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Asteroids and comets are the remnants of the swarm of planetesimals from which the planets ultimately formed, and they retain records of processes that operated prior to and during planet formation. They are also likely the sources of most of the water and other volatiles accreted by Earth. In this review, we discuss the nature and probable origins of asteroids and comets based on data from remote observations, in situ measurements by spacecraft, and laboratory analyses of meteorites derived from asteroids. The asteroidal parent bodies of meteorites formed ≤4 Ma after Solar System formation while there was still a gas disk present. It seems increasingly likely that the parent bodies of meteorites spectroscopically linked with the E-, S-, M- and V-type asteroids formed sunward of Jupiter's orbit, while those associated with C- and, possibly, D-type asteroids formed further out, beyond Jupiter but probably not beyond Saturn's orbit. Comets formed further from the Sun than any of the meteorite parent bodies, and retain much higher abundances of interstellar material. CI and CM group meteorites are probably related to the most common C-type asteroids, and based on isotopic evidence they, rather than comets, are the most likely sources of the H and N accreted by the terrestrial planets. However, comets may have been major sources of the noble gases accreted by Earth and Venus. Possible constraints that these observations can place on models of giant planet formation and migration are explored.

In this work, we present results that simultaneously constrain the dust size distribution, dust-to-gas ratio, fraction of dust re-deposition, and total mass production rates for comet 67P/Churyumov-Gerasimenko. We use a 3D Direct Simulation Monte Carlo (DSMC) gas dynamics code to simulate the inner gas coma of the comet for the duration of the Rosetta mission. The gas model is constrained by ROSINA/COPS data. Further, we simulate for different epochs the inner dust coma using a 3D dust dynamics code including gas drag and the nucleus' gravity. Using advanced dust scattering properties these results are used to produce synthetic images that can be compared to the OSIRIS data set. These simulations allow us to constrain the properties of the dust coma and the total gas and dust production rates. We determined a total volatile mass loss of (6.1 ± 1.5) · 109 kg during the 2015 apparition. Further, we found that power-laws with q=3.7-0.078+0.57 are consistent with the data. This results in a total of 5.1-4.9+6.0·109 kg of dust being ejected from the nucleus surface, of which 4.4-4.2+4.9·109 kg escape to space and 6.8-6.8+11·108 kg (or an equivalent of 14-14+22 cm over the smooth regions) is re-deposited on the surface. This leads to a dust-to-gas ratio of 0.73-0.70+1.3 for the escaping material and 0.84-0.81+1.6 for the ejected material. We have further found that the smallest dust size must be strictly smaller than ~30μm and nominally even smaller than ~12μm.

Primitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects. [ABSTRACT FROM AUTHOR]

Observations of comet nuclei indicate that the main constituent is a mix of ice and refractory materials characterized by high porosity (70–75%) and low bulk strength (10−4–10−6 MPa); however, the nature and physical properties of these materials remain largely unknown. By combining surface inspection of comet 67P/Churyumov– Gerasimenko and three-dimensional (3D) modeling of the independent concentric sets of layers that make up the structure of its two lobes, we provide clues about the large-scale rheological behavior of the nucleus and the kinematics of the impact that originated it. Large folds in the layered structure indicate that the merging of the two cometesimals involved reciprocal motion with dextral strike–slip kinematics that bent the layers in the contact area without obliterating them. Widespread long cracks and the evidence of relevant mass loss in absence of large density variations within the comet’s body testify that large-scale deformation occurred in a brittle-plastic regime and was accommodated through folding and fracturing. Comparison of refined 3D geologic models of the lobes with triaxial ellipsoids that suitably represent the overall layers arrangement reveals characteristics that are consistent with an impact between two roughly ellipsoidal cometesimals that produced large-scale axial compression and transversal elongation. The observed features imply global transfer of impactrelated shortening into transversal strain. These elements delineate a model for the global rheology of cometesimals that could be possible evoking a prominent bonding action of ice and, to a minor extent, organics. [ABSTRACT FROM AUTHOR]

