The effect of ammonia ice on the outgoing thermal radiance from the atmosphere of Jupiter

We examine the effects of NH₃ ice particle clouds in the atmosphere of Jupiter on outgoing thermal radiances. The cloud models are characterized by a number density at the cloud base, by the ratio of the scale height of the vertical distribution of particles (H_p) to the gas scale height (H_g), and by an effective particle radius. NH₃ ice particle-scattering properties are scaled from laboratory measurements. The number density for the various particle radius and scale height models is inferred from the observed disk average radiance at 246 cm^?1, and preliminary lower limits on particle sizes are inferred from the lack of apparent NH₃ absorption features in the observed spectral radiances as well as the observed minimum flux near 2100 cm^?1. We find lower limits on the particle size of 3 μm if H_p/H_g = 0.15, or 10μmif H_p/H_g = 0.50 or 0.05. NH₃ ice particles are relatively dark near the far-infrared and 8.5-μm atmospheric windows, and the outgoing thermal radiances are not very sensitive to various assumptions about the particle-scattering function as opposed to radiances at 5 μm, where particles are relatively brighter. We examined observations in these three different spectral window regions which provide, in principle, complementary constraints on cloud parameters. Characterization of the cloud scale height is difficult, but a promising approach is the examination of radiances and their center-to-limb variation in spectral regions where there is significant opacity provided by gases of known vertical distribution. A blackbody cloud top model can reduce systematic errors due to clouds in temperature sounding to the level of 1K or less. The NH₃ clouds provide a substantial influence on the internal infrared flux field near the 600-mbar level.     

The Jovian spectrum in the 3-μm window

The spectral window of Jupiter at 3 μm is analyzed and compared with previously published spectra. The two components of the spectrum, the thermal and the solar reflected contributions, are calculated at low resolution (30 cm^?1) between 3300 and 3800 cm^?1 for preparing the interpretation of the Galileo Near Infrared Mapping Spectrometer experiment. The calculations yield to the following conclusions: (1) NH₃ is the main absorber between 3300 and 3600 cm^?1 for both the thermal spectrum and the solar reflected spectrum; H₂O appears only in the thermal component above 3600 cm^?1. (2) The thermal component can be seen only on the dark side of Jupiter; the atmosphere is sounded down to temperature levels of about 210°K. (3) The solar reflected component can be modelized by a reflecting layer between 135 and 140°K with an albedo of 0.3; high spatial resolution maps of Jupiter at 3 μm should give access to the NH₃ spatial distribution on Jupiter.     

Far-infrared and submillimeter observations of the planets

New broadband observations in several passbands between 30 and 500 μm of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 ± 2°K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source of Saturn has been reconfirmed and must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 μm, which may be a result of NH₃ opacity.     

Voyager 1 imaging and IRIS observations of Jovian methane absorption and thermal emission: Implications for cloud structure

Images from three filters of the Voyager 1 wide-angle camera were used to measure the continuum reflectivity and spectral gradient near 6000 Å and the 6190-Å band methane/continuum ratio for a variety of cloud features in Jupiter's atmosphere. The dark “barge” features in the North Equatorial Belt have anomalously strong positive continuum spectral gradients suggesting unique composition, probably not elemental sulfur. Methane absorption was shown at unprecedented spatial scales for the Great Red Spot and its immediate environment, for a dark barge feature in the North Equatorial Belt, and for two hot spot and plume regions in the North Equatorial Belt. Some small-scale features, unresolvable at ground-based resolution, show significant enhancement in methane absorption. Any enhancement in methane absorption is conspicuously absent in both hot spot regions with 5-μm brightness temperature 255°K. Methane absorption and 5-μm emission are correlated in the vicinity of the Great Red Spot but are anticorrelated in one of the plume hot spot regions. Methane absorption and simultaneously maps of 5-μm brightness temperature were quantitatively compared to realistic cloud structure models which include multiple scattering at 5 μm as well as in the visible. A curve in parameter space defines the solution to any observed quantity, ranging from a shallow atmosphere and thin NH₃ cloud to a deep atmosphere with a thick ammonia cloud. Without additional constraints, such as center-to-limb information, it is impossible to specify the NH₃ cloud optical depth and pressure of a deeper cloud top independently. Variability in H₂ quadrupole lines was also investigated and it was found that the constancy of the 4-0 S(1)-line equivalent width is consistent with the constancy of the methane 6190-Å band equivalent width at ground-based resolution, but the much greater variability of the 3-0 S(1) line is inconsistent with either the methane band or 4-0 S(1) line. In hot spot regions the 255°K brightness temperature requires a cloud optical depth of about 2 or less at 5 μm in the NH₃ cloud layer. To be consistent with the observed 6190-Å methane absorption in hot spot regions, the NH₃ cloud optical depth in the visible is about 7.5, implying that aerosols in hot spot regions have effective radii near 1 μm or less.     

