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We describe the capabilities, radiometric stability, and calibration of a custom vacuum environment chamber capable of simulating the near‐surface conditions of airless bodies. Here we demonstrate the collection of spectral measurements of a suite of fine particulate asteroid analogs made using the Planetary Analogue Surface Chamber for Asteroid and Lunar Environments (PASCALE) under conditions like those found on Earth and on airless bodies. The sample suite includes anhydrous and hydrated physical mixtures, and chondritic meteorites (CM, CI, CV, CR, and L5) previously characterized under Earth‐ and asteroid‐like conditions. And for the first time, we measure the terrestrial and extra‐terrestrial mineral end members used in the olivine‐ and phyllosilicate‐dominated physical mixtures under the same conditions as the mixtures and meteorites allowing us better understand how minerals combine spectrally when mixed intimately. Our measurements highlight the sensitivity of thermal infrared emissivity spectra to small amounts of low albedo materials and the composition of the sample materials. As the albedo of the sample decreases, we observe smaller differences between Earth‐ and asteroid‐like spectra, which results from a reduced thermal gradient in the upper hundreds of microns in the sample. These spectral measurements can be compared to thermal infrared emissivity spectra of asteroid (101955) Bennu's surface in regions where similarly fine particulate materials may be observed to infer surface compositions., Key Points Thermal infrared spectra of fine particulate minerals, physical mixtures of those minerals, and meteorites were measured under simulated Bennu conditionsComparisons of mineral, physical mixture, and meteorite spectra highlight the spectral behavior when materials are mixed in increasing complexityAs albedo decreases the spectral effects due to thermal gradients due to the vacuum environment of airless bodies are reduced

The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) seismometer was deployed to the surface of Mars in December 2018–February 2019. The specific deployment conditions, which are very different from those of a standard broadband instrument on the Earth, result in resonances caused by different parts of the sensor assembly (SA) that are recorded by the seismometer. Here, we present and characterize the resonances known to be present in the SA and their causes to aid interpretation of the seismic signals observed on Mars. Briefly, there are resonances in the SA at about 2.9, 5.3, 9.5, 12, 14, 23–28, and 51 Hz. We discuss various methods and tests that were used to characterize these resonances, and provide evidence for some of them in data collected on Mars. In addition to their relevance for the high frequency analysis of seismic data from InSight, specifically for phase measurements near the resonant frequencies, the tests and observations described here are also of potential use in the further development of planetary seismometers, for example, for Mars, the Moon, or Europa.

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).

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.

One of the key problems in determining lunar surface composition for thermal-infrared measurements is the lack of comparable laboratory-measured spectra. As the surface is typically composed of fine-grained particulates, the lunar environment induces a thermal gradient within the near sub-surface, altering the emission spectra: this environment must therefore be simulated in the laboratory, considerably increasing the complexity of the measurement. Previous measurements have created this thermal gradient by either heating the cup in which the sample sits or by illuminating the sample using a solar-like source. This is the first setup able to measure in both configurations, allowing direct comparisons to be made between the two. Also, measurements across a wider spectral range and at a much higher spectral resolution can be acquired using this new setup. These are required to support new measurements made by the Diviner Lunar Radiometer, the first multi-spectral thermal-infrared instrument to orbit the Moon. Results from the two different heating methods are presented, with measurements of a fine-grained quartz sample compared to previous similar measurements, plus measurements of a common lunar highland material, anorthite. The results show that quartz gives the same results for both methods of heating, as predicted by previous studies, though the anorthite spectra are different. The new calibration pipeline required to convert the raw data into emissivity spectra is described also

By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars’ surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking’s Mars seismic monitoring by a factor of ∼2500 at 1 Hz and ∼200000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars’ surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of Mw∼3 at 40∘ epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution., Space Science Reviews, 215 (1), ISSN:1572-9672, ISSN:0038-6308

An analysis of currently available ammonia (NH$_3$) visible-to-near-infrared gas absorption data was recently undertaken by Irwin et al. (Icarus, 302 (2018) 426) to help interpret Very Large Telescope (VLT) MUSE observations of Jupiter from 0.48 - 0.93 $\mu$m, made in support of the NASA/Juno mission. Since this analysis a newly revised set of ammonia line data, covering the previously poorly constrained range 0.5 - 0.833 $\mu$m, has been released by the ExoMol project, "C2018" (Coles et al., JQSRT 219, 199 - 122, 2018), which demonstrates significant advantages over previously available data sets, and providing for the first time complete line data for the previously poorly constrained 5520- and 6475-\AA\ bands of NH$_3$. In this paper we compare spectra calculated using the ExoMol-C2018 data set (Coles et al., JQSRT 219, 199 - 122, 2018) with spectra calculated from previous sources to demonstrate its advantages. We conclude that at the present time the ExoMol-C2018 dataset provides the most reliable ammonia absorption source for analysing low- to medium-resolution spectra of Jupiter in the visible/near-IR spectral range, but note that the data are less able to model high-resolution spectra owing to small, but significant inaccuracies in the line wavenumber estimates. This work is of significance not only for solar system planetary physics, but for future proposed observations of Jupiter-like planets orbiting other stars, such as with NASA's planned Wide-Field Infrared Survey Telescope (WFIRST)., Comment: 12 Figures

Seismometers deployed on the Moon by the Apollo astronauts from 1969 to 1972 detected moonquakes and impacts, and added to our understanding of the lunar interior. Several lunar missions are currently being planned, including the Commercial Lunar Payload Services (CLPS), the Lunar Geophysical Network, and the astronaut program Artemis. We propose a microseismometer for the Moon: the Silicon Seismic Package (SSP). The SSP’s sensors are etched in silicon, and are predicted to have a noise floor below 2 × 10 − 10 ( m s − 2 ) / Hz between 0.3 and 3 Hz (similar to the Apollo instruments between 0.3 and 0.5 Hz, and better than Apollo above 0.5 Hz). The SSP will measure horizontal and vertical motion with the three sensors in a triaxial configuration. The instrument is robust to high shock and vibration and has an operational range from −80°C to +60°C, allowing deployment under harsh conditions. The first-generation version of this sensor, the SEIS-SP, was deployed on Mars in 2018 as part of the InSight mission’s seismic package. We will reconfigure the seismometer for the lower gravity of the Moon. We estimate that a single SSP instrument operating for one year would detect around 74 events above a signal-to-noise ratio of 2.5, as well as an additional 500+ above the noise floor. A mission lasting from lunar dawn until dusk, carried on a CLPS lander, could test the instrument in situ, and provide invaluable information for an extensive future network.

