Infrared properties of haze particles of Venus

The computed variation of the infrared flux and polarization of Venus as a function of phase angle, based upon multiple-scattering calculations for the cloud model of Kawabata et al. (1980) with an internal heat source, precludes the possibility of sulfuric acid as the composition of the haze particles located above the main cloud. Furthermore, our calculations reveal that the hazticle should have a large absorption coefficient at these wavelengths, i.e, $\text{k(}\text{imaginary part of the complex refractive index}\text{) ? 1.3}\text{at a wavelength}\text{λ = 3.4 μ}\text{m}$. The optical thickness of the haze layer must be about 0.15 at λ = 3.4 μm.     

The structure and microphysical properties of the Venus clouds: Venera 9, 10, and 11 data

Data processing and interpretation of the nephelometer measurements made in the Venus atmosphere aboard the Venera 9, 10 and 11 landers in the sunlit hemisphere near the equator are discussed. These results were used to obtain the aerosol distribution and its microphysical properties from 62 km to the surface. The main aerosol content is found in the altitude range between 62 km (where measurements began) and 48 km, the location of the cloud region. Three prominent layers labeled as I (between 62 and 57 km), II (between 57 and 51 km) and III (between 51 and 48 km), each with different particle characteristics are discovered within the clouds. The measured light-scattering patterns can be intrepreted as having been produced by particles with effective radii from 1 to 2 μm depending on height and indices of refractivity from 1.45 in layer I to 1.42 in layer III. These values do not contradict the idea that the droplets are made of sulfuric acid. In layers II and III the particle size distribution is at least bimodal rather than uni-modal. The index of refraction is found to decrease to 1.33 in the lower part of layer II, suggesting a predominant abundance of larger particles of different chemical origin, and chlorine compounds are assumed to be relevant to this effect. In the entire heightrange of the Venera 9–11 craft descents, the clouds are rather rarefied and are characterized by a mean volume scattering coefficient σ ～ 2 × 10^?5 cm^?1 that corresponds to the mean meteorological range of visibility of about 2 km. The average mass content of condensate is estimated to be equal to 4 × 10^?9 g/cm³, and the total optical depth of clouds to τ ～ 35. Near the bottom of layer III clouds are strongly variable. In the subcloud atmosphere a haze was observed between 48 and 32 km; that haze is mainly made of submicron particles, r_eff ～ 0.1μm. The atmosphere below that is totally transparent but separate (sometimes possibly disappearing) layers may be present up to a height of 8 km above the surface. A model of this region with a very low particle density (N ? 2–3 cm^?3) strongly refractive large particles (r_eff ? 2.5 μm; 1.7 < n < 2.0) provided satisfactory agreement. The optical depth of aerosol in the atmosphere below the subcloud haze does not exceed 2.5.     

Titan: Far-infrared and microwave remote sensing of methane clouds and organic haze

It is shown that Titan's surface and plausible atmospheric thermal opacity sources—gaseous N₂, CH₄, and H₂, CH₄ cloud, and organic haze—are sufficient to match available Earth-based and Voyager observations of Titan's thermal emission spectrum. Dominant sources of thermal emission are the surface for wavelenghts λ ? 1 cm, atmospheric N₂ for 1 cm ? λ ? 200 μm,, condensed and gaseous CH₄ for 200 μm ? λ ? 20 μm, and molecular bands and organic haze for λ ? 20 μm. Matching computed spectra to the observed Voyager IRIS spectra at 7.3 and 52.7° emission angles yields the following abundances and locations of opacity sources: CH₄ clouds: 0.1 g cm^? at a planetocentric radius of 2610–2625 km, 0.3 g cm^?2 at 2590–2610 km, total 0.4 ± 0.1 g cm^–2 above 2590 km; organic haze: $\text{4 ± 2 × 10}{}^{\mathrm{?6}}\text{,}\text{g cm}\text{,}{}^{\mathrm{?2}}$ above 2750 km; tropospheric H₂: 0.3 ± 0.1 mol%. This is the first quantitative estimate of the column density of condensed methane (or CH₄/C₂H₆) on Titan. Maximum transparency in the middle to far IR occurs at 19 μm where the atmospheric vertical absorption optical depth is $\text{?0.6}$ A particle radius $\text{r}\text{? 2 μ}\text{m}$ in the upper portion of the CH₄ cloud is indicated by the apparent absence of scattering effects.     

