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The NASA Ice Giants Pre-Decadal Survey Mission Report (2017) recommended the high scientific importance of sending a mission with an orbiter and a probe to one of the Ice Giants, with preferential launch dates in the 2029-2034 timeframe. Such a mission concept is equally well supported by European scientists and Mousis et al (P&SS, 155, 12, 2018) give compelling scientific rationales for the exploration of these worlds with missions carrying in situ probes. In this presentation we will outline the conceptual design of the Advanced Ice Giants Net Flux Radiometer (IG-NFR) instrument, currently being designed by NASA Goddard Space Flight Center to make in situ observations of the upward and downward fluxes of solar and thermal radiation in the atmospheres of Uranus and Neptune. The IG-NFR is designed to: (i) accommodate seven filter bandpass channels in the spectral range 0.25-300 µm (ii) measure up and down radiation flux in a clear unobstructed 10° FOV for each channel; (iii) use thermopile detectors that can measure a change of flux of at least 0.5 W/m2 per decade of pressure; (iv) view five distinct view angles (±80°, ±45°, and 0°); (v) predict the detector response with changing temperature environment; (vi) use application-specific integrated circuit technology for the thermopile detector readout; (vii) be able to integrate radiance for 2s or longer, and (vii) sample each view angle including calibration targets. The IG-NFR system noise equivalent power at 298 K is 73 pW in a 1 Hz electrical bandwidth. We present initial simulations of the anticipated observations using two radiative transfer and retrieval tools, NEMESIS (Irwin et al., JQSRT, 109, 1136, 2008) and the Planetary Spectrum Generator (PSG, Villanueva et al., 2017, https://psg.gsfc.nasa.gov). For the NEMESIS modelling the radiative fluxes observable at varying pressure levels were calculated with a Matrix-Operator plane-parallel multiple-scattering model, using between 5 and 21 zenith angle quadrature points and up to 38 Fourier components for the azimuth decomposition. We also employed PSG to further validate our flux estimates, providing an important benchmarking and comparison test between both models. PSG solves the scattering radiative transfer employing the discrete ordinates method, with the scattering phase function described in terms of an expansion in terms of Legendre Polynomials. Molecular cross-sections are solved via the correlated-k method employing the latest HITRAN database (Gordon et al., 2017), which are completed with the latest collision-induced-absorption (CIA, Karman et al., 2019), and UV/optical cross-sections from the MPI database (Keller-Rudek et al., 2013). For the nominal case the Sun was assumed to be at an altitude of 10° above the horizon. The internal radiance field was calculated at each internal level for a standard reference Uranus atmosphere (e.g., Irwin et al., 2017) with the addition of a single cloud layer, based at 3 bar and composed of particles with a mean radius of 1.0 µm (and size variance 0.1) and assumed complex refractive index of 1.4 + 0.001i at all wavelengths. The opacity and fractional scale height of this cloud were fitted in both models to match the combined near-infrared observations of HST/WFC3, IRTF/SpeX and VLT/SINFONI analyzed by Irwin et al. (2017). The internal radiance fields were calculated from 0.4 to 300 µm using this atmospheric model. We will show how these simulations are being used to guide the choice of spectral filter bandwidths and centres to optimize the scientific return of such an instrument. We will show that observations with such an instrument can be used to constrain effectively the radiation energy budget in the atmospheres of the Ice Giants and can also be used to determine the pressures of cloud and haze layers and broadly constrain particle size. Such modelling also allows us to simulate the visible appearance of Uranus’ atmosphere during a descent and to perform detailed validations of the simulations by comparing the two radiative transfer models (NEMESIS and PSG).