International audience; The InSight mission is due to launch in May 2018, carrying a payload of novel instruments designed and tested to probe the interior of Mars whilst deployed directly on the Martian regolith and partially isolated from the Martian environment by the Wind and Thermal Shield. Central to this payload is the seismometry package SEIS consisting of two seismometers, which is supported by a suite of environmental/meteorological sensors (Temperature and Wind Sensor for InSight TWINS; and Auxiliary Payload Sensor Suite APSS). In this work, an optimal estimations inversion scheme which aims to decorrelate the short-period seismometer (SEIS-SP) signal due to seismic activity alone from the environmental signal and random noise is detailed, and tested on both simulated and Viking data. This scheme also applies a module to identify measurements contaminated by Single Event Phenomena (SEP). This scheme will be deployed as the pre-processing pipeline for all SEIS-SP data prior to release to the scientific community for analysis.

CASTAway is a mission concept to explore our Solar System's main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10 to 20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30 to 100) spectrometer and visible context imager, a thermal (e.g. 6 to 16 microns) imager for use during the flybys, and modified star tracker cameras to detect small (approx. 10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, whilst delivering a significant increase in knowledge of our Solar System., 40 pages, accepted by Advances in Space Research October 2017

Saturn's polar stratosphere exhibits the seasonal growth and dissipation of broad, warm, vortices poleward of $\sim75^\circ$ latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini's reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly-formed NPSV was bounded by a strengthening stratospheric thermal gradient near $78^\circ$N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn's long-lived polar hexagon - which was previously expected to be trapped in the troposphere - can influence the stratospheric temperatures some 300 km above Saturn's clouds., 51 pages, 12 figures, published in Nature Communications

International audience; The first of the two missions foreseen in the ExoMars program was successfully launched on 14th March 2016. It included the Trace Gas Orbiter and the Schiaparelli Entry descent and landing Demonstrator Module. Schiaparelli hosted the DREAMS instrument suite that was the only scientific payload designed to operate after the touchdown. DREAMS is a meteorological station with the capability of measuring the electric properties of the Martian atmosphere. It was a completely autonomous instrument, relying on its internal battery for the power supply. Even with low resources (mass, energy), DREAMS would be able to perform novel measurements on Mars (atmospheric electric field) and further our understanding of the Martian environment, including the dust cycle. DREAMS sensors were designed to operate in a very dusty environment, because the experiment was designed to operate on Mars during the dust storm season (October 2016 in Meridiani Planum). Unfortunately, the Schiaparelli module failed part of the descent and the landing and crashed onto the surface of Mars. Nevertheless, several seconds before the crash, the module central computer switched the DREAMS instrument on, and sent back housekeeping data indicating that the DREAMS sensors were performing nominally. This article describes the instrument in terms of scientific goals, design, working principle and performances, as well as the results of calibration and field tests. The spare model is mature and available to fly in a future mission.

We report a micromachined silicon seismometer with a sensitivity of 0.25 ng/rtHz from 0.1 to 10 Hz. This represents the highest performance of a MEMS inertial sensor to date, and in particular is at or below the noise floor of the Earth's lowest ambient seismic levels over this bandwidth with a performance comparable to conventional seismometers. The microseismometer is robust to high shock (> 1000 g) and vibration (> 30 g rms), and can operate from +60C to −80 C allowing deployment under harsh conditions.

The martian atmosphere is host to many trace gases including water (H 2 O) and its isotopologues, methane (CH 4 ) and potentially sulphur dioxide (SO 2 ), nitrous oxide (N 2 O) and further organic compounds, which would serve as indirect tracers of geological, chemical and biological processes on Mars. With exception of the recent detection of CH 4 by Curiosity, previous detections of these species have been unsuccessful or considered tentative due to the low concentrations of these species in the atmosphere (∼10 −9 partial pressures), limited spectral resolving power and/or signal-to-noise and the challenge of discriminating between telluric and martian features when observing from the Earth. In this study, we present radiative transfer simulations of an alternative method for detection of trace gas species – the gas correlation radiometry method. Two potential observing scenarios were explored where a gas correlation filter radiometer (GCFR) instrument: (1) performs nadir and/or limb sounding of the martian atmosphere in the thermal infrared (200–2000 cm −1 from an orbiting spacecraft or (2) performs solar occultation measurements in the near-infrared (2000–5000 cm −1 ) from a lander on the martian surface. In both scenarios, simulations of a narrowband filter radiometer (without gas correlation) were also generated to serve as a comparison. From a spacecraft, we find that a gas correlation filter radiometer, in comparison to a filter radiometer (FR), offers a greater discrimination between temperature and dust, a greater discrimination between H 2 O and HDO, and would allow detection of N 2 O and CH 3 OH at concentrations of ∼10 ppbv and ∼2 ppbv, respectively, which are lower than previously-derived upper limits. However, the lowest retrievable concentration of SO 2 (approximately 2 ppbv) is comparable with previous upper limits and CH 4 is only detectable at concentrations of approximately 10 ppbv, which is an order of magnitude higher than the concentration recently measured by Curiosity. From a lander in low dust conditions, both a filter radiometer and gas correlation filter radiometer would provide measurement of H 2 O and HDO, which allows the D/H ratio in H 2 O to be determined. Detection of N 2 O, CH 4 , SO 2 , C 2 H 2 , C 2 H 6 at concentrations lower than previously-derived upper limits would be possible using a gas correlation filer radiometer in low dust conditions. However, either radiometer would be unable to detect these trace gases in high dust conditions, with the exception of H 2 O.

