High spatial and spectral resolution 10-μm observations of jupiter

Ten-micrometer spectra of the North Tropical Zone, North Equatorial Belt, and Great Red Spot at a spectral resolution of 1.1 cm^?1 are compared to synthetic spectra. These ground-based spectra were obtained simultaneously with the Voyager 1 encounter with Jupiter in March, 1979. The NH₃ vertical distribution is found to decrease with altitude significantly faster than the saturated vapor pressure curve and is different for the three observed regions. Spatial variability in the NH₃ mixing ratio could be caused by changes in the amount of NH₃ condensation or in the degree of the NH₃ photolysis. The C₂H₆ emission at 12 μm has approximately the same strength at the North Tropical Zone and North Equatorial Belt, but it is 30% weaker at the Great Red Spot. A cooler temperature inversion or a smaller abundance of C₂H₆ could explain the lower C₂H₆ emission over the Great Red Spot.     

The material of the interstellar dust and the surface of asteroids: A comparison of the spectral properties in the 0.3–1.1-μm range

From the data on bright stars of different spectral and luminosity classes from the 13-color photometry catalog, the selective extinction of light by the interstellar dust has been studied. The stars from the 1000-pc vicinity of the Sun were investigated. In the optical spectral range, the interstellar extinction curves show systematic deviations from the “λ^?1” law, which allows one to sort them into three types. The observed curves of the interstellar dust extinction were compared with the theoretical curves calculated from the reflectance spectra of the asteroids under the approximation of the Rayleigh particles. The calculated extinction curves for the surface material of D-type asteroids and the Tagish Lake carbonaceous chondrite agree rather well with the observed curves of the interstellar extinction of the first type.     

High-resolution 3-μm spectra of Jupiter: Latitudinal spectral variations influenced by molecules, clouds, and haze

We present latitudinally-resolved high-resolution (R = 37,000) pole-to-pole spectra of Jupiter in various narrow longitudinal ranges, in spectral intervals covering roughly half of the spectral range 2.86-3.53 μm. We have analyzed the data with the aid of synthetic spectra generated from a model jovian atmosphere that included lines of CH₄, CH₃D, NH₃, C₂H₂, C₂H₆, PH₃, and HCN, as well as clouds and haze. Numerous spectral features of many of these molecular species are present and are individually identified for the first time, as are many lines of and a few unidentified spectral features. In both polar regions the 2.86-3.10-μm continuum is more than 10 times weaker than in spectra at lower latitudes, implying that in this wavelength range the single-scattering albedos of polar haze particles are very low. In contrast, the 3.24-3.53 μm the weak polar and equatorial continua are of comparable intensity. We derive vertical distributions of NH₃, C₂H₂ and C₂H₆, and find that the mixing ratios of NH₃ and C₂H₆ show little variation between equatorial and polar regions. However, the mixing ratios of C₂H₂ in the northern and southern polar regions are ∼6 and ∼3 times, respectively, less than those in the equatorial regions. The derived mixing ratio curves of C₂H₂ and C₂H₆ extend up to the 10⁻⁶ bar level, a significantly higher altitude than most previous results in the literature. Further ground-based observations covering other longitudes are needed to test if these mixing ratios are representative values for the equatorial and polar regions.     

Retrieval and tentative indentification of the 3 μm spectral feature in Titan's haze