The phosphine abundance on Saturn derived from new 10-micrometer spectra

Spectra of Saturn in the spectral region 10.0–10.7 μm are presented which confirm the presence of PH₃. Comparison to synthetic spectra indicates a PH₃ mixing ratio of at least 2 × 10^?6. No spectral features due to NH₃ or C₂H₄ were observed.     

Solar infrared occultation observations by SPICAM experiment on Mars-Express: Simultaneous measurements of the vertical distributions of H2O, CO2 and aerosol

The infrared AOTF spectrometer is a part of the SPICAM experiment onboard the Mars-Express ESA mission. The instrument has a capability of solar occultations and operates in the spectral range of 1-1.7 μm with a spectral resolution of ∼3.5 cm⁻¹. We report results from 24 orbits obtained during MY28 at Ls 130°-160°, and the latitude range of 40°-55° N. For these orbits the atmospheric density from 1.43 μm CO₂ band, water vapor mixing ratio based on 1.38 μm absorption, and aerosol opacities were retrieved simultaneously. The vertical resolution of measurements is better than 3.5 km. Aerosol vertical extinction profiles were obtained at 10 wavelengths in the altitude range from 10 to 60 km. The interpretation using Mie scattering theory with adopted refraction indices of dust and H₂O ice allows to retrieve particle size (reff∼0.5-1 μm) and number density (∼1 cm⁻³ at 15-30 km) profiles. The haze top is generally below 40 km, except the longitude range of 320°-50° E, where high-altitude clouds at 50-60 km were detected. Optical properties of these clouds are compatible with ice particles (effective radius reff=0.1-0.3 μm, number density N∼10 cm−3) distributed with variance νeff=0.1-0.2 μm. The vertical optical depth of the clouds is below 0.001 at 1 μm. The atmospheric density profiles are retrieved from CO₂ band in the altitude range of 10-90 km, and H₂O mixing ratio is determined at 15-50 km. Unless a supersaturation of the water vapor occurs in the martian atmosphere, the H₂O mixing ratio indicates ∼5 K warmer atmosphere at 25-45 km than predicted by models.     

High spectral resolution infrared studies of Titan: Winds, temperature, and composition

