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The Juno Microwave Radiometer (MWR) is a six-frequency scientific instrument designed and built to investigate the deep atmosphere of Jupiter. It is one of a suite of instruments on NASA’s New Frontiers Mission Juno launched to Jupiter on August 5, 2011. The focus of this paper is the description of the scientific objectives of the MWR investigation along with the experimental design, observational approach, and calibration that will achieve these objectives, based on the Juno mission plan up to Jupiter orbit insertion on July 4, 2016. With frequencies distributed approximately by octave from 600 MHz to 22 GHz, the MWR will sample the atmospheric thermal radiation from depths extending from the ammonia cloud region at around 1 bar to pressure levels as deep as 1000 bars. The primary scientific objectives of the MWR investigation are to determine the presently unknown dynamical properties of Jupiter’s subcloud atmosphere and to determine the global abundance of oxygen and nitrogen, present in the atmosphere as water and ammonia deep below their respective cloud decks. The MWR experiment is designed to measure both the thermal radiation from Jupiter and its emission-angle dependence at each frequency relative to the atmospheric local normal with high accuracy. The antennas at the four highest frequencies (21.9, 10.0, 5.2, and 2.6 GHz) have ∼12° beamwidths and will achieve a spatial resolution approaching 600 km near perijove. The antennas at the lowest frequencies (0.6 and 1.25 GHz) are constrained by physical size limitations and have 20° beamwidths, enabling a spatial resolution of as high as 1000 km to be obtained. The MWR will obtain Jupiter’s brightness temperature and its emission-angle dependence at each point along the subspacecraft track, over angles up to 60° from the normal over most latitudes, during at least six perijove passes after orbit insertion. The emission-angle dependence will be obtained for all frequencies to an accuracy of better than one part in 10^3, sufficient to detect small variations in atmospheric temperature and absorber concentration profiles that distinguish dynamical and compositional properties of the deep Jovian atmosphere.

Material of low geometric albedo (pV⩽0.1pV⩽0.1) is found on many objects in the outer Solar System, but its distribution in the saturnian satellite system is of special interest because of its juxtaposition with high-albedo ice. In the absence of clear, diagnostic spectral features, the composition of this low-albedo (or “dark”) material is generally inferred to be carbon-rich, but the form(s) of the carbon is unknown. Near-infrared spectra of the low-albedo hemisphere of Saturn's satellite Iapetus were obtained with the Visible–Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft at the fly-by of that satellite of 31 December 2004, yielding a maximum spatial resolution on the satellite's surface of ∼65 km. The spectral region 3–3.6 μm reveals a broad absorption band, centered at 3.29 μm, and concentrated in a region comprising about 15% of the low-albedo surface area. This is identified as the CH stretching mode vibration in polycyclic aromatic hydrocarbon (PAH) molecules. Two weaker bands attributed to CH2 stretching modes in aliphatic hydrocarbons are found in association with the aromatic band. The bands most likely arise from aromatic and aliphatic units in complex macromolecular carbonaceous material with a kerogen- or coal-like structure, similar to that in carbonaceous meteorites. VIMS spectra of Phoebe, encountered by Cassini on 11 June 2004, also show the aromatic hydrocarbon band, although somewhat weaker than on Iapetus. The origin of the PAH molecular material on these two satellites is unknown, but PAHs are found in carbonaceous meteorites, cometary dust particles, circumstellar dust, and interstellar dust.

International audience; Aims:The aim of this paper is to investigate the surface composition of the Transneptunian Object (TNO) Orcus. Methods: High quality observations have been carried out with the new instrument SINFONI at the Very Large Telescope (VLT) of ESO. Results: Crystalline water ice, and possibly ammonia ice, have been found from spectroscopic observations of the TNO Orcus between 1.4 and 2.4 mum. Conclusions: The existence of such ices on the surface of Orcus may indicate a renewal mechanism on the surface and geological activity. The presence of ammonia on the surface of Orcus, if confirmed, could have important implications for the composition of the primitive solar nebula and the formation of the TNO population.