Recently, an unidentified 3.3-3.4 μm feature found in the solar occultation spectra of the atmosphere of Titan observed by Cassini/VIMS was tentatively attributed to the C-H stretching mode of aliphatic hydrocarbon chains attached to large organic molecules, but without properly extracting the feature from adjacent influences of strong CH₄ and weak C₂H₆ absorptions (Bellucci et al., 2009). In this work, we retrieve the detailed spectral feature using a radiative transfer program including absorption and fluorescent emission of both molecules, as well as absorption and scattering by haze particles. The spectral features of the haze retrieved from the VIMS data at various altitudes are similar to each other, indicating relatively uniform spectral properties of the haze with altitude. However, slight deviations observed near 127 km and above 300 km suggest inhomogeneity at these altitudes. We find that the positions of the major spectral peaks occur at 3.33-3.37 μm, which are somewhat different from the typical 3.3 μm aromatic or 3.4 μm aliphatic C-H stretches usually seen in the spectra of dust particles of the interstellar medium and comets. The peaks, however, coincide with those of the solid state spectra of C₂H₆, CH₄, and CH₃CN; and a broad shoulder from 3.37 to 3.50 μm coincides with those of C₅H₁₂ and C₆H₁₂ as well as those of typical aliphatic C-H stretches. This result combined with high-altitude (∼1000 km) haze formation process recently reported by Waite et al. (2007) opens a new question on the chemical composition of the haze particles. We discuss the possibility that the 3 μm feature may be due to the solid state absorption bands of these molecules (or some other molecules) and we advocate additional laboratory measurements for the ices of hydrocarbon and nitrogen-bearing molecules present in Titan's atmosphere for the identification of this 3 μm feature.     

Rotationally-resolved spectra of Ceres in the 3-μm region

We present observations of Ceres over the 2.2-4.0 μm region taken using the SpeX instrument on the NASA IRTF in 2005. The observations cover Ceres’ entire longitude range and show evidence for a relatively uniform surface in terms of Ceres’ composition, however there is a subtle but consistently shallower band depth over longitudes associated with bright regions in HST maps, suggesting those areas are slightly less carbonate- and brucite-rich. We also find Ceres’ beaming parameter, a measure of its thermal properties, to have changed with its viewing aspect.     

Hydrogen Dimer Features in the 2-μm Spectra of Saturn and Neptune

We report the detection of the (H₂)₂dimer in the atmospheres of Saturn and Neptune based on spectra of the fundamentalS₁(1) collision-induced band of H₂. The lines of this dimer are potentially useful for probing the (H₂)₂ortho–para ratio and its implications for atmospheric dynamical processes. We also report the detection of the (1–0)S₁(1) quadrupole absorption line of monomeric H₂in these spectra.     

Near-infrared colorimetry of J6 Himalia and S9 Phoebe: A summary of 0.3- to 2.2-μm reflectances

VJHK measurements of J6 Himalia and S9 Phoebe, using the new NASA IRTF telescope, show that these objects have carbonaceous chondritic type colors in the 0.5- to 2.2-μm region. For Phoebe, this is in contrast to the JHK colors published by Cruikshank (1980), which indicated that the satellite's surface was unlike the material found on asteroids and on the dark side of Iapetus. J6 is known to have a low albedo from thermal infrared studies (Cruikshank, 1977), and the new VJHK observations of S9 imply that it also has a low albedo. The H and K reflectances of S9 are slightly lower than those of J6, suggesting some slight difference in surface composition or a contamination by foreign material. The conjectured low albedo of S9 can be tested with measurements in the thermal infrared.     

Exploration of the Outer Planets:The Galileo and Cassini Missions

the space age has brought spectacular advances in our knowledge of the solar system.The flyby observations of the outer planets by the Voyagerspacecraft have been crost fruitful.These discoveries are now to be supple-mented by the Galileo Oribter to Jupiter and the Cassini Orbiter to Saturn.After the successful operations of the atmospheric probe in December 1995,the Galileo spacecraft is now in orbit around Jupiter and its comprehensive scientific observations of the Jovian system have just commenced.The Cassini spacecraft with the Huygens atmospheric probe to Titan will be launched in 1937 with an arrival date at Saturn in 2004.If everything goes well,these two projects will be followed by a Pluto Express mission for fast flyby reconnaissance and a Neptune Orbiter.     

