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Chaos terrains are geologically young and extensively disrupted surface features of Europa, thought to be an expression of the subsurface ocean interacting with the surface. The most prominent examples of this terrain on Europa are Conamara Chaos, and Thera and Thrace Maculae, all prime targets for the upcoming JUICE and Europa Clipper missions to assess the astrobiological potential of Europa. Of the three features, Thrace Macula is currently the least studied and understood. It intersects both Agenor Linea to the north and Libya Linea to the south, two important regional-scale bands whose interaction with Thrace is yet to be fully unraveled, especially in terms of their relative ages of emplacement and activity. Through detailed structural mapping using Galileo Solid State Imager data and terrain analysis on Digital Terrain Models, we here develop a novel hypothesis on the mechanisms that have been involved in the study area. We find that Thrace Macula is bordered along most sides by preexisting strike-slip faults that have constrained its emplacement and areal distribution. We determine a sequence of events in the area involving the formation of Agenor Linea, followed by that of Libya Linea first and Thrace Macula later, and ultimately by strike-slip tectonic activity driven by Libya Linea and displacing a portion of Thrace Macula. Therefore, Thrace’s subsurface material, uprising along faults postdating its formation, likely represents the freshest possible that could be sampled by future spacecraft in this region, a major consideration for the upcoming Europa Clipper mission.

International audience; INTRODUCTION: Organic compounds in asteroids and comets contain information about the early history of the Solar System. They could also have delivered organic material to early Earth. The Hayabusa2 spacecraft visited the carbonaceous asteroid Ryugu and collected samples of its surface materials, which were brought to Earth in December 2020. RATIONALE: We investigated the macromolecular organic matter in the Ryugu samples, measuring its elemental, isotopic, and functional group compositions along with its small-scale structures and morphologies. Analytical methods used included spectro-microscopies, electron microscopy, and isotopic microscopy. We examined intact Ryugu grains and insoluble carbonaceous residues isolated by acid treatment of the Ryugu samples. RESULTS: Organic matter is abundant in the Ryugu grains, distributed as submicrometersized organic grains and as organic matter dispersed in matrix. The Ryugu organic matter consists of aromatic carbons, aliphatic carbons, ketones, and carboxyls. The functional group

Faults and fractures may emplace fresh material onto Europa's surface, originating from shallow reservoirs within the ice shell or directly from the subsurface ocean. Ménec Fossae is a region of particular interest as it displays the interaction of several geological features, including bands, double ridges, chaotic terrains, and fossae, within a relatively small area. These features might affect the emplacement of buried material and subsequent exposure of fresh volatiles, prime targets for the upcoming JUICE and Europa Clipper missions in order to assess Europa's astrobiological potential. Previous studies have already revealed that a deep central trough is present at Ménec Fossae, flanked by several subparallel minor troughs and by a few asymmetrical scarps with lobate planforms. The presence of such features has motivated this study, given its potential to provide clear indications on the tectonic regime involved. Through detailed geomorphological-structural mapping using Galileo Solid State Imager data and terrain analysis on Digital Terrain Models, we could develop a novel hypothesis on the formation mechanisms that might have been involved in the study area. We propose that Ménec Fossae has been shaped by transtensional (strike-slip with an extensional component) tectonic activity, as indicated by the orientation and relationship of the tectonic features present. Likely, such transtensional tectonism occurred above or associated with shallow subsurface water, consistent with the overall morphology and topography of the study area and the presence of chaotic terrains and double ridges. These results strengthen the case for widely distributed shallow water reservoirs within Europa's ice shell.

Introduction While the single image coverage of the currently available Context Camera (CTX, [1]) images converges to the full coverage of the surface of Mars, the individual images show offsets of tens to hundreds of pixels from their real ground position. Current efforts for ortho-rectification and lateral control use the MOLA data as a source for global reference and geometric correction (e.g., [2]). Towards the equator this approach is unprecise due to the large discrepancy of the spatial resolutions of the two datasets (6 m/px vs.463 m/px). Automatic point matching of image pixels to DTM pixels are not reliable, therefore usually the CTX pixels are matched to imagery datasets which are themselves controlled to MOLA, such as the THEMS IR dataset [3]. This of course is sensitive to error propagation. The HRSC team expects to finalise the creation of global mosaics consisting of bundle-block-adjusted DTMs and their corresponding image mosaics [4] by the end of the year 2023. These DTMs provide an internal photogrammetric precision better than the 50 m used as the grid size. The deviations from the MOLA profile heights are also less than this single pixel resolution value [5]. Their corresponding image mosaics provide precise pixel-by-pixel alignment to the respective DTM in 12.5 m/px resolution [6]. Here we show a first approach using these HRSC products as the global reference dataset for Mars, by creating a CTX quadrangle mosaic with absolute geodetic control to HRSC (and therefore also to MOLA). Methods Generally, first the HRSC DTM is used for the ortho-rectification of the CTX images instead of MOLA. After this geometric correction, the image mosaic is used as a reference for automatic point matching and co-registration. We then apply the well-established brightness correction in a similar way we are using it for HRSC [6]. Ultimately, we combine the multitude of images from a whole quadrangle together to a seamless mosaic and export it as a single image file. The general workflow of our processing pipeline is shown in Fig. 1. Figure 1: Flow chart of the proposed CTX processing workflow from single images to a complete mosaic. Owed to the large amount of single CTX images per HRSC tile, we use a database management system (DBMS) for storage and retrieval of the CTX data catalog. In the spatially-enabled DBMS we perform geometric queries by intersection with the HMC30 boundary with the CTX footprints. The map-projection and co-registration of the data is slow - processing time can be significantly increased by high-performance computing (HPC). We define the main tasks as array jobs: The ISIS [7] processing pipeline performs image ortho-rectification using the HMC30 DTM. The resulting nominally ortho-rectified CTX images show a significant offset to HRSC based on inaccurate spacecraft attitude control (see Fig. 2 left). For correction, we introduce a subsequent co-registration based on a phase correlation approach [8]. The consecutive brightness correction uses the same HRSC image mosaic as a radiometric reference. A final step for seamline creation and image export is performed outside of the cluster using Desktop GIS software. Figure 2: Image offsets between CTX image D02_027799_1580 (6.25 m/px) and HRSC HMC30 20W (12.5 m/px); left: CTX with nominal pointing after ISIS standard processing, offsets in red; middle: CTX co-registered to HRSC by global x/y shift, offsets in blue; right: CTX co-registered by warping to dense network of tie points, no visible offsets. Results In a first qualitative assessment of dividual single CTX images, we examined the pixel offsets between the nominal images and their co-registered counterparts. First we tried to translate the images only in x/y direction as a block, but there were significant remaining offsets, increasing in the along-track direction of the spacecraft (see Fig. 2 middle). We achieved better results by transforming the CTX image to the HRSC reference image by the use of a dense network of tie points (see Fig. 2 right). In the example given in Figure 2, the offsets measure about 170 m which corresponds to 27 CTX pixels, 13 HRSC image pixels and 3 HRSC DTM pixels. Based on the processing pipeline described above, we created a complete CTX mosaic of the HMC-20W quadrangle, which will be available on our mapserver (https://maps.planet.fu-berlin.de). The ISIS processing steps were successfully applied to all of the 2062 images intersecting the DTM boundary, and 1692 of the images were successfully co-registered to the HMC30 image mosaic. The processing of the complete CTX dataset consisting of 2062 single images with a resolution of 6.25 m/px took around 3 days on the cluster, but this time is highly dependent on the cluster utilization. Discussion The results of the co-registration with a success rate of 82% are better than we initially expected. The remaining visible image gaps might be filled either by adapted parameters for co-registration or by the addition of manual tie-points. The initial offsets between the nominally-processed CTX images and the HRSC DTM (3 pixels in our example) might be large enough to expect impacting geometric artifacts during the orthorectification process, which will not be removed by the co-registration. Therefore it is planned to include an additional iterative processing step by feeding the tie-points acquired from the co-registration back into the ISIS pipeline and perform a bundle-adjustment between the CTX image and HRSC as ground and height reference. Acknowledgements This work is supported by the German Space Agency (DLR Bonn), grant 50OO2204, on behalf of the German Federal Ministry for Economic Affairs and Climate Action. We thank the HPC Service of FU for computing time [9]. References [1] M. C. Malin et al., JGR Planets (E5 2007). [2] J. L. Dickson et al., LPSC 49, #2480. [3] S. J. Robbins et al., LPSC 52, #2066. [4] K. Gwinner et al., EPSC/DPS 13, 2019, #2006. [5] K. Gwinner et al., PSS 126 (2016). [6] G. G. Michael et al., PSS 121 (2016). [7] T. Sucharski et al. (2020), DOI: 10.5281/zenodo.3962369. [8] Q. Chen et al., IEEE TPAMI 16 (1994), pp. 1156–116. [9] L. Bennett et al. (2020), DOI: 10.17169/refubium-26754.