Recent attempts using high resolution spectra to detect N+2 in several comets were unsuccessful [Cochran, A.L., Cochran, W.D., Baker, E.S., 2000. Icarus 146, 583–593; Cochran, A.L., 2002. Astrophys. J. 576, L165–L168]. The upper limits on N+2 in comparison with the positively detected CO+ for Comets C/1995 O1 Hale–Bopp, 122P/1995 S1 de Vico and 153P/2002 C1 Ikeya–Zhang range between N 2 + /CO + ( 0.65 – 5.4 ) × 10 −4 . Ar was not detected in three recent comets [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95–L98], with upper limits of Ar/CO ( 3.4 – 7.8 ) × 10 −2 for Comets C/1999 T1 McNaught–Hartley, C/2001 A2 LINEAR and C/2000 WM1 LINEAR. The Ar detected by Stern et al. [Stern, S.A., Slater, D.C., Festou, M.C., Parker, J.Wm., Gladstone, G.R., A'Hearn, M.F., Wilkinson, E., 2000. Astrophys. J. 544, L169–L172] for Comet C/1995 O1 Hale–Bopp, gives a ratio Ar/CO = 7.25 × 10 −2 , which was not confirmed by Cosmovici et al. [Cosmovici, C.B., Bratina, V., Schwarz, G., Tozzi, G., Mumma, M.J., Stalio, R., 2006. Astrophys. Space Sci. 301, 135–143]. Trying to solve the two problems, we studied experimentally the trapping of N 2 + CO + Ar in amorphous water ice, at 24–30 K. CO was found to be trapped in the ice 20–70 times more efficiently than N2 and with the same efficiency as Ar. The resulting Ar/CO ratio of 1.2 × 10 −2 is consistent with Weaver et al.'s [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95–L98] non-detection of Ar. However, with an extreme starting value for N2/CO = 0.22 in the region where the ice grains which agglomerated to produce comet nuclei were formed, the expected N2/CO ratio in the cometary ice should be 6.6 × 10 −3 , much higher than its non-detection limit.

International audience; The Composite Infrared Spectrometer (CIRS) is a remote-sensing Fourier Transform Spectrometer (FTS) on the Cassini orbiter that measures thermal radiation over two decades in wavenumber, from 10 to 1400 cm- 1 (1 mm to 7mu m), with a spectral resolution that can be set from 0.5 to 15.5 cm- 1. The far infrared portion of the spectrum (10 600 cm- 1) is measured with a polarizing interferometer having thermopile detectors with a common 4-mrad field of view (FOV). The middle infrared portion is measured with a traditional Michelson interferometer having two focal planes (600 1100 cm- 1, 1100 1400 cm- 1). Each focal plane is composed of a 1× 10 array of HgCdTe detectors, each detector having a 0.3-mrad FOV. CIRS observations will provide three-dimensional maps of temperature, gas composition, and aerosols/condensates of the atmospheres of Titan and Saturn with good vertical and horizontal resolution, from deep in their tropospheres to high in their mesospheres. CIRS's ability to observe atmospheres in the limb-viewing mode (in addition to nadir) offers the opportunity to provide accurate and highly resolved vertical profiles of these atmospheric variables. The ability to observe with high-spectral resolution should facilitate the identification of new constituents. CIRS will also map the thermal and compositional properties of the surfaces of Saturn's icy satellites. It will similarly map Saturn's rings, characterizing their dynamical and spatial structure and constraining theories of their formation and evolution. The combination of broad spectral range, programmable spectral resolution, the small detector fields of view, and an orbiting spacecraft platform will allow CIRS to observe the Saturnian system in the thermal infrared at a level of detail not previously achieved.

The Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft made infrared observations of Jupiter's atmosphere during the flyby in December 2000 to January 2001. The unique database in the 600-1400/cm region with 0.53 and 2.8/cm spectral resolutions obtained from the observations permits retrieval of global maps of the thermal structure and composition of Jupiter's atmosphere including the distributions of (14)NH3 and (15)NH3. Analysis of Jupiter's ammonia distributions from three isolated (15)NH3 spectral lines in eight latitudes is presented for evaluation of the nitrogen isotopic ratio. The nitrogen isotopic ratio (14)N/(15)N (or (15)N/(14)N) in Jupiter's atmosphere in this analysis is calculated to be: 448 +/- 62 ((2.23 +/- 0.31) x 10(exp -3)). This value of the ratio determined from CIRS data is found to be in very close agreement with the value previously obtained from the measurements by the Galileo Probe Mass Spectrometer. Some possible mechanisms to account for the variation of Jupiter's observed isotopic ratio relative to various astrophysical environments are discussed.