In this presentation we will describe recent work to model upward and downward fluxes of solar and thermal radiation in the atmosphere of Venus using the NEMESIS radiative transfer and retrieval tool (Irwin et al., JQSRT, 109, 1136, 2008). Using a plane-parallel matrix operator multiple-scattering model we simulate the internal 3D radiation field within Venus’ atmosphere and compare our simulations with the observations of the Pioneer Venus and Venera 13 and 14 entry probes. Such simulations allow us to assess the availability of sunlight and the visibility of the sun azimuth direction in the cloud layer for potential balloon missions, and also enables us to predict at what altitude the surface will become visible for probes descending on dayside. A reanalysis of the Venera 13 and 14 radiance spectra observations will be used to reassess earlier estimates of cloud structure and water vapour abundance. Such modelling also allows us to simulate the visible appearance of Venus’ atmosphere during the descent of a probe mission as will be shown.

The design of an advanced Net Flux Radiometer (NFR), for inclusion as a payload on a future Ice Giants probe mission, is given. The Ice Giants NFR (IG-NFR) will measure the upward and downward radiation flux (hence net radiation flux), in seven spectral bands, spanning the range from solar to far infra-red wavelengths, each with a 5° Field-Of-View (FOV) and in five sequential view angles (±80°, ±45°, and 0°) as a function of altitude. IG-NFR measurements within either Uranus or Neptune’s atmospheres, using dedicated spectral filter bands will help derive radiative heating and cooling profiles, and will significantly contribute to our understanding of the planet’s atmospheric heat balance and structure, tropospheric 3-D flow, and compositions and opacities of the cloud layers. The IG-NFR uses an array of non-imaging Winston cones integrated to a matched thermopile detector Focal Plane Assembly (FPA), with individual bandpass filters, housed in a diamond windowed vacuum micro-vessel. The FPA thermopile detector signals are read out in parallel mode, amplified and processed by a multi-channel digitizer application specific integrated circuit (MCD ASIC) under field programmable gate array (FPGA) control. The vacuum micro-vessel rotates providing chopping between FOV’s of upward and downward radiation fluxes. This unique design allows for small net flux measurements in the presence of large ambient fluxes and rapidly changing ambient temperatures during the probe descent to ≥10 bar pressure.

The detection of methane in the atmosphere of Mars was first reported in 2004. Since then a number of independent observations of methane have been reported, all showing temporal variability. Up until recently, the origin of methane was attributed to sources either indigenous to Mars or exogenous, where methane is a UV degradation byproduct of organics falling on to the surface. Most recently, a new hypothesis has been proposed that argues that the appearance and variation of methane are correlated with specific meteor events at Mars. Indeed, extraplanetary material can be brought to a planet when it passes through a meteoroid stream left behind by cometary bodies orbiting the Sun. This occurs repeatedly at specific times in a planet's year as streams tend to be fairly stable in space. In this paper, we revisit this latest hypothesis by carrying out a complete analysis of all available data on Mars atmospheric methane, including the very recent data not previously published, together with all published predicted meteor events for Mars. Whether we consider the collection of individual data points and predicted meteor events, whether we apply statistical analysis, or whether we consider different time spans between high methane measurements and the occurrence of meteor events, we find no compelling evidence for any correlation between atmospheric methane and predicted meteor events.

The upper jovian atmosphere is particularly transparent at wavelengths near 5 μ m . Levels well below the cloud layers, which are situated between 0.5 and 2 bar, can be sounded. Large spatial variations of the brightness are observed, which are directly related to the opacity of the overlying cloud layer. Yet, the nature of the 5- μ m absorber in the jovian atmosphere has been subject of much debate. The cloud layer has been modelled many times as a thin, non-scattering layer, the opacity adjusted to fit the overall radiance level. This has proven to work well for individual spectra. Data from the Galileo near infrared mapping spectrometer (NIMS), covering the 0.7– 5.2 μ m range, include a number of observations of the same areas, separated by several hours, at different emission angles. Should the 5 μ m absorber be a thin absorbing layer then, apart from a change in radiance level, the overall shape of the 5- μ m spectrum is also expected to change significantly with emission angle. However, comparison of the 5- μ m spectra measured by NIMS of the same location but at different viewing angles reveals that while the overall radiance level decreases with increasing emission angle, the shape of the spectra remain unchanged. In this paper we present atmospheric models that include scattering to explain this effect. We show that the 5- μ m absorbing cloud particles must be significantly scattering ( ω = 0.9 ± 0.05 ) in order to explain these observations, and find that the base of the cloud layer must reside at pressures less than 2 bar. Furthermore, we show that the scattering within this cloud has important consequences on the retrieval of gas abundances from spectra in the 5- μ m region.