The Cassini Huygens mission provides a unique opportunity to combine ground-based and spacecraft investigations to increase our understanding of chemical and dynamical processes in Titan’s atmosphere. Spectroscopic measurements from both vantage points enable retrieving global wind structure, temperature structure, and atmospheric composition. An updated analysis of Titan data obtained with the NASA Goddard Space Flight Center’s Infrared Heterodyne Spectrometer (IRHS) and Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) prior to and during the Cassini Huygens mission is compared to retrievals from measurements with the Cassini Composite Infrared Spectrometer (CIRS). IRHS/HIPWAC results include the first direct stratospheric wind measurements on Titan, constraints on stratospheric temperature, and the study of atmospheric molecular composition. These results are compared to CIRS retrievals of wind and temperature profile from thermal mapping data and ethane abundance at 10-15° South latitude, near the equatorial region. IRHS/HIPWAC wind results are combined with other direct techniques, stellar occultation measurements, and CIRS results to explore seasonal variability over nearly one Titan year and to provide an empirical altitude profile of stratospheric winds, varying from ∼50 to 210 m/s prograde. The advantage of fully resolved line spectra in species abundance measurements is illustrated by comparing the possible effect on retrieved ethane abundance by blended spectral features of other molecular constituents, e.g., acetylene (C₂H₂), ethylene (C₂H₄), allene (C₃H₄), and propane (C₃H₈), which overlap the ν₉ band of ethane, and are not resolved at lower spectral resolution. IR heterodyne spectral resolution can discriminate weak spectral features that overlap the ν₉ band of ethane, enabling ethane lines alone to be used to retrieve abundance. Titan’s stratospheric mean ethane mole fraction (8.6±3 ppmv) retrieved from IRHS/HIPWAC emission line profiles (resolving power λ?Δλ∼10⁶) is compared to past values obtained from lower resolution spectra and from CIRS measurements (resolving power λ?Δλ∼2×10³) and more compatible recent analysis. Results illustrate how high spectral resolution ground-based studies complement the spectral and spatial coverage and resolution of moderate spectral resolution space-borne spectrometers.     

Mean thermal and albedo behavior of the Mars surface and atmosphere over a Martian year

A Mars average data set (MADS) has been constructed from thermal and albedo measurements of the Viking Infrared Thermal Mapper; by merging information from all longitudes; and, ensuring reasonably complete longitudinal sampling, a representation of mean Mars behavior is obtained. Brightness temperatures at 7, 9, 11, 15, and 20 μm and albedo information in the band 0.3–3.0 μm have been binned using 2° latitude strips, 24 times of day, 3 emission angle intervals, and 23 nonoverlapping L_s periods covering 1.43 Mars years starting at L_s = 84°. The MADS is ideally suited to parametric study of latitudinal, diurnal, angular, and seasonal dependences. Data are presented for surface thermal and albedo behavior in clear and dusty atmospheric conditions; the thermal response of the atmospheric temperature to a major dust storm is found to be consistent with Mariner 9 data from the 1971 storm. Examples of use of the MADS, which is available through the Mars Consortium, indicate how averaged data reveal specific surface and atmospheric phenomena.     

Jupiter's atmosphere: Observations and interpretation of the microwave spectrum near 1.25-cm wavelength

Measurements of Jupiter's disk-temperature spectrum in the 20- to 24-GHz (1.5 cm < λ < 1.25 cm) region are reported. These data are combined with previously published data to produce a uniformly calibrated thermal spectrum of Jupiter in the wavelength interval 0.85 to 2.1 cm. Model studies are carried out to determine optimum pressure-temperature profiles for an assumed radiative-convective temperature structure. We find the temperature at the 1-bar total effective pressure level is between 140 and 165°K, with a most probable value of 153°K, provided that NH₃ is uniformly saturated in the clouds on a global scale. We show that the temperature profile for the microwave model is ～20°K cooler than the profiles derived from infrared data. An explanation of this discrepancy is discussed in terms of a model which invokes different NH₃ distributions in the belts and zones.     

Phosphine absorption in the 5-μm window of Jupiter

Since the original suggestion by Gillett et al. (1969) it has generally been assumed that the region of partial transparency near 5 μm in Jupiter's atmosphere (the 5-μm window) is bounded by the v₄ NH₃ at 6.1 μm and the v₃ CH₄ band at 3.3 μm. New measurements of Jupiter and of laboratory phosphine (PH₃) samples show that PH₃ is a significant contributor to the continuum opacity in the window and in fact defines its short-wavelength limit. This has important implications for the use of 5-mu;m observations as a means to probe the deep atmospheric structure of Jupiter. The abundance of PH₃ which results from a comparison of Jovian and laboratory spectra is about 3 to 5 cm-am. This is five to eight times less than that found by Larson et al. [Astrophys. J. (1977) 211, 972–979] in the same spectral region, but is in good agreement with the result of Tokunaga et al. [Astrophys. J. (1979) 232, 603–615] from 10-μm observations.     