This chapter reviews the estimates of the dust-to-gas and refractory-to-ice mass ratios derived from Rosetta measurements in the lost materials and the nucleus of 67P/Churyumov-Gerasimenko, respectively. First, the measurements by Rosetta instruments are described, as well as relevant characteristics of 67P. The complex picture of the activity of 67P, with its extreme North-South seasonal asymmetry, is presented. Individual estimates of the dust-to-gas and refractory-to-ice mass ratios are then presented and compared, showing wide ranges of plausible values. Rosetta's wealth of information suggests that estimates of the dust-to-gas mass ratio made in cometary comae at a single point in time may not be fully representative of the refractory-to-ice mass ratio within the cometary nuclei being observed. [ABSTRACT FROM AUTHOR]

We will briefly recapitulate the beginning of modern cometary physic. Then we will assess the results of the cometary flyby missions previous to ESA's Rosetta rendezvous with comet 67P/Churyumov–Gerasimenko. Emphasis is given to the physical properties of cometary nuclei. We will relate the results of the Rosetta mission to those of the flybys. A major conclusion is that the visited cometary nuclei seem to be alike but represent different stages of evolution. Coma composition and appearance are not only controlled by the composition of the nucleus but also strongly influenced by the shape and rotation axis orientation of the nucleus and resulting seasons that generate varying surface coverage by back fall material. Rosetta showed that the coma composition is not only varying spatially but also strongly with time during the perihelion passage. Hence past interpretations of cometary coma observations have to be re-considered. Finally, we will try to assess the impact of the cornerstone mission leading to a critical evaluation of the mission results. Lessons learned from Rosetta are discussed; major progress and open points in cometary research are reviewed. [ABSTRACT FROM AUTHOR]

This paper presents an improved algorithm for the 2D and 3D Fourier forward modeling of gravity fields caused by polyhedral bodies with constant and exponential density distributions. Three modifications have been made to the Fourier forward algorithm introduced in a previous paper. First, vertex-based Fourier-domain expressions are used instead of the original face-based Fourier-domain expressions, which simplify the computation of the anomaly spectrum considerably, especially in 3D modeling problems. Second, instead of using a pure Gauss-FFT sampling of the anomaly spectrum, we apply an improved sampling strategy by combining a nonuniform spherical sampling with a low-order Gauss-FFT sampling. In this way, the number of samplings required in the Fourier domain reduces to about 1 3 and 1 7 of those required in a pure Gauss-FFT algorithm for 2D and 3D modeling problems, respectively. A significant acceleration over the original algorithm is achieved. Third, we incorporate all three types of nonuniform fast Fourier transform algorithms to transform directly a uniform or nonuniform anomaly spectrum to gravity fields either on a regular grid, or at a set of arbitrary positions. Extra interpolation operations are no longer needed. Synthetic numerical tests show that for gravity vector components, the new algorithm runs about 3 times faster in 2D modeling and 7 times faster in 3D modeling than the original ones, while maintaining the same level of accuracy. For the gravity potential, the new algorithm is significantly superior to the pure Gauss-FFT solution both in numerical accuracy and in efficiency. We apply this novel approach to compute the gravitational fields of asteroid 101955 Bennu and comet 67 P/Churyumov –Gerasimenko. The 2D algorithm works very efficiently for the computation of gravity fields on horizontal planes. The 3D algorithm is valid both outside, on, and inside the source's bounding surface, with relative errors less than 0.1% for the gravity potential and less than 2% for the gravity vector. By comparing to modeling results of analytical and spherical harmonic-based solutions, we generally conclude that the Fourier-based algorithm introduced here is an attractive alternative to these conventional solutions, especially for nonspherical, irregularly shaped bodies with complex geometries. [ABSTRACT FROM AUTHOR]

