The search for signatures of life beyond Earth has been a primary motivator in the field of space science. The question of the ideal exploration site for the search of such signatures for life remains unanswered, despite an increase in space missions dedicated to the understanding of the formation of the Martian surface and its environmental history. The present space exploration missions focus on formerly subaqueous environments, such as water bodies and deltaic structures [1,2]. While these sites have the capability to bury organic material due to rapid sedimentation, the preservation of biosignatures in those high-energy settings is often compromised by oxidizing fluids and gases [3]. Conversely, tranquil settings, such as ancient lakes, might be more suited for biomarker preservation. Many of these lakes were saline and formed salt deposits when they dried out. During salt precipitation, biomarkers can be buried and shielded from the harsh radiation prevailing on the Martian surface. Thus, these evaporites have been previously suggested as important sites for the search for life on Mars [4]. Such salt deposits on the surface of Mars have been identified numerously, displaying distinctive polygonal surface features, visible from orbit by e.g., CRISM or HiRISE imaging [5]. Similar polygonal structures are also found at Mars analogue sites in salt deposits on Earth, like in the Atacama Desert [6] or in the Boulby Mine, United Kingdom. This contribution presents the results of our study focused on the polygonal structures within the halite deposits of the Boulby Mine. The measurements were performed using a space-prototype laser ablation ionisation mass spectrometer (LIMS) [7,8]. The polygons show two optically distinct features, consisting of dark edges and light interiors. For both features, interior and edge, the chemical composition was determined using LIMS and compared. A specific focus was placed on the difference in abundance of the CHNOPS elements, as they serve as biomarkers. A significant increase in CHNOPS and other biologically relevant minor and trace elements, necessary e.g., for the maintenance and formation of life, was observed at the polygonal edges. This shows that the edges of polygonal structured salt deposits are preferential sites for element accumulation. As a result, the edges of salt deposits might be more habitable to life as we know it and could serve as promising sites for detecting signatures of life in future in-situ space exploration missions. [1] Mangold, N. et al., 2020, https://doi.org/10.1089/ast.2019.2132[2] Vasavada, A. R., 2022, https://doi.org/10.1007/s11214-022-00882-7[3] Hays, L. E., 2017, https://doi.org/10.1089/ast.2016.1627[4] Rothschild, L. J., 1990, https://doi.org/10.1016/0019-1035(90)90188-F[5] El-Maarry, M. R. et al., 2013, https://doi.org/10.1002/2013JE004463[6] Sager, C. et al., 2021, https://doi.org/10.1016/j.geomorph.2020.107481[7] Riedo, A. et al., 2012, https://doi.org/10.1002/jms.3104[8] Tulej, M. et al., 2021, https://doi.org/10.3390/app11062562

CoPhyLabLaboratory experiments are of major importance to understand the activity of comets and to support future space missions. However, past comet simulation experiments were performed under the assumption that comets are mainly composed of water ice with only a limited amount of dust. In the past years, however, the Rosetta mission has shown that cometary nuclei consist primarily of dust and less volatile materials are present than previously thought. Hence, it is high time to set up a new series of laboratory experiments with the aim to investigate the physics of realistic cometary analogue materials. This task is currently addressed by the CoPhyLab (Comet Physics Laboratory) which is a joint project among different partner institutions. This laboratory aims at studying the physics of cometary analogue materials. This task is approached by firstinvestigating isolated physical properties in so-called small experiments (S experiments). In a next step, the experiment’s complexity is increased step-by-step by either adding further components to the sample, or by studying several physical properties under different conditions (large experiments, which will be performed in the L chamber). S1: the tensile strength of organic materialsThe knowledge of the tensile strength of the cometary surface is of key importance to better understand the activity of comets. The tensile strength determines the strain required to detach material from the surface. As organic materials are ubiquitous in space, they could have played an important role during the planet formation process and are most likely incorporated into cometary nuclei. This S experiment campaign provides new measurements on the tensile strength of various granular organic materials. These materials are investigated by the Brazilian Disc Test and the measured values are normalised to a grain size of one micrometer and a volume filling factor of 0.5 for better comparability. The experiments show that the tensile strength of organic materials ranges over four orders of magnitude. Graphite and paraffin have much higher tensile strengths values compared to silica, whereas the tensile strength of coals is very low. This work demonstrates that organic materials are not generally stickier than silicates, or water ice.S2: gas permeability of analogue materials The cometary