The latitudinal variation of Saturn's tropospheric composition (NH3, PH3 and AsH3) and aerosol properties (cloud altitudes and opacities) are derived from Cassini/VIMS 4.6-5.1μm thermal emission spectroscopy on the planet's nightside (April 22, 2006). The gaseous and aerosol distributions are used to trace atmospheric circulation and chemistry within and below Saturn's cloud decks (in the 1- to 4-bar region). Extensive testing of VIMS spectral models is used to assess and minimise the effects of degeneracies between retrieved variables and sensitivity to the choice of aerosol properties. Best fits indicate cloud opacity in two regimes: (a) a compact cloud deck centred in the 2.5-2.8bar region, symmetric between the northern and southern hemispheres, with small-scale opacity variations responsible for numerous narrow light/dark axisymmetric lanes; and (b) a hemispherically asymmetric population of aerosols at pressures less than 1.4bar (whose exact altitude and vertical structure is not constrained by nightside spectra) which is 1.5-2.0× more opaque in the summer hemisphere than in the north and shows an equatorial maximum between ±10° (planetocentric).Saturn's NH3 spatial variability shows significant enhancement by vertical advection within ±5° of the equator and in axisymmetric bands at 23-25°S and 42-47°N. The latter is consistent with extratropical upwelling in a dark band on the poleward side of the prograde jet at 41°N (planetocentric). PH3 dominates the morphology of the VIMS spectrum, and high-altitude PH3 at p

The first four complete spectra recorded by the near infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft in 1996 have been analyzed. These spectra remain the only ones which have been obtained at maximum resolution over the entire NIMS wavelength range of 0.7 - 5.2 μm. The spectra cover the edge of a "warm" spot at location 5°N, 85°W. We have analyzed the spectra first with reflecting layer models and then with full multiple scattering models using the method of correlated-k. We find that there is strong evidence for three different cloud layers composed of a haze consistent with 0.5-μm radius tholins at 0.2 bar, a cloud of 0.75-lim NH3 particles at about 0.7 bar, and a two-component NH4SH cloud at about 1.4 bars with both 50.0- and 0.45-μm particles, the former being responsible for the main 5-μm cloud opacity. The NH3 relative humidity above the cloud tops is found to decrease slightly as the 5-μm brightness increases, with a mean value of approximately 14%. We also find that the mean volume mixing ratio of ammonia above the middle (NtL4SH) cloud deck is (1.7± 0.1) × 10-4 and shows a similar, though less discernible decrease with increasing 5-μm brightness. The deep volume mixing ratios of deuterated methane and phosphine are found to be constant and we estimate their mean values to be (4.9± 0.2) × 10-7 and (7.7 ± 0.2) × 10-7, respectively. The fractional scale height of phosphine above the 1 bar level is found to be 27.1± 1.4% and shows a slight decrease with increasing 5-μm brightness. The relative humidity of water vapor is found to be approximately 7%, but while this and all the previous observations are consistent with the assumption that "hot spots" are regions of downwelling, desiccated air, we find that the water vapor relative humidity increases as the 5-μm brightness increases. Copyright 1998 by the American Geophysical Union.

