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Enceladus, an icy moon of Saturn, possesses an internal water ocean and jets expelling ocean material into space. Cassini investigations indicated that the subsurface ocean could be a habitable environment having a complex interaction with the rocky core. Further investigation of the composition of the plume formed by the jets is necessary to fully understand the ocean, its potential habitability, and what it tells us about Enceladus' origin. Moonraker has been proposed as an ESA M-class mission designed to orbit Saturn and perform multiple flybys of Enceladus, focusing on traversals of the plume. The proposed Moonraker mission consists of an ESA-provided platform, with strong heritage from JUICE and Mars Sample Return, and carrying a suite of instruments dedicated to plume and surface analysis. The nominal Moonraker mission has a duration of 13.5 years. It includes a 23-flyby segment with 189 days allocated for the science phase, and can be expanded with additional segments if resources allow. The mission concept consists in investigating: i) the habitability conditions of present-day Enceladus and its internal ocean, ii) the mechanisms at play for the communication between the internal ocean and the surface of the South Polar Terrain, and iii) the formation conditions of the moon. Moonraker, thanks to state-of-the-art instruments representing a significant improvement over Cassini's payload, would quantify the abundance of key species in the plume, isotopic ratios, and physical parameters of the plume and the surface. Such a mission would pave the way for a possible future landed mission., Accepted for publication in The Planetary Science Journal

Full list of authors: Cremonese, G.; Capaccioni, F.; Capria, M. T.; Doressoundiram, A.; Palumbo, P.; Vincendon, M.; Massironi, M.; Debei, S.; Zusi, M.; Altieri, F.; Amoroso, M.; Aroldi, G.; Baroni, M.; Barucci, A.; Bellucci, G.; Benkhoff, J.; Besse, S.; Bettanini, C.; Blecka, M.; Borrelli, D.; Brucato, J. R.; Carli, C.; Carlier, V.; Cerroni, P.; Cicchetti, A.; Colangeli, L.; Dami, M.; Da Deppo, V.; Della Corte, V.; De Sanctis, M. C.; Erard, S.; Esposito, F.; Fantinel, D.; Ferranti, L.; Ferri, F.; Ficai Veltroni, I.; Filacchione, G.; Flamini, E.; Forlani, G.; Fornasier, S.; Forni, O.; Fulchignoni, M.; Galluzzi, V.; Gwinner, K.; Ip, W.; Jorda, L.; Langevin, Y.; Lara, L.; Leblanc, F.; Leyrat, C.; Li, Y.; Marchi, S.; Marinangeli, L.; Marzari, F.; Mazzotta Epifani, E.; Mendillo, M.; Mennella, V.; Mugnuolo, R.; Muinonen, K.; Naletto, G.; Noschese, R.; Palomba, E.; Paolinetti, R.; Perna, D.; Piccioni, G.; Politi, R.; Poulet, F.; Ragazzoni, R.; Re, C.; Rossi, M.; Rotundi, A.; Salemi, G.; Sgavetti, M.; Simioni, E.; Thomas, N.; Tommasi, L.; Turella, A.; Van Hoolst, T.; Wilson, L.; Zambon, F.; Aboudan, A.; Barraud, O.; Bott, N.; Borin, P.; Colombatti, G.; El Yazidi, M.; Ferrari, S.; Flahaut, J.; Giacomini, L.; Guzzetta, L.; Lucchetti, A.; Martellato, E.; Pajola, M.; Slemer, A.; Tognon, G.; Turrini, D. -- This is an open access article, The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the BepiColombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will provide high-resolution images of about 20% of the surface, and the Visible and near-Infrared Hyperspectral Imaging channel (VIHI), with high spectral resolution (6 nm at finest) in the 400-2000 nm range and spatial resolution reaching 120 m/px, it will provide global coverage at 480 m/px with the spectral information, assuming the first orbit around Mercury with periherm at 480 km from the surface. SIMBIO-SYS will provide high-resolution images, the Digital Terrain Model of the entire surface, and the surface composition using a wide spectral range, as for instance detecting sulphides or material derived by sulphur and carbon oxidation, at resolutions and coverage higher than the MESSENGER mission with a full co-alignment of the three channels. All the data that will be acquired will allow to cover a wide range of scientific objectives, from the surface processes and cartography up to the internal structure, contributing to the libration experiment, and the surface-exosphere interaction. The global 3D and spectral mapping will allow to study the morphology and the composition of any surface feature. In this work, we describe the on-ground calibrations and the results obtained, providing an important overview of the instrument performances. The calibrations have been performed at channel and at system levels, utilizing specific setup in most of the cases realized for SIMBIO-SYS. In the case of the stereo camera (STC), it has been necessary to have a validation of the new stereo concept adopted, based on the push-frame. This work describes also the results of the Near-Earth Commissioning Phase performed few weeks after the Launch (20 October 2018). According to the calibration results and the first commissioning the three channels are working very well. © 2020, The Author(s)., We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0. The SIMBIO-SYS instrument has been developed by Leonardo under ASI contract I/054/10/0.

