 and 27 km/sec at 28 . The uncertainty in
the absolute spectro-photometric calibration accuracy was estimated at 5.6 +-
0.7 %. The MIRI calibration pipeline is able to suppress the amplitude of
spectral fringes to below 1.5 % for both extended and point sources across the
entire wavelength range. The MRS point spread function (PSF) is 60 % broader
than the diffraction limit along its long axis at 5 and is 15 % broader
at 28 . The MRS flight performance is found to be better than prelaunch
expectations. The MRS is one of the most subscribed observing modes of JWST and
is yielding many high-profile publications. It is currently humanity's most
powerful instrument for measuring the mid-infrared spectra of celestial sources
and is expected to continue as such for many years to come.Comment: 16 pages, 21 figure
Saturn's Atmosphere in Northern Summer Revealed by JWST/MIRI
International audienceSaturn's northern summertime hemisphere was mapped by JWST/Mid-Infrared Instrument (4.9-27.9 ”m) in November 2022, tracing the seasonal evolution of temperatures, aerosols, and chemical species in the 5 years since the end of the Cassini mission. The spectral region between reflected sunlight and thermal emission (5.1-6.8 ”m) is mapped for the first time, enabling retrievals of phosphine, ammonia, and water, alongside a system of two aerosol layers (an upper tropospheric haze p < 0.3 bars, and a deeper cloud layer at 1-2 bars). Ammonia displays substantial equatorial enrichment, suggesting similar dynamical processes to those found in Jupiter's equatorial zone. Saturn's North Polar Stratospheric Vortex has warmed since 2017, entrained by westward winds at p < 10 mbar, and exhibits localized enhancements in several hydrocarbons. The strongest latitudinal temperature gradients are co-located with the peaks of the zonal winds, implying wind decay with altitude. Reflectivity contrasts at 5-6 ”m compare favorably with albedo contrasts observed by Hubble, and several discrete vortices are observed. A warm equatorial stratospheric band in 2022 is not consistent with a 15-year repeatability for the equatorial oscillation. A stacked system of windshear zones dominates Saturn's equatorial stratosphere, and implies a westward equatorial jet near 1-5 mbar at this epoch. Lower stratospheric temperatures, and local minima in the distributions of several hydrocarbons, imply low-latitude upwelling and a reversal of Saturn's interhemispheric circulation since equinox. Latitudinal distributions of stratospheric ethylene, benzene, methyl, and carbon dioxide are presented for the first time, and we report the first detection of propane bands in the 8-11 ”m region
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
An intense narrow equatorial jet in Jupiterâs lower stratosphere observed by JWST
International audienceAbstract The atmosphere of Jupiter has eastâwest zonal jets that alternate as a function of latitude as tracked by cloud motions at tropospheric levels. Above and below the cold tropopause at ~100âmbar, the equatorial atmosphere is covered by hazes at levels where thermal infrared observations used to characterize the dynamics of the stratosphere lose part of their sensitivity. James Webb Space Telescope observations of Jupiter in July 2022 show these hazes in higher detail than ever before and reveal the presence of an intense (140âmâs â1 ) equatorial jet at 100â200âmbar (70âmâs â1 faster than the zonal winds at the cloud level) that is confined to ±3° of the equator and is located below stratospheric thermal oscillations that extend at least from 0.1 to 40âmbar and repeat in multiyear cycles. This suggests that the new jet is a deep part of Jupiterâs Equatorial Stratospheric Oscillation and may therefore vary in strength over time