nucleus is made of water ice, organics and silicateous dust and the ice is trapped inside the matrix of non-volatiles. Hence, the evolving gas has to stream away from its originating region inside the surface layers towards the surface. This work package has the aim to investigate the gas transport mechanisms through porous cometary analogue materials. Therefore, gas flow measurements are performed to investigate the permeability of several materials, which are chosen to mimic cometary surface properties. With these measurements, the gas permeability and the Knudsen diffusion coefficient of the sample materials are obtained. These simulants are tested with respect to different filling heights, packing properties and grain shapes. The gas flow experiments show that the grain size distribution and the packing density of the samples are primarily influencing the permeability of the sample. S3: thermal conductivity of analogue materialsMeasurements of the thermal properties of analogue materials are essential in interpreting remote sensing data and the findings of in-situ instruments. The thermal properties of the subsurface layers determine the surface temperature of asteroids and comets. The temperature stratification inside planetary object is a key parameter to understand the processing of their interior. This experiment campaign is dedicated to measure the thermal properties of analogue materials. In preparation for these measurements we have set up a small vacuum chamber equipped with an infrared camera and temperature sensors. The samples are illuminated for a short duration by a laser. We then compare the measured temperature profiles with the predictions of a thermophysical model to determine the thermal conductivity of the samples.S4: ejection of materialWhen comets approach the Sun, the sublimation pressure will be reached inside the material. If the tensile strength is exceeded by the evolving pressure, the particles can be ejected from the cometary surface and are accelerated. However, the details of the dust dynamics close to the surface are not understood in detail. The idea of this S experiment campaign is to develop an experimental routine to track ejected particles from a sample composed of granular water ice. Therefore, we recorded the power of the illumination, the temperature of the sample and measured the particle trajectories with an high speed camera. Furthermore, the experiments are also simulated by a thermophysical model. Our experiments show that samples composed of pure granular water ice can eject water-ice particles by the pressure build up of water vapour in their interior. Compressed samples posses an higher activity level (ejection events per second) compared to uncompressed samples. The ejected particles have a non-zero initial velocity which is most probably caused by a very fast acceleration of the particles before the first data point is recorded by the camera.The L chamberThe core of this project is the realisation of a comet simulation chamber which will be capable to utilise multiple instruments to monitor and measure the sample properties before, during and after the experiment campaigns. This chamber will be used to perform long duration experiments at low temperatures and low pressures. At this stage (end of June, 2020), the chamber is already installed in place and is vacuum tight, the cooling shield is assembled and the sample carrier cart as well as the self-made glove box are ready to use. The next steps comprise the integration of the cooling shield and the main cooling system. We foresee to run the first experiments in approximately six weeks from now. During the EPSC conference we will provide a technical overview of the chamber and we will present the first experiments performed in the L chamber.AcknowledgementsThis work was carried out in the framework of the CoPhyLab project funded by the D-A-CH programme (GU 1620/3-1 and BL 298/26-1 / SNF 200021E 177964 / FWF I 3730-N36). DB and JB thank the Deutsches Zentrum f\"ur Luft- und Raumfahrt for support under grant 50WM1846.

Orbital data from the Colour and Stereo Surface Imaging System (CaSSIS) onboard the ExoMars Trace Gas Orbiter showed interesting images of the circumpolar areas during spring. The winter-formed dusty CO2 ice cap goes under self-cleaning processes producing a translucent slab. With grazing spring sunlight, it starts to sublimate at the base and from overpressure, cold jets erupt leaving erosion marks in the underlying substrate and dust/sand deposits at the surface. This model, proposed by Kieffer, is commonly accepted to explain dark spots and fans deposits as well as spiders. To test different aspects of this model, we combine observational data from CaSSIS with experimental work for which Martian temperature and pressure at high latitudes could be reached in a simulation chamber. Preliminary results on sinking analogous dust material (MGS-1) on a CO2 ice slab have been promising. We aim to quantify in better details the sinking ratio, colour variations and frost (H2O and/or CO2) depositions on CO2/MGS-1 samples under various setup conditions (illumination, material distribution). Using a hyperspectral device, we can measure the reflectance and simulate the CaSSIS signal in the different filters (PAN, NIR, RED, BLU) to compare to actual images that have been acquired during southern spring.