Spatially-resolved high-resolution spectroscopy of Venus 1. Variations of CO2, CO, HF, and HCl at the cloud tops

Variations of the upper cloud boundary and the CO, HF, and HCl mixing ratios were observed using the CSHELL spectrograph at NASA IRTF. The observations were made in three sessions (October 2007, January 2009, and June 2009) at early morning and late afternoon on Venus in the latitude range of ±60°. CO₂ lines at 2.25 μm reveal variations of the cloud aerosol density (∼25%) and scale height near 65 km. The measured reflectivity of Venus at low latitudes is 0.7 at 2.25 μm and 0.028 at 3.66 μm, and the effective CO₂ column density is smaller at 3.66 μm than those at 2.25 μm by a factor of 4. This agrees with the almost conservative multiple scattering at 2.25 μm and single scattering in the almost black aerosol at 3.66 μm. The expected difference is just a factor of (1 − g)⁻¹ = 4, where g = 0.75 is the scattering asymmetry factor for Venus’ clouds. The observed CO mixing ratio is 52 ± 4 ppm near 08:00 and 40 ± 4 ppm near 16:30 at 68 km, and the higher ratio in the morning may be caused by extension of the CO morningside bulge to the cloud tops. The observed weak limb brightening in CO indicates an increase of the CO mixing ratio with altitude. HF is constant at 3.5 ± 0.2 ppb at 68 km in both morningside and afternoon observations and in the latitude range ±60°. Therefore the observations do not favor a bulge of HF, though HF is lighter than CO. Probably a source in the upper atmosphere facilitates the bulge formation. The recent measurements of HCl near 70 km are controversial (0.1 and 0.74 ppm) and require either a strong sink or a strong source of HCl in the clouds. The HCl lines of the (2-0) band are blended by the solar and telluric lines. Therefore we observed the P8 lines of the (1-0) band at 3.44 μm. These lines are spectrally clean and result in the HCl mixing ratio of 0.40 ± 0.03 ppm at 74 km. HCl does not vary with latitude within ±60°. Our observations support a uniformly mixed HCl throughout the Venus atmosphere.     

Solar radiation scattered in the Venus atmosphere: The Venera 11,12 data

Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m^?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m^?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m^?2 for H >; 43 km and ～45 W m^?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω₀, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω₀) is <10^?3 for 0.49 and 0.7 μm. The parameter (1 ? ω₀) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω₀) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10^?8 normalized to S₂ molecules is the absorber. The upper limits of the mixing ratio for Cl₂, Br₂, and NO₂ are 4 × 10^?8, 2 × 10^?11, and 4 × 10^?10, respectively. The CO₂ and H₂O bands are confidently identified in the observed spectra. The mean value of the H₂O mixing ratio is 3 × 10^?5 < F_H2O < 10^?4 in the undercloud atmosphere. The H₂O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from F_H2O = 2 × 10^?5 near the surface to a 10 to 20 times higher value in the clouds.     

Polarization studies of the Venus uv contrasts: Cloud height and haze variability

Polarimetry is able to show direct evidence for compositional differences in the Venus clouds. We present observations (collected during $\text{2}\text{1}\text{2}$ Venus years by the Pioneer Venus Orbiter) of the polarization in four colors of the bright and dark ultraviolet features. We find that the polarization is significantly different between the bright and dark areas. The data show that the “null” model of L. W. Esposito (1980, J. Geophys. Res.85, 8151–8157) and the “overlying haze” model of J. B. Pollack et al. (1980, J. Geophys. Res.85, 8223–8231) are insufficient. Exact calculations of the polarization, including multiple scattering and vertical inhomogeneity near the Venus cloud tops, are able to match the observations. Our results give a straightforward interpretation of the polarization differences in terms of known constituents of the Venus atmosphere. The submicron haze and uv absorbers are anticorrelated: for haze properties as given by K. Kawabata et al. (1980, J. Geophys. Res.85, 8129–8140) the excess haze depth at 9350 Å over the bright regions is Δτ_h = 0.03 ± 0.02. The cloud top is slightly lower in the dark features: the extra optical depth at 2700 Å in Rayleigh scattering above the darker areas is Δτ_R = 0.010 ± 0.005. This corresponds to a height difference of 1.2 ± 0.6 km at the cloud tops. The calculated polarization which matches our data also explains the relative polarization of bright and dark features observed by Mariner 10. The observed differential polarization cannot be explained by differential distribution of haze, if the haze aerosols have an effective size of 0.49 μm, as determined by K. Kawabata et al. (1982, submitted) for the aerosols overlying the Venus equator. We propose two models for the uv contrasts consistent with our results. In a physical model, the dark uv regions are locations of vertical convergence and horizontal divergence. In a chemical model, we propose that the photochemistry is limited by local variations in water vapor and molecular oxygen. The portions of the atmosphere where these constituents are depleted at the cloud tops are the dark uv features. Strong support for this chemical explanation is the observation that the number of sulfur atoms above the cloud tops is equal over both the bright and dark areas. The mass budget of sulfur at these altitudes is balanced between excess sulfuric acid haze over the bright regions and excess SO₂ in the dark regions.     