Titan’s aerosol and stratospheric ice opacities between 18 and 500 μm: Vertical and spectral characteristics from Cassini CIRS

Vertical distributions and spectral characteristics of Titan’s photochemical aerosol and stratospheric ices are determined between 20 and 560 cm^?1 (500–18 μm) from the Cassini Composite Infrared Spectrometer (CIRS). Results are obtained for latitudes of 15°N, 15°S, and 58°S, where accurate temperature profiles can be independently determined.In addition, estimates of aerosol and ice abundances at 62°N relative to those at 15°S are derived. Aerosol abundances are comparable at the two latitudes, but stratospheric ices are ～3 times more abundant at 62°N than at 15°S. Generally, nitrile ice clouds (probably HCN and HC₃N), as inferred from a composite emission feature at ～160 cm^?1, appear to be located over a narrow altitude range in the stratosphere centered at ～90 km. Although most abundant at high northern latitudes, these nitrile ice clouds extend down through low latitudes and into mid southern latitudes, at least as far as 58°S.There is some evidence of a second ice cloud layer at ～60 km altitude at 58°S associated with an emission feature at ～80 cm^?1. We speculate that the identify of this cloud may be due to C₂H₆ ice, which in the vapor phase is the most abundant hydrocarbon (next to CH₄) in the stratosphere of Titan.Unlike the highly restricted range of altitudes (50–100 km) associated with organic condensate clouds, Titan’s photochemical aerosol appears to be well-mixed from the surface to the top of the stratosphere near an altitude of 300 km, and the spectral shape does not appear to change between 15°N and 58°S latitude. The ratio of aerosol-to-gas scale heights range from 1.3–2.4 at about 160 km to 1.1–1.4 at 300 km, although there is considerable variability with latitude. The aerosol exhibits a very broad emission feature peaking at ～140 cm^?1. Due to its extreme breadth and low wavenumber, we speculate that this feature may be caused by low-energy vibrations of two-dimensional lattice structures of large molecules. Examples of such molecules include polycyclic aromatic hydrocarbons (PAHs) and nitrogenated aromatics.Finally, volume extinction coefficients Nχ_E derived from 15°S CIRS data at a wavelength of λ = 62.5 μm are compared with those derived from the 10°S Huygens Descent Imager/Spectral Radiometer (DISR) data at 1.583 μm. This comparison yields volume extinction coefficient ratios Nχ_E(1.583 μm)/Nχ_E(62.5 μm) of roughly 70 and 20, respectively, for Titan’s aerosol and stratospheric ices. The inferred particle cross-section ratios χ_E(1.583 μm)/χ_E(62.5 μm) appear to be consistent with sub-micron size aerosol particles, and effective radii of only a few microns for stratospheric ice cloud particles.     

Variability and spectral variation of 3C 66A

3C 66A was monitored by the BATC (Beijing-Arizona-Taipei-Connecticut) telescope from 2005 to 2008, 1994 observations were obtained on 89 nights. Detailed research and analysis was performed on these observations in this paper. A long term burst occurred in the whole light curve. No intra-day variability was claimed in our campaign by intra-night light curve analysis. Time lag of shorter wavelenth preceding longer wavelength was shown by correlation analysis. The results showed that the optical spectral shape turned flatter when the source brightened, and the spectral variability indicator was bigger on shorter time-scale as determined by the color indices variation analysis.     

The Mass Loss of the Main Asteroid Belt and Mars’ Zone Caused by the Impact of Solar Radiation and Jupiter: I: Numerical Calculations of the Dust Evolution

Solar System Research - The values of the mass of Mars and the asteroid belt are one and three orders of magnitude, respectively, less than those theoretically predicted from the extrapolation of...     

The 10- and 20-μm interstellar absorption bands: Comparison with the infrared spectrum of the Nogoya meteorite

For submicrometer-sized particles of the carbonaceous chondrite Nogoya and, for comparison purposes, also of terrestrial chamosite, the mass absorption coefficients have been derived from laboratory spectra for the wavenumber range 250–1300 cm^–1. Using these data the expected spectrum of an infrared source has been calculated under simple model assumptions and compared with the observed flux from the infrared source OH 26.5+0.6. Although certain discrepancies are left in the 20-m region it is concluded that phyllosilicates, especially such occurring in carbonaceous chondrites, are interesting candidates for the material of interstellar grains.     