The results for the design study of the Long Wave Infrared Module (LWIR), a goal spectroscopic channel for the EChO ESA medium class candidate mission, are presented. The requirements for the LWIR module were to provide coverage of the 11–16 μm spectral range at a moderate resolving power of at least R = 30, whilst minimising noise contributions above photon due to the thermal background of the EChO instrument and telescope, and astrophysical sources such as the zodiacal light. The study output module design is a KRS-6 prism spectrograph with aluminium mirror beam expander and coated germanium lenses for the final focusing elements. Thermal background considerations led to enclosing the beam in a baffle cooled to approximately 25–29 K. To minimise diffuse astrophysical background contributions due to the zodiacal light, anamorphic designs were considered in addition to the elliptical input beam provided by the EChO telescope. Given the requirement that measurements in this waveband place on the performance of the infrared detector array, an additional study on the likely scientific return with lower resolving power (R

NASA’s InSight lander will deploy a tripod-mounted seismometer package onto the surface of Mars in late 2018. Mars is expected to have lower seismic activity than the Earth, so minimisation of environmental seismic noise will be critical for maximising observations of seismicity and scientific return from the mission. Therefore, the seismometers will be protected by a Wind and Thermal Shield (WTS), also mounted on a tripod. Nevertheless, wind impinging on the WTS will cause vibration noise, which will be transmitted to the seismometers through the regolith (soil). Here we use a 1:1-scale model of the seismometer and WTS, combined with field testing at two analogue sites in Iceland, to determine the transfer coefficient between the two tripods and quantify the proportion of WTS vibration noise transmitted through the regolith to the seismometers. The analogue sites had median grain sizes in the range 0.3–1.0 mm, surface densities of $1.3\mbox{--}1.8~\mbox{g}\,\mbox{cm}^{-3}$ , and an effective regolith Young’s modulus of $2.5^{+1.9}_{-1.4}~\mbox{MPa}$ . At a seismic frequency of 5 Hz the measured transfer coefficients had values of 0.02–0.04 for the vertical component and 0.01–0.02 for the horizontal component. These values are 3–6 times lower than predicted by elastic theory and imply that at short periods the regolith displays significant anelastic behaviour. This will result in reduced short-period wind noise and increased signal-to-noise. We predict the noise induced by turbulent aerodynamic lift on the WTS at 5 Hz to be $\sim2\times10^{-10}~\mbox{ms}^{-2}\,\mbox{Hz}^{-1/2}$ with a factor of 10 uncertainty. This is at least an order of magnitude lower than the InSight short-period seismometer noise floor of $10^{-8}~\mbox{ms}^{-2}\,\mbox{Hz}^{-1/2}$ .

Thin-film transmission spectra of ammonium hydrosulfide (NH4SH) ice and ammonia (NH3) ice between 1300 and 12,000 cm-1 were used to determine the ice's optical constants. The films were grown on a sapphire substrate, and a Fourier-transform spectrometer and a grating spectrometer were used together to record the spectra. Lambert's law was used to directly determine the imaginary component of the complex refractive indices; from this, the real component was derived using the Kramers-Kronig algorithm. It is shown that, contrary to what is expected, the optical constants determined for NH3 ice at 80 K are in good agreement with those in the cubic phase, rather than the metastable one. The phase of the NH4SH ice was observed to change from amorphous to polycrystalline as the film was annealed to 160 K. © 2006 Optical Society of America.

Since the 1970s, it has been predicted that both CO2 and H2O clouds can form in the Martian atmosphere, and many remote-sounding instruments have directly observed layers of extinction asserted to be clouds composed of either CO2 or H2O ice on Mars. The Mars Climate Sounder, onboard the Mars Reconnaissance Orbiter (MRO/MCS), entered orbit around Mars in 2006, and has been providing near-continuous coverage of the full planet since, at wavelengths from visible through to the mid-infrared, primarily in limb-viewing geometry, making it a suitable candidate to study the parameters of these clouds. In this work, the multiple scattering radiative-transfer tool NemesisMCS has been used to create a large dataset of simulations of CO2 and H2O clouds on Mars as would be measured by MRO/MCS, using a range of atmospheric conditions as well as cloud parameters derived from literature suitable for upper atmospheric clouds, and building specifically on the work of Sefton-Nash et al. (2013). This ensemble of simulations has been used to characterise the spectral signature of plausible CO2 and H2O clouds, as well as to assess the suitability of MRO/MCS to observe, to differentiate between, and to derive properties of such clouds. It has been found, given the noise levels expected for MRO/MCS and the range of atmospheric and cloud parameters sampled in this study, that radiance signals introduced by upper atmospheric clouds having nadir optical depths greater than about 10−5 should be distinguishable, with S/N≥1. This corresponds to specific concentrations greater than about 105 particles/g, particle radii greater than around View the MathML source, and cloud depths greater than about 2 km. MRO/MCS measurements should be able to be used with confidence to differentiate between upper atmospheric cloud and dust in the lower atmosphere, and clear conditions, with high success (≈100%). Lower reliability classification is accomplished for CO2 clouds, with only 60% being correctly identified as CO2, and the remainder classified instead as H2O cloud, in the case of optical depths in the expected range for upper atmospheric cloudswhich are detectable by MRO/MCS, although this result is highly dependent upon the sampled selection of optically thin and thick clouds and the atmospheric model employed. Although almost all the H2O clouds are correctly identified, the fact that such a large proportion of CO2 clouds are misclassified as H2O clouds shows that the spectral information alone from MRO/MCS is insufficient to differentiate between CO2 and H2O clouds when optically thin—but detectable—clouds are included in the analysis. Using a simple look-up table (LUT) scheme and simulated data, retrieval of properties of upper atmospheric clouds of sufficient opacity is possible, with preliminary estimates indicating that H2O cloud and dust parameters can be correctly reproduced between 48% and 100% of the time, and between 18% and 92% of the time for CO2 cloud test cases, although it must be noted that these values must be taken as a qualitative measure which does not capture the full range of atmospheric and cloud conditions on Mars which would be present in real MRO/MCS data. Furthermore, because of the optical properties of H2O and CO2, on a like-with-like selection, the H2O clouds always produce greater perturbations in radiance, thus biasing results to a higher success rate for H2O cloud retrievals. Application of the method to MRO/MCS data with a full-optimal estimation retrieval tool such as NemesisMCS will be the topic of a future study.