The structure and composition of cometary constituents, down to their microscopic scale, are critical witnesses of the processes and ingredients that drove the formation and evolution of planetary bodies toward their present diversity. On board Rosetta's lander Philae, the Comet Infrared and Visible Analyser (CIVA) experiment took a series of images to characterize the surface materials surrounding the lander on comet 67P/Churyumov-Gerasimenko. Images were collected twice: just after touchdown, and after Philae finally came to rest, where it acquired a full panorama. These images reveal a fractured surface with complex structure and a variety of grain scales and albedos, possibly constituting pristine cometary material.

The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected-phyllosilicates and sulphates--result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.

This paper gives a survey of the Mars Express orbit design, as it evolved from before launch (Hechler and Yanez, 2003, Acta Astronautica, 53: 497–507) to arrival at Mars. The orbit selection for Mars Express has major scientific impacts, as the orbit is elliptical, with continuous changes of the latitude and local hour of the pericentre. A first target orbit was defined in 1999 by combining scientific and engineering constraints. As a very favourable launch date was achieved and the launcher injection error was ‘better than nominal’ (the error removed part of the planned re-targeting), propellant reserves turned out to be available after launch. Part of this was used to improve the target orbit. The plane turn manoeuvre was increased to start with the pericentre near the equator rather than at 20°S latitude, with the objective of increasing the early observation phase with good day-side viewing conditions. A few weeks after launch, an anomaly in the spacecraft power system was detected, with a loss of up ...

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

This chapter presents in the first section the scientific rationale and present status of planetary exploration missions. In the second section, the energy requirements and mass budgets of planetary missions are evaluated, first for leaving the Earth and then visiting (flyby missions) or going into orbit (rendezvous missions) bodies of interest in the solar system. Specifically, the first section is dedicated to remote-sensing and in situ missions to Venus and Mars. The next section discusses the evolution of orbits around planetary bodies. The next sections present the challenges of in situ missions to atmosphereless bodies, then the gravity-assist techniques that are required for high-energy targets (giant planets, Mercury, and comet rendezvous) and advanced propulsion systems (ion propulsion and solar sail). In the final section, the specific challenges of sample return missions are discussed.

Mercury is the largest of all planetary bodies for which the evolution of the surface has been driven primarily by external causes during the last few billion years. The trademark of such an evolution is a surface saturated with small craters and covered by a regolith. The most extensively studied example is the Moon. The crater formation process on Mercury should be very similar to the lunar case. On such large planetary bodies, gravity plays a major role in crater formation, contrary to small bodies such as Phobos, Deimos or asteroids. Furthermore, impact rates of large meteoroids may have been similar on the Moon and Mercury. There are however major differences in the environment of these two bodies which should have an effect on the evolution of the regolith: the ratio of micrometeoroids (mainly originating from comets) to meteoroids (which are transferred in chaotic corridors from the main belt of asteroids) is likely to be much higher than on the Moon; impact energies are larger for cometary material than for asteroidal material; the flux of the solar wind increases by a factor of up to 10 on Mercury although the relative importance of magnetospheric screening and of magnetospheric particles is difficult to evaluate; Solar Cosmic Rays which result in the formation of particle tracks also increase by a factor of up to 10 when compared to the Moon. However, surface temperatures reach 700 K, which can result over millions of years in the annealing of irradiation effects. Overall, the regolith of Mercury is expected to be significantly more mature than the lunar regolith, with smaller grain sizes and larger proportions of glassy particles. A possible exception could be radiation damage due to annealing. This has implications on the interpretation of remote sensing investigations during an orbiter mission, such as the lighter albedo of plains material on Mercury when compared to the maria of the Moon, the search for ray craters or the relationship of near-infrared spectra to the mineralogical composition.

