The spectra of Uranus and Neptune at 8–14 and 17–23 μm

An array spectrometer was used on the nights of 1985 May 30–June 1 to observe the disks of Uranus and Neptune in the spectral regions 7–14 and 17–23 μm with effective resolution elements ranging from 0.23 to 0.87 μm. In the long-wavelength region, the spectra are relatively smooth with the broad S(1) H₂ collision-induced rotation line showing strong emission for Neptune. In the short-wavelength spectrum of Uranus, an emission feature attributable to C₂H₂ with a maximum stratospheric mixing ratio of 9 × 10⁻⁹ is apparent. An upper limit of 2 × 10⁻⁸ is placed on the maximum stratospheric mixing ratio of C₂H₆. The spectrum of Uranus is otherwise smooth and quantitatively consistent with the opacity provided by H₂ collision-induced absorption and spectrally continuous stratospheric emission, as would be produced by aerosols. Upper limits to detecting the planet near 8 μm indicate a CH₄ stratospheric mixing ratio of 1 × 10⁻⁵ or less, below a value consistent with saturation equilibrium at the temperature minimum. In the short-wavelength spectrum of Neptune, strong emission features of CH₄ and C₂H₆ are evident and are consistent with local saturation equilibrium with maximum stratospheric mixing ratios of 0.02 and 6 × 10⁻⁶, respectively. Emission at 8–10 μm is most consistent with a [CH₃D]/[CH₄] volume abundance ratio of 5 × 10⁻⁵. The spectrum of Neptune near 13.5 μm is consistent with emission by stratospheric C₂H₂ in local saturation equilibrium and a maximum mixing ratio of 9 × 10⁻⁷. Radiance detected near 10.5 μm could be attributed to stratospheric C₂H₄ emission for a maximum mixing ratio of approximately 3 × 10⁻⁹. Quantitative results are considered preliminary, as some absolute radiance differences are noted with respect to earlier observations with discrete filters.     

The vertical cloud structure of Jupiter from 5 μm measurements

From 5 μm high-spatial-resolution images of Jupiter, flux-frequency histograms of the equatorial region show a trimodal distribution of brightness temperatures. Combined with limbdarkening measurements, a three-layer cloud model for Jupiter is developed. The highest, coldest clouds, apparently homogeneous and displaying relatively little limb darkening, cover the zones. These clouds are not present over the belts, allowing observational access to deeper regions. The belts appear heterogeneous: small, localized hot areas show enhanced limb darkening, while much of the belt is distinctly cooler and exhibits shallower limb darkening. These belt properties can be explained by a cool emitting layer superposed upon a hot, dense cloud deck.     

Observations of the Galilean moons of Jupiter in 2013–2015 at Pulkovo

Observational results are presented for Jupiter and its Galilean moons from the Normal Astrograph at Pulkovo Observatory in 2013–2015. The following data are obtained: 154 positions of the Galilean satellites and 47 calculated positions of Jupiter in the system of the UCAC4 (ICRS, J2000.0) catalogue; the differential coordinates of the satellites relative to one another are determined. The mean errors of the satellites’ normal places in right ascension and declination over the entire observational period are, respectively: ε_α = 0.0065″ and ε_δ = 0.0068″, and their standard deviations are σ_α = 0.0804″ and σ_δ = 0.0845″. The equatorial coordinates are compared with planetary and satellite motion theories. The average (O–C) residuals in the two coordinates relative to the motion theories are 0.05″ or less. The best agreement with the observations is achieved by a combination of the EPM2011m and V. Lainey-V.2.0|V1.1 motion theories; the average (O–C) residuals are 0.03″ or less. The (O–C) residuals for the features of the positions of Io and Ganymede are comparable with measurement errors. Jupiter’s positions calculated from the observations of the satellites and their theoretical jovicentric coordinates are in good agreement with the motion theories. The (О–С) residuals for Jupiter’s coordinates are, on average, 0.027″ and–0.025″ in the two coordinates.     