Ammonia-water ice laboratory studies relevant to outer Solar System surfaces

Although water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites in the outer Solar System, significant gaps exist in our knowledge of the spectra and behavior of such mixtures under astrophysical conditions. To that end, we have completed low-temperature spectroscopic studies (1-20 μm) of water-ammonia mixtures, with an emphasis on features in the near-IR, a region which is accessible to ground-based observations. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Spectra of both pure NH₃ and H₂O-NH₃ icy mixtures with ratios from 0.7 to 57 were measured at temperatures from 10 to 120 K. Conditions for the formation and thermal stability of the ammonia hemihydrate (2NH₃⋅H₂O) and the ammonia monohydrate (NH₃⋅H₂O) have been examined. Band positions of NH₃ in different H₂O-ices and major band positions of the hydrates were measured. We report spectral shifts that depend on concentration and temperature. The radiation-induced amorphization of the hemihydrate was observed and the radiation destruction of NH₃ in H₂O-ices was measured. Implications of these results for the formation, stability, and detection of ammonia on outer satellite surfaces are discussed.     

Mercury: Mid‐infrared (3–13.5 μm) observations show heterogeneous composition,presence of intermediate and basic soil types,and pyroxene

Abstract— The Aerospace Corporation's broadband array spectrograph system (BASS) mounted on the NASA infrared telescope facility (IRTF) on Mauna Kea, Hawaii was used to obtain spectral measurements of Mercury's thermal emission on 1998 March 21 (45–85° longitude), and on 1998 May 12 (68–108° longitude). The spectra show heterogeneous composition on Mercury's surface between longitudes 45–85° and about 68–108°. These observations include measurements from 3 to 6 μm, a spectral region not previously covered by mid‐infrared spectroscopy. Excellent quality data were obtained in the atmospheric windows between 3–4.2 and 4.6–5.5 μm. These wavelength regions exhibit high emissivity characteristic of a regolith with strong thermal gradients maintained in a vacuum environment with spectra dominated by grain sizes of ?30 μm. Emission peaks are present at 3.5 and 5 μm in the 45–85° longitude data. The 5 μm peak has been tentatively attributed to clinopyroxene. Data were also obtained in the 7.5–13.5 μm spectral region. Spectra obtained during both observing periods show well‐defined emissivity maxima (EM) in the spectral vicinity (between 7.7 and 9.2 μm) of the Christiansen frequency of silicate soils. The location of the EM for longitudes 45–85° (7.9 μm) is consistent with a surface composition of intermediate SiO₂ content. The overall spectral shape is similar to that obtained previously at the same location with different instrumentation. In the region 68–108° longitude, three EM are observed at 7.8, 8.2, and 9.2 μm, indicating the presence of distinctly different surface composition from the other location. Comparisons of these data to other mid‐infrared spectra of Mercury's surface and asteroids, and of the different instrumentation used in observations are included.     

Far-infrared spectrophotometry of Saturn and its rings

The spectrum of Saturn was measured from 80 to 350 cm^?1 (29 to 125 μm) with ≈6-cm^?1 resolution using a Michelson interferometer aboard NASA's Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm^?1, Saturn's brightness temperature rises slowly, reaching ≈111°K at 100 cm^?1. The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH₃ that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH₃ is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum (ν > 230 cm^?1) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν^1.5. This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition.     

A spectroscopic study of the surfaces of Saturn's large satellites: H2O ice, tholins, and minor constituents