Io, the world with the greatest tidal flexing, volcanic and tectonic activity, and mass-loss in our solar system, begs for dedicated exploration. Missions such as Juno and JUICE, along with Earth-based telescopes such as JWST and ALMA, will acquire important Io observations over the next 15 years, as could Europa Clipper. However, a mission designed for Io science is necessary to accomplish key science goals that have been consistently prioritized in the National Academy of Sciences Decadal Surveys and the ESA Voyage 2050 (Thomas, 2021, Experimental Astronomy online), including understanding the early evolution of terrestrial planets, tidally heated exoplanets and ocean worlds, and magnetospheric physics across the galaxy. The NASA Discovery-class Io Volcano Observer (IVO; McEwen et al., 2021, LPSC 1352) completed Phase A in 2021 and was deemed selectable, but was not chosen for programmatic (i.e., non-science/engineering) reasons. The IVO concept study demonstrated how a total of ten carefully designed, close Io flybys could determine the melt distribution in Io’s interior to confirm or refute the presence of a magma ocean, constrain Io’s global average lithospheric structure, identify where and how Io is losing heat, and determine processes and rates for Io’s volatile loss. Such encounters would also measure Io’s rate of orbital migration, key to determining the stability of the LaPlace resonance that heats Europa and Ganymede, as well as Io. The ambitious (for Discovery) science payload included a magnetometer, plasma instrument, narrow-angle camera, thermal mapper, neutral mass spectrometer, plus a telecom system for gravity science and options for a student-collaboration wide-angle camera (WAC), and a technology demonstration UV spectrometer. The next Discovery mission proposal opportunity is expected in 2025 or later, but an opportunity to propose an Io mission in NASA’s New Frontiers (NF) program is anticipated in 2023. How might that differ from a Discovery-class mission? An Io orbiter to provide better geophysical measurements has been suggested in the past, but would be very challenging deep inside Jupiter’s gravity well and high radiation zone. An orbiter might be feasible if new, more capable launch vehicles become available. On the other hand, the IVO Discovery concept would accomplish all of the science objectives of NF, and could be augmented in several key ways using the additional resources available in NF. A radiation design to support more than 10 encounters is a relatively straightforward enhancement. Ka-band would improve the data downlink capability and gravity science. With twice as many Io encounters, it would be possible to more completely map Io’s surface at multiple wavelengths; encounter Io over additional values of orbital true anomaly for improved gravity science, magnetic induction, and measuring Io’s libration; and sample more longitudes and times of day to understand Io’s atmosphere, plumes, magnetospheric interactions, and mass loss. The WAC, which is especially important for mapping Io’s topography, could be a required Baseline experiment. There are many science instruments that would be valuable additions, including altimetry, ultraviolet and near-IR spectroscopy, a dust mass spectrometer, passive radar sounding (using Jupiter radiation), active radar sounding, and additional fields and particle instruments. Greater emphasis may be placed on tracing the mass and energy flows in the Io-Jupiter system, especially because the new US Planetary Science and Astrobiology Decadal Survey places much emphasis on understanding planetary systems relevant to exoplanets. Interferometric synthetic aperture radar (InSAR) would be challenging but could transform our understanding of active processes on Io. An even more daring idea is to deliver a penetrator that could measure Io’s seismicity and conducted heat flow, perhaps also with a laser retroreflector or radio transponder to measure Io’s rotational and tidal deformation. However, getting substantial data back to the main spacecraft for transmittal to Earth is challenging in the very fast flybys that are preferred to keep the total ionizing radiation dose low. In terms of international collaboration, we expect a thermal mapper from DLR and a neutral mass spectrometer from UBE, plus science co-investigators; additional contributions are possible. In summary, a highly capable mission to one of the most exciting objects in the Solar System is overdue. Figure: Io is a spectacular target to observe both in daytime and at night (simulated hot spots).