A high-speed cyclonic vortex centered on the north pole of Saturn has been revealed by the visual-infrared mapping spectrometer (VIMS) onboard the Cassini–Huygens Orbiter, thus showing that the tropospheres of both poles of Saturn are occupied by cyclonic vortices with winds exceeding 135 m/s. High-spatial-resolution (~200 km per pixel) images acquired predominantly under night-time conditions during Saturn's polar winter—using a thermal wavelength of 5.1 μm to obtain time-lapsed imagery of discrete, deep-seated (>2.1-bar) cloud features viewed in silhouette against Saturn's internally generated thermal glow—show a classic cyclonic structure, with prograde winds exceeding 135 m/s at its maximum near 88.3° (planetocentric) latitude, and decreasing to

We present CCD photometric observations of Centaurs 2000 QC243 and 2001 PT13. For 2000 QC243 ,a large amplitude period is found at 4:57 h 0:05 h, which likely corresponds to half the rotation period of the body, or coincides with the full rotation period, depending on whether the variability is induced by an irregular shape or by albedo features. The apparent double-peaked lightcurve favors the rst interpretation. The large amplitude of the oscillations imply a very irregular shape for this object or a large albedo assymmetry between the two hemispheres. For 2001 PT13, a clear period of 4:15 h 0:05 h was detected, with an amplitude of 0.16 mag. Since 4.15 h is close to the breakup limit for typical cometary densities and tensile strengths, 8.3 h appears to be a more likely rotation period.

A lightcurve of Centaur 1999 UG 5 from R -band CCD images taken at the Calar Alto 1.52 m and La Palma 3.5 m TNG telescopes is presented. The lightcurve shows noticeable changes in brightness. Small activity outbursts do not appear to be the cause of the brightness changes because no coma was detected after coadding all the images. Thus, the changes in brightness are interpreted as being caused by rotational variability. A periodogram analysis of the lightcurve reveals significant peaks from 13.0 h to 13.8 h, with a confidence level exceeding 99.9% . The maximum spectral power corresponds to 13.25 h. The overall shape of the lightcurve can be explained by an irregular object rotating once per 26.5 h, but other possibilities exist. Assuming an ellipsoid shape for the rotating body, the $0.24\pm 0.02$ mag amplitude of the lightcurve implies a minimum axial ratio of 1.25. The mean absolute magnitude in V band was found to be $H_V=10.42\pm 0.02$ assuming a typical phase parameter $G=0.15$. This implies a diameter of 55.3 km for the object, provided that a typical albedo of 0.04 is assumed. The colours of 1999 UG 5 were found to be $B-V=0.95\pm 0.13$, $V-R=0.63\pm 0.06$, and $R-I=0.61\pm 0.09$.

We present the results of visible broad band photometry of two Centaurs, 10199 Chariklo (1997 CU26) and 1999 UG5 from data obtained at the 1.52 meter telescope of the National Astronomical Observatory at Calar Alto, Spain, during 2 separate runs in April 1999 and February 2000 and at the 1.5 meter telescope of the Sierra Nevada Observatory, Spain, in March of 1999. For Chariklo, the absolute magnitudes determined from the February 2000 data are found to be higher by about 0.27 mag than the average in the 1999 run. This may indicate long period rotational variability and possibly a G parameter higher than the assumed value of 0.15. From the best sampled R-lightcurve obtained in the February 2000 run, no short term rotational variability was found. The V R colours for this object in all runs are similar to previously published values. For 1999 UG5, colours were found to be very red: B V =0 :88 0:18, V R =0 :60 0:08 and R I =0 :72 0:13. These results place this object in the group of the reddest known bodies in the Solar System. HR and HV are found to be 10:06 0:09 and 10:61 0:07 respectively, and its diameter is estimated to be on the order of 47 2k m.

The aim of this work is to deduce physical characteristics of the aerosols that compose the thin detached haze layer of Titan, for which the composition and origin are currently unknown. We have used four images at three different phase angles and three different wavelengths where the detached haze clearly appears. The low optical path in the layer permits assumptions that greatly simplify the treatment and allow us to consider the scattered intensity as the product of the scattering cross section, the phase function at the considered phase angle, and the number of aerosols. Physical arguments are given to support fractal aerosols in the detached haze, and we investigate a wide range of monomer radii, monomer numbers, and imaginary refractive indexes. This study yields information about the spectral variation of the refractive index for the detached haze tholins that are clearly different from those for the main haze. On the other hand, no firm values are given for the monomer radius and number, but these two parameters are strongly linked through a simple relation.

