Search

Aims. From April 2008 to August 2011 Mars Express carried out 74 Phobos flybys at distances between 669 and 5579 km. Images taken with the Super Resolution Channel (SRC) were used to determine the spacecraft-centered right ascension and declination of this Martian moon. Methods. Image positions of Phobos were measured using the limb-fit and control-point measurement techniques. Camera pointing and pointing drift were controlled by means of background star observations that were compared to corresponding positions from reference catalogs. Blurred and noisy images were restored by applying an image-based point spread function in a Richardson-Lucy deconvolution. Results. Here, we report on a set of 158 Phobos astrometric observations with estimated accuracies between 0.224 and 3.405 km circular w.r.t. the line of sight to the satellite. Control point measurements yield slightly more accurate results than the limb fit ones. Our observations are in good agreement with the current Phobos ephemerides by the Jet Propulsion Laboratory (JPL) and the Royal Observatory of Belgium (ROB) with mean offsets of up to 335 m. Our data can be used for the maintenance and update of these models. [ABSTRACT FROM AUTHOR]

We have developed a Geo-information system (GIS) for Phobos, based on data from the Mars Express and Viking Orbiter missions, which includes orthoimages, global maps, terrain- and gravity field models, all referenced to the Phobos coordinate system. The data are conveniently stored in the ArcGIS software system, which provides an environment for mapping and which allows us to carry out joint data analysis and miscellaneous data cross-comparisons. We have compiled catalogs of Phobos craters using manual and automated techniques, which includes about 5500 and 6400 craters correspondingly. While crater numbers are biased by available image data resolution and illumination, we estimate that our catalog of manually detected craters contains all Phobos craters with diameters D >250 m which is a total of 1072 and catalog of automated detected craters are complete for craters D >400 m (360 craters). Statistical analysis of these large craters reveals a surplus of craters on the anti-Mars hemisphere, whereas differences in crater abundance between leading and trailing hemisphere cannot be confirmed. This in contrast to previous papers, where no such asymmetry was found ( Schmedemann et al., 2014 ). But we cannot rule out remaining biases due to resolution, viewing angles or illumination effects. Using digital terrain model (DTM) derived from photogrammetry image processing we estimate depths of 25 craters larger than 2 km using geometric and dynamic heights (for discussion of Phobos crater morphometry see Kokhanov et al., 2014 ). We also have compiled catalogs of lineaments, and boulders. In particular, we mapped 546 individual grooves or crater chains, which extend in length from 0.3 km to 16.2 km. We identified and determined the sizes and locations of 1379 boulders near crater Stickney. Cross-comparisons of gravity field models against distribution patterns of grooves and boulders are currently under way and may shed light on their possible origins. Finally, we have developed a Geo-portal, which allows the science community to conveniently search for, analyze, and download data of interest from our system. Additionally we provide access to color electronic maps (e-maps) with support for layers based on Phobos geodatabase and ArcGIS tools. [ABSTRACT FROM AUTHOR]

A new global control point network was derived for Phobos, based on SRC (Mars Express), Phobos-2, and Viking Orbiter image data. We derive 3-D Cartesian coordinates for 813 control points as well as improved pointing data for 202 SRC and Viking images in the Phobos-fixed coordinate system. The point accuracies vary from 4.5 m on the Phobos nearside, to up to 67.0 m on the farside, where we rely on Viking images (average point accuracy: 13.7 m). From tracking of the control points we detect a librational motion synchronous to the Phobos orbital period and measure libration amplitude of 1.09°, in agreement with predictions from shape information assuming a uniform interior. This suggests that the interior of Phobos is homogeneous – but small local mass anomalies, e.g., associated with crater Stickney, cannot be ruled out. Our new control point network has a higher number of data points and higher point accuracy than previous data products and will be an important basis for accurate shape models and maps. [ABSTRACT FROM AUTHOR]

Abstract: We have derived a stereo-topographic model and an orthoimage mosaic based on Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images to study the Luna-17 landing site. In the images (0.33–0.5m/pixel), the Lunokhod-1, the Luna-17 landed spacecraft, and the rover tracks can clearly be identified and mapped for 99% of the traverse. The traverse was found to be 9.93km long, approximately 0.50km shorter over what had been estimated earlier (10.54km). The total topographic relief along the traverse was found to be within 26m. Along its traverse, the rover encountered slopes of up to 5°, estimated over 2.5m baselength. By comparison with previously published topographic maps and using our orthomosaic as a reference (which had been tied to the well-known Lunokhod-1 Laser reflector coordinates), we report on coordinates of Lunokhod-1's panorama points and overnight stops. Comparisons of currently mapped tracks with previous traverse reconstructions show good matches on small scale, but reveal that previous maps had long-wavelength geometric distortions of up to 100-m level. Agreement in topographic trends was very limited. [Copyright &y& Elsevier]

Abstract: Monitoring the lunar surface for impacts is a highly rewarding approach to study small asteroids and large meteoroids encountering the Earth–Moon System. The various effects of meteoroids impacting the Moon are described and results from different detection and study techniques are compared. While the traditional statistics of impact craters allow us to determine the cumulative meteoroid flux on the lunar surface, the recent successful identification of fresh craters in orbital imagery has the potential to directly measure the cratering rate of today. Time-resolved recordings, e.g., seismic data of impacts and impact flash detections clearly demonstrate variations of the impact flux during the lunar day. From the temporal/spatial distribution of impact events, constraints can be obtained on the meteoroid approach trajectories and velocities. The current monitoring allows us to identify temporal clustering of impacts and to study the different meteoroid showers encountering the Earth–Moon system. Though observational biases and deficiencies in our knowledge of the scaling laws are severe, there appears to be an order-of-magnitude agreement in the observed flux within the error limits. Selenographic asymmetries in the impact flux (e.g., for equatorial vs. polar areas) have been predicted. An excess of impacts on the lunar leading hemisphere can be demonstrated in current data. We expect that future missions will allow simultaneous detections of seismic events and impact flashes. The known locations and times of the flashes will allow us to constrain the seismic solutions. While the numbers of flash detections are still limited, coordinated world-wide observations hold great potential for exploiting this observation technique. The potential for identification of fresh craters in high-resolution orbital image data has just barely been tapped, but should improve significantly with the LRO extended mission. [Copyright &y& Elsevier]

Abstract: We investigate the expected performance of a wide-angle camera in Martian orbit, which, unlike previous cameras that have flown to Mars, is capable of recording meteor activity in that planet''s atmosphere. We show that, based on our current understanding of meteor physics and the interplanetary meteoroid population, several meteors will be detected by this instrument during a single nightside pass on a low Martian orbit. The instrument will also record the signatures of meteor showers expected to occur every Martian year (1.88 Earth years). The results of this investigation will test models of the flux of “large” (mm-cm) meteoroids at the orbit of Mars and their interaction with the Martian atmosphere. [Copyright &y& Elsevier]