Introduction The ESA/JAXA joint mission BepiColombo comprises two spacecraft, one of which is the Mercury Planetary Orbiter (MPO). It will arrive at the Mercury orbit in 2025, and the BepiColombo Laser Altimeter (BELA) onboard MPO will start to characterize the Mercury’s surface, such as topographic reliefs. During the nominal and extended operations, the whole surface of Mercury will be covered by the BELA footprints, and separations between neighboring tracks were expected to vary from 3 km at the equator down to less than 250 m in polar regions [1]. One of the scientific objectives of BELA is to measure surface roughness, local slope, and albedo variations of Mercury [2]. In general, laser altimetry is a useful remote sensing tool to reveal the surficial features because the shape of the received pulse contains various information about footprints. For example, vegetation structure within footprints was observed in the waveforms measured by the Ice, Cloud, and land Elevation Satellite (ICESat) [3], and the martian roughness was estimated from the pulse width received by the Mars Orbiter Laser Altimeter [4]. Thus, BELA is expected to help characterize geologic features on Mercury, such as hollows [5] In contrast, the effects of surficial features on the BELA pulse shape have not been investigated numerically. Until recently, semi-analytical pulse shape models have been employed to demonstrate the BELA measurements after the operation starts [1, 6]. Therefore, we develop the procedure to simulate realistic pulse shapes, incorporating digital terrain models (DTMs) and noise data from previous in-cruse checkouts of BELA. Then, we discuss the detectability of the surficial properties of Mercury. Method To simulate the realistic pulse shape returning from the Mercury surface, we first numerically model pulses returning from DTMs. Assuming a Gaussian pulse transmission and a Lambertian surface, we integrate photons from all the facets. Then, after the pulse shape is widened by the receiver optics, the number of photons is converted to signals in the avalanche photodiode. With 16 gain channels ranging from 4 to 44 dB, the Analog Electronics Unit amplifies the signal. The simulated signal is finally compared with the sum of dark, solar, and shot noises. Data from in-cruise checkouts by June 2021 is used as the dark noise for respective gain channels. The solar and shot noise levels are analytically estimated [1]. By incorporating these noises, the signal-to-noise ratio (SNR) of the received pulse is calculated for various surfaces. Results and discussions Figure 1 shows pulse shape examples simulated with various ideal topographies. For the flat surface, time of flight is almost uniform for all the photons from the footprint. However, slopes change distances between facets and BELA, widening pulse shapes. If bimodal height distribution, such as depression, cliff, and rocks, is contained within the footprint, a split pulse can be detected, depending on the height gaps. Figure 1. Pulse shapes returning from a flat surface, slope (20 degrees), and round depression. The altitude is set to be 1000 km above the Mercury surface. Detectability of rocks within a footprint is also examined in our analysis. Locating a hemispherical rock on a flat plain and changing its radius, we calculated pulse shapes with two peaks from the rock and its surroundings (Figure 2). In order to receive the rock’s signal with an SNR of 1 or higher, our estimate suggests that the radius of the rock needs to be larger than a few meters at an altitude higher than 400 km. Figure 2. Pulse shapes without noises simulated for hemispherical rocks with various radii. Black shades show a standard deviation of dark noise. Dashed lines show the sum of dark, shot, and solar noises. Left peaks correspond to laser pulses reflected by the rock surface. Furthermore, roughness estimation within the footprint requires accurate slope values because they similarly widen the pulse shape. Although only one-dimensional slopes can be constrained with BELA, possible constraints on roughness will be estimated using these pulse shape simulations. This presentation will report on such further implications for Mercury’s surfaces in future BELA observations. Acknowledgment This research is granted by JSPS Overseas Challenge Program for Young Researchers. Reference [1] G. Steinbrügge, A. Stark, H. Hussmann, K. Wickhusen, J. Oberst, The performance of the BepiColombo Laser Altimeter (BELA) prior launch and prospects for Mercury orbit operations. Planetary and Space Science. 159, 84-92 (2018). [2] N. Thomas et al., The BepiColombo Laser Altimeter. Space Sci Rev. 217(2021). [3] D. J. Harding, C. C. Carabajal, ICESat waveform measurements of within-footprint topographic relief and vegetation vertical structure. Geophysical Research Letters. 32, L21S10-n/a (2005). [4] G. A. Neumann et al., Mars Orbiter Laser Altimeter pulse width measurements and footprint-scale roughness. Geophysical Research Letters. 30, 1561-n/a (2003). [5] T. Blewett David et al., Hollows on Mercury: MESSENGER Evidence for Geologically Recent Volatile-Related Activity. Science. 333, 1856-1859 (2011). [6] A. HosseiniArani et al., Comprehensive in-orbit performance evaluation of the BepiColombo Laser Altimeter (BELA). Planetary and Space Science. 195, 105088 (2021).

