E. Lellouch

“TNOs are Cool”: a survey of the trans-Neptunian region - VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects

Trans-Neptunian objects (TNO) represent the leftovers of the formation of the Solar System. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer Solar System. Based on a sample of 19 classical TNOs we determine radiometric sizes, geometric albedos and beaming parameters. Our sample is composed of both dynamically hot and cold classicals. We study the correlations of diameter and albedo of these two subsamples with each other and with orbital parameters, spectral slopes and colors. We have done three-band photometric observations with Herschel/PACS and we use a consistent method for data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70.0, 100.0 and 160.0 \mu m. Additionally, we use Spitzer/MIPS flux densities at 23.68 and 71.42 \mu m when available, and we present new Spitzer flux densities of eight targets. We derive diameters and albedos with the near-Earth asteroid thermal model (NEATM). As auxiliary data we use reexamined absolute visual magnitudes from the literature and data bases, part of which have been obtained by ground based programs in support of our Herschel key program. We have determined for the first time radiometric sizes and albedos of eight classical TNOs, and refined previous size and albedo estimates or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347 Salacia indicate that they are among the 10 largest TNOs known. Our new results confirm the recent findings that there are very diverse albedos among the classical TNOs and that cold classicals possess a high average albedo (0.17 +/- 0.04). Diameters of classical TNOs strongly correlate with orbital inclination in our sample. We also determine the bulk densities of six binary TNOs.

Latitudinal distribution of carbon monoxide in the deep atmosphere of Venus

Abstract A large number of i.r. spectra of Venus was obtained using the Near-Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft, during the February 1990 encounter. Preliminary results show an apparent increase in the tropospheric CO volume mixing ratio (vmr) in the northern polar region. Other possible explanations of the observations are examined and rejected and an increase of the CO abundance north of 47°N of (35 ± 15)% is inferred. Some possible causes of this enhancement are suggested.

Search for spatial variations of the H2O abundance in the lower atmosphere of Venus from NIMS-Galileo

Abstract The spectroscopic data of the Near-Infrared Mapping Spectrometer (NIMS), recorded during the Galileo flyby of Venus, are analysed to retrieve the water vapour abundance variations in the lower atmosphere of Venus at night. The 1.18 μm spectral window, which probes altitude levels below 20 km, is used for this purpose. Constraints on the CO2 continuum and far-wing opacity from existing ground-based high-resolution observations are included in the modelling of the NIMS spectra. The NIMS measurements can be fitted with a water vapour mixing ratio of 30 ± 15 ppm, in agreement with analyses of ground-based nightside observations. The water vapour abundance shows no horizontal variations exceeding 20% over a wide latitude range (40°S, 50°N) on the nightside of Venus. Within the same selection of NIMS spectra, a large enhancement in the O2 fluorescence emission at 1.27 μm is observed at a latitude of 40°S, over a spatial area about 100 km wide.

“TNOs are Cool”: A survey of the trans-Neptunian region - X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations

Context. The Kuiper belt is formed of planetesimals which failed to grow to planets and its dynamical structure has been affected by Neptune. The classical Kuiper belt contains objects both from a low-inclination, presumably primordial, distribution and from a high-inclination dynamically excited population. Aims. Based on a sample of classical trans-Neptunian objects (TNOs) with observations at thermal wavelengths we determine radiometric sizes, geometric albedos and thermal beaming factors for each object as well as study sample properties of dynamically hot and cold classicals. Methods. Observations near the thermal peak of TNOs using infrared space telescopes are combined with optical magnitudes using the radiometric technique with near-Earth asteroid thermal model (NEATM). We have determined three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and 160.0 mu m and Spitzer/MIPS at 23.68 and 71.42 mu m when available. We use reexamined absolute visual magnitudes from the literature and ground based programs in support of Herschel observations. Results. We have analysed 18 classical TNOs with previously unpublished data and re-analysed previously published targets with updated data reduction to determine their sizes and geometric albedos as well as beaming factors when data quality allows. We have combined these samples with classical TNOs with radiometric results in the literature for the analysis of sample properties of a total of 44 objects. We find a median geometric albedo for cold classical TNOs of 0.14(-0.07)(+0.09) and for dynamically hot classical TNOs, excluding the Haumea family and dwarf planets, 0.085(-0.045)(+0.084). We have determined the bulk densities of Borasisi-Pabu (2.1(-1.2)(+2.6) g cm(-3)), Varda-Ilmare (1.25(-0.43)(+0.40), g cm(-3)) and 2001 QC(298) (1.14(-0.30)(+0.34) g cm(-3)) as well as updated previous density estimates of four targets. We have determined the slope parameter of the debiased cumulative size distribution of dynamically hot classical TNOs as q = 2.3 +/- 0.1 in the diameter range 100 \textless D \textless 500 km. For dynamically cold classical TNOs we determine q = 5.1 +/- 1.1 in the diameter range 160 \textless D \textless 280 km as the cold classical TNOs have a smaller maximum size.