Abstract: We have developed a camera dedicated to imaging faint transient noctilucent phenomena, such as aurorae, electric discharges, meteors or impact flashes, on dark planetary hemispheres. The Smart Panoramic Optical Sensor Head (SPOSH) is equipped with a back-illuminated 1024×1024 CCD chip E2V 47–20 with up to 90% quantum efficiency and has a custom-made optical system of high light-gathering power with a wide field of view of 120°×120°. Images can be obtained over extended periods at high rate to make monitoring for transient events possible. To reduce the data transmission rate, only those images (or relevant portions thereof) that contain events are returned to the user. The camera has a sophisticated processing unit prepared to interface with a spacecraft system, for image processing and event detection at rates of up to 3 images per second at full resolution. While software optimized for detection of any noctilucent phenomenon can be implemented, the software is currently optimized for the detection of meteors. Over the past years, we have routinely carried out outdoor tests with 4 camera breadboard units that demonstrate that the camera has excellent radiometric performance and geometric resolution at low light levels over its large field of view. The camera has been demonstrated to capture meteors of magnitudes as faint as +6m moving at angular speeds of 5°/s. The camera opens up new science opportunities for planetary missions. [ABSTRACT FROM AUTHOR]

Abstract: A new independent control point network for Phobos was computed from image data obtained by the SRC (Super Resolution Channel) on board the European Mars Express Mission. The network solution includes 3D coordinates of 665 surface control points and was used to observe the forced libration amplitude of Phobos. Based on the network control points a spherical harmonic function model to degree and order 17 was derived, from which volume, bulk density and moments of inertia were computed. The modeled forced libration amplitude agrees to our observation within the error bands, indicating a homogeneous mass distribution for Phobos. To bring both values into exact agreement with the observations, different mass distribution models were applied. It appears that the amplitude is relatively insensitive to a simple two-layer density model. [Copyright &y& Elsevier]

Abstract: The Mars Express spacecraft carries the pushbroom scanner high-resolution stereo camera (HRSC) and its added imaging subsystem super resolution channel (SRC). The SRC is equipped with its own optical system and a 1024×1024 framing sensor. SRC produces snapshots with 2.3m ground pixel size from the nominal spacecraft pericenter height of 250km, which are typically embedded in the central part of the large HRSC scenes. The salient features of the SRC are its light-weight optics, a reliable CCD detector, and high-speed read-out electronics. The quality and effective visibility of details in the SRC images unfortunately falls short of what has been expected. In cases where thermal balance cannot be reached, artifacts, such as blurring and “ghost features” are observed in the images. In addition, images show large numbers of blemish pixels and are plagued by electronic noise. As a consequence, we have developed various image improving algorithms, which are discussed in this paper. While results are encouraging, further studies of image restoration by dedicated processing appear worthwhile. The SRC has obtained more than 6940 images at the time of writing (1 September 2007), which often show fascinating details in surface morphology. SRC images are highly useful for a variety of applications in planetary geology, for studies of the Mars atmosphere, and for astrometric observations of the Martian satellites. This paper will give a full account of the design philosophy, technical concept, calibration, operation, integration with HRSC, and performance, as well as science accomplishments of the SRC. [Copyright &y& Elsevier]

Abstract: The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has conducted a systematic inter-comparison of different alternatives for the production of high resolution digital terrain models (DTMs) from the multi look HRSC push broom imagery. Based on carefully chosen test sites the test participants have produced DTMs which have been subsequently analysed in a quantitative and a qualitative manner. This paper reports on the results obtained in this test. [Copyright &y& Elsevier]

Stereo images obtained during the DS1 flyby were analyzed to derive a topographic model for the nucleus of Comet 19P/Borrelly for morphologic and photometric studies. The elongated nucleus has an overall concave shape, resembling a peanut, with the lower end tilted towards the camera. The bimodal character of surface-slopes and curvatures support the idea that the nucleus is a gravitational aggregate, consisting of two fragments in contact. Our photometric modeling suggests that topographic shading effects on Borrelly''s surface are very minor (<10%) at the given resolution of the terrain model. Instead, albedo effects are thought to dominate Borrelly''s large variations in surface brightness. With 90% of the visible surface having single scattering albedos between 0.008 and 0.024, Borrelly is confirmed to be among the darkest of the known Solar System objects. Photometrically corrected images emphasize that the nucleus has distinct, contiguous terrains covered with either bright or dark, smooth or mottled materials. Also, mapping of the changes in surface brightness with phase angle suggests that terrain roughness at subpixel scale is not uniform over the nucleus. High surface roughness is noted in particular near the transition between the upper and lower end of the nucleus, as well as near the presumed source region of Borrelly''s main jets. Borrelly''s surface is complex and characterized by distinct types of materials that have different compositional and/or physical properties. [Copyright &y& Elsevier]

We have characterised the Perseid meteoroid stream from data acquired in a series of observing campaigns between 2010 and 2016. The data presented in this work were obtained by the Smart Panoramic Optical Sensor Head (SPOSH), an all-sky camera system designed to image faint transient noctilucent phenomena on dark planetary hemispheres. For the data reduction, a sophisticated software package was developed that utilises the high geometric and photometric quality of images obtained by the camera system. We identify 934 meteors as Perseids, observed over a long period between late July (~124°) and mid-to-late August (~147°). The maximum meteor activity contributing to the annual shower was found at λ⊙ = 140°.08 ± 0°.07. The radiant of the shower was estimated at RA = 47°.2 and Dec = 57°.5 with a median error of 0°.6 and 0°.2, respectively. The mean population index of the shower between solar longitudes of 120°.68 and 145°.19 was r = 2.36 ± 0.05, showing strong temporal variation. A predicted outburst in shower activity for the night of August 11–12, 2016 was confirmed, with a peak observed 12.75 hr before the annual maximum at 23:30 ± 15′ UT. We measure a peak flux of 6.1 × 10−4 km−2 hr−1 for meteoroids of mass 1.6 × 10−2 g or more, appearing in the time period between 23:00 and 00:00 UT. We estimate the measured flux of the outburst meteoroids to be approximately twice as high as the annual meteoroid flux of the same mass. The population index of r = 2.19 ± 0.08, computed from the outburst Perseids in 2016, is higher than the value of r = 1.92 ± 0.06 derived from meteors observed in 2015 belonging to the annual Perseid shower which was active near the time of the outburst. A dust trail with an unusually high population index of r = 3.58 ± 0.24 was encountered in 2013 between solar longitudes 136°.261 and 137°.442. The relatively high r-value implies an encounter with a dust trail rich in low-mass particles. [ABSTRACT FROM AUTHOR]