The Galileo Near Infrared Mapping Spectrometer (NIMS) has returned many spectra of the Jovian atmosphere in the range 0.7-5.2 mum. Although communications restrictions have limited the data return, several wide-area maps have been recorded at near full NIMS resolution. Using these data it is possible to determine both the average shape of the near-infrared (NIR) spectra with very thick clouds (and zero 5-mum brightness) and how these spectra vary as the 5-mum brightness increases.In most of the cases studied, we find that the variable part of the reflectivity has a very different shape to the mean part and may best be explained by variable reflectivity in the cloud layers at pressures greater than 1 bar. In these cases it would thus appear that a variable opacity in a cloud deck based between 1 and 2 bars is mainly responsible for the NIR albedo variations, and not a higher ammonia cloud based above 1 bar as has often been previously suggested. While the composition of this main variable cloud deck could well be ammonium hydrosulphide, other candidates include ammonia (should the much higher estimate of its deep gaseous fractional abundance resulting from the Galileo probe mission be correct), and perhaps even the upper reaches of a deeper water cloud. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

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. © 1993.

Scientific results from NIMS observations of Venus have been extensively reported in the literature, while those of Jupiter have, at the time of writing, just barely commenced. The planning and interpretation of studies of these planets, with their massive atmospheres and exotic compositions (by terrestrial standards), requires a comprehensive treatment of radiative transfer in both. This paper describes work done at Oxford to develop the underlying theory and practical radiative transfer schemes, with particular reference to the NIMS wavelength range, spectral resolution, and scientific objectives for Jupiter. Equivalent work for Venus has already been reported in the literature (e.g. Kamp and Taylor, 1990) and will not be covered in detail here. (C) 1997 COSPAR. Published by Elsevier Science Ltd.

Three aspects of the Venusian middle atmosphere are considered. First, we discuss the current state of understanding of the polar collar/ polar dipole phenomenon on Venus discovered by Pioneer Venus and subsequently investigated by Venera 15. Next, the measurements of water vapour above the clouds by these two missions are compared and contrasted. Finally, the new data which will be obtained in the future by, for example, the Near Infrared Mapping Spectrometer (NIMS) on the Galileo mission during its Venus fly-by in 1990, are discussed. New models of the Venusian atmosphere derived using Earth-based observations by Allen et al. /1/ suggest that the NIMS may yield the first spatially-resolved maps of the deep cloud structure on Venus. To further elucidate the mysterious dipole, an infrared imaging experiment is proposed.

With the exception of in situ atmospheric probes, the most useful way to study the atmospheres of other planets is to observe their electromagnetic spectra through remote observations, either from ground-based telescopes or from spacecraft. Atmospheric properties most consistent with these observed spectra are then derived with retrieval models. All retrieval models attempt to extract the maximum amount of atmospheric information from finite sets of data, but while the problem to be solved is fundamentally the same for any planetary atmosphere, until now all such models have been assembled ad hoc to address data from individual missions. In this paper, we describe a new general-purpose retrieval model, Non-linear Optimal Estimator for MultivariatE Spectral analySIS (NEMESIS), which was originally developed to interpret observations of Saturn and Titan from the composite infrared spectrometer on board the NASA Cassini spacecraft. NEMESIS has been constructed to be generally applicable to any planetary atmosphere and can be applied from the visible/near-infrared right out to microwave wavelengths, modelling both reflected sunlight and thermal emission in either scattering or non-scattering conditions. NEMESIS has now been successfully applied to the analysis of data from many planetary missions and also ground-based observations. © 2007 Elsevier Ltd. All rights reserved.

We present new measurements and modelling of low-resolution transmission spectra of self-broadened ammonia gas, one of the most important absorbers found in the near-infrared spectrum of the planet Jupiter. These new spectral measurements were specifically designed to support measurements of Jupiter's atmosphere made by the Near-Infrared Mapping Spectrometer (NIMS) which was part of the Galileo mission that orbited Jupiter from 1995 to September 2003. To reach approximate jovian conditions in the lab, a new gas spectroscopy facility was developed and used to measure self-broadened ammonia spectra from 0.74 to 5.2 μm, virtually the complete range of the NIMS instrument, for the first time. Spectra were recorded at temperatures varying from 300 to 215 K, pressures from 1000 to 33 mb and using three different path lengths (10.164, 6.164 and 2.164 m). The spectra were then modelled using a series of increasingly complex physically based transmittance functions. © 2008 Elsevier Inc. All rights reserved.

The surface and lower atmosphere of Venus lie below long path-lengths of carbon dioxide and water vapour, and thick cloud layers that were, until recently, thought to be essentially opaque to electromagnetic radiation at wavelengths shorter than a few millimetres. It was unexpected, therefore, when Alien and Crawford 1 announced the detection of measurable quantities of near-infrared radiation leaving the night side. Here we investigate the origin of this radiation by calculating theoretical spectra which we compare with the observations. It is found that the observed radiation can be fully accounted for by thermal emission from the deep atmosphere, and that the intensities suggest surprisingly low abundances for water vapour and carbon monoxide in those layers. These results have implications for probing the atmospheric structure and composition on Venus from the Galileo spacecraft, which is scheduled to make a close encounter with Venus in February 1990. © 1988 Nature Publishing Group.