Infrared spectral variations of three Mira variable carbon stars with the 11.3 μm SiC feature

The spectral variations of three Mira variable carbon stars, V CrB, T Dra and V Cyg in the infrared are investigated based on ISO SWS data. It is found that either continua or molecular/dust features were variable with time in the infrared for these carbon stars during one and a half year observations. When stars were brighter the infrared continuum spectra became blue while stars were fainter the infrared continuum spectra became red. In addition, during spectral variations there were the correlation between the 3.05 μm HCN+C₂H₂ and the 5.2 μm C₃ molecular band strengths and the anti-correlation between the 3.05 μm HCN+C₂H₂ molecular band strengths and 13.7 μm C₂H₂ band strengths while during variations the 11.3 μm SiC dust emission strengths were not clearly changed.     

Modelling the atmospheric CO2 10-μm non-thermal emission in Mars and Venus at high spectral resolution

A study of the CO₂ atmospheric emissions at 10-μm in the upper atmospheres of Mars and Venus is performed in order to explain a number of ground-based measurements of these emissions recently taken at very high spectral resolution in both planets. The measurements are normally used to derive atmospheric temperatures and winds, but uncertainties on the actual emission layers were so far a serious drawback for their correct interpretation. The non-LTE models used for Mars and Venus in the present analysis are entirely similar in order to perform consistent comparisons between the two planets. In particular, the same scheme of CO₂ states and ro-vibrational bands are used, with similar assumptions on collisional routes and rate coef?cients, and also the same radiative transfer approximations. The emissions at 10-μm are produced in both atmospheres by the same excitation mechanism: radiative pumping of the CO₂(00⁰1) vibrational state by direct solar absorption(at 4.3 μm) and indirect absorption (at 2.7 μm, followed by collisional quenching). The computed radiances are specially strong in the upper mesosphere and lower thermosphere of the two planets during maximum solar illumination, producing a population inversion in such conditions with the lower states of the bands, the CO₂ (10⁰0) and CO₂(02⁰0). We obtained that other population inversions are also possible, involving higher energy CO₂ states. The larger solar ?ux available on Venus is found to produce larger vibrational populations and stronger emissions than equivalent atmospheric layers on Mars, in agreement with the observations. A number of perturbation studies were used to determine the exact emission altitudes, or weighting function peaks, for usual nadir sounding. The sensitivity of the emission to non-LTE model uncertainties and to atmospheric variations in temperature and CO₂ density is also presented. The dependence with the solar zenith angle and with the emission angle, as obtained with this model, could also be useful for guiding future observations.     

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.     

3- to 14-μm Spectroscopy of Comet C/1999 T1 (McNaught-Hartley)

We report spectroscopy of Comet C/1991 T1 (McNaught-Hartley) at 3-13 μm on January 31.62 and February 1.7 2001 UT (delta=1.29 AU, r=1.40 AU) using the broadband array spectrograph system on the IRTF. The spectrum showed a silicate emission feature extending about 20% above the continuum. Two emission features at 10.3 and 11.2 μm appeared above the silicate band, the latter seemingly indicative of crystalline olivine. The 10.3-μm feature is only a 1-2 sigma detection but if real could indicate the presence of hydrated silicates. The color temperature at 8-13 μm was 260±10 K, approximately 6% above the blackbody radiative equilibrium temperature of 235 K. The magnitude at [N] was 3.13±0.02. On the second night, the comet had brightened slightly ([N]=2.98±0.02) and the two prominent emission features were absent, although the silicate emission feature maintained its trapezoidal shape with shoulders at 9.5 and 11.2 μm.     