We present spectra of Saturn's icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Hyperion, 1.0-2.5 μm, with data extending to shorter (Mimas and Enceladus) and longer (Rhea and Dione) wavelengths for certain objects. The spectral resolution (R=λ/Δλ) of the data shown here is in the range 800-1000, depending on the specific instrument and configuration used; this is higher than the resolution (R=225 at 3 μm) afforded by the Visual-Infrared Mapping Spectrometer on the Cassini spacecraft. All of the spectra are dominated by water ice absorption bands and no other features are clearly identified. Spectra of all of these satellites show the characteristic signature of hexagonal H₂O ice at 1.65 μm. We model the leading hemisphere of Rhea in the wavelength range 0.3-3.6 μm with the Hapke and the Shkuratov radiative transfer codes and discuss the relative merits of the two approaches to fitting the spectrum. In calculations with both codes, the only components used are H₂O ice, which is the dominant constituent, and a small amount of tholin (Ice Tholin II). Tholin in small quantities (few percent, depending on the mixing mechanism) appears to be an essential component to give the basic red color of the satellite in the region 0.3-1.0 μm. The quantity and mode of mixing of tholin that can produce the intense coloration of Rhea and other icy satellites has bearing on its likely presence in many other icy bodies of the outer Solar System, both of high and low geometric albedos. Using the modeling codes, we also establish detection limits for the ices of CO₂ (a few weight percent, depending on particle size and mixing), CH₄ (same), and NH₄OH (0.5 weight percent) in our globally averaged spectra of Rhea's leading hemisphere. New laboratory spectral data for NH₄OH are presented for the purpose of detection on icy bodies. These limits for CO₂, CH₄, and NH₄OH on Rhea are also applicable to the other icy satellites for which spectra are presented here. The reflectance spectrum of Hyperion shows evidence for a broad, unidentified absorption band centered at 1.75 μm.     

High-resolution spectroscopy of Saturn at 3 microns: CH4, CH3D, C2H2, C2H6, PH3, clouds, and haze

We report observation and analysis of a high-resolution 2.87-3.54 μm spectrum of the southern temperate region of Saturn obtained with NIRSPEC at Keck II. The spectrum reveals absorption and emission lines of five molecular species as well as spectral features of haze particles. The ν₂+ν₃ band of CH₃D is detected in absorption between 2.87 and 2.92 μm; and we derived from it a mixing ratio approximately consistent with the Infrared Space Observatory result. The ν₃ band of C₂H₂ also is detected in absorption between 2.95 and 3.05 μm; analysis indicates a sudden drop in the C₂H₂ mixing ratio at 15 mbar (130 km above the 1 bar level), probably due to condensation in the low stratosphere. The presence of the ν₃+ν₉+ν₁₁ band of C₂H₆ near 3.07 μm, first reported by Bjoraker et al. [Bjoraker, G.L., Larson, H.P., Fink, U., 1981. Astrophys. J. 248, 856-862], is confirmed, and a C₂H₆ condensation altitude of 10 mbar (140 km) in the low stratosphere is determined. We assign weak emission lines within the 3.3 μm band of CH₄ to the ν₇ band of C₂H₆, and derive a mixing ratio of 9±4×¹⁰⁻⁶ for this species. Most of the C₂H₆ 3.3 μm line emission arises in the altitude range 460-620 km (at ∼μbar pressure levels), much higher than the 160-370 km range where the 12 μm thermal molecular line emission of this species arises. At 2.87-2.90 μm the major absorber is tropospheric PH₃. The cloud level determined here and at 3.22-3.54 is 390-460 mbar (∼30 km), somewhat higher than found by Kim and Geballe [Kim, S.J., Geballe, T.R., 2005. Icarus 179, 449-458] from analysis of a low resolution spectrum. A broad absorption feature at 2.96 μm, which might be due to NH₃ ice particles in saturnian clouds, is also present. The effect of a haze layer at about 125 km (∼12 mbar level) on the 3.20-3.54 μm spectrum, which was not apparent in the low resolution spectrum, is clearly evident in the high resolution data, and the spectral properties of the haze particles suggest that they are composed of hydrocarbons.     