A fast method is presented for deriving the tropospheric CO concentrations in the Venus atmosphere from near-infrared spectra using the night side 2.3 μm window. This is validated using the spectral fitting techniques of Tsang et al. [Tsang, C.C.C., Irwin, P.G.J., Taylor, F.W., Wilson, C.F., Drossart, P., Piccioni, G., de Kok, R., Lee, C., Calcutt, S.B., and the Venus Express/VIRTIS Team, 2008a. Tropospheric carbon monoxide concentrations and variability on Venus with Venus Express/VIRTIS-M observations. J. Geophys. Res. 113, doi: 10.1029/2008JE003089. E00B08] to show that monitoring CO in the deep atmosphere can be done quickly using large numbers of observations, with minimal effect from cloud and temperature variations. The new method is applied to produce some 1450 zonal mean CO profiles using data from the first eighteen months of operation from the Visible and Infrared Thermal Imaging Spectrometer infrared mapping subsystem (VIRTIS-M-IR) on Venus Express. These results show many significant long- and short-term variations from the mean equator-to-pole increasing trend previously found from earlier Earth- and space-based observations, including a possible North-South dichotomy, with interesting implications for the dynamics and chemistry of the lower atmosphere of Venus. © 2009 Elsevier Inc. All rights reserved.

The composite infrared spectrometer (CIRS) instrument on board the Cassini Saturn orbiter employs two 1x10 HgCdTe detector arrays for mid-infrared remote sensing of Titan's and Saturn's atmospheres. In this paper we show that the real detector spatial response functions, as measured in ground testing before launch, differ significantly from idealized "boxcar" responses. We further show that neglecting this true spatial response function when modeling CIRS spectra can have a significant effect on interpretation of the data, especially in limb-sounding mode, which is frequently used for Titan science. This result has implications not just for CIRS data analysis but for other similar instrumental applications.

International audience; Mid- and far-infrared spectra from the Composite InfraRed Spectrometer (CIRS) have been used to determine volume mixing ratios of nitriles in Titan's atmosphere. HCN, HC 3N, C 2H 2, and temperature were derived from 2.5 cm -1 spectral resolution mid-IR mapping sequences taken during three flybys, which provide almost complete global coverage of Titan for latitudes south of 60° N. Three 0.5 cm -1 spectral resolution far-IR observations were used to retrieve C 2N 2 and act as a check on the mid-IR results for HCN. Contribution functions peak at around 0.5-5 mbar for temperature and 0.1-10 mbar for the chemical species, well into the stratosphere. The retrieved mixing ratios of HCN, HC 3N, and C 2N 2 show a marked increase in abundance towards the north, whereas C 2H 2 remains relatively constant. Variations with longitude were much smaller and are consistent with high zonal wind speeds. For 90°-20° S the retrieved HCN abundance is fairly constant with a volume mixing ratio of around 1 × 10 -7 at 3 mbar. More northerly latitudes indicate a steady increase, reaching around 4 × 10 -7 at 60° N, where the data coverage stops. This variation is consistent with previous measurements and suggests subsidence over the northern (winter) pole at approximately 2 × 10 -4 m s -1. HC 3N displays a very sharp increase towards the north pole, where it has a mixing ratio of around 4 × 10 -8 at 60° N at the 0.1-mbar level. The difference in gradient for the HCN and HC 3N latitude variations can be explained by HC 3N's much shorter photochemical lifetime, which prevents it from mixing with air at lower latitude. It is also consistent with a polar vortex which inhibits mixing of volatile rich air inside the vortex with that at lower latitudes. Only one observation was far enough north to detect significant amounts of C 2N 2, giving a value of around 9 × 10 -10 at 50° N at the 3-mbar level.

Venus as a planet resembles the Earth, but has a much hotter and denser atmosphere due to an extreme case of the greenhouse effect, caused by compositional differences and the thick cloud cover. Studies of the lower atmosphere are inhibited by the cloud opacity, which makes remote measurements at most frequencies short of the radio range quite difficult. Progress in understanding of the composition and thermal structure below the clouds has been made by the Pioneer and Venera entry probes of the 1970s, and more recently with results from the Galileo fly-by in 1990. The latter exploited the newly discovered near-infrared ‘windows’ to achieve measurements of carbon monoxide and water vapour abundances in the deep atmosphere, and provided the first detailed view of the global cloud structure. The morphology and spatial variations seen in the main mass of clouds are remarkable, and suggest a powerful and diverse meteorology dominated by convection. Carbon monoxide is significantly more abundant at high northern latitudes than at low latitudes in either hemisphere.

Thermal infrared spectra of Saturn from 10-1400 cm-1 at 15 cm-1 spectral resolution and a spatial resolution of 1°-2° latitude have been obtained by the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297]. Many thousands of spectra, acquired over eighteen-months of observations, are analysed using an optimal estimation retrieval code [Irwin, P.G.J., Parrish, P., Fouchet, T., Calcutt, S.B., Taylor, F.W., Simon-Miller, A.A., Nixon, C.A., 2004. Icarus 172, 37-49] to retrieve the temperature structure and para-hydrogen distribution over Saturn's northern (winter) and southern (summer) hemispheres. The vertical temperature structure is analysed in detail to study seasonal asymmetries in the tropopause height (65-90 mbar), the location of the radiative-convective boundary (350-500 mbar), and the variation with latitude of a temperature knee (between 150 and 300 mbar) which was first observed in inversions of Voyager/IRIS spectra [Hanel, R., and 15 colleagues, 1981. Science 212, 192-200; Hanel, R., Conrath, B., Flasar, F.M., Kunde, V., Maguire, W., Pearl, J.C., Pirraglia, J., Samuelson, R., Cruikshank, D.P., Gautier, D., Gierasch, P.J., Horn, L., Ponnamperuma, C., 1982. Science 215, 544-548]. Uncertainties due to both the modelling of spectral absorptions (collision-induced absorption coefficients, tropospheric hazes, helium abundance) and the nature of our retrieval algorithm are quantified. Temperatures in the stratosphere near 1 mbar show a 25-30 K temperature difference between the north pole and south pole. This asymmetry becomes less pronounced with depth as the radiative time constant for the atmospheric response increases at deeper pressure levels. Hemispherically-symmetric small-scale temperature structures associated with zonal winds are superimposed onto the temperature asymmetry for pressures greater than 100 mbar. The para-hydrogen fraction in the 100-400 mbar range is greater than equilibrium predictions for the southern hemisphere and parts of the northern hemisphere, and less than equilibrium predictions polewards of 40° N. The temperature knee between 150-300 mbar is larger in the summer hemisphere than in the winter, smaller and higher at the equator, deeper and larger in the equatorial belts and small at the poles. Solar heating on tropospheric haze is proposed as a possible mechanism for this effect; the increased efficiency of ortho- to para-hydrogen conversion in the southern hemisphere is consistent with the presence of larger aerosols in the summer hemisphere, which we demonstrate to be qualitatively consistent with previous studies of Saturn's tropospheric aerosol distribution. © 2007 Elsevier Inc. All rights reserved.