During the last two minutes before closest approach of Deep Space 1 to Comet 19P/Borrelly, a long exposure was made with the short-wavelength infrared (SWIR) imaging spectrometer. The observation yielded 46 spectra covering 1.3–2.6 μm; the footprint of each spectrum was ∼160 m × width of the nucleus. Borrelly's highly variegated and extremely dark 8-km-long nucleus exhibits a strong red slope in its short-wavelength infrared reflection spectrum. This slope is equivalent to J–K and H–K colors of ∼0.82 and ∼0.43, respectively. Between 2.3–2.6 μm thermal emission is clearly detectable in most of the spectra. These data show the nucleus surface to be hot and dry; no trace of H2O ice was detected. The surface temperature ranged continuously across the nucleus from ⩽300 K near the terminator to a maximum of ∼340 K, the expected sub-solar equilibrium temperature for a slowly rotating body. A single absorption band at ∼2.39 μm is quite evident in all of the spectra and resembles features seen in nitrogen-bearing organic molecules that are reasonable candidates for compositional components of cometary nuclei. However as of yet the source of this band is unknown.

The effect of water ice formation temperature and rate of ice deposition on a cold plate on the amount of trapped argon (equivalent to CO), and the ratios of Ar/Kr/Xe trapped in the water ice were studied at 50, 27 and 22 K and at ice formation rates ranging over four orders of magnitude, from 10−1 to 10−5 μm min−1. Contrary to our previous conclusions that cometary ices were formed at 50–60 K, we now conclude that these ices were formed at about 25 K. At 25 K the enrichment ratios for Ar, Kr, and Xe remained the same as those at 50 K, reinforcing our suggestion of cometary contribution of these noble gases to the atmospheres of Earth and Mars.

Observations of emissivity features of 10 Hygiea have been made for the first time in the relatively unexplored thermal-infrared wavelength region with the ISO (Infrared Space Observatory) satellite. Spectrophotomer (PHT-S) and short wavelength spectrometer (SWS) spectra of 10 Hygiea, obtained at 5.8–11.6 and 7–45 μm, respectively, are presented. In order to remove the thermal emission continuum, an advanced thermo–physical model has been applied to the observational data. To better interpret the spectral features above the thermal emission continuum, we compared the ISO observations with laboratory spectra available in the literature. Several laboratory experiments on minerals and meteorites have been performed to complete the analysis and to study the spectral behavior at various grain sizes. A possible spectral similarity with CO carbonaceous chondrites at small grain size is demonstrated.

Adaptive optics (0.15″ resolution) infrared images of the rings and satellites of Saturn were obtained in August 1995 as the Earth was crossing the ring plane. Twelve clumps were detected in the F ring, including HST S5 and S7 objects. For the first time H magnitudes were obtained for Prometheus, Pandora, Telesto, and Calypso, and J magnitudes for Epimetheus, Janus, Mimas, Telesto, and Helene.

The isotopic enrichment of HDO over H 2 O when water vapor freezes into ice at 60–170 K was studied experimentally. No such enrichment was detected (1.003–1.007 in the 95% confidence interval). Thus HDO cannot be enriched when ice is formed by freezing of water vapor. The very similar D/H ratio in the water of Comets Halley, Hyakutake, and Hale–Bopp (∼3 × 10 −4 ) is 10–20 times larger then the D/H ratio in the solar nebula. Therefore the cometary water had to originate in a giant molecular cloud, where the HDO is enriched by ion–molecule reactions. We cannot determine whether the ice grains which agglomerated into these comets were formed in a ∼50 K warm clump in the giant molecular cloud and settled intact to the solar nebula or sublimated and refroze in the ∼50 K Uranus–Neptune region. The HDO/H 2 O ratio in Earth's oceans suggests that the water was delivered by both comets and rocky material formed in Earth's region of the solar nebula.

The near-infrared reflectance spectrum of Saturn's satellite Phoebe shows a broad absorption band at 2.0 micrometers and absorption at lambda > 2.2 micrometers, both characteristic of H2O ice. We have successfully modeled the surface of Phoebe with an intimate (granular) mix of H2O ice (3% by weight, grain size 500 micrometers) mixed with fine grains of H2O ice (0.25%) with amorphous carbon (grain size 900 micrometers) as the dominant component. This model reproduces the shape of the measured spectrum and the observed albedo of 0.10 for Phoebe, but it is not unique. The presence of ice establishes Phoebe as an original member of the outer Solar System rather than a renegade asteroid.

Since August 1995, near-infrared images of Neptune have regularly been obtained with the University-of-Hawaii telescope. These images reveal Neptune's cloud structure with an angular resolution reaching 0.12″ in the H band.