Earth global mosaic observations with NIMS-Galileo

Abstract During the Earth-1 Galileo flyby (December 1990). the Near-Infrared Mapping Spectrometer (NIMS) experiment investigated the illuminated side of the Earth in the spectral range 0.7–5.2 μm. Mosaics of the entire terrestrial globe were recorded with a spatial resolution ranging from 100 to 500 km. From these spectra, information is retrieved upon the largescale temperature structure in the stratosphere and in the mesosphere (0–70 km altitude range) from the inversion of the CO2 bands at 4.3 and 4.8 μm. These data also permit monitoring of the cloud temperatures, and derivation of the abundances of several minor atmospheric constituents (H2O, CO, N2O. CH4 and O3). These observations constitute a continuation of the study of the atmospheres of the three planets (i.e. Venus, the Earth and Jupiter) targeted by the Galileo spacecraft during its mission. Observing these atmospheres with the NIMS instrument in the near-infrared will provide a unique data set, useful for comparative planetary studies.

Jovian atmospheric studies with the Galileo near infrared mapping spectrometer: An update

Abstract In its first two years of operation since arrival at Jupiter in December 1995, the Near Infrared Mapping spectrometer (NIMS) on the Galileo orbiter spacecraft obtained extensive coverage of the planet, including detailed coverage of the north equatorial belt (NEB) ‘hot spot’ region and the Great Red Spot. We will present the current state of data analysis including recent results on the abundances and variability of several minor constituents (H 2 O, CH 4 , NH 3 , GeH 4 , CH 3 D and PH 3 ) and the cloud structure and morphology.

TNOs are Cool: A survey of the trans-Neptunian region. XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ84 with Herschel/PACS

Context. Time series observations of the dwarf planet Haumea and the Plutinos 2003 VS 2 and 2003 AZ 84 with Herschel /PACS are presented in this work. Thermal emission of these trans-Neptunian objects (TNOs) were acquired as part of the “TNOs are Cool” Herschel Space Observatory key programme. Aims. We search for the thermal light curves at 100 and 160 μ m of Haumea and 2003 AZ 84 , and at 70 and 160 μ m for 2003 VS 2 by means of photometric analysis of the PACS data. The goal of this work is to use these thermal light curves to obtain physical and thermophysical properties of these icy Solar System bodies. Methods. When a thermal light curve is detected, it is possible to derive or constrain the object thermal inertia, phase integral and/or surface roughness with thermophysical modeling. Results. Haumea’s thermal light curve is clearly detected at 100 and 160 μ m. The effect of the reported dark spot is apparent at 100 μ m. Different thermophysical models were applied to these light curves, varying the thermophysical properties of the surface within and outside the spot. Although no model gives a perfect fit to the thermal observations, results imply an extremely low thermal inertia ( -2 s −1/2 K -1 , hereafter MKS) and a high phase integral (>0.73) for Haumea’s surface. We note that the dark spot region appears to be only weakly different from the rest of the object, with modest changes in thermal inertia and/or phase integral. The thermal light curve of 2003 VS 2 is not firmly detected at 70 μ m and at 160 μ m but a thermal inertia of (2 ± 0.5) MKS can be derived from these data. The thermal light curve of 2003 AZ 84 is not firmly detected at 100 μ m. We apply a thermophysical model to the mean thermal fluxes and to all the Herschel /PACS and Spitzer /MIPS thermal data of 2003 AZ 84 , obtaining a close to pole-on orientation as the most likely for this TNO. Conclusions. For the three TNOs, the thermal inertias derived from light curve analyses or from the thermophysical analysis of the mean thermal fluxes confirm the generally small or very small surface thermal inertias of the TNO population, which is consistent with a statistical mean value Γ mean = 2.5 ± 0.5 MKS.