<p>Lineaments are prominent features on the surface of Jupiter's moon Europa. Analysing these linear features thoroughly leads to insights on their formation mechanisms and the interactions between the subsurface ocean and the surface. The orientation and position of lineaments is also important for determining the stress field on Europa. The Europa Clipper mission is planned to launch in 2024 and will fly by Europa more than 40 times. In the light of this, an autonomous lineament detection and segmentation tool would prove useful for processing the vast amount of expected images efficiently and would help to identify processes affecting the ice sheet. </p><p>We have trained a convolutional neural network to detect, classify and segment lineaments in images of Europa returned by the Galileo mission. The Galileo images that make up the training set are segmented manually, following a dedicated guideline. For better performance, we make use of synthetically generated data to pre-train the network. The current status of the work will be described.</p>

The solid-state imaging experiment onboard the Galileo mission returned around 700 images of Jupiter’s icy moon Europa [1]. These images revealed a young surface that seems to have undergone resurfacing processes, mainly caused by ridges that overprint older ridged terrains [2]. Tidal stress fields from resonances with other Galilean moons and non-synchronous rotation seem to drive geophysical surface processes. Although the Galileo images have undergone substantial study, formation mechanisms of linear surface features and connected to that, the thickness of the ice layer, are not well constrained, but many hypotheses are proposed [3]. However, a statistical analysis of linear surface features in terms of photometric properties has not yet been done. With this work, we aim to provide a deeper understanding of geophysical processes on the surface of Europa. Furthermore, it is valuable for future mission design and planning, e.g. for the upcoming Europa Clipper mission [4], to find places that show anomalies or that would benefit from further investigations. We analyse manually segmented linear surface features in selected Galileo images of intermediate resolution (150 - 600 m/px). The surface feature categories we investigate are 1) bands, 2) double ridges, 3) ridge complexes and 4) undifferentiated lineae. Additionally, we also segment cusps, which indicate cycloidal features. Since the cross-cutting relationships are preserved during segmentation, we can gain insights into the geological history. With these segmentations, we can retrieve the length, width and the main direction of each linear feature, while taking the number of overprints into account, in order to analyse the tidal stress field and its development over time. We look into differences in radiance between the different linear surface features with respect to the geological history to learn about endogenic and exogenic processes. More specifically, we extract radiance profiles along the direction of maximal change. For double ridges for example, we extract a w-shaped profile that let’s us investigate symmetry and differences between instances of double ridges. These analyses could turn out useful in constraining formation mechanisms for linear surface features and in reconstructing the geological history of Europa’s surface. The current status of our work is presented. References: [1] Belton, M. J. S., et al., The Galileo solid-state imaging experiment, Space Sci. Rev., 60, No. 1/4, 413-455. [2] Greeley, R., et al., Europa: Initial Galileo Geological Observations, Icarus, Vol. 135, No. 1, 4-24, 1998 [3] Daubar, I., et al., Planned Geological Investigations of the Europa Clipper Mission, in prep. [4] Richey, C., et al., The Europa Clipper Mission: Science Objectives and Mission Status Update, AGU Fall Meeting Abstracts, 2018