The 5-μm window in the spectrum of Jupiter is one of the few regions that gives access to the vertical structure of the troposphere between pressure levels of approximately 4 and 8 bar. Voyager/IRIS spectra obtained in 1979 during the Voyager flybys have been analyzed intensively over the past two decades. Most of these analyses concluded on a vertical cloud structure consisting of three layers: an ammonia cloud layer with a base around 0.5 bar, an ammonium-hydrosulfide layer at about 2 bar, and a water cloud layer with a base somewhere between 5 and 7 bar. However, the recent Galileo entry probe measurements of the vertical atmospheric structure in a hot spot region show a quite different picture. The data indicate only two cloud layers, at about 0.7 bar and 1.34 bar, and no significant cloud opacity between 2 and 22 bar, where the Probe measurements ended. New data from the Galileo/NIMS and ISO/SWS experiments agree with the Probe findings. The inclusion of cloud opacity between 5 and 7 bar in the model atmosphere results in a poor fit to the NIMS and ISO data. A comparison between Voyager/IRIS spectra and the ISO/SWS and Galileo/NIMS spectra shows a slope in the continuum level of the IRIS spectra for wavelengths shorter than 5 μm, not present in either SWS spectrum or the NIMS spectra. We show that to fit the IRIS spectra, an additional opacity somewhere between 3 and 8 bar is needed in the model atmosphere. We suggest that, most likely, a calibration problem occurred with the Voyager/IRIS data in this spectral region, even though temporal variations in the deep atmospheric structure of Jupiter cannot be ruled out altogether.

The Galileo Near Infrared Mapping Spectrometer (NIMS) obtains spectral images in the wavelength range 0.7 to 5.2 μm with a spectral resolving power of approximately 200. This spectral range allows NIMS to sense cloud-reflected solar radiation, thermal emission produced in the deep atmosphere, and auroral emission from the thermosphere of Jupiter. Using 5 μm thermal emission spectroscopy, the amount of water vapor in the deep atmosphere, at approximately the (i to 8 bar level, is found to vary by a factor > 100. Deep atmosphere ammonia was also found to vary, with a spatial behavior different from that of water vapor. No evidence is found for a massive water cloud. Using reflected solar radiation in conjunction with thermal emission, two cloud layers are found, the upper at 0.5 bars and a lower one at 1-1.3 bars. The inferred absorption properties of these clouds are consistent with ammonia crystals (the upper cloud) and ammonium hydrosulfide particles (the lower cloud).

High resolution spectroscopy of the impacts and impact sites of comet P/Shoemaker-Levy 9 in Jupiter has been performed at the Pic-du-Midi observatory, France. The transient emission of seven emission lines from five different metals (Na, Fe, Ca, Li, K) and of the Hα line have been identified in spectra from the fresh impact sites of fragments L and Q1.

著者人数：43名, Accepted: 2008-10-06, 資料番号: SA1000997000

Received 2 March 2008; revised 29 July 2008; accepted 18 September 2008; published 31 December 2008. [1] We evaluated the spatial variation of Venusian surface emissivity at 1.18 mm wavelength and that of near-surface atmospheric temperature using multispectral images obtained by the Near-Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. The Galileo NIMS observed the nightside thermal emission from the surface and the deep atmosphere of Venus, which is attenuated by scattering from the overlying clouds. To analyze the NIMS data, we used a radiative transfer model based on the adding method. Although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere, our analysis revealed that the horizontal temperature variation in the near-surface atmosphere is no more than ±2 K on the Venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands. One interpretation for the latter result is that highland materials are generally composed of felsic rocks. Since formation of a large body of granitic magmas requires water, the presence of granitic terrains would imply that Venus may have had an ocean and a mechanism to recycle water into the mantle in the past.