A concept has been developed for a remote sensing experiment to investigate the physics of the Martian atmosphere from a spin-stabilized orbiter, like that planned for the InterMarsNet mission. Using coincident infrared and microwave channels and limb-to-limb scanning, it can map the planet much more extensively than previously in temperature, atmospheric dust loading, and humidity. When combined with one or more surface stations measuring the same variables, the sounder experiment can contribute to major progress in understanding the general circulation and dust and water cycles of the atmosphere of Mars, and the characterization of medium-scale meteorological systems. Copyright © 1996 Elsevier Science Ltd.

International audience; Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.

A short description is given of the Occultation Radiometer which has been flown recently on the EURECA carrier. A brief outline of the scientific rationale, instrument characteristics and status of the data reduction is presented.

The Diviner Lunar Radiometer Experiment on NASA's Lunar Reconnaissance Orbiter will be the first instrument to systematically map the global thermal state of the Moon and its diurnal and seasonal variability. Diviner will measure reflected solar and emitted infrared radiation in nine spectral channels with wavelengths ranging from 0.3 to 400 microns. The resulting measurements will enable characterization of the lunar thermal environment, mapping surface properties such as thermal inertia, rock abundance and silicate mineralogy, and determination of the locations and temperatures of volatile cold traps in the lunar polar regions. © The author(s) 2009.

The 3-5 micrometer thermal emission of the nightside of Venus, recorded by the Near-Infrared Mapping Spectrometer (NIMS) instrument at the time of the Galileo flyby of Venus, is analysed to infer the properties of the upper cloud boundary. From the global maps of Venus at fixed wavelengths, the limb darkening of the flux is measured at several latitudes, within each infrared channel. By using the nominal Pioneer Venus thermal profile, these data give access to two parameters: the cloud deck temperature and the cloud scale height. It is verified independently, from the NIMS spectra, that this thermal profile is consistent with all the NIMS observations, and that the thermal structure does not vary significantly in the latitude range (25 deg S, 30 deg N). Within this range, the cloud scale height is found to be constant with latitude, and is H = 5.2 km, with an accuracy of about 15%, taking into account the various sources of theoretical and observational uncertainties. At higher latitudes, the temperature profile becomes more isothermal and the presented method to retrieve H is no longer valid.

The spectroscopic data of the Near-Infrared Mapping Spectrometer (NIMS), recorded during the Galileo flyby of Venus, are analysed to retrieve the water vapor abundance variations in the lower atmosphere of Venus at night. The 1.18 micrometer 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 vapor mixing ratio of 30 +/- 15 ppm, in agreement with analyses of ground-based nightside observations. The water vapor abundance shows no horizontal variations exceeding 20% over a wide latitude range (40 deg S, 50 deg N) on the nightside of Venus. Within the same selection of NIMS spectra, a large enhancement in the O2 fluorescence emission at 1.27 micrometer is observed at a latitude of 40 deg S, over a spatial area about 100 km wide.

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.

Radiance from the surface of Titan can be detected from space through a spectral window of low opacity in the thermal infrared at 19 μm (530 cm -1). By combining Composite Infrared Spectrometer observations from Cassini's first four years, we have mapped the latitude distribution of zonally averaged surface brightness temperatures. The measurements are corrected for atmospheric opacity as derived from the dependence of radiance on the emission angle. At equatorial latitudes near the Huygens landing site, the surface brightness temperature is found to be 93.7 0.6 K, in excellent agreement with the in situ measurement. Temperature decreases toward the poles, reaching 90.5 0.8 K at 87°N and 91.7 0.7 K at 88°S. The meridional distribution of temperature has a maximum near 10°S, consistent with Titan's late northern winter. © 2009 The American Astronomical Society. All rights reserved.

The Cassini Composite Infrared Spectrometer (CIRS) has been used to derive the vertical and meridional variation of temperature and phosphine (PH3) abundance in Saturn's upper troposphere. PH3 has a significant effect on the measured radiances in the thermal infrared and between May 2004 and September 2005 CIRS recorded thousands of spectra in both the far (10-600 cm-1) and mid (600-1400 cm-1) infrared, at a variety of latitudes covering the southern hemisphere. Low spectral resolution (15 cm-1) data has been used to constrain the temperature structure of the troposphere between 100 and 500 mbar. The vertical distributions of phosphine and ammonia were retrieved from far-infrared spectra at the highest spectral resolution (0.5 cm-1), and lower resolution (2.5 cm-1) mid-infrared data were used to map the meridional variation in the abundance of phosphine in the 250-500 mbar range. Temperature variations at the 250 mbar level are shown to occur on the same scale as the prograde and retrograde jets in Saturn's atmosphere [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The PH3 abundance at 250 mbar is found to be enhanced at the equator when compared with mid-latitudes. At mid latitudes we see anti-correlation between temperature and PH3 abundance at 250 mbar, phosphine being enhanced at 45° S and depleted at 25 and 55° S. The vertical distribution is markedly different polewards of 60-65° S, with depleted PH3 at 500 mbar but a slower decline in abundance with altitude when compared with the mid-latitudes. This variation is similar to the variations of cloud and aerosol parameters observed in the visible and near infrared, and may indicate the subsidence of tropospheric air at polar latitudes, coupled with a diminished sunlight penetration depth reducing the rate of PH3 photolysis in the polar region. © 2006 Elsevier Inc. All rights reserved.