We have used the latest available shape model for gas and dust simulations of the inner coma of comet 67P/Churyumov-Gerasimenko for the period around May 2015 (equinox). We compare results from a purely insolation-driven model with a complementary set of observations made by ROSINA, VIRTIS, MIRO, and OSIRIS within the same period. The observations include - for the first time - inverted MIRO measurements of gas density, temperature and bulk velocity to constrain the model. The comparisons show that, as in November 2014 (Marschall et al., 2016), insolation-driven activity does not provide an adequate fit to the data. Both VIRTIS and MIRO observations indicate that emissions from the Hatmehit and Imhotep regions of the nucleus are strongly depleted in total gas, H 2 O, and dust emissions in this case. The MIRO inversion provides a challenging constraint to the models as a consequence of the terminator orbit and nucleus pointing of the spacecraft. Nonetheless a consistent picture with a dominance of outgassing from the Hapi region, even at equinox, is clearly evident. An inhomogeneous model consistent with models proposed for the November 2014 time-frame was constructed and provides a better fit to the data. As far as we are aware this is the first time comae data from four Rosetta instruments have been used to constrain within one self-contained model the emission distribution at the nucleus surface and study the dynamics of the gas and dust outflow. • Inhomogeneous gas & dust emission needed to understand Rosetta data of comet 67P • Different Rosetta instruments provide different constraints that lift model degeneracies. • MIRO data indicate, lower H 2 O density, warmer temperature, and higher velocity models. • OSIRIS data show strong source from Ma'at d) and slow moving particles from Imhotep. [ABSTRACT FROM AUTHOR]

Abstract The previously defined regions on the nucleus of comet 67P/Churyumov-Gerasimenko have been mapped back onto the 3D SHAP7 model of the nucleus (Preusker et al., 2017). The resulting regional definition is therefore self-consistent with boundaries that are well defined in 3 dimensions. The facets belonging to each region are provided as supplementary material. The shape model has then been used to assess inhomogeneity of nucleus surface morphology within individual regions. Several regions show diverse morphology. We propose sub-division of these regions into clearly identifiable units (sub-regions) and a comprehensive table is provided. The surface areas of each sub-region have been computed and statistics based on grouping of unit types are provided. The roughness of each region is also provided in a quantitative manner using a technique derived from computer graphics applications. The quantitative method supports the sub-region definition by showing that differences between sub-regions can be numerically justified. Highlights • Regions are defined upon the latest 3D shape model (SHAP7) of comet 67P/Churyumov-Gerasimenko. • The definition is provided in a publicly accessible shape file. • Sub-regions of similar properties are defined to support more detailed work. • Roughness calculations are performed to quantify differences between regions and sub-regions. [ABSTRACT FROM AUTHOR]

Recent space experiments suggest that electron and ion energy analyzers using microchannel plates (MCPs) as detectors are also registering direct hits by nanodust particles. To allow the analysis and interpretation of these putative dust events, the detection efficiency of MCPs has to be characterized. We report on a series of experiments to investigate the detection efficiency of MCP detectors to direct impacts for both positively and negatively charged micron and submicron sized iron particles. A double‐stack MCP detector in a chevron configuration was mounted as a target in a dust accelerator. A range of particle velocities and masses were used for a comprehensive examination. The MCP detected and produced definite signals associated with confirmed particle impacts of the MCP for both positively and negatively charged dust particles. The detection efficiency was found to be (6 ± 1)% for positively charged dust and (9 ± 3)% for negatively charged dust particles with a characteristic mass of 6.0 × 1011μ (10−15 kg) and speed of 100 m/s. The examined particle velocity range accurately replicates Rosseta's interaction with dust grains emanating from comet 67P/ Churyumov‐Gerasimenko's nucleus. Additionally, the MCP detection efficiency for low velocity particles shows a possible underestimate of higher speed nanograin signals from Cassini's electron plasma spectrometer during its flyby through Enceladus' active south pole. Plain Language Summary: Recent space experiments suggest that electron and ion energy analyzers using microchannel plates (MCP) as detectors are also registering direct hits by nanodust particles. In this study we explore the efficiency of these detectors to measure dust impacts. Once we know the detection efficiency, we can better understand the dust density of localized areas, such as Rosseta's orbit around comet 67P/Churyumov‐Gerasimenko's nucleus, or Cassini's flyby through Enceladus's active south pole. To characterize these detectors, an MCP was placed in a dust accelerator and bombarded at potential orbital velocities. The detection efficiency was found to be around 8% for the selected velocity range. This result can help further define dust density when space‐based MCP detectors encounter nanograin dust regions. Key Points: Microchannel plate detectors report direct dust impacts; calibrating detection efficiencies allows for space‐based dust density studiesStudied velocity range accurately replicates Rosseta's interaction with dust grains emanating from comet 67P/Churyumov‐Gerasimenko's nucleusEfficiency shows a possible overestimate of high speed dust signals from Cassini's plasma spectrometer during a flyby through Enceladus south pole [ABSTRACT FROM AUTHOR]

