Jupiter: New retrieved thermal profiles and ammonia distributions

New thermal profiles of Jupiter are retrieved from recent far infrared spectral measurements and for H₂ mixing ratios varying from 0.8 to 0.94. The effective temperature corresponding to the inferred thermal profile is 123.15 ± 0.35°K. Far-infrared brightness temperature spectra computed from these profiles are compared to experimental data including measurements made at high spectral resolution in the NH₃ν₂ band at 10 μm and in NH₃ pure rotational bands between 40 and 110 μm. It is found that a strong depletion of NH₃ does occur in the Jovian stratosphere and that ammonia seems to be undersaturated in the upper troposphere.     

The diameter and thermal inertia of 433 Eros

Radiometry of Eros at 10 and 20 μm demonstrates that the thermal conductivity of the upper centimeter of the surface is approximately as low as that of the Moon, suggesting that the asteroid has a regolith of highly porous rocky material. When combined with photoelectric photometry, these infrared measurements yield an effective diameter of Eros at maximum light of D₀ = 22 ± 2 km and a geometric albedo of p_v = 0.18 ± 0.03.     

The diameter and albedo of asteroid 1976 AA

We present a radiometric observation of asteroid 1976 AA, and formulate a simple model for the infrared thermal phase function so that our data can be compared with similar measurements made at different phase angles. The radiometric diameter of 1976 AA from our observation is 940⁺²⁰⁰_?100 meters and the geometric albedo is 0.18 ± 0.06, in satisfactory agreement with another published radiometric observation.     

Discussion of infrared measurements of T Tauri stars and related objects

It is at first reported that certain kinds of stars which have been classified as T Tauri stars or related objects are in reality not of this type. After the exclusion of those objects, the infrared measurements accessible in the literature permit to draw some astrophysical inferences. It is then possible to distinguish three classes of light variations. All T Tauri stars have an infrared excess. From the colour indices H – K and K – L it can be deduced that the infrared excess for more than one half of the objects is due to the thermal radiation of the circumstellar dust envelope; for the remaining stars also free-free radiation from the gas envelope can play an essential part. The largest infrared excesses E_H–K were found with the hotter stars (spectral type A) and the strongest emission lines with the cooler stars (spectral types G, K, M). This can finally be explained by the fact that the convection zone in cooler stars reaches far down into their interior than in hotter stars.     

The opacity of some local Martian dust storms observed by the Viking IRTM

In this paper we analyze some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between L_s=225 and 262°. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be ≈6. Away from the individual clouds, the opacity is ≈2, which is still about four times the background level of dustiness in the Martian atmosphere. We find considerable structure in the derived opacity which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds.     

Spectral properties of hydrogen,helium, methane,and ammonia at thermal infrared wavelengths

We present some results of a theoretical and laboratory program to determine the thermal infrared spectral properties of the principal gaseous constituents of the atmosphere of Jupiter. G. Birnbaum has measured laboratory spectra in the 16 to 1000 um wavelength range for hydrogen and hydrogen-helium mixtures at Jovian temperatures. These are compared to theoretically computed spectra in order to determine the temperature dependence of the line strengths in the pressure-induced rotational band and the overlap parameters from the translational band. Existing spectral data for methane do not agree well with measurements of the ν₄ band at room temperature. A revised allocation of line intensities is proposed. Existing data for the ν₂ (10 um) band of ammonia do agree reasonably well with measurements at room temperature and at ?77δC, but there are some important discrepancies which remain to be explained.     

The Thermal Destruction of Solids Near the Sun

We consider the thermal evolution of both icy and non-icy solids moving in highly eccentric orbits using an analytical solution of the heat diffusion equation. The thermal stresses which arise inside and at the surface of solids can exceed by several orders of magnitude the tidal stresses in the neighbourhood of the Sun for all material considered. This means that thermal disintegration is the most important factor in the evolution of cometary and meteorite-like bodies. This problem may be directly connected with the origin of the variable part of the infrared radiation excess in the F-corona observed at 4R_ô and 9R_ô from the Sun. The possible scenario of the disintegration of the distant solids due to the thermal stresses is also given.     

On the thermal structure of Uranus

Uranus has an effective temperature close to the solar equilibrium value and undoubtedly a thermal inversion of at least 140 K at a pressure of ～3 dyncm^?2. With the inversion and the thermal opacity provided by a HeH₂ mixture in a ratio close to solar abundance, acceptable agreement can be achieved with the available infrared observations. The cause of the inversion is, however, uncertain. The use of the HeH₂ opacity for Uranus is justified by the excellent agreement of the frequency variation of that opacity with the thermal spectrum of Jupiter.     

A laboratory study of magnesium-tetrabenz-porphyrin; Lack of agreement with diffuse interstellar bands

We have measured the visible and infrared spectra and thermal behavior of the moleculebis-pyridal-magnesium-tetrabenz-porphyrin, the molecule proposed as the carrier of the diffuse interstellar bands. Of the six band coincidences reported by F. M. Johnson, only one, 4430 Å, occurs in our experiments. This coincidence requires a special environment, not likely in interstellar space. The infrared spectrum does not support Johnson's vibrational scheme. Our spectroscopic and thermal measurements contradict the hypothesis that this molecule causes the diffuse bands.     

The albedo and diameter of 1862 Apollo

We report infrared thermal emission measurements of 1862 Apollo, which is the type example of an Earth-crossing asteroid. We derive a geometric albedo of 0.21 ± 0.02 which is within the albedo range of the S class of asteroids. The effective diameter was observed to vary with rotation from 1.2 ± 0.1 to 1.5 ± 0.1 km.     