Spectrophotometry of J8, J9, and four Trojan asteroids from 0.32 to 1.05 μm

New 30-channel narrowband photometry from 0.32 to 1.05 μm of the retrograde Jovian satellites J9 (to 0.7 μm) and J8 and the trailing Trojan asteroids 617, 884, 1172, and 1173 is presented. The data confirm previous measurements of J8, 617, 884, and 1172 at λ < 0.8 μm, but the extension into the infrared shows that the normalized spectral reflectance of these objects rises steadily from ～0.8 at 0.4 μm to ～ 1.4 at 1.05 μm, suggesting they are too bright in the near infrared to be C-type asteroids. The C classification of 1173 is confirmed. J9 is markedly redder than J8 at visible wavelengths. The results indicate a greater taxonomic contrast between these distant objects and main-belt asteroids than previously thought.     

Infrared photometry of Venus: Variation during 10 years?

The infrared flux of Venus has been observed with a narrowband filter (λ = 3.6 μm, Δλ = 0.08 μm) from 1982 through 1984, covering a range of the phase angle α from 27 to 94°. Normalized values of flux at the Venus-Earth distance of 1 AU were (4.0–5.4) × 10^?17W/cm²/cm^?1 and the α dependence of the data is rather weak. Furthermore, when the evening terminator of Venus was seen, lower values of flux were obtained in contrast with higher values at the morning terminator. The α dependence is quite different from that of J.V. Martonchik and R. Beer (1975, J. Atmos. Sci.32, 1151–1156). Since we cannot find any significant problem in the two observational methods, the difference might suggest an intrinsic time variation of haze particles during these 10 years in the upper haze layer of the Venus cloud.     

Venus: Mesospheric hazes of ice,dust, and acid aerosols

We speculate on the origin and physical properties of haze in the upper atmosphere of Venus. It is argued that at least four distinct types of particles may be present. The densest and lowest haze, normally seen by spacecraft, probably consists of a submicron sulfuric acid aerosol which extends above the cloud tops (at ～70 km) up to ～80 km; this haze represents an extension of the upper cloud deck. Measurements of the temperature structure between 70 and 120 km indicate that two independent water ice layers may occasionally appear. The lower one can form between 80 and 100 km and is probably the detached haze layer seen in high-contrast limb photography. This ice layer is likely to be nucleated on sulfuric acid aerosols, and is analogous to the nacreous (stratospheric) clouds on Earth. At the Venus “mesopause” near 120 km, temperatures are frequently cold enough to allow ice nucleation on meteoric dust or ambient ions. The resulting haze (which is analogous to noctilucent clouds on Earth) is expected to be extremely tenous, and optically invisible. On both Earth and Venus, meteoric dust is present throughout the upper atmosphere and probably has similar properties.     

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.     

Spectral imaging of martian water ice clouds and their diurnal behavior during the 1999 aphelion season (Ls = 130°)