Direct link to the interactive map: https://maps.planet.fu-berlin.de/jezero Introduction: We welcome you to explore the landing site of the Mars 2020 Perseverance rover in an interactive hiking map loaded with orbital imagery, terrain data and virtual 3D panoramic views of Jezero crater and its surrounding area! The map allows fast zooming and panning for the exploration of the available data in several magnitudes of scale levels from far away until centimeter detail. It also seamlessly integrates several waypoints with pre-rendered virtual 360° panoramas and several real panoramas each stitched together from a multitude of single images of the MastcamZ instrument. System Design: The general architecture follows the principles used for the HRSC Mapserver [1], see Figure 1. In contrast to the Mapserver’s intended use as a science-based data-portal and dissemination platform, the Jezero map was also planned as an public outreach application. But it serves as the first prototype of a next-generation infrastructure for disseminating upcoming data products from Freie Universität. Major parts of the existing set-up could be re-used but had to be updated. The layer menu had to be completely re-designed as it was implemented statically and hard-wired into the main code, which made it impossible to maintain and update its module dependencies. The most fundamental changes to the HRSC Mapserver are: Integrated A-Frame panoramic views, enabled switching between map views and 3D/VR/AR scenes Sidebar element for improved user experience on mobile devices and small screens, by Tobias Bieniek (https://github.com/Turbo87/sidebar-v2) LayerSwitcher element integrated into the sidebar, by Matt Walker (https://github.com/walkermatt/ol-layerswitcher) Transition from OpenLayers 3 to OpenLayers 5 involving a major migration from the underlying Google™ Closure compiler infrastructure to ES-based modules Usage of the Parcel packager to bundle the application for production IAU2015-based Mars spatial reference system as the base reference Figure 1: Flow chart of the web-GIS application’s general system design outlining front-end (client) and back-end (server) components. Data: The base layer of the customized map consists of a merged data-set from three different instruments. The Mars Express High-Resolution Stereo Camera (HRSC, [2]) Mars-Chart 30 data [3] are used as reference data-sets providing the geodetically controlled topography base and the seamless base imagery covering the complete landing site. 33 single images of the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX, [4]), empirically corrected for their inherent ”smile” effect and bundle-adjusted with absolute geodetic control to the HMC-13E tile [5]. The single CTX images have then been radiometrically normalized using the HMC13 tile as brightness reference with the well-established methods from [6], re-implemented and adapted to CTX. To provide the orbital image data from the landing site in the highest available detail, we included image and topography data from the MRO High Resolution Imaging Science Experiment (HiRISE, [7]). We use the ortho-rectified image mosaic provided by the Terrain Relative Navigation (TRN) team of the JetPropulsion Laboratory (JPL) [8], which provided sufficient alignment to the underlying CTX and HRSC reference data. All three data-sets have been colourised by the HRSC color channels using pan-sharpening techniques and logarithmically stretched to Byte format. Outlook: The new web-GIS client presented here will also serve as the prototype for the re-design of the HRSC Mapserver for data dissemination and download. Its unique features for single image visualization and download will be re-implemented and integrated into the new design. It will serve more image data products for time-series analysis and vizualitation, mainly the complete co-registered set of CTX images. Figure 2: Jezero front-end showing the inflow-channel Neretva vallesJezero delta as a map frame. The droplet icons are clickable and switch the interface from the web-based view to the 3D-virtual panorama view as seen in Figure 3. Figure 3: Jezero front-end showing the 3D-virtual panorama view of the ”Pliva Vallis” outflow channel. The underlying A-Frame library allows 360 degree-orientation in 3D or VR. Acknowledgements: This work is supported by theGerman Space Agency (DLR Bonn), grant 50OO2204, on behalf of the German Federal Ministry for Economic Affairs and Climate Action. References: [1] S.H.G. Walter et al., ESS 7 (2018). [2] R. Jaumann et al., PSS 55 (2007). [3] K. Gwinner et al., PSS 126 (2016). [4] M. C. Malin et al., JGR Planets (2007). [5] A. Neesemann et al., LPSC 52, 2021, #2509. [6] G. Michael et al., PSS 121 (2016). [7] A. S. McEwen et al., JGR Planets (2007). [8] R. L. Fergason et al., LPSC 51, 2020, #2020.

After 18 years in orbit Mars Express remains one of ESA’s most scientifically productive Solar System missions, with a publication record now exceeding 1450 papers. Characterization of the surface geology on a local-to-regional scale by HRSC, OMEGA and partner experiments on NASA spacecraft has allowed constraining land-forming processes in space and time. Recent studies characterized the geology of Jezero crater in great detail and provided Digital Elevation Model (DEM) of several equatorial regions at 50 m/px resolution. New maps and catalogues of surface minerals with 200 m/px resolution were released. MARSIS radar published new observations and analysis of the multiple subglacial water bodies underneath the Southern polar cap. Modelling suggested that the “ponds” can be composed of hypersaline perchlorate brines.Spectrometers and imagers SPICAM, PFS, OMEGA, HRSC and VMC continue adding to the longest record of atmospheric parameters such as temperature, dust loading, water vapor and ozone abundance, water ice and CO2 clouds distribution and observing transient phenomena. More than 27,000 ozone profiles derived from SPICAM UV spectra obtained in MY#26 through MY#28 were assimilated in the OpenMARS database. A new PFS “scan” mode of the spacecraft was designed and implemented to investigate diurnal variations of the atmospheric parameters. Observations of Tharsis region and Hellas basin contribute to mesoscale meteorology.ASPERA measurements together with MAVEN “deep dip” data enabled assessment of the conditions that lead to the formation of the dayside ionopause in the regions with and without strong crustal magnetic fields suggesting that the ionopause occurs where the total ionospheric pressure (magnetic + thermal) equals the upstream solar wind dynamic pressure.In 2021 Mars Express successfully performed two types of novel observations. In egress-only radio-occultations a two-way radio link was locked at a tangent altitude of about 50 km. This is well below the ionospheric peak and would allow perfect sounding of the entire ionosphere thus doubling the number of ionospheric soundings. MEX and TGO performed several test UHF occultations. The dual-spacecraft radio-occultation technique would allow much broader spatial distribution of the missions’ radio occultation profiles. Mars Express is extended till the end of 2022. A science case for the mission extension till the end of 2025 will be developed and submitted in March 2022. The talk will give the Mars Express status, review the recent science highlights, and outline future plans including synergistic science with TGO and other missions.

Context. After landing on C-type asteroid Ryugu, MASCOT imaged brightly colored, submillimeter-sized inclusions in a small rock. Hayabusa2 successfully returned a sample of small particles from the surface of Ryugu, but none of these appear to harbor such inclusions. The samples are considered representative of Ryugu. Aims. To understand the apparent discrepancy between MASCOT observations and Ryugu samples, we assess whether the MASCOT landing site, and the rock by implication, is perhaps atypical for Ryugu. Methods. We analyzed observations of the MASCOT landing area acquired by three instruments on board Hayabusa2: a camera (ONC), a near-infrared spectrometer (NIRS3), and a thermal infrared imager. We compared the landing area properties thus retrieved with those of the average Ryugu surface. Results. We selected several areas and landforms in the landing area for analysis: a small crater, a collection of smooth rocks, and the landing site itself. The crater is relatively blue and the rocks are relatively red. The spectral and thermophysical properties of the landing site are very close to those of the average Ryugu surface. The spectral properties of the MASCOT rock are probably close to average, but its thermal inertia may be somewhat higher. Conclusions. The MASCOT rock can also be considered representative of Ryugu. Some of the submillimeter-sized particles in the returned samples stand out because of their atypical spectral properties. Such particles may be present as inclusions in the MASCOT rock.