We processed and analyzed one-way laser ranging data from International Laser Ranging Service ground stations to NASA's Lunar Reconnaissance Orbiter (LRO), obtained from June 13, 2009 until September 30, 2014. We pair and analyze the one-way range observables from station laser fire and spacecraft laser arrival times by using nominal LRO orbit models based on the GRAIL gravity field. We apply corrections for instrument range walk, as well as for atmospheric and relativistic effects. In total we derived a tracking data volume of ≈ 3000 hours featuring 64 million Full Rate and 1.5 million Normal Point observations. From a statistical analysis of the dataset we evaluate the experiment and the ground station performance. We observe a laser ranging measurement precision of 12.3 cm in case of the Full Rate data which surpasses the LOLA timestamp precision of 15 cm. The averaging to Normal Point data further reduces the measurement precision to 5.6 cm. We characterized the LRO clock with fits throughout the mission time and estimated the rate to 6.9 × 10 −8 , the aging to 1.6 × 10 −12 /day and the change of aging to 2.3 × 10 −14 /day 2 over all mission phases. The fits also provide referencing of onboard time to the TDB time scale at a precision of 166 ns over two and 256 ns over all mission phases, representing ground to space time transfer. Furthermore we measure ground station clock differences from the fits as well as from simultaneous passes which we use for ground to ground time transfer from common view observations. We observed relative offsets ranging from 33 to 560 ns and relative rates ranging from 2 × 10 −13 to 6 × 10 −12 between the ground station clocks during selected mission phases. We study the results from the different methods and discuss their applicability for time transfer. [ABSTRACT FROM AUTHOR]

We used one-way laser ranging data from International Laser Ranging Service (ILRS) ground stations to NASA's Lunar Reconnaissance Orbiter (LRO) for a demonstration of orbit determination. In the one-way setup, the state of LRO and the parameters of the spacecraft and all involved ground station clocks must be estimated simultaneously. This setup introduces many correlated parameters that are resolved by using a priori constraints. Moreover the observation data coverage and errors accumulating from the dynamical and the clock modeling limit the maximum arc length. The objective of this paper is to investigate the effect of the arc length, the dynamical and modeling accuracy and the observation data coverage on the accuracy of the results. We analyzed multiple arcs using lengths of 2 and 7 days during a one-week period in Science Mission phase 02 (SM02, November 2010) and compared the trajectories, the post-fit measurement residuals and the estimated clock parameters. We further incorporated simultaneous passes from multiple stations within the observation data to investigate the expected improvement in positioning. The estimated trajectories were compared to the nominal LRO trajectory and the clock parameters (offset, rate and aging) to the results found in the literature. Arcs estimated with one-way ranging data had differences of 5–30 m compared to the nominal LRO trajectory. While the estimated LRO clock rates agreed closely with the a priori constraints, the aging parameters absorbed clock modeling errors with increasing clock arc length. Because of high correlations between the different ground station clocks and due to limited clock modeling accuracy, their differences only agreed at the order of magnitude with the literature. We found that the incorporation of simultaneous passes requires improved modeling in particular to enable the expected improvement in positioning. We found that gaps in the observation data coverage over 12 h (≈6 successive LRO orbits) prevented the successful estimation of arcs with lengths shorter or longer than 2 or 7 days with our given modeling. [ABSTRACT FROM AUTHOR]

We computed a 3D control point network for Ganymede using combinations of 126 Voyager-1 and -2 and 87 Galileo images, benefiting from reconstructed trajectory data for the three spacecraft and a more complete Galileo image data base than was available for earlier studies. Using more than 3000 control point coordinates, we determine global shape parameters, including mean radius, spheroid- and ellipsoidal axes, and make tests for various equilibrium shape models, constrained by the most recent estimates for gravity field parameters. We confirm that Ganymede has a pronounced ellipsoidal shape, approximately aligned with the Jupiter-direction, in agreement with Ganymede being in tidal equilibrium. The point heights, suffering from large individual errors, do not reveal any large-scale topography below our typical error levels (97% <5 km). By analysis of data residuals we search for, but cannot detect Ganymede longitudinal forced librations. We conclude that libration amplitudes cannot be larger than 0.1° (corresponding to a lateral displacement of 4.6 km at the equator). [ABSTRACT FROM AUTHOR]

Aims. We describe a new algorithm for extracting photometric information from meteor images. Methods. The time history of a moving point source of variable brightness is explicitly deconvolved from the spatial distribution of the meteor signal on the image. The method can be applied to time-integrated meteor images if kinematic information is independently available or, alternatively, assumed. Formal uncertainty estimation and reporting is included. Results. We test the algorithm on synthetic meteor images and meteors recorded during a recent double-station meteor observing campaign in Greece. In the first case, we find that both the synthetic signal and the a priori time variation of the flux are faithfully reproduced. In the second, the fluxes obtained from the two stations agree to ~20%. [ABSTRACT FROM AUTHOR]

The global shape and the dynamic environment are fundamental properties of a body. Other properties such as volume, bulk density, and models for the dynamic environment can subsequently be computed based on such models. Stereo-photogrammetric methods were applied to derive a global digital terrain model (DTM) with 100 m/pixel resolution using High Resolution Stereo Camera images of the Mars Express mission and Viking Orbiter images. In a subsequent least-squares fit, coefficients of the spherical harmonic function to degree and order 45 are computed. The dynamic models for Phobos were derived from a polyhedron representation of the DTM. The DTM, spherical harmonic function model, and dynamic models, have been refined and represent Phobos' dynamic and geometric topography with much more detail when compared to Shi et al. (2012) and Willner et al. (2010) models, respectively. The volume of Phobos has been re-determined to be in the order of 5741 km 3 with an uncertainty of only 0.6% of the total volume. This reduces the bulk density to 1.86±0.013 g/cm 3 in comparison to previous results. Assuming a homogeneous mass distribution a forced libration amplitude for Phobos of 1.14° is computed that is in better agreement with observations by Willner et al. (2010) than previous estimates. [ABSTRACT FROM AUTHOR]