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3-1 μm range), VIRTIS-M-IR (imaging spectrometer in the 1-5 μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2-5 μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H2O, OCS and SO2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 μm fundamental band of CO2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation. © 2007 Elsevier Ltd. All rights reserved.

International audience; We present an automated method for cloud tracking which can be applied to planetary images. The method is based on a digital correlator which compares two or more consecutive images and identifies patterns by maximizing correlations between image blocks. This approach bypasses the problem of feature detection. Four variations of the algorithm are tested on real cloud images of Jupiter's white ovals from the Galileo mission, previously analyzed in Vasavada et al. [Vasavada, A.R., Ingersoll, A.P., Banfield, D., Bell, M., Gierasch, P.J., Belton, M.J.S., Orton, G.S., Klaasen, K.P., Dejong, E., Breneman, H.H., Jones, T.J., Kaufman, J.M., Magee, K.P., Senske, D.A. 1998. Galileo imaging of Jupiter's atmosphere: the great red spot, equatorial region, and white ovals. Icarus, 135, 265, doi:10.1006/icar.1998.5984]. Direct correlation, using the sum of squared differences between image radiances as a distance estimator (baseline case), yields displacement vectors very similar to this previous analysis. Combining this distance estimator with the method of order ranks results in a technique which is more robust in the presence of outliers and noise and of better quality. Finally, we introduce a distance metric which, combined with order ranks, provides results of similar quality to the baseline case and is faster. The new approach can be applied to data from a number of space-based imaging instruments with a non-negligible gain in computing time.

International audience; Recent improvements in a comprehensive non-local thermodynamic equilibrium (non-LTE) model of CO 2 atmospheres has permitted a better understanding of a number of Venusian atmospheric measurements taken more than a decade ago by the "Near Infrared Mapping Spectrometer" (NIMS) on board the Galileo spacecraft during its Venus fly-by. Those data, containing a strong non-LTE component, showed a structure in the 4.3-mum spectral region which was challenging for non-LTE models so far. The model used in this work was refined after analysis of Martian CO 2 atmospheric emission taken by the "Planetary Fourier Spectrometer" (PFS) and the "Visible and Infrared Mineralogical Mapping Spectrometer" (OMEGA) instruments on board Mars Express. Here we show that both the limb and the nadir measurements of the Venus daylight atmosphere taken at 4.3-mum by NIMS can be fitted reasonably well with the revised model. This gives confidence in the usage of such model for the analysis of the Venus Express mission, in particular for the "Visible Infrared Thermal Imaging Spectrometer" (VIRTIS) instrument which will systematically observe these emissions. We present here non-LTE simulations for VIRTIS which demonstrate its capabilities and potential for detecting atmospheric emissions of CO and CO 2 under non-LTE, both in limb and nadir observations and we discuss briefly the perspectives to use them in order to improve our understanding of the physics of the upper atmosphere of Venus.

This report is a brief summary of some of the major achievements in studies of planets and satellites that have been accomplished during the years 2003–2005. Unlike previous years, we do not attempt to provide a detailed overview of the field but rather choose to highlight aspects which are of particular novelty.

We have analysed all the available high phase angle images of Titan limb taken by Voyager 1 and 2, in early 1980. For several different phase angles and wavelengths, we seek for a consistent set of haze parameters able to fit all data simultaneously. Our main purpose is to obtain an accurate estimate of the latitudinal variation of haze opacity at 200 km altitude at the time of the Voyager flyby's. We find that haze opacity at 200 km is about constant in the southern hemisphere and drops between equator and 60 ∘ N by about 30–50%, sharply increasing again beyond 60 ∘ N . The latter feature is clearly due to the north polarhood. This behaviour is opposite to total optical depth variations retrieved from IRIS observation, at the same epoch. The IRIS data refer to levels below 100 km altitude. A comparison of our results with calculations from a general circulation model, shows that (1) our results are realistic and can be considered as robust (2) the opacity variations at 200 km (this work) and at ground (IRIS data), although opposite, are not inconsistent with each other.