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

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

Emissivity measurements of analogue materials for the interpretation of data from PFS on Mars Express and MERTIS on Bepi-Colombo

The Planetary Fourier Spectrometer (PFS) onboard the Mars Express Mission provides thermal infrared, hyperspectral images of Mars and in the future the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS), part of the selected payload for the Bepi-Colombo Mission, will collect analogous data for Mercury. To interpret these remote sensing data it is essential to understand the spectral emittance of planetary analogue materials and a spectral library of emissivity measurements is needed. Here we introduce the emissivity device built at DLR (Berlin). The device is coupled to a Fourier transform infrared spectrometer (Bruker IFS 88), purged with dry air and equipped with a cooled MCT-detector. We discuss theoretical background of our thermal emission measurements and describe our standard experimental procedures, which are being used to create the Berlin emissivity database (BED). This study presents and discuss the 6.3-22 μm thermal emission spectra of fine-grained feldspar separates ranging from <25 to 90-125 μm. We discuss diagnostic potential of the features present in the emission spectra of plagioclase and alkali feldspars and the particle size effects.     

10 μm polarimetry of ceres

Linear polarimetry of Ceres at 10 μm is presented. These data represent the first published polarization measurements of an asteroid in the thermal infrared. It is found that Ceres is polarized at the 0.2-0.6% level. This data set is compared with theoretical models of the linear polarization of emitted radiation from a spherical plane. These models are used to derive the pole position and thermal inertia of Ceres. Ceres is best fit with a thermal inertia of $\text{0.0010±0.0003}\text{cal}\text{cm}{}^{\mathrm{?2}}\text{°}\text{K}{}^{\mathrm{?1}}\text{sec}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and a pole orientation of β_p = 36° ± 5°, λ_p = 270° ± 3°. It is concluded that 10μm polarimetry is a potentially powerful technique for remotely sensing the pole orientation and thermal inertia of asteroids.     

The Infrared Spectral Energy Distribution And Polarization Of Comet C/1995 O1 (Hale–Bopp) During 1997

Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = T_color/T_BB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135° This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared spectra of quasars and related objects

An attempt is made to explain the infrared radiation observed for several quasars and Seyfert galaxies as thermal radiation of a dust envelope surrounding the cores of these objects. Two kinds of dust particles (graphite and silica) are taken into consideration. It is shown that the observed spectral behaviour and the luminosity in the infrared can be introduced as thermal radiation of silica grains. In the case of 3C 273 one finds that the radius of the dust envelope is about 50 pc and the total mass of dust is about 600M _⊙.     

Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions

The third most abundant species in Titan’s atmosphere is molecular hydrogen with a tropospheric/lower stratospheric mole fraction of 0.001 derived from Voyager and Cassini infrared measurements. The globally averaged thermospheric H₂ mole fraction profile from the Cassini Ion Neutral Mass Spectrometer (INMS) measurements implies a small positive gradient in the H₂ mixing ratio from the tropopause region to the lower thermosphere (∼950-1000 km), which drives a downward H₂ flux into Titan’s surface comparable to the H₂ escape flux out of the atmosphere (∼2 × 10¹⁰ cm⁻² s⁻¹ referenced to the surface) and requires larger photochemical production rates of H₂ than obtained by previous photochemical models. From detailed model calculations based on known photochemistry with eddy, molecular, and thermal diffusion, the tropospheric and thermospheric H₂ mole fractions are incompatible by a factor of ∼2. The measurements imply that the downward H₂ surface flux is in substantial excess of the speculative threshold value for methanogenic life consumption of H₂ (McKay, C.P., Smith, H.D. [2005], Icarus 178, 274-276. doi:10.1016/j.icarus.2005.05.018), but without the extreme reduction in the surface H₂ mixing ratio.     

2060 Chiron: Visual and thermal infrared observations

Five-color (λλ = 0.36?0.85 μm) and thermal infrared (λ = 22.5 μm) photometric observations of the unusual asteroid 2060 Chiron were made. Between 0.36 and 0.85 μm, Chiron's reflectance spectrum is similar to those of C-class asteroids as well as Saturn's satellite Phoebe. However, the thermal IR measurements imply an albedo≥0.05 (i.e., a diameter ≤250 kmat the level 2σ level) that is probably higher than those of C-class asteroids or Phoebe.     

Thermal infrared spectra of experimentally shocked andesine anorthosite

Andesine-rich (An_36–46) anorthosite rocks experimentally shocked to high pressures (16–57 GPa) exhibit changes in spectral features with increasing pressure in laboratory thermal infrared emission spectra (250–1400 cm^?1). These results are similar to previous studies of shocked bytownite- and albite-rich rocks, albeit with differences in absorption band centers characteristic of mineralogy and composition. Typical spectral absorptions result from Si–O antisymmetric stretch motions of the silica tetrahedral (1000–1250 cm^?1) and weaker absorptions due to Si–O–Si octahedral bending vibrations (350–700 cm^?1). Many of these features persist to higher pressures in the andesine spectra compared to similar features in measurements of shocked bytownite. This is consistent with previous thermal infrared absorption studies of shocked feldspars and likely is related to differences in density, hardness, and Al content. A transparency feature at ～832 cm^?1 observed in powdered andesine spectra also degrades with increasing pressure, intermediate between the ～828 cm^?1 and ～855 cm^?1 transparency features in spectra of powders of shocked bytownite and albitite, respectively. These data can be incorporated into thermal infrared spectral analyses of cratered planetary surfaces (or laboratory spectra of shocked samples) to help constrain the occurrence and degree of shock in plagioclase feldspars.     

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.