Abstract: We have derived algorithms and techniques to precisely co-register laser altimeter profiles with gridded Digital Terrain Models (DTMs), typically derived from stereo images. The algorithm consists of an initial grid search followed by a least-squares matching and yields the translation parameters at sub-pixel level needed to align the DTM and the laser profiles in 3D space. This software tool was primarily developed and tested for co-registration of laser profiles from the Lunar Orbiter Laser Altimeter (LOLA) with DTMs derived from the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) stereo images. Data sets can be co-registered with positional accuracy between 0.13m and several meters depending on the pixel resolution and amount of laser shots, where rough surfaces typically result in more accurate co-registrations. Residual heights of the data sets are as small as 0.18m. The software can be used to identify instrument misalignment, orbit errors, pointing jitter, or problems associated with reference frames being used. Also, assessments of DTM effective resolutions can be obtained. From the correct position between the two data sets, comparisons of surface morphology and roughness can be made at laser footprint- or DTM pixel-level. The precise co-registration allows us to carry out joint analysis of the data sets and ultimately to derive merged high-quality data products. Examples of matching other planetary data sets, like LOLA with LRO Wide Angle Camera (WAC) DTMs or Mars Orbiter Laser Altimeter (MOLA) with stereo models from the High Resolution Stereo Camera (HRSC) as well as Mercury Laser Altimeter (MLA) with Mercury Dual Imaging System (MDIS) are shown to demonstrate the broad science applications of the software tool. [Copyright &y& Elsevier]

Abstract: Phobos flyby images obtained by the High Resolution Stereo Camera (HRSC) and the Super Resolution Channel (SRC) onboard the Mars Express spacecraft were used to produce a global Digital Terrain Model and orthoimage mosaics. We derived a set of Phobos topographic image maps, which are combined into an atlas that consists of four quadrangles on three map sheets at the scale of 1: 50,000. The lateral geometric accuracy of these maps of ±20m is more than four times better than that of past products. They are based on a shape model with 0.52°×0.52° grid spacing and show significantly more detail in comparison to previous data products. [Copyright &y& Elsevier]

We point out some errors in the most recent report from the International Astronomical Union (IAU) Working Group on Cartographic Coordinates and Rotational Elements (Archinal et al. 2018). [ABSTRACT FROM AUTHOR]

Abstract We report on the Lunar Stereo Topographic Camera (LSTC), currently being developed for the upcoming Luna-Resurs-1 Orbiter mission, which will perform observations from an orbit with the altitude to be optimized in the range from 50 to 100 km. The LSTC is composed of two identical optical heads and a common data processing unit. Each optical head has a similar optical system and an area array detector of 5120 × 3840 pixels, covering an area of 14 × 10 km (cross-track x along-track) from a 50-km spacecraft orbit. One of the optical heads looks forward within the orbit plane and the other looks backwards. The mission will focus on mapping mid- and polar latitudes up to 80° north and south to derive cartographic/topographic data products needed to support navigating future Luna-Resurs lander missions in polar regions. Extensive image simulations were produced to study the effects of illumination conditions and shadows on surface coverage and the precision of digital image matching for stereo photogrammetric processing. Also we studied a variety of possible off-nadir angles of the two camera systems and how these might affect the point measurement accuracy. We found that off-nadir angles of ±12.5° is a reasonable compromise to maximize topographic accuracy in varying observation conditions over both flat and rugged lunar terrains. Also, we investigate data compression algorithms at different compression ratios to minimize the impact of compression artifacts upon the photogrammetric image processing. The LSTC will take up to 400 images per orbit, i.e., 4800 images per day. During one month, we expect to cover 20% of the lunar surface on average, including the northern or southern polar areas. Imaging schemes and operation schedules will be optimized to maximum stereo coverage while producing the best DTM quality. We propose to increase the orbit altitude from the minimum altitude of 50 km to 70 km to enhance both along and cross track image overlap, yielding more geometrically stable image blocks. Highlights • The exploration of the lunar polar regions is central to the Russian Lunar program. • The Luna-Resurs-1 orbiter is scheduled for launch in 2020. • Stereo imaging in the Luna-Resurs-1 orbiter mission will be performed with the Lunar Stereo Topographic Camera (LSTC). [ABSTRACT FROM AUTHOR]

Abstract We apply cartographic methods on remote sensing data obtained by Lunar Reconnaissance Orbiter (LRO) and Kaguya (SELENE) to characterize potential landing sites for the "Luna-25" mission, previously selected. To identify presumable hazards (steep slopes, high ruggedness, cratered terrain) we developed special algorithms and GIS-tools. Sets of hazard maps for 3 high-priority potential landing sites were created. Highlights • For three landing ellipses the maps of hazards are created. • The tool for comprehensive GIS-analysis of landing sites is developed. • We have created a high-resolution DEM for parts of landing ellipse 4. [ABSTRACT FROM AUTHOR]

We explore the perspectives of the BepiColombo Laser Altimeter (BELA) onboard ESA / JAXA's Mercury mission BepiColombo and present an updated semi-analytical instrument performance model, in which we estimate signal-to-noise ratio, single shot probability of false detection, range errors and the accuracy of pulse width reconstruction. The model is generally applicable for other laser altimeters using matched filter algorithms for pulse detection and has been validated against the recently tested BELA flight model after integration on the BepiColombo spacecraft. Further, we perform numerical simulations of the instrument performance expected in orbit about Mercury. In particular, we study the measurement accuracy of topography, slopes and surface roughness, which will allow us to estimate local and global topographic coverage based on the current trajectory design. We also assess the potential for measuring the tidal Love number h 2 using cross-over points, which we estimate to be constrained with an absolute accuracy of 0.14 corresponding to a relative accuracy of about 18% after two years in Mercury orbit. [ABSTRACT FROM AUTHOR]

This report continues the practice where the IAUWorking Group on Cartographic Coordinates and Rotational Elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every 3 years. The Working Group has now become a "functional working group" of the IAU, and its membership is open to anyone interested in participating. We describe the procedure for submitting questions about the recommendations given here or the application of these recommendations for creating a new or updated coordinate system for a given body. Regarding body orientation, the following bodies have been updated: Mercury, based on MESSENGER results; Mars, along with a refined longitude definition; Phobos; Deimos; (1) Ceres; (52) Europa; (243) Ida; (2867) Šteins; Neptune; (134340) Pluto and its satellite Charon; comets 9P/Tempel 1, 19P/Borrelly, 67P/Churyumov-Gerasimenko, and 103P/Hartley 2, noting that such information is valid only between specific epochs. The special challenges related to mapping 67P/Churyumov-Gerasimenko are also discussed. Approximate expressions for the Earth have been removed in order to avoid confusion, and the low precision series expression for the Moon's orientation has been removed. The previously online only recommended orientation model for (4) Vesta is repeated with an explanation of how it was updated. Regarding body shape, text has been included to explain the expected uses of such information, and the relevance of the cited uncertainty information. The size of the Sun has been updated, and notation added that the size and the ellipsoidal axes for the Earth and Jupiter have been recommended by an IAU Resolution. The distinction of a reference radius for a body (here, the Moon and Titan) is made between cartographic uses, and for orthoprojection and geophysical uses. The recommended radius for Mercury has been updated based on MESSENGER results. The recommended radius for Titan is returned to its previous value. Size information has been updated for 13 other Saturnian satellites and added for Aegaeon. The sizes of Pluto and Charon have been updated. Size information has been updated for (1) Ceres and given for (16) Psyche and (52) Europa. The size of (25143) Itokawa has been corrected. In addition, the discussion of terminology for the poles (hemispheres) of small bodies has been modified and a discussion on cardinal directions added. Although they continue to be used for planets and their satellites, it is assumed that the planetographic and planetocentric coordinate system definitions do not apply to small bodies. However, planetocentric and planetodetic latitudes and longitudes may be used on such bodies, following the right-hand rule. We repeat our previous recommendations that planning and efforts be made to make controlled cartographic products; newly recommend that common formulations should be used for orientation and size; continue to recommend that a community consensus be developed for the orientation models of Jupiter and Saturn; newly recommend that historical summaries of the coordinate systems for given bodies should be developed, and point out that for planets and satellites planetographic systems have generally been historically preferred over planetocentric systems, and that in cases when planetographic coordinates have been widely used in the past, there is no obvious advantage to switching to the use of planetocentric coordinates. The Working Group also requests community input on the question submitting process, posting of updates to theWorking Group website, and on whether recommendations should be made regarding exoplanet coordinate systems. [ABSTRACT FROM AUTHOR]