Broadband Submillimeter Spectroscopy of HCN, NH3, and PH3in the Troposphere of Jupiter

We report measurements of the Jupiter brightness spectrum in the 850-μm and 1100-μm atmospheric windows with a spectral resolution of 125 MHz, obtained with a Fourier transform spectrometer on the James Clerk Maxwell Telescope. Three results were obtained. First, the predicted absorption features due to the rotational lines of HCN at 266 and 354 GHz were not detected within our error limits of less than 1%. We establish new upper limits for the HCN abundance in the jovian troposphere for five assumed abundance distributions and for two assumed NH₃abundances. The upper limits are 1.7 to 13 times smaller than the abundance value obtained in the only reported detection of HCN in Jupiter prior to the impact of Shoemaker–Levy 9. Second, the continuum brightness temperature spectrum at 850 μm was determined and is in agreement with previous measurements, but has large error bars due to uncertainties in the photometric calibration. We estimate the ammonia abundance in the 1–2 bar region to be 1.7 times solar, but this result is tentative since scattering by NH₃cloud particles and absorption by gaseous H₂S were neglected in our atmospheric model. Finally, the first rotational line of PH₃at 267 GHz was not detected, a result which we demonstrate is consistent with the statistical noise level in these measurements, with current values of the spectroscopic parameters, and with phosphine measurements at other wavelengths.     

Thermal infrared constraints on ammonia ice particles as candidates for clouds in the atmosphere of Saturn

It is possible for large particles of NH₃ ice to explain two phenomena associated with observations of thermal infrared emission from the atmosphere of Saturn: (1) the depression of thermal brightness near the equator, which is coincident with a visibly bright zone-like region, and (2) some disagreements between infrared and radio occultation results. Particles of NH₃ ice can provide the requisite opacity to explain the contrast between the equatorial region and the brighter area near 15°S for Pioneer Saturn Infrared Radiometer 45-μm channel data. NH₃ ice particle clouds can also reconcile the 45-μm brightness of both regions (near the equator and near 15°S) with the mean temperatures structure of the Voyager 2 radio occultation results. A cloud model with ice particles distributed in equal ratio with gas particles up to the 100-mbar pressure level best fits the equatorial data; a thinner cloud or one which does not extend higher than the 400-mbar limit of the convective region best matches data for the 15°S region. At 20 μm, however, the radio occultation temperature structure predicts brightnesses which are lower than those observed for both regions, and it could indicate the possibility that another source of opacity which is latitudinally variable exists in the stratosphere.     

Far-infrared brightness temperature of Saturn's disk and rings

We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find T_D, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of T_D and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm.     

The Jovian atmospheric window at 2.7 μm: A search for H2S

The atmospheric transmission window at 2.7 μm in Jupiter's atmosphere was observed at a spectral resolution of 0.1 cm^?1 from the Kuiper Airborne Observatory. From analysis of the CH₄ abundance (～80m-am) and the H₂O abundance (<0.0125cm-am) it was determined that the penetration depth of solar flux at 2.7 μm is near the base of the NH₃ cloud layer. The upper limit to H₂O at 2.7 μm and other recent results suggest that photolytic reactions in Jupiter's lower troposphere may not be as significant as was previously thought. The search for H₂S in Jupiter's atmosphere yielded an upper limit of ～0.1cm-am. The corresponding limit to the elemental abundance ratio [S]/[H] was ～1.7 × 10^?8, about 10^?3 times the solar value. Upon modeling the abundance and distribution of H₂S in Jupiter's atmosphere it was concluded that, contrary to expectations, sulfur-bearing chromophores are not present in significant amounts in Jupiter's visible clouds. Rather, it appears that most of Jupiter's sulfur is locked up as NH₄SH in a lower cloud layer. Alternatively, the global abundance of sulfur in Jupiter may be significantly depleted.     

Simultaneous measurements of No and No2 in the stratosphere

Simultaneous measurements of NO and NO₂ in the stratosphere leading to an NO_x determination have been performed by means of i.r. absorption spectrometry using the Sun as a source in the 5·2 μm band of NO and in the 6·2 μm band of NO₂. The observed abundance of NO_P peaks at 26 km where it is equal to (4·2 ± 1) × 10⁹ cm^?3. The volume mixing ratio of NO_p was observed to vary from 1·3 × 10^?9 at 20 km to 1·3 × 10^?8 at 34 km.