— The COMET program is a program for the collection of micron to submicron interplanetary dust particles in low Earth orbits. Since collection takes place as the Earth crosses a given meteor stream, the particles are mainly of cometary origin. The grain remnants, located at their impact positions on high purity metallic collectors, are analysed in the laboratory for chemical and isotopical identification. The COMET-1 experiment took place in 1985 October, during encounter with the Draconid meteor stream, related to the Giacobini-Zinner comet. The fluence of extraterrestrial grains that had impacted our detectors was ∼10x higher than the value of the mean meteroid fluence at ∼1AU, which suggests that most of the grains originated from the Giacobini-Zinner comet. One of the most important results of their chemical analysis was that ∼90% of them are enriched in low Z elements (C and O have undoubedly been identified). They could contain a CHON phase similar to that observed in the close environment of Halley's nucleus. The first imagery of the grain remnants by field emission scanning electron microscopy suggests that they are very low density aggregates still present at the impacting positions which, in most cases, are very different from the impact craters observed for the same mean relative velocity for full grains of the same size. These results show that the COMET program has constituted an important step towards the analysis of cometary material and the understanding of the evolution of the early Solar System.

Phobos is the first asteroid-like body to be observed at close range: during the Viking mission, several close fly-bys made possible extensive mapping of its surface at resolutions down to a few m. During the Phobos mission, two encounters at a distance of about 200 km were performed before the premature termination of the mission, on March 28th 1989. The images from the camera system (FREGAT) complement the Viking coverage, improving upon it for about 25% of the surface. The KRFM/ISM infrared complex obtained two tracks across the equatorial region, and (for ISM) a 25 × 25 pixels image, with a pixel size of .7 km. They provide the first spatially resolved data on a small solar system body in the infrared spectral range. The surface of Phobos is found to be markedly heterogeneous at a km scale. This is surprising given the expected high efficiency of lateral transport processes on the surface of Phobos. During the next decade, several main belt asteroids will be observed with similar resolutions during the GALILEO, C.R.A.F and CASSINI missions. This comparison will be essential for unravelling the relationship between Phobos and small main belt asteroids, and for understanding the specific aspects of surface evolution on a close planetary satellite.

In orbit on board the European Space Agency's (ESA) Mars Express spacecraft, the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activite (OMEGA) visible to near-infrared spectral imager is acquiring a global compositional surface mapping dataset of Mars in order to reveal its major mineralogical and icy constituents. These data provide insights on the evolution of Mars on timescales ranging from seasonal variations to geological epochs. In particular, the identification and mapping of the spatial distribution of pristine magmatic rocks (including olivine, high-Ca pyroxene, and low-Ca pyroxene) and of three classes of altered minerals (hydrated phyllosilicates, hydrated sulfates, and anhydrous ferric oxides) in distinct areas has enabled the development of a new model for the evolution of the surface. The model includes three major eras spanning Martian history. The first era, during which phyllosilicates appear to have formed, was the most favorable to have hosted habitable conditions, with perennial and neutral to slightly alkaline pH surface liquid water. Mars then underwent a global environmental and climatic change, coupled to the formation of Tharsis and the release of large amounts of SO 2 and other volcanic gases, and the likely loss of most of its CO 2 -rich atmosphere. This second era was characterized by low-pH (acidic) surface and subsurface groundwater, and the creation of large deposits of sulfate minerals. The third and most recent era in this model is dominated by atmospheric processes, leading primarily to the generation of anhydrous weathering products.

International audience; The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth Moon system.

(1982). On the registration of low energy (E 1 keV/amu) ion tracks in dielectric. Radiation Effects: Vol. 65, No. 1-4, pp. 133-137.