We used 126 Voyager-1 and -2 as well as 87 Galileo images of Ganymede and searched for stereo images suitable for digital 3D stereo analysis. Specifically, we consider image resolutions, stereo angles, as well as matching illumination conditions of respective stereo pairs. Lists of regions and local areas with stereo coverage are compiled. We present anaglyphs and we selected areas, not previously discussed, for which we constructed Digital Elevation Models and associated visualizations. The terrain characteristics in the models are in agreement with our previous notion of Ganymede morphology, represented by families of lineaments and craters of various sizes and degradation stages. The identified areas of stereo coverage may serve as important reference targets for the Ganymede Laser Altimeter (GALA) experiment on the future JUICE (Jupiter Icy Moons Explorer) mission. [ABSTRACT FROM AUTHOR]

The Lunar Reconnaissance Orbiter Camera (LROC) system consists of a Wide Angle Camera (WAC) and Narrow Angle Camera (NAC). NAC images (∼0.5 to 1.7 m/pixel) reveal details of the Luna-21 landing site and Lunokhod-2 traverse area. We derived a Digital Elevation Model (DEM) and an orthomosaic for the study region using photogrammetric stereo processing techniques with NAC images. The DEM and mosaic allowed us to analyze the topography and morphology of the landing site area and to map the Lunokhod-2 rover route. The total range of topographic elevation along the traverse was found to be less than 144 m; and the rover encountered slopes of up to 20°. With the orthomosaic tied to the lunar reference frame, we derived coordinates of the Lunokhod-2 landing module and overnight stop points. We identified the exact rover route by following its tracks and determined its total length as 39.16 km, more than was estimated during the mission (37 km), which until recently was a distance record for planetary robotic rovers held for more than 40 years. [ABSTRACT FROM AUTHOR]

We searched for the sources of ice block falls at the steep scarps of the martian North Polar Layered Deposits (NPLD). We focused on two study areas at the NPLD, i.e., Scarp 1 (centered at 85.0°N, 151.5°E with a length of ∼20 km) and Scarp 2 (centered at 83.8°N, 235.5°E with a length of ∼12.5 km). Repeat High Resolution Imaging Science Experiment (HiRISE) observations with image scales of up to 0.25 m/pixel were used. Specifically, we identified changes in the shadow patterns at the scarps which attest to block fall activity. An automated change detection method, which searches for the grayscale difference between multi-temporal images, was developed to identify these patches where shadows have changed. The method was evaluated in six areas of Scarp 1 over all detection periods, and achieved an average true positive rate of 97.6% and false discovery rate of 9.4%. The spatio-temporal distribution showed that ice block falls were an active process. Along Scarp 1, about 129 ice block falls occurred per Mars year per km2, mostly at elevations 0–300 m of the 500 m high scarp, where the slope is over 30°. The amount of ice block falls increased with steeper slope angles. Along Scarp 2, about 237 ice block falls occurred per Mars year per km2, resting in the form of smaller blocks and fine particles, or spreading outward in fan-shaped patterns. We compared the detected source areas at Scarp 2 with the fresh ice blocks observed on the underlying Basal Unit (BU) between MY 30 and MY 31 to analyze the dynamic process of ice block falls. Underneath the areas with large numbers of detached ice-fragments, many fresh ice blocks were found on the BU. On the other hand, some regions of Scarp 2 did not show evidence of detached ice-fragments despite fresh ice blocks on the BU areas below. Our comparison proved that both the NPLD and the BU scarps are active source areas of ice block falls. The detections of block fall sources at the NPLD scarps can help to distinguish events from the NPLD and those from the BU and refine the estimates of active polar scarp retreat, which will improve the understanding of the polar cap evolution. • We successfully demonstrate an automated change detection method to search for sources of ice block falls at two NPLD scarps. • The method reached a true positive rate of 97.6% and a false discovery rate of 9.4%. • Ice block falls are an active process at both steep scarps. • The scarp presented a positive feedback between ice block falls and steepness. • Ice blocks found on the BU came from both the NPLD scarp and the BU scarp. [ABSTRACT FROM AUTHOR]

The new technique for generation of coordinate control point networks based on photogrammetric processing of heterogeneous planetary images (obtained at different time, scale, with different illumination or oblique view) is developed. The technique is verified with the example for processing the heterogeneous information obtained by remote sensing of Ganymede by the spacecraft Voyager-1, -2 and Galileo. Using this technique the first 3D control point network for Ganymede is formed: the error of the altitude coordinates obtained as a result of adjustment is less than 5 km. The new control point network makes it possible to obtain basic geodesic parameters of the body (axes size) and to estimate forced librations. On the basis of the control point network, digital terrain models (DTMs) with different resolutions are generated and used for mapping the surface of Ganymede with different levels of detail (Zubarev et al., 2015b). [ABSTRACT FROM AUTHOR]