The thermal structure of Jupiter II. Observations and analysis of 8–14 micron radiation

Observations of Jovian limb structure at 8.11 and 8.45 microns are reported. These are used along with other limb structure and spectral data in the 8–14 micron region to derive a model of the thermal and cloud structure within the 1.0-0.01 bar pressure regime. The model is generally consistent with models derived from Pioneer 10 infrared radiometer data reported by Orton (1975b). The temperature is about 165K at 1.00 bar, 108K at 0.01 bar, and 143K at 0.03 bar. In zones, an optically opaque cloud of NH₃ exists near the 143K (0.60 bar) level. A partly transparent haze of solid NH₃ particles overlies the cloud. Belts are free of the cloud and have a much lower abundance of NH₃ haze than the zones. The data are consistent with an NH₃ gas abundance defined by saturation equilibrium, with a mixing ratio of 1.5 × 10^?4 deep in the atmosphere, and with a CH₄ mixing ratio of 2 × 10^?3, about three times the currently accepted value.     

8–13 μm spectrophotometry of Comet Kohoutek

Spectrophotometry of Comet Kohoutek (1973f) covering the wavelength range 8–13 μm is presented. The spectral shape of the derived flux excess above a blackbody closely resembles that seen in circumstellar and interstellar dust and generally attributed to metallic silicates.     

The rings of Saturn: New near-infrared reflectance measurements and a 0.326–4.08 μm summary

A new high photometric precision reflectance spectrum of Saturn's rings covering the spectral region 0.65 to 2.5-μm is presented and three previously unreported absorption features at 1.25, 0.85, and probably 1.04 μm are identified. The 1.25- and 1.04-μm absorptions are due to water ice. The 0.85-μm feature may be due to a combination of 0.81- and 0.90-μm ice absorptions but this feature appears too strong relative to the 1.04-μm band to be completely explained by weater ice. Another possibility is that the 0.85-μm band is due to Fe³⁺-bearing minerals in an ice-mineral mixture. This explanation could also account for the drop in the visible and ultraviolet reflectance and the rise in reflectance around 3.6 μm. Finally, a composite spectrum from 0.325 to 4.08 μm is presented which will be useful for future analysis and laboratory studies.     

Interstellar absorptions at λ=3.2 μm and 3.3 μm

Unidentified interstellar absorption bands at =3.2 m and 3.3 m might be due to amino-acids in bacterial grains.     

Spatially resolved infrared observations of Saturn: I. Equatorial limb scans at 20 μm

Drift scans of the equator of Saturn have been obtained through narrow band filters at 17.8, 19.7, and 22.7 μm. Spatial resolution was ?17% of the equatorial diameter. These observations clearly differentiate otherwise tenable atmospheric models. A published model by A. Tokunaga and R.D. Cess [Icarus32, 321–327 (1977)] is shown to represent these new observations significantly better than other models from the literature.     

Infrared radiometry of Uranus and Neptune at 21 and 32 μm

Radiometric measurement of Uranus and Neptune near 21 and 32 μm have been made with filters with widths of 8 and 5 μm, respectively. The observations at 21 μm, made on 1985 June 19 at the NASA Infrared telescope facility at Mauna Kea, Hawaii, were calibrated against α Boo and corresponded to brightness temperatures of 54.1 ± 0.3 K for Uranus and 58.1 ± 0.3 K for Neptune. The observations at 32 μm were made on three nights: 1983 May 1 and 1984 May 30 and 31, also at the NASA IRTF. Calibrated against the Jovian satellites Callisto (J4) and Ganymede (J3), these measurements corresponded to brightness temperatures of 51.8 ± 1.5 K for Uranus and 55.6 ± 1.2 K for Neptune. The observations are consistent with higher-resolution studies and confirm the general decrease of brightness temperatures going from about 20 to 30 μm.     