The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) onboard the European Space Agency's Rosetta spacecraft acquired images of comet 67P/Churyumov–Gerasimenko (67P) and its surrounding dust coma starting from May 2014 until September 2016. In this paper we present methods and results from analysis of OSIRIS images regarding the dust outflow in the innermost coma of 67P. The aim is to determine the global dust outflow behaviour and place constraints on physical processes affecting particles in the inner coma. We study the coma region right above the nucleus surface, spanning from the nucleus centre out to a distance of about 50 km comet centric distance (approximately 25 average comet radii). We primarily adopt an approach used by Thomas and Keller (1990) to study the dust outflow. We present the effects on azimuthally-averaged values of the dust reflectance of non-radial flow and non-point-source geometry, acceleration of dust particles, sublimation of icy dust particles after ejection from the surface, dust particle fragmentation, optical depth effects and the influence of gravitationally bound particles. All of these physical processes could modify the observed distribution of light scattered by the dust coma. In the image analysis, profiles of azimuthally averaged dust brightness as a function of impact parameter b (azimuthal average, “Ā-curve”) were fitted with a simple function that best fits the shape of our profile curves ( f ( b ; u , v , w , z ) = u / b v + w b + z ). The analytical fit parameters ( u, v, w, z ), which hold the key information about the dust outflow behaviour, were saved in a comprehensive database. Through statistical analysis of these information, we show that the spatial distribution of dust follows free-radial outflow behaviour (i.e. force-free radial outflow with constant velocity) beyond distances larger than ∼11.9 km from the comet centre, which corresponds to a relative distance of about 6 average comet radii from the comet centre. Hence, we conclude that beyond this distance, and on average, fragmentation and gravitationally bound particles are negligible processes in determining the optically scattered light distribution in the innermost coma. Closer to the nucleus we observe dust outflow behaviour that deviates from free-radial outflow. A comparison of our result profiles with numerical models using a Direct Simulation Monte Carlo (DSMC) approach with dust particle distributions calculated using a test particle approach has been used to demonstrate the influence of a complex shape and particle acceleration on the azimuthal average profiles. We demonstrate that, while other effects such as fragmentation or sublimation of dust particles cannot be ruled out, acceleration of the dust particles and effects arising from the shape of the irregular nucleus (non-point source geometry) are sufficient to explain the observed dust outflow behaviour from image data analysis. As a by-product of this work, we have calculated “Afρ” values for the 1/r regime. We found a peak in the coma activity in terms of Afρ (normalised to a phase angle of 90°) of ∼210 cm 20 days after perihelion. Furthermore, based on simplified models of particle motion within bound orbits, it is shown that limits on the total cross-sectional area of bound particles might be derived through further analysis. An example is given. [ABSTRACT FROM AUTHOR]