The Io Volcano Observer (IVO) is a proposed NASA Discovery-class mission (currently in Phase A), that would launch in early 2029, arrive at Jupiter in the early 2033, and perform ten flybys of Io while in Jupiter's orbit. IVO's mission motto is to 'follow the heat', shedding light onto tidal heating as a fundamental planetary process. Specifically, IVO will determine (i) how and where heat is generated in Io's interior, (ii) how heat is transported to the surface, and (iii) how Io has evolved with time. The answers to these questions will fill fundamental gaps in the current understanding of the evolution and habitability of many worlds across our Solar System and beyond where tidal heating plays a key role, and will give us insight into how early Earth, Moon, and Mars may have worked. One of the five key science questions IVO will be addressing is determining Io's mass loss via atmospheric escape. Understanding Io's mass loss today will offer information on how the chemistry of Io has been altered from its initial state and would provide useful clues on how atmospheres on other bodies have evolved over time. IVO plans on measuring Io's mass loss in situ with the Ion and Neutral Mass Spectrometer (INMS), a successor to the instrument currently being built for the JUpiter Icy moons Explorer (JUICE). INMS will measure neutrals and ions in the mass range 1 – 300 u, with a mass resolution (M/ΔM) of 500, a dynamic range of > 105, a detection threshold of 100 cm–3 for an integration time of 5 s, and a cadence of 0.5 – 300 s per spectrum. In preparation for IVO, we model atmospheric density profiles of species known and expected to be present on Io's surface from both measurements and previous modelling efforts. Based on the IVO mission design, we present three different measurement scenarios for INMS we expect to encounter at Io based on the planned flybys: (i) a purely sublimated atmosphere, (ii) the 'hot' atmosphere generated by lava fields, and (iii) the plume gases resulting from volcanic activity. We calculate the expected mass spectra to be recorded by INMS during these flybys for these atmospheric scenarios.

Navigation of deep space probes is most commonly operated using the spacecraft Doppler tracking technique. Orbital parameters are determined from a series of repeated measurements of the frequency shift of a microwave carrier over a given integration time. This study addresses the work that is done on Doppler orbit determination of MPO - one of the two spacecraft of the European Space Agency’s BepiColombo mission- using Bernese software. For modelling the orbit of MPO around Mercury, we use a full force model, including Mercury gravity field GGMES-100V07 (up to degree and order 50), solid tides and third body perturbations. We also have an extensive modelling of non-gravitational forces that act on the orbit of spacecraft. This modelling includes the solar radiation pressure and planetary IR and albedo radiation together with a 33-plates macromodel of MPO. We propagate the orbit using this force model. Our simulations of Doppler tracking measurements include 2-way X-band and K-band Doppler measurements, station and planetary eclipses and the relativistic corrections. The imperfect knowledge of the non-gravitational forces due to the proximity of Mercury to the Sun, together with the effect of desaturation maneuvers uncertainties, makes the use of the accelerometer necessary. Therefore, in our modelling of the orbit recovery, the models for the non-conservative forces were replaced by the noisy simulated accelerometer measurements. We find out that the modelling of the accelerometer noise has a huge impact on the results of the POD. We perform several orbit reconstruction tests using daily arcs with noise modulated Doppler data with different settings on the arc lengths, arcs initial conditions, dynamical model, observation mode and orbit determination process and we solve for the initial state vector of each arc. We also run sensitivity analysis with respect to the different accelerometer model. The final goal of this study is to provide an independent solution for the precise orbit determination of Mercury planetary orbiter (MPO) using the planetary extension of the Bernese GNSS software. We present out latest results and then compare our results with the existing ones from the MORE team.