Introduction The formation of Ganymede’s light terrain and its possible interaction with a subsurface ocean, have made its investigation one of the top goals of the upcoming JUICE mission [1, 2]. In this study we present a detailed stratigraphic analysis of areas that were observed by the Galileo SSI camera at highest possible spatial resolution (scales of ~11 m/pxl) in order to see what information of the light terrain’s stratigraphic position in Ganymede’s surface evolution can be gained from mapping and crater counting results and to identify what still has to be done in order to prepare for the upcoming JUICE mission. Study areas Based on the available data set, we selected four major regions (Region A, B, C and D) that are covered by more than one high-resolution SSI image for our study (Fig. 1): Region A and D from the anti-Jovian hemisphere and Region B and C from sub-Jovian hemisphere. Region A comprises of Byblus Sulcus (G2GSGRVLNS01), Nippur and Philus Sulcus (G2GSNIPPUR01) and the Transitional region (G2GSTRANST01) with the context info provided by the SSI observation G8GSREGCON01. Region B is dominated by Arbela Sulcus (28GSARBELA01+02/ G7GSNICHOL01), Region C is the Harpagia Sulcus region (28GSBRTDRK02, 28GSCALDRA02 and 28GSSMOOTH02) and Region D comprises Erech Sulcus (G8GSERECH01), Mummu and Sippar Sulci (G8GSCALDRA01). Mapping results Geologic maps are prepared for the four regions using ArcGIS. The naming/categorization of geological units follows from [4, 5] but are refined and modified wherever necessary (Fig. 2). Among the light terrain units, ls and lg are the most commonly occurring than li. Stratigraphic correlation: On the whole, the relative ages from crater density measurements (Fig. 5) follow the mapping results. In brief, in Byblus Sulcus the two light terrain units are of similar age from crater counts while lg3 is younger than lg2 from crosscutting relationships. (Fig. 2). In case of Region B (Arbela Sulcus), we could find that the age relationship of the two light terrain units and two dark terrain units agree with the relative age inferred from crosscutting relationship (Fig. 3a) In more extensively resurfaced areas of the light terrain the situation appears to be more complex. In Region C, the terrain units ls also have comparatively higher age than lg terrain units (Fig. 3b-3d). In Region D the terrain units (Fig. 4) are highly interrupted by the secondary craters formed during the Osiris and Melkart impact events [6]. Discussion We used two most favored chronology models LDM (Lunar Derived Model by [7]) and JCM (Jupiter Comets Model by [8]) (Fig.6). In general, based on the LDM ages the crater densities point to a relatively high age of the light terrain units not much younger that the ancient dark terrain and could imply a relatively short time period of formation for most of our mapped light terrain units. This relatively high age fits into the theory that the light terrain could have formed as a direct result of internal differentiation followed by a global expansion [9]. On the contrary, the JCM derived ages point to a longer formation period of light terrain units around 2 Ga [9]. While the impact chronology in the Jovian system and of its satellites is still not fully solved, newest results infer that the craters on these bodies were created from members of a collisionally evolved impactor family, similar to those in the inner solar system [10]. This does not straightforwardly support the lunar-derived chronology model (LDM) by [7] but allows to derive a Ganymede-specific crater production function empirically from the lunar one. We used this production function to fit our crater distributions and to derive absolute model ages for both model chronologies [7][8]. Figure 1: Regions of Interest in this study with the available Galileo SSI coverage indicated. Figure 2: Geologic mapping results for Region A: a) Byblus Sulcus (G2GSGRVLNS01), b) Nippur and Philus Sulcus (G2GSNIPPUR01) and c) the Transitional region (G2TRANST01). The legend applies also to Figures 3 and 4. Figure 3: Geologic mapping results for Region B dominated by Arbela Sulcus (28GSARBELA01+02/ G7GSNICHOL01) and Region C by Harpagia Sulcus (b) 28GSBRTDRK02, c) 28GSCALDRA02 and d) 28GSSMOOTH02). Figure 4: Geologic mapping results for Region D comprises of a) Erech (G8GSERECH01) and b) Mummu and Sippar Sulci (G8GSCALDRA01). Figure 5: Comparison of relative ages of different terrain units from a) Region A (Byblus Sulcus), b) Region B (Arbela Sulcus), c) Region C (Harpagia Sulcus - 28GSBRTDRK02) and d) Region D (Erech Sulcus) based on crater size frequency distributions. Figure 6: Stratigraphic correlation of Region a) A, b) B, c) C and d) D in which relative ages are determined by plotting the N(10) values with respect to each terrain units and corresponding ages based on LDM [7] and JCM [8]models. Please note that ages of fresh impact craters such as Nergal (N), Kittu (K), Enkidu (E), Melkart (M) and Osiris (O) have been added as additional stratigraphic markers. Since terrain types often appear more than one time in a geologic map the different facies are indicated by different colors. References: [1] Grasset, O., et al.: Planetary and Space Science, 78, 1-21, 2013. [2] Stephan, K., et al.: Planetary and space science, 208, 105324, 2021. [3] Pappalardo, R. T., et al.: Jupiter: The Planet, Satellites and Magnetosphere, 363-396, 2004. [4] Collins, G.C., et al.: Global geologic map of Ganymede (p. 3237), US Geological Survey, 2013. [5] Patterson, G. W. et al.: Icarus, 207, 845-867, 2010. [6] Baby, N. R., et al.: LPI Contributions, 2678, abstr. #1350, 2022. [7] Neukum, G., et al.: LPSC XXIX, abstr. #1742, 1998. [8] Zahnle, K., et al.: Icarus 163, 263-289, 2003. [9] Bland, M. T. et al. : Icarus 200, 207- 221, 2009. [10] Bottke et al.: LPSC, #2638, 2022.

Perseverance’s Mastcam-Z instrument provides high-resolution stereo and multispectral images with a unique combination of spatial resolution, spatial coverage, and wavelength coverage along the rover’s traverse in Jezero crater, Mars. Images reveal rocks consistent with an igneous (including volcanic and/or volcaniclastic) and/or impactite origin and limited aqueous alteration, including polygonally fractured rocks with weathered coatings; massive boulder-forming bedrock consisting of mafic silicates, ferric oxides, and/or iron-bearing alteration minerals; and coarsely layered outcrops dominated by olivine. Pyroxene dominates the iron-bearing mineralogy in the fine-grained regolith, while olivine dominates the coarse-grained regolith. Solar and atmospheric imaging observations show significant intra- and intersol variations in dust optical depth and water ice clouds, as well as unique examples of boundary layer vortex action from both natural (dust devil) and Ingenuity helicopter–induced dust lifting. High-resolution stereo imaging also provides geologic context for rover operations, other instrument observations, and sample selection, characterization, and confirmation.

Dust and melt ponds have been studied on planetary bodies including Eros, Itokawa, and the Moon. However, depending on the nature of the regolith material properties and the location of the planetary body, the formation mechanism of the ponded features varies. On Eros and Itokawa, ponded features are formed from dry regolith materials whereas on the Moon similar features are thought to be produced by ejecta melt. On the surface of Vesta, we have identified type 1, ejecta ponds, and type 2, dust ponds. On Vesta type 1 pond are located in the vicinity of ejecta melt of large impact craters. The material is uniformly distributed across the crater floor producing smooth pond surfaces which have a constant slope and shallow depth. The hosting crater of melt-like ponds has a low raised rim and is located on relatively low elevated regions. Whereas, the type 2 ponds on Vesta reveal an undulating surface that is frequently displaced from the crater center or extends toward the crater wall with an abruptly changing slope. We suggested that for the production of the type 2 ponds, localized seismic diffusion and volatile-induced fluidization may be responsible for Vesta. Due to Vesta's large size (in comparison to Eros and Itokawa), the surface may have experienced local-scale rare high-amplitude seismic diffusion which was sufficient to drift fine material. Similarly, short-lived volatile activities were capable to transfer dusty material on to the surface. Segregation and smoothing of transferred material lack further surface activities, hindering the formation of smooth morphology.

Introduction: Observations of C-type NEAs and properties of carbonaceous chondrites indicate a high porosity of C-type asteroids. Hayabusa2 demonstrated that Ryugu is a low-density rubble-pile[1] dominated by large surface boulders[2]. Boulder thermal properties imply a microporosity of ϕboulder≈28-55%[3,4], substantially higher than for meteorites and indicative of distinct evolution for Ryugu’s parent body from that of water-rich CI/CM chondrites, despite spectral similarities. High microporosity values are consistent with a bulk density of 1190±20 kg m-3[5], a bulk porosity of ≈50%[1], and a macroporosity of ≈16%[6]. We calculated the temperature and porosity evolution for primordial planetesimals and constrained the range of parameters resulting in microporosities compatible with Ryugu’s and likely burial depths for the surface boulders. By varying the accretion time t0 and radius R and by comparing the porosity distribution with ϕboulder, hydration, and partial dehydration, we constrained a field within the (R,t0)-diagram appropriate for bodies that are likely to have produced such material. Methods: Within the sequence of the parent body evolution, a series of suggested disruption and accretion of intermediate bodies events, and the accretion of Ryugu[5], the boulder microporosity results mainly from parent body processes, e.g., 26Al-induced internal heating, hydration, compaction, and dehydration prior to the first disruption. We used global thermal evolution and compaction models[7] that predict the microporosity established due to creep processes driven by the joint action of temperature and pressure. No notable creep can be expected in late formed and small objects such as Ryugu or in intermediate objects between the first and last disruption events. Thus, we calculated the interior microporosity of primordial planetesimals with different sizes and accretion times in order to reproduce ϕboulder. Fig. 1: Final porosity profiles for R=1, 5, 10, and 100 km (left to right, top to bottom). Profiles for different accretion times are shown and compared with the ϕboulder. Results: The bulk porosity ϕbulk calculated shows that large (i.e., slowly cooling and with a higher pressure) and early accreted (i.e., 26Al-rich) planetesimals compact more efficiently, retaining only a thin porous blanket. By contrast, low-pressure small and late accreted bodies remain highly porous. While ϕbulk provides no information about the porosity distribution, it shows that intermediate conditions with a trade-off between R and t0 should result in high volume fractions of material matching ϕboulder. Of importance for the accretion of Ryugu from the rubble of a larger object is the location of such material within the parent body. The final porosity distribution is shown in Fig. 1 and compared with ϕboulder. Profiles for R=1, 5, 10, and 100 km and several accretion times shown represent different types of structures with up to three layers defined by the comparison ϕ>ϕboulder, ϕ≈ϕboulder, and ϕ<ϕboulder. Fig. 2: Volume fraction of the material with ϕ=ϕboulder. Isolines for Tmax: 273 K (onset of aqueous alteration), 873 K (serpentine dehydration), and 1450 K (onset of silicate melting). White squares correspond to bodies from Fig. 1. A likely parent body needs to have a high fraction fboulder of the material with ϕ≈ϕboulder, in particular, if materials from all depths contribute to rubble-piles produced after a disruption[5]. Fig. 2 shows that for an initial porosity of ϕ0≥0.6, diagonal maximum fields emerge for fboulder, confining objects limited by a maximum radius of ≈10 km and an accretion at 5 Myr after CAIs. Further observations to be reproduced is aqueous alteration and a partial dehydration. A first-order indicator for hydration (assumed as quasi-instantaneous[8,9]) is the water ice melting temperature that is surpassed for a variety of parameter values (Fig. 2, black dashed line), e.g., t0≲4.5 Myr for km-sized objects (an effect of the rapid decay of 26Al), and for a late accretion of larger bodies (an effect of their weaker cooling). An upper limit on the thermal conditions is post-dehydration partial melting, occurring for 1≲t0≲1.8 Myr (Fig. 2, white dashed line), that would contradict Ryugu’s composition. Thus, only the objects between the black and red lines should have experienced thermal conditions allowing for hydration, and remained cool enough not to dry out. Tmax obtained for a number of models satisfies the CI/CM alteration temperature range, while those between red and white dashed lines indicate dehydration at ≈873 K, consistent with some carbonaceous chondrites that match Ryugu spectrally[5,10]. Based on the recent detection of boulders with a porosity of 70-90%, additional calculations with an initial porosity of ϕ0=90% that goes beyond the range of 50-80% addressed initially[7] were carried out[11]. They confirm a parent body size of only a few km (Fig. 3). Fig. 3: Peak temperature (left panels) and porosity fraction (right panels) for ϕ0=90%. Porosity distribution for km is most consistent with that of the boulders on Ryugu, i.e., high abundance of boulders with 30%<ϕ0Tmax of the abundant materials is consistent with the estimated dehydration temperature and is homogeneous (≈800 K), consistent with the globally uniform spectra on Ryugu. Conclusions: Our calculations indicate a parent body of only a few km that accreted early within ≲2-3 Myr. Gradual porosity profiles of best-fit bodies indicate production of both low-and high-density boulders from one parent body. By contrast, fits of the carbonate formation data indicate a CI/CM parent body with R≈20-25 km and t0≈3.75 Myr[7], implying a population of km-sized early accreting highly porous planetesimals as parent bodies of Ryugu and a population of larger and late accreting less porous planetesimals as parent bodies of water-rich chondrites. References: [1] Watanabe S. et al. (2019) Science, 364, 268-272. [2] Michikami T. et al. (2019) Icarus, 331, 179-191. [3] Grott M. et al. (2019) NatAst, 3, 971-976. [4] Hamm M. et al. (2020) MNRAS, 496, 2776-2785. [5] Sugita S. et al. (2019) Science, 364, eaaw0422. [6] Grott M. et al. (2020) JGR, 125, e2020JE006519. [7] Neumann W. et al. (2021) Icarus, doi.org/10.1016/j.icarus.2020.114166. [8] Jones C. L. and Brearley A. J. (2006) GCA, 70, 1040-1058. [9] Neumann W. et al. (2020) A&A, 633, A117. [10] King A. J. et al. (2018) MAPS, 54, 521-543. [11] Sakatani N. et al. (2021) NatAst, https://doi.org/10.1038/s41550-021-01371-7.