The ESA Rosetta spacecraft has been tracking its target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, in close vicinity for over two years. It hosts the OSIRIS instruments: the Optical, Spectroscopic, and Infrared Remote Imaging System composed of two cameras, see e.g. Keller et al. (2007) . In some imaging sequences dedicated to observe dust particles in the comet's coma, the two cameras took images at the same time. The aim of this work is to use these simultaneous double camera observations to calculate the dust particles’ distance to the spacecraft. As the two cameras are mounted on the spacecraft with an offset of 70 cm, the distance of particles observed by both cameras can be determined by a shift of the particles’ apparent trails on the images. This paper presents first results of the ongoing work, introducing the distance determination method for the OSIRIS instrument and the analysis of an example particle. We note that this method works for particles in the range of about 500–6000 m from the spacecraft. [ABSTRACT FROM AUTHOR]

Aims. We aim to explore the behavior of the opposition e ect as an important tool in optical remote sensing on the nucleus of comet 67P/ Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in di erent filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably di erent from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and flu y layer. [ABSTRACT FROM AUTHOR]

The Rosetta Lander Philae is part of the ESA Rosetta Mission which reached comet 67P/Churyumov–Gerasimenko after a 10 year cruise in August 2014. Since then, Rosetta has been studying both its nucleus and coma with instruments aboard the Orbiter. On November 12th, 2014 the Lander, Philae, was successfully delivered to the surface of the comet and operated for approximately 64 h after separation from the mother spacecraft. Since the active cold gas system aboard the Lander as well as the anchoring harpoons did not work, Philae bounced after the first touch-down at the planned landing site “Agilkia”. At the final landing site, “Abydos”, a modified First Scientific Sequence was performed. Due to the unexpectedly low illumination conditions and a lack of anchoring the sequence had to be adapted in order to minimize risk and maximize the scientific output. All ten instruments could be activated at least once, before Philae went into hibernation. In June 2015, the Lander contacted Rosetta again having survived successfully a long hibernation phase. This paper describes the Lander operations around separation, during descent and on the surface of the comet. We also address the partly successful attempts to re-establish contact with the Lander in June/July, when the internal temperature & power received were sufficient for Philae to become active again. [ABSTRACT FROM AUTHOR]

After the final landing of Philae at the Abydos site on comet 67/P Churyumov–Gerasimenko, the MUPUS (Multipurpose Sensors for Surface and Sub-Surface Science) device started hammering itself into the cometary ground on 14th November 2014, and continued hammering for more than 3 h. During this period, the CASSE (Comet Acoustic Surface Sounding Experiment) instrument, part of SESAME (Surface Electric Sounding and Acoustic Monitoring Experiment), was listening to the hammer strokes of MUPUS, which was the strongest available source for a seismic–acoustic experiment to determine mechanical properties of the ground. All sensors survived the multiple touchdowns of Philae undamaged and provided recordings of 14 hammer strokes at audible frequencies. The data suggests that Philae was slightly rocking or swinging during the initial phase of the experiment, finally finding an attitude that not only stopped this motion but also improved the coupling of sensors to the ground and thus the recordings. The experiment provides several lessons that might be useful for the development of similar experiments on future spacecraft. The most serious issues concerning the CASSE recordings are clock accuracy and synchronicity and the timing of the source. Future designs may want to consider additional sensors in close proximity to the source, and direct communication between experiments to overcome this. The present design allows the evaluation of arrival time differences only, rather than absolute travel times. In this contribution, we focus on the technical and operational aspects of this experiment. A scientific evaluation of the data received will follow in a second paper. [ABSTRACT FROM AUTHOR]