The High Resolution Stereo Camera (HRSC) of ESA׳s Mars Express is designed to map and investigate the topography of Mars. The camera, in particular its Super Resolution Channel (SRC), also obtains images of Phobos and Deimos on a regular basis. As HRSC is 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. The sub-pixel accuracy of 3D points derived from stereo analysis allows producing DTMs with grid size of up to 50 m and height accuracy on the order of one image ground pixel and better, as well as corresponding orthoimages. Such data products have been produced systematically for approximately 40% of the surface of Mars so far, while global shape models and a near-global orthoimage mosaic could be produced for Phobos. HRSC is also unique because it bridges between laser altimetry and topography data derived from other stereo imaging instruments, and provides geodetic reference data and geological context to a variety of non-stereo datasets. This paper, in addition to an overview of the status and evolution of the experiment, provides a review of relevant methods applied for 3D reconstruction and mapping, and respective achievements. We will also review the methodology of specific approaches to science analysis based on joint analysis of DTM and orthoimage information, or benefitting from high accuracy of co-registration between multiple datasets, such as studies using multi-temporal or multi-angular observations, from the fields of geomorphology, structural geology, compositional mapping, and atmospheric science. Related exemplary results from analysis of HRSC data will be discussed. After 10 years of operation, HRSC covered about 70% of the surface by panchromatic images at 10–20 m/pixel, and about 97% at better than 100 m/pixel. As the areas with contiguous coverage by stereo data are increasingly abundant, we also present original data related to the analysis of image blocks and address methodology aspects of newly established procedures for the generation of multi-orbit DTMs and image mosaics. The current results suggest that multi-orbit DTMs with grid spacing of 50 m can be feasible for large parts of the surface, as well as brightness-adjusted image mosaics with co-registration accuracy of adjacent strips on the order of one pixel, and at the highest image resolution available. These characteristics are demonstrated by regional multi-orbit data products covering the MC-11 (East) quadrangle of Mars, representing the first prototype of a new HRSC data product level. [ABSTRACT FROM AUTHOR]

Invaluable information about the interior of icy satellites orbiting close to the giant planets can be gained by monitoring the response of the satellite's surfaces to external tidal forces. Due to its geodetic accuracy, laser altimetry is the method of choice to measure time-dependent radial surface displacements from orbit. We present an instrument performance model with special focus on the capabilities to determine the corresponding tidal Love number h 2 and apply the model to the Ganymede Laser Altimeter (GALA) on board of the Jupiter Icy Moons Explorer (JUICE). Based on the instrument and spacecraft performance, we derive the range error and the measurement capabilities of the GALA instrument to determine the amplitude of the tide induced radial displacement of Ganymede's surface using the cross-over technique. We find that h 2 of Ganymede can be determined with an accuracy of better than 2% by using data acquired during the nominal mission. Furthermore, we show that this accuracy is sufficient to confirm the presence of a putative subsurface water ocean and, additionally, to constrain the thickness of the overlaying ice shell to ± 20km. [ABSTRACT FROM AUTHOR]

A new Phobos Atlas has been prepared, which includes a variety of thematic maps at various projections and scales, emphasizing dynamic topography, surface multispectral properties, geomorphology, as well as grooves- and crater statistics. The atlas benefits from innovative mapping techniques and recent results from Mars Express image processing: new derived control point networks, shape models and gravity field working models. A structure of the atlas is presented and some examples of the maps are shown. The Phobos Atlas can be useful for the future mission planning to the Martian satellite. [ABSTRACT FROM AUTHOR]

Characterization of the potential landing sites for the planned Luna-Glob and Luna-Resurs Russian missions requires cartographic and geodetic support prepared with special methods and techniques that are briefly overviewed here. The data used in the analysis, including the digital terrain models (DTMs) and the orthoimages acquired in the survey carried out from the Lunar Reconnaissance Orbiter and Kaguya spacecraft, are described and evaluated. By way of illustration, different regions of the lunar surface, including the subpolar regions of the Moon, are characterized with the suggested methods and the GIS-technologies. The development of the information support for the future lunar missions started in 2011, and it is now carried on in MIIGAiK Extraterrestrial Laboratory (MExLab), which is a department of the Moscow State University of Geodesy and Cartography (MIIGAiK). [ABSTRACT FROM AUTHOR]

The illumination conditions of the lunar south pole are investigated using a geometrically adjusted, 20 m/pixel Digital Terrain Model (DTM) from laser tracks of the Lunar Orbiter Laser Altimeter (LOLA). Several comparisons with Narrow Angle Camera (NAC) images have been made to cross-validate the results. Illumination conditions were first evaluated over a region of 20 × 20 km over a one-year period (October 22, 2018 – October 22, 2019) at surface level and 2 m above ground. Three potential landing sites are investigated in more detail. A 19-year study covering the lunar precessional cycle was carried out at surface level, 2 and 10 m above ground for a site found at “Connecting Ridge”, the ridge connecting the Shackleton and de Gerlache crater. This area was found to be an ideal site for future landing missions with respect to illumination conditions. We identified locations receiving sunlight for 92.27% of the time at 2 m above ground and 95.65% of the time at 10 m above ground. At these locations the longest continuous periods in darkness are typically only 3–5 days. [ABSTRACT FROM AUTHOR]

This paper presents an overview of developments in the cartography of the Martian moons Phobos and Deimos from the early satellite images to recent maps based on data from past and on-going Mars missions, especially Viking and Mars Express . We describe in detail the definition and use of special projections for these irregular-shaped bodies. New controlled Phobos mosaics and a topographic atlas in a scale of 1: 50,000 derived from images of the High Resolution Stereo Camera/Super Resolution Channel (HRSC/SRC) camera on Mars Express are presented. [ABSTRACT FROM AUTHOR]

MarcoPolo-R is a sample return mission to a primitive Near-Earth Asteroid (NEA) proposed in collaboration with NASA. It will rendezvous with a primitive NEA, scientifically characterize it at multiple scales, and return a unique sample to Earth unaltered by the atmospheric entry process or terrestrial weathering. MarcoPolo-R will return bulk samples (up to 2 kg) from an organic-rich binary asteroid to Earth for laboratory analyses, allowing us to: explore the origin of planetary materials and initial stages of habitable planet formation; identify and characterize the organics and volatiles in a primitive asteroid; understand the unique geomorphology, dynamics and evolution of a binary NEA. This project is based on the previous Marco Polo mission study, which was selected for the Assessment Phase of the first round of Cosmic Vision. Its scientific rationale was highly ranked by ESA committees and it was not selected only because the estimated cost was higher than the allotted amount for an M class mission. The cost of MarcoPolo-R will be reduced to within the ESA medium mission budget by collaboration with APL (John Hopkins University) and JPL in the NASA program for coordination with ESA's Cosmic Vision Call. The baseline target is a binary asteroid (175706) 1996 FG3, which offers a very efficient operational and technical mission profile. A binary target also provides enhanced science return. The choice of this target will allow new investigations to be performed more easily than at a single object, and also enables investigations of the fascinating geology and geophysics of asteroids that are impossible at a single object. Several launch windows have been identified in the time-span 2020-2024. A number of other possible primitive single targets of high scientific interest have been identified covering a wide range of possible launch dates. The baseline mission scenario of MarcoPolo-R to 1996 FG3 is as follows: a single primary spacecraft provided by ESA, carrying the Earth Re-entry Capsule, sample acquisition and transfer system provided by NASA, will be launched by a Soyuz-Fregat rocket from Kourou into GTO and using two space segment stages. Two similar missions with two launch windows, in 2021 and 2022 and for both sample return in 2029 (with mission duration of 7 and 8 years), have been defined. Earlier or later launches, in 2020 or 2024, also offer good opportunities. All manoeuvres are carried out by a chemical propulsion system. MarcoPolo-R takes advantage of three industrial studies completed as part of the previous Marco Polo mission (see ESA/SRE (2009)3, Marco Polo Yellow Book) and of the expertise of the consortium led by Dr. A.F. Cheng (PI of the NASA NEAR Shoemaker mission) of the JHU-APL, including JPL, NASA ARC, NASA LaRC, and MIT. [ABSTRACT FROM AUTHOR]