We investigated the paramagnetic defects formed by high‐energy ions in amorphous SiO2 using electron spin resonance. We show that the variation of paramagnetic defect densities with both the residual range and the atomic number of the ion is not simply correlated with the total energy deposited in the sample, which is the major controlling parameter for other types of irradiation (γ rays, electrons). This specificity of ion irradiation is most likely related to the high local density of deposited energy. The observed populations of paramagnetic defects constitute a small fraction of the formed defects. However, their characteristics can be related to results on ion track structure obtained by small‐angle scattering and track etching methods.

A mission to Mars and small solar system bodies is presently studied as a possible collaboration between INTERCOSMOS, CNES, ESA and eventually other participants. The VESTA concept, based on the same strategy as the successful VEGA mission, is more ambitious, as two spacecrafts separate soon after launch: a soviet spacecraft, dedicated to the study of Mars, and a spacecraft dedicated to the study of small bodies, under the responsibility of CNES and ESA. This spacecraft would use Mars gravity assists to visit up to 4 small bodies in less than 5 years. The mission is duplicated, which means that up to 8 small bodies could be studied (e.g. 6 main belt asteroids, 1 apollo-amor asteroid and 1 short period comet). Low relative velocities (

Le laser au néodyme du GRECO I.L.M. délivrant des impulsions de l'ordre de 100 J en quelques ns, nous a permis de simuler des impacts de micrométéorites silicatées de quelques dixièmes de μg, de vitesse comprise entre 5 et 45 km/s, sur une cible d'aluminium. Les cratères produits dans la cible sont hémisphériques, et le rapport Km, de la masse éjectée sur la masse de la particule incidente simulée, varie avec la vitesse d'impact Vp selon la loi Km = 1,17 V 1,52p.

Most insulator materials so far proposed for storing high-level radioactive wastes, such as glass and and the constituent minerals of ceramics are nuclear track detectors. Lead ion implantation experiments show that such materials should be transformed into “giant” nuclear tracks, when the internal fluence of heavy recoils emitted during the α-decay of actinide elements stored in them exceeds a critical value, which corresponds to an equivalent storage period of a few thousand years for the wastes expected from a pressurized water reactor. In contrast, actinide bearing minerals are much more stable against α-recoil damage. As nuclear tracks are extremely chemical reactive, α-recoil damage is expected to shorten the lifetime of storage materials such as glass and ceramics against dissolution in ground waters. Fortunately new nuclear track concepts are already yielding guidelines for predicting and improving the long-term stability of storage materials. The results of the present studies also bear on the physics of ion implantation phenomena an insulator targets exposed to high fluences of low energy ions.

The annealing and etching behavior of tracks produced by 6 and 14 MeV/amu U ions was investigated both in labradorite and muscovite mica. Our results are best interpreted in terms of a continuous structure of these tracks. In particular, their annelaing is a global process dominated by the thermal stability of the region intersecting the surface.

A new microprobing procedure is used to characterize both the physical and chemical surface properties of individual grains on a microscale. In this procedure the same sub-micrometre sized area of a given grain is successively analysed with a high voltage electron microscope, an Auger microprobe and a field emission scanning electron microscope. This analytical technique has been applied to study lunar weathering effects and to tentatively infer the irradiation history of a Nerich fraction of the Orgueil meteorite.

The microscopic structure of latent tracks in silicates is analyzed using small-angle x-ray scattering methods. Latent tracks are constituted of extended defects, separated by gap zones loaded with point defects. The variation of the linear density of extended defects along the path of the incident ions cannot be scaled with functions previously used, such as the primary rate of ionization. Upon a thermal annealing, the extended defects are much more stable than point defects. These latent tracks are chemically etched and their etching rates are inferred from optical and scanning electron-microscope observations. From these combined studies of latent and etched tracks, a model for the registration of etchable tracks in silicates is developed. In this model, the extended defects dominate the chemical etching and thermal annealing behavior of etchable tracks. The marked differences observed in the sensitivity of various silicates are no longer attributed to a radiation damage mechanism, which would operate much more efficiently in specific silicates, but to the etching behavior of each mineral. Indeed, for a given incident ion, the linear density of extended defects in a given part of the ion residual range appears to be similar in all silicates. This model is used in the framework of a Monte Carlo statistical code to predict etched track-length distributions in silicates, including those relevant to partially annealed tracks. The striking agreement between these predictions and the corresponding observations strongly support our model. It enables us to discuss the most important concepts previously proposed to account for the registration of etchable tracks in silicates, and to suggest a few preliminary guidelines for improving the use of solid-state track detectors.