The design of a versatile dual-telescope thermal-infrared radiometer spanning the spectral wavelength range 8–200 µm, in five spectral pass bands, for outer planet fly-by missions is described. The dual-telescope design switches between a narrow-field-of-view and a wide-field-of-view to provide optimal spatial resolution images within a range of spacecraft encounters to the target. The switchable dual-field-of-view system uses an optical configuration based on the axial rotation of a source-select mirror along the optical axis. The optical design, spectral performance, radiometric accuracy, and retrieval estimates of the instrument are discussed. This is followed by an assessment of the surface coverage performance at various spatial resolutions by using the planned NASA Europa Mission 13-F7 fly-by trajectories as a case study.

The Hera Saturn entry probe mission is proposed as an M--class mission led by ESA with a contribution from NASA. It consists of one atmospheric probe to be sent into the atmosphere of Saturn, and a Carrier-Relay spacecraft. In this concept, the Hera probe is composed of ESA and NASA elements, and the Carrier-Relay Spacecraft is delivered by ESA. The probe is powered by batteries, and the Carrier-Relay Spacecraft is powered by solar panels and batteries. We anticipate two major subsystems to be supplied by the United States, either by direct procurement by ESA or by contribution from NASA: the solar electric power system (including solar arrays and the power management and distribution system), and the probe entry system (including the thermal protection shield and aeroshell). Hera is designed to perform in situ measurements of the chemical and isotopic compositions as well as the dynamics of Saturn's atmosphere using a single probe, with the goal of improving our understanding of the origin, formation, and evolution of Saturn, the giant planets and their satellite systems, with extrapolation to extrasolar planets. Hera's aim is to probe well into the cloud-forming region of the troposphere, below the region accessible to remote sensing, to the locations where certain cosmogenically abundant species are expected to be well mixed. By leading to an improved understanding of the processes by which giant planets formed, including the composition and properties of the local solar nebula at the time and location of giant planet formation, Hera will extend the legacy of the Galileo and Cassini missions by further addressing the creation, formation, and chemical, dynamical, and thermal evolution of the giant planets, the entire solar system including Earth and the other terrestrial planets, and formation of other planetary systems., Comment: Accepted for publication in Planetary and Space Science

This paper describes new measurements and modelling of the absorption of methane gas, one of the most important gases observed in the atmospheres of the outer planets and Titan, between 9000 and 14,000 cm −1 (0.7 to 1.1 μm) and compares them with current best available spectral models. A series of methane spectra were measured at the UK's Natural Environment Research Council (NERC) Molecular Spectroscopy Facility (based at the Rutherford Appleton Laboratory, Oxfordshire, UK) using a Bruker 125HR Fourier transform spectrometer. To approximate the conditions found in outer planet atmospheres, the spectra were measured over a wide range of pressures (5 bar to 38 mbar) and temperatures (290–100 K) with path lengths of 19.3, 17.6, 16.0 and 14.4 m. The spectra were recorded at a moderate resolution of 0.12 cm −1 and then averaged to 10 cm −1 resolution prior to fitting a series of increasingly complex band-models including temperature dependence. Using the most complex model, a Goody line distribution with a Voigt line shape and two lower energy state levels, the typical rms residual error in the fit is between 0.01 and 0.02 in the wings of the main absorption bands. The new spectral parameters were then compared with the measured spectra and spectra calculated using existing data and shown to be able to accurately reproduce the measured absorption. The improvement in the temperature dependence included in the model is demonstrated by comparison with existing cold methane spectral data for a typical Jovian path.

Observations of Neptune were made in September 2009 with the Gemini-North Telescope in Hawaii, using the NIFS instrument in the H-band covering the wavelength range 1.477-1.803 μm. Observations were acquired in adaptive optics mode and have a spatial resolution of approximately 0.15-0.25″. The observations were analysed with a multiple-scattering retrieval algorithm to determine the opacity of clouds at different levels in Neptune's atmosphere. We find that the observed spectra at all locations are very well fit with a model that has two thin cloud layers, one at a pressure level of ∼2. bar all over the planet and an upper cloud whose pressure level varies from 0.02 to 0.08. bar in the bright mid-latitude region at 20-40°S to as deep as 0.2. bar near the equator. The opacity of the upper cloud is found to vary greatly with position, but the opacity of the lower cloud deck appears remarkably uniform, except for localised bright spots near 60°S and a possible slight clearing near the equator. A limb-darkening analysis of the observations suggests that the single-scattering albedo of the upper cloud particles varies from ∼0.4 in regions of low overall albedo to close to 1.0 in bright regions, while the lower cloud is consistent with particles that have a single-scattering albedo of ∼0.75 at this wavelength, similar to the value determined for the main cloud deck in Uranus' atmosphere. The Henyey-Greenstein scattering particle asymmetry of particles in the upper cloud deck are found to be in the range g∼ 0.6-0.7 (i.e. reasonably strongly forward scattering).Numerous bright clouds are seen near Neptune's south pole at a range of pressure levels and at latitudes between 60 and 70°S. Discrete clouds were seen at the pressure level of the main cloud deck (∼2. bar) at 60°S on three of the six nights observed. Assuming they are the same feature we estimate the rotation rate at this latitude and pressure to be 13.2 ± 0.1. h. However, the observations are not entirely consistent with a single non-evolving cloud feature, which suggests that the cloud opacity or albedo may vary very rapidly at this level at a rate not seen in any other giant-planet atmosphere. © 2011 Elsevier Inc.