Rosetta is an ambitious mission launched in March 2004 to study comet 67P/Churyumov–Gerasimenko. It is composed of a space probe (Rosetta) and the Philae Lander. The mission is a series of premieres: among others, first probe to escort a comet, first time a landing site is selected with short turnaround time, first time a lander has landed on a comet nucleus. In November 2014, once stabilized on the comet, Philae has performed its “First Science Sequence”. Philae’s aim was to perform detailed and innovative in-situ experiments on the comet’s surface to characterize the nucleus by performing mechanical, chemical and physical investigations on the comet surface. The main contribution to the Rosetta lander by the French space agency (CNES) is the Science Operation and Navigation Center (SONC) located in Toulouse. Among its tasks is the scheduling of the scientific activities of the 10 lander experiments and then to provide it to the Lander Control Center (LCC) located in DLR Cologne. The teams in charge of the Philae activity scheduling had to cope with considerable constraints in term of energy, data management, asynchronous processes and co-activities or exclusions between instruments. Moreover the comet itself, its environment and the landing conditions remained unknown until separation time. The landing site was selected once the operational sequence was already designed. This paper will explain the specific context of the Rosetta lander mission and all the constraints that the lander activity scheduling had to face to fulfill the scientific objectives specified for Philae. A specific tool was developed by CNES and used to design the complete sequence of activities on the comet with respect to all constraints. The baseline scenario for the lander operation will also be detailed as well as the sequence performed on the comet to highlight the difficulties and challenges that the operational team faced. [ABSTRACT FROM AUTHOR]

Topographic mapping, e.g. the generation of Digital Elevation Models (DEM), is of general interest to the remote sensing community and scientific research. Commonly, photogrammetric methods, e.g. stereo image analysis methods (SIAM) or bundle adjustment methods (BAM), are applied to derive 3D information based on multiple images of an area. These methods require the detection of control points, i.e. common points within multiple images, which relies on a similarity measure and usually yields a sparse map of 3D points. The full spatial DEM is then obtained by interpolation techniques or imposed restrictions, e.g. smoothness constraints. Since BAM utilizes all images of the area, it is assumed to provide a more accurate DEM than SIAM which utilizes only pairs of images. Intensity-based shape recovery, e.g. shape from shading (SfS), utilizes the reflectance behavior of the object surface and thus provides a dense map of relative height changes, which provide the possibility to refine the photogrammetric DEMs. Based on Rosetta NavCam images of 67P/Churyumov-Gerasimenko we compare intensity-based DEM refinement methods which use DEMs obtained based on SIAM and BAM as a reference. We show that both the SIAM based DEM refinement and the BAM based DEM refinement are of similar quality. It is thus possible to derive DEMs of high lateral resolution by applying the intensity-based refinement to the less complex SIAM. [ABSTRACT FROM AUTHOR]

Polarimetric observations of comets have provided crucial insight into the composition and evolution of cometary dust particles. Herein, we present a brief overview of the polarization properties observed in comets, and some possible interpretations. We also discuss recent imaging polarimetry observations of C/2012 S1 (ISON) and 67P/Churyumov–Gerasimenko using the Hubble Space Telescope . The observations of 67P/Churyumov–Gerasimenko are of particular interest, as they were timed to be contemporary with the initial rendezvous of Rosetta and the subsequent landing of the probe Philae. We also outline some unanswered questions and future developments that will greatly enhance our ability to further leverage the power of polarimetry for cometary research. [ABSTRACT FROM AUTHOR]

The increasing number and complexity of planetary exploration space missions require new tools to access, visualize and analyse data to improve their scientific return. ASI Science Data Center (ASDC) addresses this request with the web-tool MATISSE (Multi-purpose Advanced Tool for the Instruments of the Solar System Exploration), allowing the visualization of single observation or real-time computed high-order products, directly projected on the three-dimensional model of the selected target body. Using MATISSE it will be no longer needed to download huge quantity of data or to write down a specific code for every instrument analysed, greatly encouraging studies based on joint analysis of different datasets. In addition the extremely high-resolution output, to be used offline with a Python-based free software, together with the files to be read with specific GIS software, makes it a valuable tool to further process the data at the best spatial accuracy available. MATISSE modular structure permits addition of new missions or tasks and, thanks to dedicated future developments, it would be possible to make it compliant to the Planetary Virtual Observatory standards currently under definition. In this context the recent development of an interface to the NASA ODE REST API by which it is possible to access to public repositories is set. [ABSTRACT FROM AUTHOR]