Asteroid 21 Lutetia at 3 μm: Observations with IRTF SpeX

We present observations of Asteroid 21 Lutetia collected 2003–2008 using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) covering 2–4 μm. We also reevaluate NSFCam observations obtained in 1996 (Rivkin, A.S., Lebofsky, L.A., Clark, B.E., Howell, E.S., Britt, D.T. [2000]. Icarus 145, 351–368). Taken together, these show deeper 3-μm band depths (of order 3–5%) in the southern hemisphere of Lutetia, and shallower band depths (of order 2% or less) in the north. Such variation is consistent with observations at shorter wavelength by previous workers (Nedelcu, D.A. et al. [2007]. Astron. Astrophys. 470, 1157–1164; Lazzarin, M. et al. [2010]. Mon. Not. R. Astron. Soc. 408, 1433–1437), who observed hemispheric-level variations from C-like spectra to X-like spectra.While the shallowness of absorption bands on Lutetia hinders identification of its surface composition, goethite appears plausible as a constituent in its southern hemisphere (Beck, P., Quirico, E., Sevestre, D., Montes-Hernandez, G., Pommerol, A., Schmitt, B. [2011]. Astron. Astrophys. 526, A85–A89). Mathematical models of space weathered goethite are most consistent with Lutetia’s southern hemisphere spectrum, but more work and further observations are necessary to confirm this suggestion.     

Modelling The 5–30 μm Spectrum of Comet Halley

The 5–30 μm spectrum of Comet P/Halley is modelled for various grain compositions on the basis of an observationally determined distribution of grain sizes. We compute the distribution function of grain temperatures and fluxes arising from (1) a mineral grain model, and (2) an organic grain model comprised of a diatom/POM mixture. The organic/POM model yields excellent accord with the cometary observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photometry of the asteroid 1976 AA at 0.56 and 2.2 μm

We report observations at 0.56 and 2.2 μm of the Apollo asteroid 1976 AA made during its discovery apparition. We derive a 2.2-μm relative spectral reflectance (scaled to unity at 0.56 μm) of R(2.2 μm) = 1.5 ± 0.3. This 2.2-μm reflectance is not compatible with a carbonaceous surface composition. However, it is compatible with a wide variety of meteoritic types including ordinary chondrites, stony irons, and mesosiderites. Thus, 1976 AA may have a silicate surface similar to other Apollo-Amor objects.     

Orbital Evolution of the Sun–Jupiter–Saturn–Uranus–Neptune Four-Planet System on Long-Time Scales

The four-planet problem is solved by constructing an averaged semi-analytical theory of secondorder motion by planetary masses. A discussion is given of the results obtained by numerical integration of the averaged equations of motion for the Sun–Jupiter–Saturn–Uranus–Neptune system over a time interval of 10 Gyr. The integration is based on high-order Runge–Kutta and Everhart methods. The motion of the planets is almost periodic in nature. The eccentricities and inclinations of the planetary orbits remain small. Short-period perturbations remain small over the entire interval of integration. Conclusions are drawn about the resonant properties of the motion. Estimates are given for the accuracy of the numerical integration.     

Mid-IR (8–13 μm) images of the 21 μm,carbon rich proto-planetary nebulae

We present 9.7 and 11.8 m narrow band (/=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 m feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M hydrogen burning core star.     

Correlation of simultaneous ultraviolet (0.36 μm) and infrared (8 to 14 μm) images of Venus

We present evidence for a correlation between features observed in simultaneous infrared (8 to 14 μm) and ultraviolet (0.36 μm) images obtained during Venus' 1975 and 1977 apparitions. The sense of the observed correlation is such that bright uv markings correspond to bright (warm) ir features, and similarly, dark uv markings correspond to dark (cool) ir features.     

Analysis of thermal emission from the nightside of Venus at 1.51 and 1.55 μm

We present radiative transfer modelling of thermal emission from the nightside of Venus in two ‘spectral window’ regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. [Erard, S., Drossart, P., Piccioni, G., 2009. J. Geophys. Res. Planets 114, doi:10.1029/2008JE003116. E00B27], was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ∼20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude.In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20-35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance.     