著者人数: 60名 (所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 渡邊, 誠一郎; 野口, 里奈; 嶌生, 有理; 吉川, 真; 菊地, 翔太; 橘, 省吾; 石原, 吉明; 坂谷, 尚哉; 竹内, 央; 岡田, 達明; 安部, 正真; 山本, 幸生; 田中, 智; 白井, 慶; 松岡, 萌; 横田, 康弘; 山口, 智宏; 尾川, 順子; 三桝, 裕也; 高橋, 忠輝; 竹井, 洋; 藤井, 淳; 岩田, 隆浩; 早川, 雅彦; 細田, 聡史; 森, 治; 澤田, 弘崇; 嶋田, 貴信; Soldini, Stefania; 矢野, 創; 月崎, 竜童; 尾崎, 正伸; 飯島, 祐一; 藤本, 正樹; 照井, 冬人; 佐伯, 孝尚; 中澤, 暁; 津田, 雄一), Accepted: 2019-03-07, 資料番号: SA1180386000

The distinctive bright regions within Occator crater are one of the most remarkable discoveries of the Dawn mission's exploration of Ceres. The central region is named Cerealia Facula and the additional regions in the eastern crater floor are named Vinalia Faculae. Here we summarize and synthesize the results of this special issue, which aimed to identify the driving forces behind the formation of Occator and the faculae, and thus lead us to a new understanding of the processes and conditions that occurred in Ceres’ past, and potentially in its present. The investigations presented here used Dawn data, theoretical modeling and laboratory experiments to deduce the sequence of events that led to the formation of Occator, Cerealia Facula and Vinalia Faculae, which are broken into stages 1–3. Stage 1: Occator's ejecta blanket, terraces and hummocky crater floor material formed during and shortly after crater formation. These features are located in many Cerean complex craters. However, Occator also contains the lobate materials and faculae, which are unique to Occator. We interpret the lobate materials as a slurry of water, soluble salts and boulders of unmelted silicates/salts, which flowed around the crater interior before solidifying. At least portions of the lobate materials were solidified prior to the formation of the central pit, which is suggested to form via the ‘melted uplift model’ and provides insights into central pit formation across the Solar System. We propose the outer edge of Cerealia Facula formed shortly after the Occator-forming impact, via impact-induced hydrothermal brine deposition or via salt-rich water fountaining (perhaps sourced in a pre-existing reservoir). Stage 2: the majority of Cerealia Facula is located within the central pit and is interpreted to have formed later, at least ∼18 Myr after the Occator-forming impact, via multiple depositional events. The Cerealia-Facula-forming brines may have flowed out of fractures in the walls of the central pit and/or been driven to the surface by freezing of a subsurface reservoir and/or deposited via salt-rich water fountains. Further investigations are required to identify whether the formation of the majority of Cerealia Facula is driven by processes triggered by an impact, i.e. an exogenic event, or by a combination of impact-driven and endogenic processes. Cryomagmatic intrusions are suggested to uplift the crater floor, resulting in concentric floor fractures and an asymmetric dome. Injection of a similar material is proposed to inflate part of the lobate materials, giving them a hummocky texture. The resulting stresses formed fractures in the hummocky lobate material, which allowed the Vinalia-Faculae-forming brines to travel to the surface, where they ballistically erupted. The central dome within the central pit was one of the last features to form, by laccolithic intrusion, or by volume expansion from freezing of volatiles, or by extrusion of brines. Stage 3: mixing with Ceres’ average materials and/or space weathering darken the faculae over time. Cerealia Facula and Vinalia Faculae are the brightest and freshest of the bright regions identified on Ceres’ surface. Bright regions darken over time until their eventual erasure. Thus, it is likely that faculae formation has occurred throughout Ceres’ history, but that Occator's faculae are visible today because they are geologically young. Through synthesis of the studies presented in this special issue, we find that entirely exogenic driving forces, triggered by the impact, or a combination of endogenic and impact-derived forces could explain the formation of Occator and its faculae. Whether activity is impact-triggered and/or endogenic in nature is a key question for all investigations of Ceres, and future studies may favor one possibility over the other. The investigations presented in our special issue indicate Ceres is an active world where brines have been mobile in the geologically recent past. As such, Ceres is an intriguing world that we have only begun to explore.

Occator crater, a Ceres crater that hosts multiple bright spots on its floor, has several sets of fractures associated with it. A tectonic analysis of each of these fracture sets suggests that the concentric and radial fractures around the central pit and the concentric fractures high on the crater wall (near the rim) most likely formed due to well known impact cratering processes. Uplift of the crater floor due to magmatic injection is suggested to have resulted in the concentric floor fractures at the base of the crater wall, as well as the cross-cutting fractures in the lower part of the southwestern wall. A mathematical analysis shows that a cryomagmatic plume (diapir) could have both reached the height necessary to cause fracturing within Occator, and that the stresses required are reasonable. Expansion a lobate flow from beneath is proposed to have formed those linear fractures associated with the Vinalia Faculae. Circumferential fractures surrounding Occator appear to have formed due to the volumetric compaction of the ejecta blanket over the buried pre-existing topography.

Impact craters of different geological ages, sizes and morphologies are not only the most obvious surface features on Ceres’ surface. The investigation of their spectral properties in combination with Ceres’ geology and topography reveals not only lateral compositional variations in Ceres’ surface material but also possible stratigraphic differences within Ceres’ crust. Spectral properties of impact craters with different ages do show distinct trends implying variations with increasing exposure duration of the impact material onto Ceres’ surface. Local concentrations of H2O ice and carbonates are associated with the youngest, either recently emplaced or excavated, surface deposits. On the contrary, regionally higher amounts of ammoniated phyllosilicates originate from deeper regions of Ceres’ crust and strengthen the theory of ammonia being a primordial constituent of Ceres. The blue spectral slope, clearly associated with relatively weak absorptions of OH-bearing and/or ammoniated phyllosilicates, is limited to fresh impact material. Either, the blue spectral slope diminishes slowly with increasing geologic age due to space weathering processes, or shortly as a result of gravitation-induced slumping, forming a fine and loosely consolidated regolith.

The Dawn Framing Camera repeatedly imaged Ceres’ North Pole quadrangle (Ac-1 Asari, latitudes >66°N) at a resolution of ∼35 m/pixel through a panchromatic filter, enabling the derivation of a digital terrain model (DTM) and an ortho-rectified mosaic. Using this dataset, a photo-geologic map and stratigraphy, complemented with absolute model ages of impact craters, were produced. We identified the following key surface features: an ancient 4.5 km high isolated dome with a non-impact origin; recent lobate materials on crater interiors possibly formed as high-speed flows of collapsed rim material; and recent bright areas in permanently shadowed regions (PSRs), which we interpret as ice accumulation mostly by infall of exogenic material. Crater morphologies and dimensions do not differ from those in other quadrangles, suggesting the widespread influence of a rheologically weak target during the crater formation process. There is a paucity of lobate materials associated with impact cratering, in contrast to previous identifications with lower spatial resolution imagery.