The sub-millimetre/microwave range of the spectrum has been exploited in the field of Earth observation by many instruments over the years and has provided a plethora of information on atmospheric chemistry and dynamicshowever, this spectral range has not been fully explored in planetary science, having been exclusively employed to carry out ground-based measurements. To this end, a sub-millimetre instrument, the Orbiter Terahertz Infrared Spectrometer (ORTIS), is studied by the University of Oxford and the Rutherford Appleton Laboratory, to meet the requirements of the European Space Agency's Cosmic Visions 2015-2025 programme-in particular, the Europa Jupiter System Mission (EJSM), which has the European Space Agency and the National Aeronautics and Space Administration as partners. ORTIS is designed to measure atmospheric temperature, the abundance of stratospheric water vapour and other jovian gases, and is intended to be capable of retrieving vertical profiles of horizontal windspeed in the stratosphere for the first time, from Doppler-shifted emission lines measured at high spectral resolution. In this work, a preliminary study and implementation of the estimation of windspeed profiles on simulated spectra representative of Jupiter is presented, detailing the development of the retrieval algorithm, showing that a sub-millimetre instrument such as ORTIS should be able to retrieve windspeed profiles to an accuracy of about 15 m/s between 70 and 200 km/0.1-10 mb using a single near-limb measurement, for expected noise amplitudes. © 2010 Elsevier B.V.. All rights reserved.

Current understanding of weather, climate and global atmospheric circulation on Mars is incomplete, in particular at altitudes above about 30 km. General circulation models for Mars are similar to those developed for weather and climate forecasting on Earth and require more martian observations to allow testing and model improvements. However, the available measurements of martian atmospheric temperatures, winds, water vapour and airborne dust are generally restricted to the region close to the surface and lack the vertical resolution and global coverage that is necessary to shed light on the dynamics of Mars middle atmosphere at altitudes between 30 and 80 km (ref.7). Here we report high-resolution observations from the Mars Climate Sounder instrument on the Mars Reconnaissance Orbiter. These observations show an intense warming of the middle atmosphere over the south polar region in winter that is at least 10-20 K warmer than predicted by current model simulations. To explain this finding, we suggest that the atmospheric downwelling circulation over the pole, which is part of the equator-to-pole Hadley circulation, may be as much as 50 more vigorous than expected, with consequences for the cycles of water, dust and CO"2 that regulate the present-day climate on Mars. © 2008 Macmillan Publishers Limited.

A major limitation in the development of wind sensors for use on Mars is the lack of suitable testing and calibration facilities. A low-density wind tunnel has been developed at Oxford University for calibration of wind sensors for Mars landers, capable of providing stable or dynamically varying winds, of air or carbon dioxide, at Martian pressures (5-10 mbar) and speeds (0.5-30 m/s), and temperatures of 200-300 K. The flow field in the test section was calculated using analytical and computational modelling techniques, and validated experimentally using a pitot probe. This facility's stability and accuracy offer significant advantages with respect to previous calibration facilities. © 2008 Elsevier Ltd. All rights reserved.

International audience; Mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer (CIRS) between July 2004 and January 2007 ( L=293°-328°) have been used to determine stratospheric temperature and abundances of C 2H 2, C 3H 4, C 4H 2, HCN, and HC 3N. Over 65,000 nadir spectra with spectral resolutions of 0.5 and 2.5 cm -1 were used to probe spatial and temporal composition variations in Titan's stratosphere. Cassini's 180° orbital transfer in mid-2006 allowed low emission angle observations of the north polar region for the first time in the mission and allowed us to probe the full latitude range. We present the first measurements of composition variations within the polar vortex, which display increasing abundances right up to 90° N. The lack of a homogeneous abundance-latitude variation within the vortex indicates limited horizontal mixing and suggests that subsidence is greatest at the vortex core. Contrary to numerical model predictions and tropospheric cloud observations, we do not see any evidence for a secondary circulation cell near the south pole, which suggests a single Hadley-type circulation in the stratosphere at this epoch. This difference can be reconciled if the secondary cell is restricted to altitudes below 100 km, where there is no sensitivity in our data. Temporal variations in composition were observed in the south, with volatile species becoming less abundant as the season progressed. The observed variations are compared to numerical model predictions and observations from Voyager.

These are the first results from nadir studies of meridional variations in the abundance of stratospheric acetylene and ethane from Cassini/CIRS data in the southern hemisphere of Saturn. High resolution, 0.5 cm −1 , CIRS data was used from three data sets taken in June–November 2004 and binned into 2° wide latitudinal strips to increase the signal-to-noise ratio. Tropospheric and stratospheric temperatures were initially retrieved to determine the temperature profile for each latitude bin. The stratospheric temperature at 2 mbar increased by 14 K from 9° to 68° S, including a steep 4 K rise between 60° and 68° S. The tropospheric temperatures showed significantly more meridional variation than the stratospheric ones, the locations of which are strongly correlated to that of the zonal jets. Stratospheric acetylene abundance decreases steadily from 30 to 68° S, by a factor of 1.8 at 2.0 mbar. Between 18° and 30° S the acetylene abundance increases at 2.0 mbar. Global values for acetylene have been calculated as ( 1.9 ± 0.19 ) × 10 −7 at 2.0 mbar, ( 2.6 ± 0.27 ) × 10 −7 at 1.6 mbar and ( 3.1 ± 0.32 ) × 10 −7 at 1.4 mbar. Global values for ethane are also determined and found to be ( 1.6 ± 0.25 ) × 10 −5 at 0.5 mbar and ( 1.4 ± 0.19 ) × 10 −5 at 1.0 mbar. Ethane abundance in the stratosphere increases towards the south pole by a factor of 2.5 at 2.0 mbar. The increase in stratospheric ethane is especially pronounced polewards of 60° S at 2.0 mbar. The increase of stratospheric ethane towards the south pole supports the presence of a meridional wind system in the stratosphere of Saturn.