Astrometric Observations of the Galilean Moons of Jupiter at the Pulkovo Normal Astrograph in 2016−2017

We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2016?2017. We obtained 761 positions of the Galilean moons of Jupiter in the system of the Gaia DR1 catalog (ICRF, J2000.0) and 854 differential coordinates of the satellites relative to each other. The mean errors in the satellites’ normal places and the corresponding root-mean-square deviations are ε_α = 0.0020′′, ε_δ = 0.0027′′, σ_α = 0.0546′′, and σ_δ = 0.0757′′. The equatorial coordinates of the moons are compared to the motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are less than 0.031′′. The best agreement with observations is achieved by a combination of the EPM2015 and V. Lainey-V.2.0|V1.1 motion theories, which yields the average (O–C) residuals of approximately 0.02″. Peculiarities in the behavior of the (O–C) residuals and error values in Ganymede have been noticed.     

Solar Cycle Effects on the Dynamics of Jupiter’s and Saturn’s Magnetospheres

The giant planetary magnetospheres surrounding Jupiter and Saturn respond in quite different ways, compared to Earth, to changes in upstream solar wind conditions. Spacecraft have visited Jupiter and Saturn during both solar cycle minima and maxima. In this paper we explore the large-scale structure of the interplanetary magnetic field (IMF) upstream of Saturn and Jupiter as a function of solar cycle, deduced from solar wind observations by spacecraft and from models. We show the distributions of solar wind dynamic pressure and IMF azimuthal and meridional angles over the changing solar cycle conditions, detailing how they compare to Parker predictions and to our general understanding of expected heliospheric structure at 5 and 9 AU. We explore how Jupiter’s and Saturn’s magnetospheric dynamics respond to varying solar wind driving over a solar cycle under varying Mach number regimes, and consider how changing dayside coupling can have a direct effect on the nightside magnetospheric response. We also address how solar UV flux variability over a solar cycle influences the plasma and neutral tori in the inner magnetospheres of Jupiter and Saturn, and estimate the solar cycle effects on internally driven magnetospheric dynamics. We conclude by commenting on the effects of the solar cycle in the release of heavy ion plasma into the heliosphere, ultimately derived from the moons of Jupiter and Saturn.     

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.     

The Galilean satellites: New near-infrared spectral reflectance measurements (0.65–2.5 μm) and a 0.325–5 μm summary

New near-infrared (0.65–2.5 μm) reflectance spectra of the Galilean satellites with 1.5% spectral resolution and ≈2% intensity precision are presented. These spectra more precisely define the water ice absorption features previously identified on Europa, Ganymede, and Callisto at 1.55 and 2.0 μm. In addition, previously unreported spectral features due to water ice are seen at 1.25, 1.06, 0.90, and 0.81 μm on Europa, and at 1.25, 1.04, and possibly 0.71 μm on Ganymede. Unreported absorption features in Callisto's spectrum occur at 1.2 μm, probably due to H₂O, and a weak, broad band extending from 0.75 to 0.95 μm, due possibly to other minerals. The spectrum of Io has only weak absorption features at 1.15 μm and between 0.8 and 1.0 μm. No water absorptions are positively identified in the Io spectra, indicating an upper limit of areal water frost coverage of 2% (leading and trailing sides). It is found for Callisto, Ganymede, and Europa that the water ice absorption features are due to free water and not to water bound or absorbed onto minerals. The areal coverage of water frost is ≈ 100% on Europa (trailing side), ≈65% on Ganymede (leading side), and 20–30% on Callisto (leading side). An upper limit of ≈5% bound water (in addition to the 20–30% ice) may be present on Callisto, based on the strong 3-μm band seen by other investigators. A summary of spectra of the satellites from 0.325 to about 5 μm to aid in laboratory and interpretation studies is also presented.