We report high-spectral-resolution (λ/δλ = 800-2300) near-infrared mapping observations of Mars at L_s = 130° (April 1999), which were obtained by drift-scanning the cryogenic long-slit spectrometer at the KPNO 2.2-m telescope across the disk. Data were reformatted into calibrated spectral image cubes (x,y,λ) spanning 2.19 to 4.12 μm, which distinguish atmospheric CO₂ features, solar lines, and surface and aerosol features. Maps of relative band depth between 3.0 and 3.5 μm trace water ice clouds and show the diurnal evolution of features in the persistent northern summer aphelion cloud belt, which was mapped contemporaneously but at fixed local time by the Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES). Cloud optical depth, particle sizes, and ice aerosol content were estimated using a two-stream, single-layer scattering model, with Mie coefficients derived from recently published ice optical constants, followed by a linear spectral deconvolution process. A comparison of data and model spectra shows evaporating nighttime clouds in the morning followed by afternoon growth of a prominent orographic cloud feature on the west flank of Elysium Mons. Cloud optical depth at 3.2 μm evolved to 0.28 ± 0.13 and ice aerosol column abundance to 0.9 ± 0.3 pr μm in the afternoon. Column abundances as large as 0.17 pr μm were retrieved in nonorographic clouds within the aphelion cloud band around midday. These clouds exhibit a modest decline in optical depth during the afternoon. Results show that ice particle radii from <2 μm to >4 μm exist in both cloud types. However, large particles dominate the spectra, consistent with recent MGS/TES emission phase function measurements of aphelion cloud aerosol properties.     

Aircraft observations of Venus' near-infrared reflection spectrum: Implications for cloud composition

We have obtained measurements of Venus' reflection spectrum in the 1.2 to 4.1-μm spectral region from a NASA-Ames operated Lear jet. This was accomplished by observing both Venus and the sun with a spectrometer that contained a circular, variable interference filter, whose effective spectral resolution was 2%. The aircraft results were compared with computer generated spectra of a number of cloud candidates. The only substance which gave an acceptable match to the profile of Venus' strong 3-μm absorption feature, was a water solution of sulfuric acid, that had a concentration of 75% or more H₂SO₄ by weight. However, our spectra also show a modest decline in reflectivity from 2.3 μm towards 1.2-μm wavekength, which is inconsistent with the flat spectrum of sulfuric acid in this spectral region. We hypothesize that this decline is due to impurities in the sulfuric acid droplets.We also compared our list of cloud candidates with several other observed properties of the Venus clouds. While this comparison does not provide as unique an answer as did our analysis of the 3-μm band, we find that, in agreement with the results of Young (1973) and Sill (1973), concentrated sulfuric acid solutions are compatible with these additional observed properties of the Venus clouds. We conclude that the visible cloud layer of Venus is composed of sulfuric acid solution droplets, whose concentration is 75% H₂SO₄, or greater, by weight.     

Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010

The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.     

Photometry of 433 Eros from 0.65 to 2.2 μm

Lightcurves of 433 Eros are reported for 11 bandpasses ranging from 0.65 to 2.2 μm in wavelength. The relative spectral reflectance, R(λ), was not seen to vary during our observations. Eros has R(1.6 μm) = 1.5 ± 0.1 and R(2.2 μm) = 1.7 ± 0.1, where R(λ) is the spectral reflectance scaled to unity at λ = 0.56 μm. This spectral reflectance is suggestive of a mixture of silicates and material with high infrared reflectance, perhaps a metallic phase such as meteoritic “iron”.     

The brightness temperatures of Saturn and its rings at 39 microns

We have resolved the relative rings-to-disk brightness (specific intensity) of Saturn at 39 μm (δλ ? 8 μm) using the 224-cm telecscope at Mauna Kea Oservatory, and have also measured the total flux of Saturn relative to Jupiter in the same bandpass from the NASA Learjet Observatory. These two measurements, which were made in early 1975 with Saturn's rings near maximum inclination (b′ ? 25°), determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it possible to compare existing measurementsunambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 μm are all compatible (within 2σ) of a disk brightness temperature of 94°K, and do not agree with the radiative equilibrium models of Trafton; (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for λ ? 40 μm and (3) there is a decrease of ～22% in the relative ring: disk brightness between effective wavelengths of 33.5 and 39 μm.     

Venus: The 17- to 38-micron spectrum

The Venus emission spectrum was measured from the NASA Lear Jet on five nights in June 1975. A cooled grating spectrometer with a resolution of γ/δγ ? 25 over the spectral interval 17 to 38μm was used. The main features in the observed spectrum are consisten with the theoretical emission spectrum of a haze of aqueous sulfuric acid droplets suspended in a CO₂ atmosphere.     