In bistatic radar systems utilizing elliptical polarization on both the sending and receiving side, great care must be taken to correctly calculate the received power, as a mismatch in polarization may incur significant additional losses. In this paper, we present a method to simulate the link budget of the CONSERT instrument aboard the Rosetta mission, including polarization effects. The correctness of the simulation method is demonstrated by comparing with a state-of-the-art Method of Moments solver. The CONSERT instrument's components aboard the Philae lander and the Rosetta orbiter need to be synchronized before the actual sounding. This synchronization can only be performed in line-of-sight conditions. In order to maximize sounding time for the propagation through 67P's core, the synchronization should happen as close to the approximate point of occultation as possible. A statistical analysis is presented to determine the probability of sufficient received power for the synchronization regarding uncertainties in the orbiter's pointing accuracy. [ABSTRACT FROM AUTHOR]

We report here the observations of the hydrogen cloud in Lyman alpha emission of Comet 67P/Churyumov–Gerasimenko at the last three passages through its perihelion, in 1996, 2002 and 2009. This comet became the target of ESA space mission Rosetta in 2003, and is therefore of particular interest. The data were collected with the SWAN instrument on board SOHO, the main mission of which is to record all-sky images of interplanetary neutral hydrogen, in order to monitor the solar wind latitude distribution. For the 2009 perihelion, a dedicated campaign was implemented and allowed to collect 26 smaller and more refined images around the position of the comet, from which a unique series of H2O production rates could be derived by comparison with a model, for the period from 2 to 50 days after perihelion. To our knowledge, these are the only determination of H2O production rate for 2009. In addition, we could retrieve the H emission at the two previous perihelia in 1996 and 2002, thanks to serendipitous observations of comets as part of the all-sky monitoring program: 4 and 10 respectively for 1996 and 2002. While the perihelion distance to sun decreased continuously (1.300, 1.292, 1.246AU respectively for 1996, 2002, 2009), the average production Q(H2O) just after perihelion did not increase accordingly: 1.30×1028, 1.70×1028, and 5.65×1027 mols−1. Comparison with 1982 IUE measurement of 6×1027 mols−1 suggests no rapid aging of the comet, and we may expect a similar level of activity at the next perihelion in August 2015. The production rate in 2009 showed a peak around 16.4 days post-perihelion, with a suggestion of a second peak at ~40 days, and a somewhat reduced rate in between (though SWAN measurements are incomplete). These measurements may help in planning of Rosetta activities around the next perihelion. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study investigating the performance of using the CONSERT instrument aboard the Rosetta spacecraft as a radar sounder during the Separation–Descent–Landing (SDL) phase of the Rosetta mission. Gathering scientifically valuable data during this phase will support CONSERT's primary target, the reconstruction of the 3D permittivity distribution within the comet 67P/Churyumov–Gerasimenko, by providing a permittivity map of the surface around the landing site. Simulation results will show the performance of the instrument, using a realistic setup including the antenna characteristics of both orbiter and landing unit as well as a realistic orbitography for the descent phase. It will be shown that operating the CONSERT instrument will indeed provide very valuable data, thereby providing tremendous aid to the experiment's main objective. Furthermore, by including knowledge of the antenna characteristics, it is possible to calculate attitude and descent profile of the Philae lander during descent, using the data of the line-of-sight propagation path and the echoes reflected from the comet's surface. [Copyright &y& Elsevier]

Abstract: The ESA's Rosetta spacecraft will arrive at comet 67P/Churyumov–Gerasimenko in 2014. The study of gas and dust emission is primary objective of several instruments on the Rosetta spacecraft, including the Microwave Instrument for the Rosetta Orbiter (MIRO). We developed a model of dust thermal emission to estimate the detectability of dust in the vicinity of the nucleus with MIRO. Our model computes the power received by the MIRO antenna in limb viewing as a function of the geometry of the observations and the physical properties of the grains. We show that detection in the millimeter and submillimeter channels can be achieved near perihelion. [Copyright &y& Elsevier]