Dawn is the first spacecraft to visit and orbit Ceres, the largest object in the asteroid belt and the only dwarf planet in the inner Solar System. The Dawn science team undertook a systematic geologic mapping campaign of Ceres’ entire surface. Here we present our contribution to this mapping campaign, a geologic map and geologic history of the Ezinu quadrangle, located in the northern mid latitudes from 21–66° N and 180–270° E. From our map, we reconstruct the geologic history of Ezinu quadrangle, which is dominated by impact cratering. Large impact craters that formed a few hundreds to tens of millions of years ago, such as Datan, Messor, Ninsar and Occator, are surrounded by ejecta and contain the products of mass wasting (hummocky crater floor material and talus material) and crater-wall collapse (terrace material). Two of these large impact craters are the sources of lobate flows, which we interpret as melt flows emplaced after the ballistically deposited ejecta. Morphological evidence suggests these lobate flows are rich in water–ice-bearing material that was excavated during the formation of the impact craters. There are only a few localized occurrences of lobate flows, suggesting that the water–ice-bearing source materials have restricted extents and/or are deeply buried within Ceres’ subsurface. The quadrangle also contains a variety of linear features: secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub-surface fractures. The Ezinu quadrangle contains the northern portion of Occator crater, which is the host crater of prominent bright regions called faculae. Our geologic analysis therefore also provides context for the future investigation of Occator and its intriguing faculae.

We conducted a geologic mapping investigation of Dawn spacecraft data to determine the geologic history of the Kerwan impact basin region of dwarf planet Ceres, which is mostly located in the Ac-7 Kerwan Quadrangle. Geological mapping was applied to Dawn Framing Camera images from the Low Altitude Mapping Orbit (LAMO, 35 m/pixel) and supplemented by digital terrain models and color images from the High Altitude Mapping Orbit (HAMO, 135 m/pixel), as well as preliminary Visible and Infrared Spectrometer (VIR) and gravity data. The 284-km diameter Kerwan impact basin is the oldest unequivocal impact crater on Ceres, and has a highly discontinuous, polygonal, degraded rim and contains a ‘smooth’ unit that both fills the basin floor and surrounds the degraded rim to the west, south, and east. Although there are some subtle topographic features in the Kerwan basin that could be interpreted as flow boundaries, there is no indisputable evidence of cryovolcanic features in or around the basin (however if such features existed they could be buried). Nevertheless, all data point to impact-induced melting of a cerean crust enriched in a volatile, likely water ice, to produce the Kerwan smooth material. Subsequent geologic activity in this region includes emplacement of impact craters such as Dantu, which produced a variety of colorful deposits, and rayed craters such as Rao and Cacaguat. Based on the crater size-frequency distribution absolute model ages of the Kerwan smooth material in and around the basin, marking a minimum age for the Kerwan basin, our mapping defines this as the oldest boundary within the cerean geologic timescale, separating the Pre-Kerwanan and Kerwanan Periods at > 1.3 Ga (Lunar-derived chronology model) or > 230–850 Ma (Asteroid-derived chronology model, depending on strength of target material).

Since its arrival at Ceres, DAWNs Framing Camera has been imaging the dwarf planet at different altitudes, using 8 different filters. Based on these images, global clear filter mosaics, digital terrain models, and global color mosaics were produced. These datasets are basis for the derived photogeologic map of the Ac2 Coniraya quadrangle, located between 0° and 90° eastern longitude and between 20° and 40° northern latitude. Crater size frequency distribution (CSFD) measurements have been applied to derive the stratigraphic history of the identified geologic units in the Ac2 Coniraya quadrangle. Based on these investigations, we found that the Ac2 Coniraya quadrangle shows evidence for a long geologic history lasting over 3.5 Ga. Most of the identified geologic units are related to impact cratering at different periods of time. While the oldest unit identified in the Ac2 Coniraya quadrangle, the cratered terrain, shows an absolute model age (AMA) of 3.3 to 3.5 Ga, the youngest units, including fresh impact craters and lobate flows, show AMAs of < 100 Ma. The large number of different sized impact craters excavated a variety of materials with different colors and albedo, indicative of a heterogeneous crustal composition, including water or volatiles. Pits identified at Ikapati craters smooth deposits might further indicate the presence of volatiles in the subsurface. Furthermore, our mapping of the Ac2 Coniraya quadrangle shows that possible H 2 O ice in the crust is heterogeneously distributed, as lobate flows, bright spots, and pits are only found at certain locations, related to relatively fresh impact craters.

Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high-resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant bould...

Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

21st EGU General Assembly, EGU2019, proceedings from the conference held 7-12 April, 2019 in Vienna, Austria, id.11100, After 15 years in orbit Mars Express remains one of ESA's most scientifically productive Solar System missions whose publication record now exceeds 1200 papers. Characterization of the geological processes on a local-to-regional scale by HRSC, OMEGA and partner experiments on NASA spacecraft has allowed constraining land-forming processes in space and time. Recent results suggest episodic geological activity as well as the presence of large bodies of liquid water in several provinces (e.g. Eridania Planum, Terra Chimeria) in the early and middle Amazonian epoch and formation of vast sedimentary plains north of the Hellas basin. Mars Express observations and experimental teams provided essential contribution to the selection of the Mars-2020 landing sites. Recent discovery of subglacial liquid water underneath the Southern polar cap has proven that the mission science potential is still not exhausted. More than a decade-long record of the atmospheric parameters such as temperature, dust loading, water vapor and ozone abundance, water ice and CO2 clouds distribution, collected by SPICAM, PFS, OMEGA, HRSC and VMC together with subsequent modeling have provided key contributions to our understanding of the martian climate. Recent spectroscopic monitoring of the 2018 dust storm revealed dust properties, their spatial and temporal variations and atmospheric circulation. More than 10,000 crossings of the bow shock by Mars Express allowed ASPERA-3 to characterize complex behavior of the magnetic boundary topology as function of the solar EUV flux. Observations of the ion escape during complete solar cycle revealed important dependencies of the atmospheric erosion rate on parameters of the solar wind and EUV flux and established global energy balance between the solar wind and escaping ion flow. The observations showed that ion escape can be responsible for removal of about 10 mbar over the Mars history that implies existence of other more effective escape channels. The structure of the ionosphere sounded by the MARSIS radar and the MaRS radio science experiment was found to be significantly affected by the solar activity, the crustal magnetic field, as well as by the influx of meteorite and cometary dust. MARSIS and ASPERA-3 observations suggest that the sunlit ionosphere over the regions with strong crustal fields is denser and extends to higher altitudes as compared to the regions with no crustal anomalies. Several models of the upper atmosphere and plasma environment are being developed based on and in support of the collected experimental data. The models aim at creating user-friendly data base of plasma parameters similar to the Mars Climate Database that would be of great service to the planetary community. A significant recent achievement was the flawless transition to the >gyroless> attitude control and operations mode on the spacecraft, that would allow mitigating the onboard gyros aging and extending the mission lifetime. In November 2018 ESA's Science Programme Committee (SPC) confirmed the mission operations till the end of 2020 and notionally approved its extension till the end of 2022. The talk will give the Mars Express status, review the recent science highlights, and outline future plans focusing on synergistic science with TGO.

We have analyzed mass wasting features, their distribution and deposit geometry on the two largest main asteroid belt objects—protoplanet Vesta and dwarf planet Ceres—and compared their geomorphology and mobility. Both asteroids have similar surface accelerations, but different surface compositions. Based on our observations and previous studies, we categorized three distinct morphological mass wasting classes: slumps, slides, and flow‐like movements. We conclude that Ceres has abundant features of flow‐like mass movements. Further, sliding and flow‐like characteristics are identified in craters within mid‐latitudes which supports the possibility of the presence of water ice in the near subsurface of Ceres. Vesta predominantly shows characteristics of dry granular‐like slide features which are distributed homogenously across the surface. By plotting the ratio between fall height (H) and run‐out length (L) (effective coefficient of friction, H/L) against the run‐out length and spreading width (W), we demonstrate that deposits on Vesta terminate on shorter distances, whereas on Ceres they travel longer distances. The deposit geometry and the similar surface gravity on both asteroids suggest that the material composition and volatile component have a significant effect on deposit emplacement. However, both bodies’ mass movements have similar effective coefficients of friction, even though Vesta's regolith is comparatively dry, whereas Ceres is rich in water ice. This leads to the conclusion that volatile content alone cannot be responsible for low effective coefficients of friction, and that more than one geological process is needed to explain the mass motion behavior and morphology., Plain Language Summary: Landslides are one of the most studied geological events on planetary bodies. Many scientists have contributed to a diverse database of knowledge with the aim to better understand these processes. They have been observed for various environmental conditions and are affected by gravity and the physical and chemical composition of the hosting body. However, it is challenging to delineate which specific type or morphology of landslide is sensitive to which parameter. On airless asteroids Vesta and Ceres, landslides have been well preserved, allowing for in‐depth analysis using remote sensing data. Interestingly, Vesta and Ceres’ substantially different surface compositions have a major effect on landslides, despite their similar gravity. In our study, we have examined and updated the landslide inventory on both bodies, and performed an analysis of deposit mobility which will further enhance our understanding related to the material conditions, their mobility, and surface evolution., Key Points: We classified and estimated the H/L of mass movements to investigate the mechanisms of deposition on Vesta and Ceres Vesta has dry, granular‐like slides as dominant mass wasting feature, whereas Ceres has abundant features of flow‐like mass movements The mass wasting deposit mobility is influenced by the material composition and volatile content on Vesta and Ceres