We present a new spectrum of the Centaur object 5145 Pholus between 1.15 and 2.4 micro meters. We model this, and the previously published (0.4- to 1.0- micrometer) spectrum, using Hapke scattering theory. Seen in absorption are the 2.04- micrometer band of H2O ice and a strong band at 2.27 micrometer, interpreted as frozen methanol and/or a photolytic product of methanol having small molecular weight. The presence of small molecules is indicative of a chemically primitive surface, since heating and other processes remove the light hydrocarbons in favor of macromolecular carbon of the kind found in carbonaceous meteorites. The unusually red slope of Pholus' spectrum is matched by fine grains of a refractory organic solid (tholin). Olivine (which we model with Fo 82) also appears to be present on Pholus. We present a five-component model for the composite spectrum of all spectroscopic and photometric data available for 5145 Pholus and conclude that this is a primitive object which has not yet been substantially processed by solar heat. The properties of Pholus are those of the nucleus of a large comet that has never been active.

We obtained I–J–H–K band spectroscopy of 18 low-albedo objects of the Solar System using the University of Hawaii 88-in. telescope equipped with the near-infrared spectrograph KSPEC. Most of our targets were selected from among the population of the Cybele, Hilda, and Trojan groups of asteroids, based on their low albedos and the relatively steep slopes of their reflection spectra at visible wavelengths. The outer jovian satellite Himalia and the Apollo object 3200 Phaethon were also observed. None of the spectra show absorptions similar to those found in the spectrum of 5145 Pholus, which remains the only asteroid-like object whose H–K band reflection spectrum contains a few broad absorptions due to organics. The near-infrared slope and the (1.0- to 2.2-μm) infrared color-index have been derived for each surface. This sample of primitive objects of the Solar System can be interpreted in terms of cometary-like objects that have undergone different degrees of aging.

Millimeter and submillimeter heterodyne observations performed with the IRAM 30-m telescope (Pico Veleta, Spain) and the JCMT (Mauna Kea, Hawaii) have been used to derive the stratospheric distribution of carbon monoxide on Titan. Rotational transition lines from 12 CO J (0 → 1), J (1 → 2), J (2 → 3) at 115.271, 230.538, 345.796 GHz, respectively, as well as the J (1 → 2) and J (2 → 3) lines of the 13 CO isotope at 220.399 and 330.588 GHz, respectively, were recorded with a spectral resolution of 1 MHz. Flux calibration uncertainties were estimated to 10% for all the data. A terrestrial value of the 12 C/ 13 C ratio has been assumed in the analysis as suggested by T. Hidayat et al . (1997, Icarus 126, 170–182) from recent observations of the H 12 CN(1–0) and H 13 CN(4–3) lines. The 13 CO lines sound the 60- to 180-km altitude range, while the 12 CO lines permit us to probe the atmosphere up to an altitude of about 350 km. Below 180 km, the 13 CO data impose a constant-with-height CO mixing ratio of ∼2.5 × 10 −5 . Extending this uniform mixing ratio profile throughout the stratosphere, all the 12 CO observations could be matched only if the systematic calibration errors were greater than our estimated value by at least a factor of 2. Uncertainties related to the temperature profile adopted in the stratosphere have been also investigated. Taking into account random and systematic uncertainties, the entire set of data indicates a CO mixing ratio equal to 2.9 +0.9 −0.5 × 10 −5 at 60 km, decreasing to 2.4 ± 0.5 × 10 −5 at 175 km, and reaching a value of 4.8 +3.8 −1.5 × 10 −6 at 350 km.

The close approach to the Earth of comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassing from the nucleus. We report the detection of deuterated water (HDO) through its 1(sub 01)-0(sub 00) rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive research for the J(5-4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 +/- 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 +/- 0.28) x 10(exp 26)/s on March 23-24, 1996. Available IR, UV and radio measurements lead to a water production rate of (2.1 +/- 0.5) x 10(exp 29)/s at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 +/- 10) x 10(exp -5) in good agreement with the values of (30.8(sub - 5.3, sup +3.8) (Balsiger et al. 1995) and (31.6 +/- 3.4) x 10(exp -5) (Eberhardt et al. 1995) determined in comet P/Halley from in situ ion mass spectra. The inferred 3 a upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2 in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion-molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2 in the Solar Nebula. Scenarios of formation of comets consistent with these results are discussed.