High energy heavy ions in insulators induce the formation of defects which have been studied by track etching methods and small angle X-ray scattering1-3. These previous studies have shown that the formation of defects is linked to electronic energy losses. However, the processes which result in lattice defects following such interactions are not well understood. In order to characterize the defects formed and their lattice environment, we studied amorphous SiO2 (dry Tetrasil SE) irradiated by heavy ions using Electron Spin Resonance (ESR). The paramagnetic defects formed in this material by γ-ray, X-ray and electron irradiation have already been extensively studied4–7. After such irradiation, two major types of defects have been observed: the E 1 ′ center8 (hole trapped by an oxygen vacancy) and the oxygen hole center 9 (or OHC, associated with a peroxy radical). The density of defects observed was closely related to the total energy deposited in the sample. We previously showed 10 that high energy heavy ions also induce the formation of E 1 ′ centers and OHC’s. However, the ion irradiated samples present specific characteristics, which are linked to the very high density of energy deposited near the path of heavy ions11. We present here a study of the dependence of the defects on the residual energy, the atomic number and the fluence of the incident ions. We show that, in contrast to γ-ray irradiations, the total energy deposited is not the single parameter controlling the formation of paramagnetic defects by high energy heavy ions.

Leaching of samples externally irradiated with low energy (~ lkeV/nucleon) heavy ions shows that the accumulation of a-recoils in glass can drastically reduce the life-time of waste storage glasses in geological environments against complete dissolution by ground water solutions.

Surface modifications induced by high energy heavy ions on quartz (SiO 2 ) and sapphire (Al 2 O 3 ) have been studied by means of photoelectron spectroscopy and extended X-ray absorption fine structure spectroscopy. Results are interpreted in the frame of density of states calculations performed using a semiempirical tight binding method. Under oxygen ion irradiation, it appears that the induced damage consists mainly of lattice distortion plus a population of point defects identified as oxygen vacancies.

We describe an image‐processing equipment designed and built to meet the specific requirements of an astrophysical experiment, but having probably useful applications in other fields of science and technology. It locates and makes the inventory of specified micrometer‐sized holes in thin metallic films. The data acquisition is made by a CCD camera looking at the film through an optical microscope. The information goes to a microcomputer through a special interface. The program and the electronics were designed for optimum acquisition speed, automatic operation, and minimum need for human intervention.

A new technique has been developed to exploit the heterogeneous fission track distributions registered in quartz from the Oklo uranium mine both for dating and neutron dosimetry purposes. In this technique etched fission tracks are observed by means of electron microscope replica, and the density of the fossil tracks is easily distinguished from that of the artificially induced ones on track length criteria. Tracks originating from tiny inclusions (fission stars) can then be used to infer the formation age of the quartz grains and gradients in the neutrons fluence active in the borders of the Oklo nuclear reactors.

ESR studies of amorphous silica samples irradiated by high energy heavy ions show that the paramagnetic defects formed when electronic interactions dominate are similar to those observed after γ-ray irradiation (E' centers and oxygen hole centers, or OHC). However, spectra of ion-irradiated samples exhibit specific features, due to the high density of energy deposit which is specific to heavy ion irradiation. Furthermore, the concentrations of defects cannot be interpreted from the total energy deposit alone, as the atomic number plays an important role. When the energy deposit increases, we observe a transfer from E' centers to OHC, which is also observed after annealing. This supports the concept of a “ thermal spike” reorganization phase in the wake of the incident ion. Optical spectroscopy results are consistent with ESR for E' centers, and show that the B2 centers, which are interpreted as diamagnetic oxygen vacancies, are less abundant than the E' centers.

Analysis of the data from Giotto's Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.