The High Resolution Stereo Camera (HRSC) of ESA’s Mars Express mission [1, 2] is still running nominally and delivering new image strips to fill remaining gaps that lead to a contiguous coverage of the Martian surface at high resolution stereo. As a push broom scanning instrument with nine CCD line detectors mounted in parallel, its unique feature is the ability to obtain along-track stereo images and four colors during a single orbital pass. Thus, panchromatic stereo and color images from single orbits of the HRSC have been used to produce digital terrain models (DTMs) and orthoimages of the Martian surface since 2004 [3].Since 2010 new HRSC multi-orbit data products have been generated, which have been developed into a global mapping program organized into MC-30 half-tiles, since 2014 [4,5]. Based on continuous coverage of an area, regional DTMs and orthomosaics can be produced by combining image data from multiple orbits using specifically adapted techniques for block-adjustment, DTM interpolation and image equalization [6]. The resulting DTMs and color orthomosaics are the baseline for a controlled topographic map series of Mars. The extents of the regional products follow the MC-30 (Mars Chart) global mapping scheme of Greeley and Batson [7]. For the generation of the DTMs and color mosaics, the MC-30 quadrangles are further divided into East (E) and West (W). In parallel to the completion of the first half-tile DTM and color mosaic (MC-11-E) we developed a concept for a topographic map series of Mars [8,9]. To limit data volumes and map sizes, each quadrangle is subdivided into eight tiles (i.e. each half-tile into four tiles). The map scale of 1:700,000 is a compromise between the high DTM and orthomosaic resolution of 50 m/pxl and an acceptable hardcopy format of about 1 m in width to 2 m in height (≜14 pxl/mm). MC-11 was selected to be produced first because it contains the finally selected landing site, Oxia Planum, of ESA’s ExoMars mission with the Rosalind Franklin rover. After MC-11, the Global Topography and Mosaics Task Group (GTMTG) of the HRSC Science Team focussed on MC-13, which hosts the landing site of the Perseverance rover from NASA’s Mars 2020 mission, Jezero crater. The next HRSC MC quadrangles will also be equatorial ones (i.e. 19 and 20).All maps are available for the public at the HRSC team website (http://hrscteam.dlr.de/HMC30/index.html).[1] Neukum, G., et al., ESA Special Publication, 1240, pp. 17-36, 2004. [2] Jaumann, R., et al., Planetary and Space Science 55, pp. 928-952, 2007. [3] Gwinner, K., et al., Earth and Planetary Science Letters, 294, pp. 506-519, 2010. [4] Gwinner, K, et al., 41st Lunar and Planetary Science Conference, #2727, 2010. [5] Dumke, A., et al., Lunar and Planetary Science Conference, #1533, 2010. [6] Gwinner, K. et al., Planetary and Space Science, 126, pp. 93-138, 2016. [7] Greeley, R. and Batson, G., Planetary Mapping, Cambridge University Press, Cambridge, 1990. [8] Schulz, K., Bachelor Thesis, Beuth Hochschule für Technik Berlin, 2017. [9] Kersten, E., et al., EPSC Abstracts Vol. 12, EPSC2018-352, 2018.

The occurrence of pitted impact deposits (PIDs) and widespread OH-bearing minerals on the differentiated asteroid Vesta shows that volatiles delivered by exogenic sources play an important role for surface appearance and processes on airless bodies. The young, large crater Marcia features widely spread PIDs in its crater-fill and ejecta deposits. In order to derive more details on their formation, we studied the spectral and geomorphological properties of PIDs associated with Marcia. Our observations imply that the formation of PIDs is linked to topography-controlled accumulation of ejecta and the accompanying increase of deposit thickness as well as internal heat. This is best illustrated where PIDs are located within pre-existing craters (i.e., pre-Marcia), enabling the estimation of pre-impact topography and deposit thickness. Previous studies reported a lower than average reflectance at visible wavelengths for the crater-fill PIDs, which we confirm. However, several PIDs outside the crater exhibit higher reflectance and pyroxene band strength than the average Vesta and the majority of PIDs exhibit higher reflectance and pyroxene band strength with respect to their immediate surroundings (which belong to the same impact deposit). Furthermore, at least six PIDs (many are ambiguous) show resolvable, diminished absorption bands at 2.8 μm, corresponding to a depletion in OH. These spectral observations are most consistent with less contamination by exogenic carbonaceous chondrite materials, i.e., a loss of hydroxyl groups as well as dark components. Our observations are inconsistent with differences in grain size, pyroxene composition, glass content or age-related differences. Regarding reflectance at 750 nm and pyroxene band depth (750/917 [nm]), we present a unique spectral trend for PIDs with respect to ‘typical Vestan’ materials, suggesting a likewise unique formation process occurring on this asteroid. The crater-fill PIDs display ambiguous spectral characteristics that we attribute to post-impact inflow of dark material from the crater rim. PIDs are ubiquitous in the Marcia region (>100 individual clusters). Yet volatiles lost at these sites might only represent a minor fraction (

Mastcam-Z is a multispectral, stereoscopic imaging investigation on the Mars 2020 mission’s Perseverance rover. Mastcam-Z consists of a pair of focusable, 4:1 zoomable cameras that provide broadband red/green/blue and narrowband 400-1000 nm color imaging with fields of view from 25.6° × 19.2° (26 mm focal length at 283 μrad/pixel) to 6.2° × 4.6° (110 mm focal length at 67.4 μrad/pixel). The cameras can resolve (≥ 5 pixels) ∼0.7 mm features at 2 m and ∼3.3 cm features at 100 m distance. Mastcam-Z shares significant heritage with the Mastcam instruments on the Mars Science Laboratory Curiosity rover. Each Mastcam-Z camera consists of zoom, focus, and filter wheel mechanisms and a 1648 × 1214 pixel charge-coupled device detector and electronics. The two Mastcam-Z cameras are mounted with a 24.4 cm stereo baseline and 2.3° total toe-in on a camera plate ∼2 m above the surface on the rover’s Remote Sensing Mast, which provides azimuth and elevation actuation. A separate digital electronics assembly inside the rover provides power, data processing and storage, and the interface to the rover computer. Primary and secondary Mastcam-Z calibration targets mounted on the rover top deck enable tactical reflectance calibration. Mastcam-Z multispectral, stereo, and panoramic images will be used to provide detailed morphology, topography, and geologic context along the rover’s traverse; constrain mineralogic, photometric, and physical properties of surface materials; monitor and characterize atmospheric and astronomical phenomena; and document the rover’s sample extraction and caching locations. Mastcam-Z images will also provide key engineering information to support sample selection and other rover driving and tool/instrument operations decisions.

Hayabusa-2, a JAXA mission, reached C-type asteroid (162173) Ryugu in June 2018. Hayabusa2 carried MASCOT (Ho et al., 2016), a small lander developed by DLR and CNES. The goal of MASCOT was to perform in situ measurements on the surface of the asteroid by means of its four scientific instruments, substantially contributing in this way to the overall scientific return of Hayabusa2 mission. MASCOT landing occurred the October 3, 2018. After its release by Hayabusa2 spacecraft, the MASCOT lander experienced 17 ​min of descent and bounces. Then after stabilization it collected measurements during 17 ​h, visiting three slightly different sites. A comprehensive knowledge of MASCOT’s attitudes on the various moment of its mission is essential for the understanding of the science data gathered by the scout. CNES flight dynamics team was involved in the reconstruction of MASCOT landing trajectory and attitude. This paper presents the attitude reconstruction of MASCOT during its descent and on its second landing site. The reconstruction used as inputs the housekeeping data generated by the 6 Photo Electric Cells of MASCOT, as well as the images acquired by Hayabusa2 ONC camera and the MASCAM camera. The assessment was very complex but we determined the attitude with a mean accuracy around 10° during descent and 8° when MASCOT was stable once the second landing site was successfully reached. Nevertheless, for the other phases - bounces, first landing site and last landing site-the lander attitude is still undetermined.

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/., The goal of Project GAUSS (Genesis of Asteroids and evolUtion of the Solar System) is to return samples from the dwarf planet Ceres. Ceres is the most accessible candidate of ocean worlds and the largest reservoir of water in the inner Solar System. It shows active volcanism and hydrothermal activities in recent history. Recent evidence for the existence of a subsurface ocean on Ceres and the complex geochemistry suggest past habitability and even the potential for ongoing habitability. GAUSS will return samples from Ceres with the aim of answering the following top-level scientific questions:What is the origin of Ceres and what does this imply for the origin of water and other volatiles in the inner Solar System?What are the physical properties and internal structure of Ceres? What do they tell us about the evolutionary and aqueous alteration history of dwarf planets?What are the astrobiological implications of Ceres? Is it still habitable today?What are the mineralogical connections between Ceres and our current collections of carbonaceous meteorites? © 2023 Elsevier B.V., All rights reserved., The early concept of the white paper has benefitted from various discussions with Professor Adam Showman, who sadly passed away in March 2020. His contribution and influence are gratefully acknowledged and sorely missed. Part of this work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). J.-Y.L. acknowledges partial support from the Solar System Exploration Research Virtual Institute 2016 (SSERVI16) Cooperative Agreement (grant NNH16ZDA001N), SSERVI-TREX to the Planetary Science Institute. J.A. acknowledges support from the European Research Council Starting Grant 757390 (CAstRA). A.J.C. and G.H.J. acknowledge support from the STFC consolidated grant to UCL-MSSL STS0002401. P. Santos-Sanz, and R. Duffard acknowledges financial support by the Spanish grant AYA- RTI2018-098657-J-I00 ’LEO-SBNAF’ (MCIU/AEI/FEDER, UE). J.L. Ortiz, P. Santos-Sanz, and R. Duffard acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ’Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). J.M.T-R. acknowledges support from the Spanish Ministry of Science and Innovation (project PGC2018-097374-B-I00). J.M.T-R.’s research has been funded by the research project (PGC2018-097374-B-I00), funded by FEDER/Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación. Open Access funding enabled and organized by Projekt DEAL.