We report new observations of the (1–0) line of HCN at 88.63 GHz, emitted by Titan, made in May 1995 with the IRAM 30-m radiotelescope located at Pico Veleta (Spain). Compared to previous observations of Tanguy et al. (1990, Icarus 85, 43–57), the signal-to-noise ratio has been improved by a factor of 5, permitting us to retrieve the vertical distribution of HCN in the 80–350 km altitude range. Using the production rate of HCN predicted from photochemical models, we derive a profile of the eddy diffusion coefficient up to 350 km altitude consistent with the observed HCN vertical distribution. This coefficient increases with height more rapidly than the standard n −0.5 dependence in the stratosphere. The (4–3) line of H 13 CN at 345.34 GHz was subsequently observed with the JCMT on Mauna Kea (Hawaii) in June 1995. The analysis of the two spectra yields a 12 C/ 13 C ratio between 70 and 120, consistent with the terrestrial value. Taking into account possible fractionation processes, we show that the C-bearing species which formed Titan should have had a carbon isotopic ratio in the same range.

There are now a large number of small bodies in the outer solar system that are known to be covered with dark material. Attempts to identify that material have been thwarted by the absence of discrete absorption features in the reflection spectra of these planetesimals. An absorption at 2.2 micrometers that appeared to be present in several objects has not been confirmed by new observations. Three absorptions in the spectrum of the unusually red planetesimal 5145 Pholus are well-established, but their identity remains a mystery.

Near-infrared (J, H and K bands) spectra of nine dark asteroids (chosen among a sample of supposed primitive objects between C and D classes) have been obtained at the Mauna Kea Observatory (Hawaii) with the 2.2-m telescope using KSPEC as spectrograph. The aim of this work was to search for evidence of the presence of organic materials in these objects as found in other planetary bodies as 5145 Pholus, and in some cometary nuclei. A careful analysis of the data has revealed flat or slightly redder spectra than the solar one for all observed asteroids. No evidence of distinct absorption features was found.

The reflectance spectrum of Jupiter's sixth satellite, Himalia, is featureless in the wavelength region 1.95–2.50 μm as seen at a spectral resolution of 0.005 μm, with no absorptions deeper than a few percent. From model calculations we establish an upper limit of 10% by weight of H 2 O (30-μm grains) mixed intimately in the soil of Himalia, or alternatively 0.3% of the surface covered by exposures of H 2 O ice spatially segregated from the darker soil. For CH 4 and CO 2 ices the upper limits in spatially segregated models are both 0.3%.

International audience; We describe observations of Neptune carried out using the James Clerk Maxwell Telescope (Mauna Kea, Hawaii) during September 1998. High-quality data for the sub-mm-wavelength rotational transitions of HCN (J=4-3) and CO (J=3-2 and 4-3) were obtained, and we use the data to make improved determinations of the abundances of these trace species and the temperature profile of Neptune's atmosphere.

Spectra of Asteroid 9969 Braille in the 1.25–2.6 µm region returned by the Deep Space 1 (DS1) Mission show a ∼ 10% absorption band centered at 2 µm, and a reflectance peak at 1.6 µm. Analysis of these features suggest that the composition of Braille is roughly equal parts pyroxene and olivine. Its spectrum between 0.4 and 2.5 µm suggests that it is most closely related to the Q taxonomic type of asteroid. The spectrum also closely matches that of the ordinary chondrites, the most common type of terrestrial meteorite. The geometric albedo of Braille is unusually high (pv = 0.34), which is also consistent with its placement within the rarer classes of stony asteroids, and which suggests it has a relatively fresh, unweathered surface, perhaps due to a recent collision.

We have obtained new observations of Triton with the ESO New Technology Telescope (La Silla, Chile) in October 2002. Using the high quality of NTT instrumentation, we were able to cover the entire 0.4–2.5 μm spectral range in a single night. We applied this procedure for two nights, well selected along the orbit of Triton, in order to cover essentially the trailing side one night, and the leading one the other night, obtaining the first face-resolved 0.4–2.4 μm spectra of Triton. We discuss here the spectra and the differences between the two faces, and the implications of these new results for a better understanding of the surface composition of Triton. In particular we found possible clues for the presence of rocky materials on Triton's surface.