SPICAV on Venus Express: Three spectrometers to study the global structure and composition of the Venus atmosphere

Spectroscopy for the investigation of the characteristics of the atmosphere of Venus (SPICAV) is a suite of three spectrometers in the UV and IR range with a total mass of 13.9 kg flying on the Venus Express (VEX) orbiter, dedicated to the study of the atmosphere of Venus from ground level to the outermost hydrogen corona at more than 40,000 km. It is derived from the SPICAM instrument already flying on board Mars Express (MEX) with great success, with the addition of a new IR high-resolution spectrometer, solar occultation IR (SOIR), working in the solar occultation mode. The instrument consists of three spectrometers and a simple data processing unit providing the interface of these channels with the spacecraft.A UV spectrometer (118–320 nm, resolution 1.5 nm) is identical to the MEX version. It is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation. In nadir orientation, SPICAV UV will analyse the albedo spectrum (solar light scattered back from the clouds) to retrieve SO₂, and the distribution of the UV-blue absorber (of still unknown origin) on the dayside with implications for cloud structure and atmospheric dynamics. On the nightside, γ and δ bands of NO will be studied, as well as emissions produced by electron precipitations. In the stellar occultation mode the UV sensor will measure the vertical profiles of CO₂, temperature, SO₂, SO, clouds and aerosols. The density/temperature profiles obtained with SPICAV will constrain and aid in the development of dynamical atmospheric models, from cloud top (∼60 km) to 160 km in the atmosphere. This is essential for future missions that would rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow studies of the ionosphere through the emissions of CO, CO⁺, and CO₂⁺, and its direct interaction with the solar wind. It will study the H corona, with its two different scale heights, and it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere.The SPICAV VIS-IR sensor (0.7–1.7 μm, resolution 0.5–1.2 nm) employs a pioneering technology: an acousto-optical tunable filter (AOTF). On the nightside, it will study the thermal emission peeping through the clouds, complementing the observations of both VIRTIS and Planetary Fourier Spectrometer (PFS) on VEX. In solar occultation mode this channel will study the vertical structure of H₂O, CO₂, and aerosols.The SOIR spectrometer is a new solar occultation IR spectrometer in the range λ=2.2–4.3 μm, with a spectral resolution λ/Δλ>15,000, the highest on board VEX. This new concept includes a combination of an echelle grating and an AOTF crystal to sort out one order at a time. The main objective is to measure HDO and H₂O in solar occultation, in order to characterize the escape of D atoms from the upper atmosphere and give more insight about the evolution of water on Venus. It will also study isotopes of CO₂ and minor species, and provides a sensitive search for new species in the upper atmosphere of Venus. It will attempt to measure also the nightside emission, which would allow a sensitive measurement of HDO in the lower atmosphere, to be compared to the ratio in the upper atmosphere, and possibly discover new minor atmospheric constituents.     

Red clouds in reducing atmospheres

A dark reddish-brown high-molecular-weight polymer is produced by long wavelength ultraviolet irradiation of abundant gases in reducing planetary atmospheres. The polymer i examined by paper chromatography, mass spectrometry, and infrared, visible, and ultraviolet spectroscopy. High carbon-number straight-chain alkanes with NH₂ and, probably, OH and CO groups are identified, along with the previously reported amino acids. There are chemical similarities between this polymer and organic compounds recovered from carbonaceous chondrites and precambrian sediments. The visible and near-ultraviolet transmission spectrum of the polymer shows its absorption optical depth to be redder than λ^?2 and perhaps similar in coloration to the clouds of Jupiter, Saturn, and Titan. The near-ultraviolet absorption coefficient is ～10³ cm^?1, and typical grain sizes ～30 μm. The nitrile content is small, and the polymer should be semitransparent in the 5 μm atmospheric window. Such polymers may be a common constituent of clouds in the outer solar system and on the early Earth.     

Observations of Jupiter and Saturn at 5–8 μm

Moderate-resolution spectrophotometry (Δλ/λ～0.015) has shown the effects of known atmospheric constituents (NH₃, CH₄, C₂H₆) on the 5–8 μm spectrum of Jupiter. Broadband observations of Saturn at 6.5 μm are also reported.     

Surface composition of Pluto

Infrared photometric observations (1–4 μm) of Pluto have been made using broadband (Δλ/λ ～ 0.3) and narrowband (Δλ/λ ～ 0.05–0.1) filters. We confirm the probable presence of methane in some form, though, in detail the match between the spectrum of Pluto and the laboratory spectrum of methane frost is poor.