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars' satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Šteins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn. [ABSTRACT FROM AUTHOR]

Abstract: We report on the results of the Mars Express High-Resolution Stereo Camera (HRSC) experiment pertaining to one of its major aims, mapping the surface of Mars by high-resolution digital terrain models (DTM, up to 50m grid spacing) and orthoimages (up to 12.5m resolution). We introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation. We also address the performance characteristics of the mapping project related to different aspects of internal accuracy, accuracy with respect to the global reference system, and regional aspects. Using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data, a mean precision of the resulting 3D points of about 12m is obtained, exceeding the mean ground resolution of the stereo images. Using Mars Orbiter Laser Altimeter (MOLA) data, the HRSC models are firmly tied to the global reference system at the scale of the HRSC DTM grid spacing in the lateral dimension, and to within few meters vertically. HRSC high-resolution DTMs are typically generated using a grid size of about 2 times the mean ground resolution, but usually not larger than 3 times the mean ground resolution, and not smaller than 3 times the precision of the integrated 3D points derived from stereo image analysis. Statistically, every grid cell is based on at least one measured 3D point. Thus, horizontal DTM resolution is well established with regard to the precision and density of the derived 3D points, while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued. Comparison with the DTM derived from MOLA data allows us to identify specific advancements related to this updated view of Martian topography. We also address the mapping performance of HRSC in comparison to MOLA with respect to latitude and to different surface types and morphologies. Finally, comparison with MOLA highlights typical complementarities of the two different approaches for mapping planetary surfaces. [Copyright &y& Elsevier]

A global lunar topographic map with a spatial resolution of finer than 0.5 degree has been derived using data from the laser altimeter (LALT) on board the Japanese lunar explorer Selenological and Engineering Explorer (SELENE or Kaguya). In comparison with the previous Unified Lunar Control Network (ULCN 2005) model, the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers. Spherical harmonic analysis of global topographic data for the Moon, Earth, Mars, and Venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales. However, simple rigid support is suggested to dominate for the Moon, Venus, and Mars for smaller scares, which may indicate a drier lithosphere than on Earth, especially for the Moon and Venus. [ABSTRACT FROM AUTHOR]

Abstract: The BepiColombo Laser Altimeter (BELA) has been selected for flight on board the European Space Agency''s BepiColombo Mercury Planetary Orbiter (MPO). The experiment is intended to be Europe''s first planetary laser altimeter system. Although the proposed system has similarities to the Mercury Laser Altimeter (MLA) currently flying on board NASA''s MESSENGER mission to Mercury, the specific orbit and construction of the MPO force the use of novel concepts for BELA. Furthermore, the base-lined range-finding approach is novel. In this paper, we describe the BELA system and show preliminary results from some prototype testing. [Copyright &y& Elsevier]

Abstract: ESA''s Mars Express has successfully completed its nominal mission of one Martian year covering about 25% of the surface in stereo and color with resolutions up to 10m/pixel by its high-resolution stereo camera (HRSC). Mars Express is now in its extended mission phase, during which much of the remaining part of the Martian surface is envisaged to be covered in stereo and color. The HRSC instrument is designed to map the morphology, topography, structure and geologic context of the surface as well as atmospheric phenomena. This paper discusses the measurement principles and operations of the instrument as well as the acquisition, calibration and processing of regional and global data sets. As HRSC is a push-broom scanning instrument with nine CCD line detectors mounted in parallel on a focal plane, its unique feature is the ability to obtain near-simultaneous imaging data at high resolution, with along-track triple stereo, four colors and five different phase angles, avoiding any time-dependent variations of the observing conditions. The HRSC spatial resolution is 10m/pixel at the nominal periapsis altitude of 250km, with an image swath of 53km, and 2.3m/pixel for an additional framing CCD device, called super resolution channel (SRC), practically working as an additional tenth channel of the HRSC and yielding nested-in black and white images for studies of small-scale geologic features. The sub-pixel accuracy of the three-dimensional point determination allows the derivation of digital terrain models (DTMs) with a grid size of up to 50m and a height accuracy of a single pixel with up to 10m, thus enabling us to carry out detailed quantitative analyses of the surface structure. The HRSC (1) bridges the gap between the medium–high-resolution Viking imagery and the very-high-resolution Global Surveyor mission, thus providing geological context, and (2) fills the gaps in the three-dimensional coverage and DTM grid of the MOLA laser altimetry data, and (3) helps characterize landing sites for in-situ measurements. HRSC also builds the basis for extended compositional mapping when combining spectral information with topographic photomaps over large areas. So far the HRSC measurements have made a significant contribution to the study of the evolution of volcanism and the role of water and ice throughout the Martian history. [Copyright &y& Elsevier]

Spectra of Asteroid 9969 Braille in the 1.25–2.6 μm region returned by the Deep Space 1 (DS1) Mission show a ∼10% absorption band centered at 2 μm, and a reflectance peak at 1.6 μm. Analysis of these features suggest that the composition of Braille is roughly equal parts pyroxene and olivine. Its spectrum between 0.4 and 2.5 μm suggests that it is most closely related to the Q taxonomic type of asteroid. The spectrum also closely matches that of the ordinary chondrites, the most common type of terrestrial meteorite. The geometric albedo of Braille is unusually high (pv=0.34), which is also consistent with its placement within the rarer classes of stony asteroids, and which suggests it has a relatively fresh, unweathered surface, perhaps due to a recent collision. [Copyright &y& Elsevier]

The flyby of the nucleus of the Comet 19P/Borrelly by the Deep Space 1 spacecraft produced the best views to date of the surface of these interesting objects. It transformed Borrelly from an astronomical object shrouded in coma of gas and dust into a geological object with complex surface processes and a rich history of erosion and landform evolution. Based on analysis of the highest resolution images, stereo images, photometry, and albedo we have mapped four major morphological units and four terrain features. The morphological units are named dark spots, mottled terrain, mesas, and smooth terrain. The features are named ridges, troughs, pits, and hills. In strong contrast to asteroids, unambiguous impact craters were not observed on Borrelly''s surface. Because of the relatively short period of this comet, surface erosion by volatile sublimation is, in geologic terms, a very active process. The formation and the morphologies of units and features appear to be driven by differential rates of sublimation erosion. Erosional rates across the comet are probably controlled by solar energy input and the location of the subsolar point during perihelion. Differences in energy input may produce different varieties of sublimation erosional landforms. The terrains on Borrelly suggest that solar energy input could map directly into erosional processes and landforms. [Copyright &y& Elsevier]