Introduction: Surface processes driven by carbon dioxide sublimation and condensation are well documented in the high latitude and polar regions of Mars [1-3] and are closely tied to the seasonal exchange of CO2 between the Martian surface and atmosphere [4]. Similarly, it is suggested that a diurnal CO2 cycle is possibly responsible for formation of enigmatic slope streaks in the low thermal inertia regions [5]. This season-independent model suggests that CO2 frost growth is active in dusty equatorial and mid latitudes, where night temperatures are low enough for CO2 to condense. It is estimated that, at sunrise, carbon dioxide on the surface will sublimate in seconds to several tens of minutes. This diurnal sublimation and condensation cycle would prevent soil induration and increase regolith porosity, which drives avalanching, fluidization and dust gardening effects. However, no observational evidence of a diurnal CO2 frost cycle exists, due to the physical and technical limitations of the imaging instruments currently in orbit around Mars. First, a non-Sunsynchronous orbit is required to observe a location at different times throughout the Martian day. Further, optical instruments rely on light reflected from the surface to achieve a high enough signal-to-noise ratio, so dawn observations are difficult. In this study, we present new early morning observations at the equatorial and low latitude regions of Mars, taken by The Colour and Stereo Surface Imaging System (CaSSIS) [6] onboard the ExoMars Trace Gas Orbiter (TGO). TGO is in a non-Sun-synchronous orbit, therefore, CaSSIS can monitor surface changes at varying local solar times (LST), returning to approximately the same location every 30 days. CaSSIS also has an excellent absolute calibration and is sensitive enough to maintain good SNR for high incidence angle observations. Results: As of CaSSIS’ 2019-11-30 data release, 71 images with incidence angles ranging from 80° to 90° were acquired in regions predicted by Piqueux et al (2016) to include CO2 frost at sunrise (see Fig. 1). 19 of those 71 observations have incidence angles between 85° and 90°. On some images we applied a 2x2 binning algorithm, which increases the SNR by a factor of 2. All of these images are single observations without repeated coverage yet. An example of a high incidence angle (88.2°) target is shown in Fig. 2. This color image was taken with 3 CaSSIS filers (BLU, PAN and NIR), and corresponds to an early Martian morning, around 10 minutes after sunrise. Visual inspection does not reveal CO2 frost, however, in-depth photometric analysis is currently ongoing. Future Work: Repeated observations of the locations shown in Fig. 1 are planned. By comparing them with ones taken later during the day, spectral analysis of the color band ratios will allow us to identify the possible presence of CO2. Also, more observations are expected at high incidence angles just before dawn >90° (night). At incidences angles of and above 90° the local surface is diffusely illuminated by aerosols, which makes spectral identification rather difficult. CO2 frost is predicted to survive from seconds to several tens of minutes in the areas outlined in Fig. 1 [5], hence, several observations with varying parameters are needed. Another alternative idea is to target higher elevation targets where CO2 is predicted to be thicker and long lasting. Furthermore, the CaSSIS database includes only a few equatorial observations. These areas are also known for slope streak activity [7].

Introduction: The ExoMars Trace Gas Orbiter (TGO) was launched on 14 March 2016 and entered Mars orbit on 19 October 2016. The spacecraft reached its primary science orbit (360 km x 420 km; inclination = 74°) on 9 April 2018. TGO carries a high-resolution colour and stereo camera system: the Colour and Stereo Surface Imaging System (CaSSIS) [1]. The objectives of CaSSIS are to (1) characterise sites on the Martian surface which have been identified as potential sources of trace gases, (2) investigate dynamic surface processes (e.g. sublimation, erosional processes, volcanism) that may help to constrain the atmospheric gas inventory, and (3) certify potential future landing sites by characterising local slopes (down to ~10 m). The instrument capabilities include acquisition of images (1) at scales of ~4.5 m/px, (2) in 4 broad-band colours optimised for Mars photometry, (3) with swathes up to 9.5 km in width, and (4) with quasisimultaneous stereo pairs over the full swath width for high res. digital terrain models. A full instrument description is provided in [2], and details about the ground calibration in [3]. Spectral-image simulations to assess the colour and spatial capabilities of CaSSIS are in [4], with recommended colour display combinations given in [5]. Photometric correction of instrument data is presented in [6]. Although the spacecraft orbit inclination is only 74 deg, this still allows observations of seasonal processes as well as layered terrains in, for example, the Ultima Lingula formation. CaSSIS observations at high latitudes will be discussed. The European Space Agency has recently issued a call for “White Papers” for future mission concepts and ideas across the science community. Martian climate studies featured significantly in the responses to this call. The options for ESA (including the possibilities for collaboration with NASA) will be discussed. We include additional details on these two aspects.