In this paper, we attempt to place constraints on the possible global abundance of water and the average vertical cloud structure in the atmosphere of Jupiter. Based on the analysis of the Galileo Near-Infrared Mapping Spectrometer data, we find that in the atmosphere of Jupiter down to 6– 8 bar , particularly in the North Equatorial Belt (NEB) region, the overall O/H ratio is compatible with one or more times the solar value of this ratio. We also find that if water clouds form at the levels where they are expected from thermochemical equilibrium calculations for a given deep O/H ratio, then subsolar values of the O/H ratio cannot be reconciled with the analyzed data. However, these results are dependent on the model atmosphere, in particular the detailed vertical distribution of cloud opacity. Therefore, they should be considered with care, until new observations on the vertical cloud structure become available. The water vapor mixing ratio in the NEB displays large spatial variations. The same set of data yield subsaturated mixing ratios of ammonia to atmospheric levels of about 4 bar . This depletion of ammonia to great depths, as seen by the Galileo Probe in the hot spot where it entered, appears to be a common phenomenon in the entire NEB.

[1] Triboelectric charging of saltating and colliding sand and dust particles produces strong electric fields in terrestrial dust devils and dust storms. Acceleration of the charged particles, as well as microdischarges between them, generates wideband electromagnetic radiation. Similar phenomena are expected to be ubiquitous on Mars, because Martian dust devils and dust storms are larger, stronger and more frequent than their terrestrial analogues, and electrical discharges occur at a much lower potential gradient in the thin Martian atmosphere. We present theoretical arguments and observational evidence that Martian dust events produce nonthermal wideband electromagnetic radiation detectable from Earth. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0654 Electromagnetics: Plasmas; 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 5445 Planetology: Solid Surface Planets: Meteorology (3346). Citation: Renno, N. O., A.-S. Wong, S. K. Atreya, I. de Pater, and M. Roos-Serote, Electrical discharges and broadband radio emission by Martian dust devils and dust storms, Geophys. Res. Lett., 30(22), 2140, doi:10.1029/2003GL017879, 2003.

Lavoisier mission is a joint effort of eight European countries and a technological challenge aimed at investigating the lower atmosphere and the surface of Venus. The mission consists of a descent probe and three balloons to be deployed below the cloud deck. Its main scientific objectives may be summarized as following : (i) composition of the deep atmosphere : noble gas (elemental/isotopic), molecular species (elemental/isotopic), oxygen fugacity; vertical/horizontal/temporal variability; (ii) infrared spectroscopy and radiometry (molecular composition, radiative transfer); (iii) dynamics of the atmosphere : p, T, acceleration measurements, balloon localization through VLBI, meteorological events signed by acoustic waves, atmospheric mixing as imprinted on radioactive tracers; (iv) surface morphology and mineralogy through near infrared imaging on dayside, surface temperature through NIR imaging on nightside. Additional tentative objectives are search for (a) atmospheric electrical activity (optically, radioelectrically, acoustically), (b) crustal outgassing and/or volcanic activity : acoustic activity, horizontal/vertical distribution of radioactive tracers, (c) seismic activity : acoustic waves transmitted from crust to atmosphere, and (d) remanent and/or intrinsic magnetic field. Lavoisier was proposed to ESA in response to the F2/F3 mission Announcement of Opportunity at the beginning of 2000, but it was not selected for the assessment study, A wide international partnership was created for this occasion, including Finland (FMI), France (IPSL, MAGIE, Universite Orsay, IPSN, INPG, CEA, IPGP, Obs. Paris-Meudon), Germany (MPAe, Univ. Muenster), Hungary (KFKI, Univ. Eotvos), Portugal (OAL), Russia (IKI), Spain (IAA), United Kingdom (Univ. Oxford). (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Models of Jupiter's formation and structure predict that its atmosphere is enriched in oxygen, relative to the Sun, and that consequently water clouds should be present globally near the 5-bar pressure level1,2. Past attempts to confirm these predictions have led to contradictory results3,4,5; in particular, the Galileo probe revealed a very dry atmosphere at the entry site, with no significant clouds at depths exceeding the 2-bar level6,7. Although the entry site was known to be relatively cloud-free, the contrast between the observed local dryness and the expected global wetness was surprising. Here we analyse near-infrared (around 5 µm) observations of Jupiter, a spectral region that can reveal the water vapour abundance and vertical cloud structure in the troposphere8. We find that humid and extremely dry regions exist in close proximity, and that some humid regions are spatially correlated with bright convective clouds extending from the deep water clouds to the visible atmosphere.