The 1.10- and 1.18-μm nightside windows of Venus observed by SPICAV-IR aboard Venus Express

Observations of the 1.10- and 1.18-μm nightside windows by the SPICAV-IR instrument aboard Venus Express were analyzed to characterize the various sources of gaseous opacity and determine the H₂O mole fraction in the lower atmosphere of Venus. We showed that the line profile model of Afanasenko and Rodin (Afanasenko, T.S., Rodin, A.V. [2007]. Astron. Lett. 33, 203–210) underestimates the CO₂ absorption in the high-wavelength wing of the 1.18-μm window and we derived an empirical lineshape that matches this wing well. An additional continuum opacity is required to reproduce the variation of the 1.10- and 1.18-μm radiances with surface elevation as observed by the VIRTIS-M instrument aboard Venus Express. A constant absorption coefficient of 0.7 ± 0.2 × 10⁻⁹ cm⁻¹ am⁻² best reproduces the observed variation. We compared spectra calculated with different CO₂ and H₂O line lists. We found that the CDSD line list lacks the 5ν₁ + ν₃ series of CO₂ bands, which provide significant opacity in Venus’ deep atmosphere, and we have constructed a composite line list that best reproduces the observations. We also showed for the first time that HDO brings significant absorption at 1140–1190 nm. Using the best representation of the atmospheric opacity we could reach, we retrieved a water vapor mole fraction of ppmv, pertaining to the altitude range 5–25 km. Combined with previous measurements in the 1.74- and 2.3-μm windows, this result provides strong evidence for a uniform H₂O profile below 40 km, in agreement with chemical models.     

Cassini spectra and photometry 0.25-5.1 μm of the small inner satellites of Saturn

The nominal tour of the Cassini mission enabled the first spectra and solar phase curves of the small inner satellites of Saturn. We present spectra from the Visual Infrared Mapping Spectrometer (VIMS) and the Imaging Science Subsystem (ISS) that span the 0.25-5.1 μm spectral range. The composition of Atlas, Pandora, Janus, Epimetheus, Calypso, and Telesto is primarily water ice, with a small amount (∼5%) of contaminant, which most likely consists of hydrocarbons. The optical properties of the “shepherd” satellites and the coorbitals are tied to the A-ring, while those of the Tethys Lagrangians are tied to the E-ring of Saturn. The color of the satellites becomes progressively bluer with distance from Saturn, presumably from the increased influence of the E-ring; Telesto is as blue as Enceladus. Janus and Epimetheus have very similar spectra, although the latter appears to have a thicker coating of ring material. For at least four of the satellites, we find evidence for the spectral line at 0.68 μm that Vilas et al. [Vilas, F., Larsen, S.M., Stockstill, K.R., Gaffley, M.J., 1996. Icarus 124, 262-267] attributed to hydrated iron minerals on Iapetus and Hyperion. However, it is difficult to produce a spectral mixing model that includes this component. We find no evidence for CO₂ on any of the small satellites. There was a sufficient excursion in solar phase angle to create solar phase curves for Janus and Telesto. They bear a close similarity to the solar phase curves of the medium-sized inner icy satellites. Preliminary spectral modeling suggests that the contaminant on these bodies is not the same as the exogenously placed low-albedo material on Iapetus, but is rather a native material. The lack of CO₂ on the small inner satellites also suggests that their low-albedo material is distinct from that on Iapetus, Phoebe, and Hyperion.     

Latitudinal distribution of HDO abundance above Venus’ clouds by ground-based 2.3 μm spectroscopy

The abundance of HDO above the clouds in the dayside atmosphere of Venus was measured by ground-based 2.3 μm spectroscopy over 4 days. This is the first HDO observation above the clouds in this wavelength region corresponding to a new height region. The latitudinal distributions found show no clearly defined structure. The disk-averaged mixing ratio is 0.22 ± 0.03 ppm for a representative height region of 62–67 km. This is consistent with measurements found in previous studies. Based on previous H₂O measurements, the HDO/H₂O ratio is found to be 140 ± 20 times larger than the telluric ratio. This lies between the ratios of 120 ± 40 and 240 ± 25, respectively, reported for the 30–40 km region by ground-based nightside spectroscopy and for the 80–100 km region by solar occultation measurement on board the Venus Express.