We have determined the dust coma brightness ratio between the dayside and the nightside (DS:NS) in OSIRIS images of comet 67P/Churyumov-Gerasimenko and compared them to results from numerical dust coma simulations to learn more about the dynamic processes that are involved in coma formation. The primary focus of this paper lies in the analysis of a subset of OSIRIS images acquired during one comet rotation on 11. April 2015 when the spacecraft was at a phase angle of 90 degrees and therefore directly above the terminator. The DS:NS ratio was found to be 2.49 +/- 0.18 on average - a very low value if insolation-driven sublimation of water dominates dust emission. We investigated two possible hypotheses: First, the influence of direct activity from non-illuminated (nightside) areas of the comet and second, the brightness contribution of large gravity-dominated particles in the innermost coma. For our numerical simulations, we used a combination of DSMC gas dynamics simulation and particle propagation by an equation of motion to simulate the dust coma. Our simulations show that direct activity from the nightside is preferred, contributing approximate to 10% of the total emission. We show that intensity profiles, used to quantify dust outflow behaviour, fit the observations better when nightside activity is present and we suggest that nightside gas emission by CO2 or CO is responsible for the observed dust flux. With the help of a simplified Keplerian modelling approach we exclude large particles on gravitationally bound or ballistic orbits from being the major contributor to the observed dust coma brightness. Additionally, we show the DS:NS ratio as a function of days to perihelion and observe that it is on a similar level as in the April OSIRIS time series from February to mid-June 2015, but increases towards a maximum of >= 4.07 +/- 0.49 shortly after perihelion passage. We suggest that this is correlated to the increasing importance of H2O production when approaching perihelion.

DATA PRODUCTS AND THEIR USE FOR SCIENTIFIC INVESTIGATIONS. L.L. Tornabene1, N. Thomas2, G. Cremonese3, M. Almeida2, S. Douté4, P. Grindrod5, R. Heyd6, A. Luchetti3, A. McEwen6, M. Pajola3, J. Perry6, E. Pilles1, A. Pommerol2, M.R. Read2, F. Seelos7, and J. Wray8 and the CaSSIS science & ops teams, 1CPSX, Earth Sci., Western University, London, Canada (ltornabe@uwo.ca), 2Physikalisches Institut, Univ. Bern, Bern, Switzerland, 3INAF, Osservatorio Astronomico di Padova, Padova, Italy, 4Laboratoire de Planétologie de Grenoble, Saint Martin-d’He`res, France, 5Earth Sci., Natural History Museum, London, UK, 6LPL, Univ. of Arizona, Tucson, AZ, 7JHU/APL, Laurel MD, 8Earth & Atmos. Sci., GIT, Atlanta, GA. Introduction: The Colour and Stereo Surface Imaging System (CaSSIS) is a full-colour visible to near-infrared (VNIR) bi-directional pushframe stereo camera onboard the ExoMars 2016 Trace Gas Orbiter (TGO) [1]. CaSSIS provides colour surface images with four broadband colour filters optimized for Mars photometry (Table 1.) and generally £ 9.5 km wide and ~30-40 km long; images are acquired at ~ 4.5 m/px resolution from TGO’s nearly circular ~360 km x 420 km orbit and are resampled to 4 m/px. TGO’s orbit is not Sun-synchronous due to an inclination of 74° [1]. Therefore, CaSSIS images the surface at different local solar times (LSTs), covering a wider range of observation geometries than previous Mars imagers, and includes very low phase for optimal surface colour/spectral contrast. The combination of fixed pointing at ~10° off nadir and a rotation mechanism are used to acquire stereo images in a single pass over the target [1]. TGO is currently permitted to roll up to a maximum of 5° to facilitate the targeting of key locations on the surface by CaSSIS.