Infrared observations of Venus' night-side between 3 and 5 μm provide a valuable means to study the upper cloud structure (at approximately 68 km) and the thermal structure above the clouds. New observations between 3.67 and 5.08 μm, concerning spectral images of Venus obtained in October 1991 with the ProtoCAM/IRTF and a Circular Variable Filter, are presented. A cloud particle scale height for the upper clouds of 3.9±1 km is retrieved from limb darkening measurements, which is in good agreement with measurements from both space probes and Earth-based observatories. The observations show an increase in temperature from the centre towards the poles when sounding altitudes above 72 km. This, along with temperatures at cloud top levels, implies isothermal profiles between 68 and 74 km at high latitudes.

An analysis of thermal profiles and dynamics over a wide range of latitudes for the venusian atmosphere between 70 and 90 km is presented based on high spatial resolution infrared spectra of the night side obtained by the near infrared mapping spectrometer (NIMS) experiment during the Galileo-Venus encounter in February 1990. Using the 4.3-μm CO2 absorption band, the temperature profile is retrieved in the 75- to 91-km altitude region over a latitudinal range of -59° to + 64°. Compared to earlier observations from the Pioneer Venus mission, the temperature at 91 km is about 10 K higher and between 74 and 83 km about 3.6 K colder. An equator to pole warming at constant pressure levels is found and implications for the zonal wind profiles are drawn under the assumption that the atmosphere is in cyclostrophic balance in the region of 70 to 90 km. The results are in correspondence with direct wind measurements from ground-based observations at 95 km and 105 km altitude. © 1995 Academic Press. All rights reserved.

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 (H2O, CH4, NH3, GeH4, CH3D and PH3) and the cloud structure and morphology. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

This paper presents the analysis of hot spot observations in the Jovian North Equatorial Belt obtained with the near-infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft. The data were acquired during the closest approach sequences between June 1996 and April 1997. We focus on the spectral window between 4.5 and 5.2 [Jim determining the cloud opacity above 2 bar, the water vapor relative humidity, and the ammonia abundance between 4 and 8 bar. We find a linear relationship between the cloud opacity and the continuum level of the spectrum. For a given radiance level of an individual spectrum, significant variations in the water vapor relative humidity are seen. However, no clear evidence for a relationship between the cloud opacity and the water relative humidity is seen. A cloud structure similar to that measured by the Galileo entry probe, with no significant cloud opacity below 2 bar, is adequate. The air in the hot spots is found to be overall dry, consistent with the probe measurements. None of the considered spectra show water vapor relative humidities exceeding 10%. Significant spatial variations of the water vapor relative humidity are found, and the distribution over the observed hot spot regions is complex. Because of a low sensitivity of the NIMS spectra to ammonia, uncertainties in the derived ammonia abundance are much higher than for water. There is, however, a possible trend in all the observed hot spots toward more ammonia inside than outside the hot spots at the sounded pressure levels. Copyright 1998 by the American Geophysical Union.