Alteration processes on asteroid and comet surfaces, such as thermal fracturing, (micrometeorite) impacts or volatile outgassing, are complex mechanisms that form diverse surface morphologies and roughness on various scales. These mechanisms and their interaction may differ on the surfaces of different bodies. Asteroid Ryugu and comet 67P/Churyumov–Gerasimenko, both, have been visited by landers that imaged the surfaces in high spatial resolution. We investigate the surface morphology and roughness of Ryugu and 67P/Churyumov–Gerasimenko based on high-resolution in situ images of 0.2 and 0.8 mm pixel resolution over an approximately 25 and 80 cm wide scene, respectively. To maintain comparability and reproducibility, we introduce a method to extract surface roughness descriptors (fractal dimension, Hurst exponent, joint roughness coefficient, root-mean-square slope, hemispherical crater density, small-scale roughness parameter, and Hapke mean slope angle) from in situ planetary images illuminated by LEDs. We validate our method and choose adequate parameters for an analysis of the roughness of the surfaces. We also derive the roughness descriptors from 3D shape models of Ryugu and orbiter camera images and show that the higher spatially resolved images result in a higher roughness. We find that 67P/Churyumov–Gerasimenko is up to 6 per cent rougher than Ryugu depending on the descriptor used and attribute this difference to the different intrinsic properties of the materials imaged and the erosive processes altering them. On 67P/Churyumov–Gerasimenko sublimation appears to be the main cause for roughness, while on Ryugu micrometeoroid bombardment as well as thermal fatigue and solar weathering may play a significant role in shaping the surface.

In response to ESA Voyage 2050 announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn largest moon Titan. Titan, a "world with two oceans", is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a "heavy" drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan northern latitudes with an orbiter and in situ element(s) would be highly complementary with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan equatorial regions in the mid-2030s., Comment: arXiv admin note: substantial text overlap with arXiv:1908.01374

Introduction:Current efforts for image mosaics from the High Resolution Stereo Camera (HRSC, Jaumann, 2007) on board Mars Express are ongoing (Michael et al. 2016, Michael et al., 2019). Usually, illumination effects between adjacent single images related to the planetary curvature are reduced by using a Lambert correction and subsequent normalization to a common brightness reference. Here we present an extended correction of topography-induced shading effects by using the illumination angles with reference to the local topography represented by the digital terrain model (DTM) associated to every single HRSC scene, resulting in top-of-the-atmosphere albedo images of the surface. Scattering models:When used for illumination corrections taking the local topography into account, the Lambertian model and its associated cosine correction tends to over-correct on large incidence angles (under-illuminated pixels), as observed on crater slopes at low Sun angles. Therefore we do not consider it for our work but use it as a reference for comparison reasons (see Fig. 1 top -- the saturation level of one is reached at around 70° effective incidence angle). The one-parameter model by Minnaert (Minnaert, 1941) is known for its good reproduction of the Martian surface. Depending on its power-law parameter k, the saturation effect of the correction appears at very high incidence angles only and is therefore better suited for topographic corrections. Still, in the case of HRSC, the Sun incidence angle on the ellipsoid is often higher than 60° and adding the slope angles results in incidence angles higher than 80°. This leads to very bright over-corrected pixels in highly inclined areas facing away from the Sun (see Fig. 1 middle -- depending on the k parameter, the saturation level is reached at around 80° incidence). The correction used by Teillet et al. (1982) is well suited for topographic corrections due to its minimal amount of overcorrection (cf. Fig. 1 bottom for plots of varying parameter settings and Fig. 2 for the result). The single parameter is derived by a relation of the incidence on the ellipsoid to the mean incidince with regards to the topography. Figure 1: Correction curves using different photometric functions; top: Lambert model; middle: Minnaert model, emission angle=0°; bottom: Teillet model, incidence on ellipsoid=60°. A reflectance of 0.3 is assumed for all plots. Results:We corrected a common set of HRSC images using the three mentioned scattering models and assembled a respective mosaic for each by correcting the single images for the illumination effects and then normalizing the images to TES albedo data (see Fig. 2). The parameters for the models are estimated using non-linear least square minimization for every single HRSC scene assuming constant parameters over the full image. The results for the Minnaert and the Teillet model appear very consistent by visual inspection. Due to the very high slope angles often appearing in HRSC scenes, the Minnaert model sometimes results in saturated pixels, while the Teillet model achieves the most modest levels of correction. We have not observed any advantage of the Minnaert model over the Teillet model, although it additionally includes emission angle values in the model. This lets us assume that the emission angles have a minor effect on the topography-induced illumination effects. Figure 2: Subsets of the image mosaics; top: uncorrected image mosaic as shown in Michael et al., 2016; middle: Image mosaic with removed shading using the Minnaert scattering model, bottom: Image mosaic with removed shading using the Teillet scattering model. Outlook:The albedo mosaics here serve for a broad range of applications: Image classification using computer vision algorithms, geologic interpretation without influences of the topography and therefore better differentiation between albedo and shading, data fusion with uniform illumination characteristics, as well as the ability to add homogeneous shading from a uniform illumination direction for the application in Virtual Reality scenarios.

The ESA-Russia Rosalind Franklin (ExoMars 2022) rover, with its unique 2m drill, will address key questions in the search for life on Mars. PanCam will establish the surface context, with other instruments, providing geology, atmospheric science and 3D vision. PanCam uses a pair of Wide Angle Cameras (WACs), each with an 11 position filter wheel, and a High Resolution Camera (HRC). The cameras and electronics are in an optical bench that provides the interface to the rover and planetary protection. PanCam includes a calibration target mounted on the rover deck for radiometric calibration, fiducial markers for geometric calibration and a rover inspection mirror.

Starting in September 2018, a daily repeating extremely elongated cloud was observed extending from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, and MARCI on MRO. We study the daily cycle of this cloud, showing how the morphology and other parameters of the cloud evolved with local time. The cloud expands every morning from the western slope of the volcano, at a westward velocity of around 150m/s, and an altitude of around 30-40km over the local surface. Starting around 2.5 hours after sunrise (8.2 Local True Solar Time, LTST), the formation of the cloud resumes, and the existing cloud keeps moving westward, so it detaches from the volcano, until it evaporates in the following hours. At this time, the cloud has expanded to a length of around 1500km. Short time later, a new local cloud appears on the western slope of the volcano, starting around 9.5 LTST, and grows during the morning.This daily cycle repeated regularly for at least 90 sols in 2018, around Southern Solstice (Ls 240-300) in Martian Year (MY) 34. According with these and previous MEx/VMC observations, this elongated cloud is a seasonal phenomenon occurring around Southern Solstice every Martian Year. We study the interannual variability of this cloud, the influence of the Global Dust Storms in 2018 on the cloud’s properties (Sánchez-Lavega et al., Geophys. Res. Lett. 46, 2019), and its validity as a proxy for the global state of the Martian atmosphere (Sánchez-Lavega et al., J. Geophys. Res., 123, 3020, 2018). We discuss the physical mechanisms behind the formation of this peculiar cloud in Mars.

The ExoMars mission will deploy a stationary surface platform and a rover in Oxia Planum (OP), a region at the transition between the heavily cratered highlands of Mars and the ancient and filled impact basin, Chryse Planitia. While the fundamental geologic characteristics of the area have been investigated during the landing site selection process, detailed geologic or morpho-stratigraphic mapping is still missing. To fill this knowledge gap, two complementary mapping approaches were initiated by the ExoMars RSOWG: (1) Local HiRISE-scale mapping of the landing ellipse(s) area (reported elsewhere: Sefton-Nash et al., LPSC 2020). (2) Regional mapping at ~CTX-scale [this study] will provide a more synoptic view of the wider landing site within OP, enabling the contextualization of the units within the stratigraphy of western Arabia Terra and Chryse Planitia, and a comparison to other sites with similar key geologic and physiographic characteristics. It is also expected that this map will serve as a geologic reference throughout the mission and subsequent data analysis. The study area is located between 16.5°N and 19.5°N, and 334°E to 338°E. The data sets used for mapping include HRSC, THEMIS IR (day and night), CTX, and CaSSIS. Mapping scale in a GIS environment is 1:100,000, which will result in a final printable map at a scale of 1:1M. Mapping started in mid-October 2019. Overall, the identified map units are very similar to those described by Quantin et al. (Astrobiology, submitted): The spatially most widespread units are the phyllosilicate-bearing unit that is the prime ExoMars target (with distinctly enhanced THEMIS nighttime temperatures when compared to its surroundings), a dark resistant unit of possibly volcanic or sedimentary origin, and a mantling unit that was likely emplaced by eolian processes. Multiple channels of various morphology and degradation state as well as sedimentary fan-shaped deposits (with low nighttime temperatures) imply a diverse and possibly long-lived history of surface runoff, perhaps accompanied or replaced by groundwater processes such as sapping. Inverted landforms (channels, impact craters) are the result of intense erosion. Additional mapped features include tectonic structures such as wrinkle ridges and lobate scarps (delineating a basin-like depression in the central mapping area), remnant erosional buttes in the northwestern portion of the mapping area (i.e. towards Chryse Planitia), craters and their ejecta blankets, and fields of eolian bedforms and secondary craters. At the time of writing, the mapping is incomplete and only initial and limited conclusions can be drawn. Overall, the mapping confirms previous geologic analyses. However, some features (e.g., contractional structures, channels, possible sapping landforms) need further attention as the may provide important constraints on the tectonic and aqueous evolution of the ExoMars landing area. A comparison to a distant, but geologically very similar site in Xanthe Terra, southeast of the Hypanis fan-shaped deposits, may enable testing of hypotheses raised by the geologic mapping of OP.