Aims. The objective of this work is to summarize the discussion of a workshop aimed at investigating the properties, origins, and evolution of the materials that are responsible for the red coloration of the small objects in the outer parts of the solar system. Because of limitations or inconsistencies in the observations and, until recently, the limited availability of laboratory data, there are still many questions on the subject. Our goal is to approach two of the main questions in a systematic way: – Is coloring an original signature of materials that are presolar in origin (“nature”) or stems from post-formational chemical alteration, or weathering (“nurture”)? – What is the chemical signature of the material that causes spectra to be sloped towards the red in the visible? We examine evidence available both from the laboratory and from observations sampling different parts of the solar system and circumstellar regions (disks). Methods. We present a compilation of brief summaries gathered during the workshop and describe the evidence towards a primordial vs. evolutionary origin for the material that reddens the small objects in the outer parts of our, as well as in other, planetary systems. We proceed by first summarizing laboratory results followed by observational data collected at various distances from the Sun. Results. While laboratory experiments show clear evidence of irradiation effects, particularly from ion bombardment, the first obstacle often resides in the ability to unequivocally identify the organic material in the observations. The lack of extended spectral data of good quality and resolution is at the base of this problem. Furthermore, that both mechanisms, weathering and presolar, act on the icy materials in a spectroscopically indistinguishable way makes our goal of defining the impact of each mechanism challenging. Conclusions. Through a review of some of the workshop presentations and discussions, encompassing laboratory experiments as well as observational data, we infer that both “nature” and “nurture” are instrumental in the coloration of small objects in the outer parts

Observations are presented which show that CO is present in both the troposphere and stratosphere of Neptune, whereas is confined to the Neptune stratosphere with a mean mole fraction in the 0.003-30 mbar pressure level range of 1.0 x 10 exp -9. CO is present in both the stratosphere and in the troposphere with a uniformly mixed model fraction of 1.2 x 10 exp -6. Upper limits of 1.0 x 10 exp -10 and 3.0 x 10 exp -8 mole fractions are derived for HCN and CO respectively on Uranus. The origin of these species in the atmosphere of Neptune and their nondetection in that of Uranus are discussed in detail. It is concluded that the most plausible scenario involves upward convection of CO and N2 from Neptune's deep interior and a failure of chemical equilibrium at deep atmospheric levels, allowing excess CO and presumably N2 to reach the upper atmosphere. Nondetection in Uranus may be explained by the lack of a significant internal heat source in the planet and consequent suppression of vertical convection.

We have detected the 3 nu 2 band of CH3D in the spectrum of Neptune near 1.6 micrometers recorded at a spectral resolution of 4 cm-1 with the Cassegrain Fourier Transform Spectrometer at the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. Our analysis of this spectrum, using spectral synthesis techniques, yielded a CH3D/CH4 ratio of 6(+6)(-4) x 10(-4), which corresponds to a global D/H ratio for Neptune of 1.2(+1.2)(-0.8) x 10(-4), if CH3D is in isotopic fractionation equilibrium with HD. This value is about an order of magnitude larger than an earlier estimate by Orton et al. based on deconvolution measurements of unresolved molecular emission in the 8-10 micrometers region. Comparison of this new determination with previous studies of CH3D in the outer solar system shows that, as in the case of Uranus, the D/H on Neptune is strongly enhanced over that found on Jupiter and Saturn and is comparable to the D/H in methane on Titan and in terrestrial methane and water.

Emission from C-H groups at 3.4 microns and an emission feature at 2.8 microns were detected in comet Wilson (1986l). A high-resolution spectrum confirms features at 3.52 microns. There is a possible emission feature at 3.04 microns. The spectra are strikingly similar to those of comet Halley. Derived abundances of the organic compounds are comparable. A model of the fluorescence spectrum of formaldehyde does not match the structure longward of 3.5 microns. The polymerized form of formaldehyde, polyoxymethylene, is a possible contributor to the 3.4-micron emission. The similarity between the 3.4-micron emission in a dynamically old (Halley) and a new (Wilson) comet suggests that these organics were incorporated into comets at the time of their formation. 38 references.

The paper examines the far-UV spectrum of Jupiter recorded by observations with the International Ultraviolet Explorer, noting that only the upper levels of the plant's atmosphere are sampled. It is shown that there are several absorptions caused by C2H2 and indications that NH3 may also be present at these altitudes. In addition, it is suggested that PH3 may also play a role as a continuum absorber, and a new upper limit of 5 x 10 to the -9 on H2S/H2 forbidden line ratio. It is concluded that these results are consistent with existing models for Jovian photochemistry and atmospheric structure.