The NASA-JPL Deep Space 1 Mission (DS1) encountered the short-period Jupiter-family Comet 19P/Borrelly on September 22, 2001, about 8 days after perihelion. DS1''s payload contained a remote-sensing package called MICAS (Miniature Integrated Camera Spectrometer) that included a 1024 square CCD and a near IR spectrometer with ∼12 nm resolution. Prior to its closest approach of 2171 km, the remote-sensing package on the spacecraft obtained 25 CCD images of the comet and 45 near-IR spectra (L. Soderblom et al., 2002, Science 296, 1087–1091). These images provided the first close-up view of a comet''s nucleus sufficiently unobscured to perform quantitative photometric studies. At closest approach, corresponding to a resolution of 47 meters per pixel, the intensity of the coma was less than 1% of that of the nucleus. An unprecedented range of high solar phase angles (52–89 degrees), viewing geometries that are in general attainable only when a comet is active, enabled the first quantitative and disk resolved modeling of surface photometric physical parameters, including the single particle phase function and macroscopic roughness. The disk-integrated geometric albedo of Borrelly''s nucleus is 0.029±0.006, comparable to the dark hemisphere of Iapetus, the lowest albedo C-type asteroids, and the uranian rings. The Bond albedo, 0.009±0.002, is lower than that of any Solar System object measured. Such a low value may enhance the heating of the nucleus and sublimation of volatiles, which in turn causes the albedo to decrease even further. A map of normal reflectance of Borrelly shows variations far greater than those seen on asteroids. The two main terrain types, smooth and mottled, exhibit mean normal reflectances of 0.03 and 0.022. The physical photometric parameters of Borrelly''s nucleus are typical of other small dark bodies, particularly asteroids, except preliminary modeling results indicate its regolith may be substantially fluffier. The nucleus exhibits significant variations in macroscopic roughness, with the oldest, darkest terrain being slightly smoother. This result suggests the infilling of low-lying areas with dust and particles that have not been able to leave the comet. The surface of the comet is backscattering, but there are significant variations in the single particle phase function. One region exhibits a flat particle phase function between solar phase angles of 50° and 75° (like cometary dust and unlike planetary surfaces), suggesting that its regolith is controlled by native dust rather than by meteoritic bombardment. [Copyright &y& Elsevier]

The nucleus, coma, and dust jets of short-period Comet 19P/Borrelly were imaged from the Deep Space 1 spacecraft during its close flyby in September 2001. A prominent jet dominated the near-nucleus coma and emanated roughly normal to the long axis of nucleus from a broad central cavity. We show it to have remained fixed in position for more than 34 hr, much longer than the 26-hr rotation period. This confirms earlier suggestions that it is co-aligned with the rotation axis. From a combination of fitting the nucleus light curve from approach images and the nucleus'' orientation from stereo images at encounter, we conclude that the sense of rotation is right-handed around the main jet vector. The inferred rotation pole is approximately perpendicular to the long axis of the nucleus, consistent with a simple rotational state. Lacking an existing IAU comet-specific convention but applying a convention provisionally adopted for asteroids, we label this the north pole. This places the sub-solar latitude at ∼60° N at the time of the perihelion with the north pole in constant sunlight and thus receiving maximum average insolation. [Copyright &y& Elsevier]

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (≤345 kelvin, with no trace of water ice or hydrated minerals), consistent with ∼10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus. [ABSTRACT FROM AUTHOR]

The primary poles for (243) Ida and (134340) Pluto and its satellite (134340) Pluto : I Charon were redefined in the IAU Working Group on Cartographic Coordinates and Rotational Elements (WGCCRE) 2006 report (Seidelmann et al. in Celest Mech Dyn Astr 98:155, ), and 2009 report (Archinal et al. in Celest Mech Dyn Astr 109:101, ), respectively, to be consistent with the primary poles of similar Solar System bodies. However, the WGCCRE failed to take into account the effect of the redefinition of the poles on the values of the rotation angle W at J2000.0. The revised relationships in Table 3 of Archinal et al. ) are where d is the time in TDB days from J2000.0 (JD2451545.0). [ABSTRACT FROM AUTHOR]

At the margins of the north polar deposits of dusty water ice on Mars, steep scarps reveal layered deposits that preserve a record of the planet's recent climate changes. Some of these scarps are currently the most active places on Mars with annual avalanches and block falls. We estimated the erosion rate of a steep north polar scarp by automatically identifying newly apparent blocks throughout a time series of HiRISE images. The total depositional volume over three Mars years corresponds to a minimum erosion rate of ~0.3 m3 per Mars year per meter along the scarp, or a minimum average scarp retreat rate of ~0.2 m/kyr. This rate cannot balance published 0.01–1 m/yr viscous flow rates, implying that either lower rates of the latter occur or that other processes contribute more than block falls to the slopes' steepness. • We monitored block falls along a north polar scarp over 3 Mars years by using automatic detection techniques. • The resulting erosion rate, ~0.3 m3 per Mars year per meter along the scarp, corresponds to a scarp retreat rate of ~0.2 m/kyr. • This erosion rate cannot counteract published estimates of viscous flow velocities. [ABSTRACT FROM AUTHOR]

We developed a change detection method for the identification of ice block falls using NASA's HiRISE images of the north polar scarps on Mars. Our method is based on a Support Vector Machine (SVM), trained using Histograms of Oriented Gradients (HOG), and blob detection. The SVM detects potential new blocks between a set of images; the blob detection, then, confirms the identification of a block inside the area indicated by the SVM and derives the shape of the block. The results from the automatic analysis were compared with block statistics from visual inspection. We tested our method in 6 areas each consisting of 1000 × 1000 pixels, where several hundreds of blocks were identified. The results for the given test areas produced a true positive rate of ~75% for blocks with sizes larger than 0.5 m2 (i.e., approx. 3 times the available ground pixel size) and a false discovery rate of ~8.5%. Using blob detection, we were also able to recover the size of each block within 3 pixels of their actual size. • A change detection method for block falls' identification on Mars is proposed. • The images and a training data set are prepared. • A combination of SVM/HOG and blob detection is used. • The results show a true positive rate of ~75% and a false detection rate of ~8.5%. [ABSTRACT FROM AUTHOR]