For planetary sciences, the main archives to archived access to mission data are ESA's Planetary Science Archive (PSA) and the Planetary Data System (PSA) nodes in the USA. Along with recent and upcoming planetary missions the amount of different data (remote sensing/in-situ data, derived products) increases constantly and serves as basis for scientific research resulting in derived scientific data and information. Within missions to Mercury (BepiColombo), the Outer Solar System moons (JUICE), and asteroids (NASA`s DAWN), one way of scientific analysis, the systematic mapping of surfaces, has received new impulses, also in Europe. These systematic surface analyses are based on the numeric and visual comparison and combination of different remote sensing data sets, such as optical image data, spectral-/hyperspectral sensor data, radar images, and/or derived products like digital terrain models. The analyses mainly results in map figures, data, and profiles/diagrams, and serves for describing research investigations within scientific publications.Handling these research products equivalently to missions´ base data in the main archives, web-based geographic information systems became a common mean to impart spatial knowledge to all kinds of possible users in the last years. So, further platforms and initiatives came up handling planetary data within web-based GIS, services, or/and virtual infrastructures. Those systems are either built upon proprietary software environments, but more common upon a well-established stack of open source software such as PostgreSQL, GeoServer (server for sharing geospatial data) and a graphical user interface based on JavaScript. Applicable standards developed by the Open Geospatial Consortium (OGC), such as the Web Map Service (WMS) and the Web Feature Service (WFS) server-based data storage as interface between the user interface and the server. This contribution aims to a prototypical system for the structured storage and visualization of planetary data compiled and developed within or with the contribution of Institute for Planetary Research (PF, DLR). Consequently, it enables user groups to store and spatially explore research products centrally, sustainably across multiple missions and scientific disciplines [1]. Technically, the system is based on two components: 1) an infrastructure that provides data storage and management capabilities as well as OGC-compliant interfaces for collaborative and web-based data access services, such as the EOC Geoservice [2]. 2) UKIS (Environmental and Crisis Information Systems), a framework developed at DFD for the implementation of geoscientific web applications [3]. Substantially the prototype based on a recent approach developed within PF [4] where an existing database established at Planetary Spectroscopy Laboratory (PSL), handling different kind of spatial data, meets a vector-based data collection of thematic, mainly geologic and geomorphologic mapping results [5]. An information system of this kind is essential to ensure the efficient and sustainable utilization of the information already obtained and published. This is considered a prerequisite for guaranteeing a continuous and long-term use of scientific information and knowledge within institutional frameworks. [1] Naß, et al (2019) EPSC #1311[2] Dengler et al. (2013) PV 2013, elib.dlr.de/86351/[3] Mühlbauer (2019) dlr.de/eoc/UKIS/en/[4] Naß, d ’Amore, Helbert (2017) EPSC #646-1[5] Naß, Dawn Science Team (2019) EPSC #1304

Abstract Ponded craters have been predominantly identified on small, dry planetary bodies like (433) Eros and Itokawa. We identified similar features on Vesta, where loose fragmented ponded materials are present on small crater floors. While the morphological details of the ponded features on Vesta and Eros/Itokawa are similar, their production mechanisms may vary, due to differences in gravity or the insolation environment Previous studies conducted on Vesta have provided evidence for volatile outgassing in some regions. In this study, we investigate the morphology of the ponded crater and possible involvement of volatiles outgassing and its interaction with surface material in producing ponded craters on Vesta. Introduction Ponded craters have widely received lime light due to its unusual characteristics on Eros revealed by the NEAR Shoemaker mission (Sears et al., 2015, Robinson et al., 2001,2002). In general, ponded craters show a smooth layer of fine-grained material with grain size less then cm (Robinson et al., 2001) partially covering topography of the crater floor (Figure 1). They may also possess varying sized boulders or unconsolidated material (Sears et al., 2015). The depth of the pond is about ~5% of the depth of the original crater (Robinson et al., 2001) on Eros. Other than the distinct morphological impression (smooth and flat floor), ponded crater regolith also shows sharp variation in the spectral signature (Robinson et al., 2001) which can be due to mineral heterogeneity (Robinson et al., 2001), space weathering (Sears et al., 2015, Heldmann et al., 2010, Robinson et al., 2001) or the difference in grain size between regolith and the surrounding region (Heldmann et al., 2010, Robinson et al., 2001).Based on the evidences on Eros, the formation mechanisms of ponded craters include electrostatic levitation, seismic shaking and/or boulder comminution (Robinson et al., 2001). However, the effects of these mechanisms may vary on other dry planetary bodies with different compositions, gravity or insolation intensity. In our study, we characterize ponded craters on Vesta to understand their formation mechanisms and how interactions with the regolith may have influenced the generation of ponded craters.Figure 1: A classic example of pond crater on Eros. The crater has diameter of ~0.09km (Robinson et al., 2001). The pond material has sharp boundary, low albedo and flat smooth surface which makes it easy to distinguish from the original carter floor. Image source: Robinson et al., 2001 Data For the identification of ponded craters on Vesta, HAMO mosaics (~70 m/pixel) and LAMO mosaics (~20 m/pixel) provided by the NASA Dawn Mission were considered. To extract elevation information, a DTM of HAMO resolution was used (92 m/pixel) (Preusker et al., 2016) prepared from stereo-pairs.Results So far, we have identified 10 ponded craters nearby the equator (0°-30°) on Vesta. Overall, the crater floor is fully or partially covered by fine and loose material. The usual diameter of ponds ranges from 0.9 -6.4 km within craters of 1.78- 8.43 km diameter. Most of the identified ponded craters, have clear flat floors in which the fine material is evenly distributed within the bowl-shaped depression (Figure 1) covering the original floor of the crater entirely. An example is given in Figure 2, located at 15°S,189°E. The carter has a diameter of ~8km. By fitting a polynomial shape (e.g. a parabola) to the crater walls, we estimated the original depth of the crater with ~0.66km. The ponded material has filled the original crater surface, producing a shallow depth crater. The material has filled ~0.31km of the crater, which means half of the original crater depth is infilled by the fine material. On Eros ponds have average infilling depths of ~10cm or 5% of the original depth (Robinson et al., 2001). The smaller infilling might be due to the fact that craters on Eros are significantly smaller in comparison with Vesta. However, it is unreasonable to draw any conclusions based on a single example. At the meeting we will present measurements of the rest of the identified ponded sites to understand the overall morphology and discuss formation mechanisms for ponds on Vesta based on our findings.Figure 2: Example of a ponded crater on Vesta. (a) The ponded material is covering the original surface within central crater region and exhibits a flat and smooth texture. (b) The elevation profile of the crater in (a) highlighting the flat ponded material in red. The ponded material infilled the deeper parts of the crater depression, masking the original shape (dash-dotted line) and generating a flat floor. References[1] Heldamann et al., 2010, Icarus, 206, 685-690. [2] Robinson et al., 2001, Nature, 413,396-400. [3] Robinson et al., 2002, Meteorit. Planet. Sci., 37 1651-1684. [4] Sears et al., 2015, PSS, 117, 106-118.

Although the present environmental conditions on Mars prohibit the generation of significant volumes of liquid water, observations of several very young landforms, such as gullies and recurrent slope lineae, have been interpreted as signals for aqueous processes. To explore the range of conditions under which such features can be formed on Earth, a field site in northern Victoria Land, East Antarctica, was geomorphologically investigated. Despite the small size of the icefree area, the site displays gullies, water tracks and other traces of liquid water. The gullies show clear evidence of sediment transport by debris flows, and are typical of paraglacial processes on steep slopes in a recently deglaciated area. Water tracks appear in different forms, and seem to recur seasonally in the austral summer. Melting of snow and surface glacier ice is the major water source for both debris flows and water tracks. The observations presented here highlight the potential for hyperarid polar deserts to generate morphogenetically significant amounts of meltwater. The gullies are morphologically analogous to Martian gullies, and water tracks on steep slopes appear very similar to recurrent slope lineae. The observations suggest that even small icefree sites in continental Antarctica may enable observations which can serve as a basis for working hypotheses in Mars analogue studies, and future field work should consider more areas in Antarctica in addition to the McMurdo Dry Valleys to search for Mars analogue landforms.

Imaging by the Dawn-spacecraft reveals that fresh craters on Ceres below 40 km often exhibit numerous boulders. We investigate how the fast rotating, low-gravity regime on Ceres influences their deposition. We analyze size-frequency distributions of ejecta blocks of twelve boulder craters. Global and local landing sites of boulder crater ejecta and boulder velocities are determined by the analytical calculation of elliptic particle trajectories on a rotating body. The cumulative distributions of boulder diameters follow steep-sloped power-laws. We do not find a correlation between boulder size and the distance of a boulder to its primary crater. Due to Ceres’ low gravitational acceleration and fast rotation, ejecta of analyzed boulder craters (8–31 km) can be deposited across the entire surface of the dwarf planet. The particle trajectories are strongly influenced by the Coriolis effect as well as the impact geometry. Fast ejecta of high-latitude craters accumulate close to the pole of the opposite hemisphere. Fast ejecta of low-latitude craters wraps around the equator. Rotational effects are also relevant for the low-velocity regime. Boulders are ejected at velocities up to 71 m/s.