Search

This talk will introduce the The Canary Island Long-Baseline Observatory (CILBO), a double station meteor camera setup located on the Canary Islands and operated by ESA’s Meteor Research Group since 2010. Our observations of meteors are obtained in the visual wavelength band by intensified video cameras from both stations, supplemented by an intensified video camera mounted with a spectral grating at one of the locations. The cameras observe during cloudless and precipitation-free nights and data are transferred to a main computer located at ESA/ESTEC once a day. The image frames that contain spectral information are calibrated, corrected, and finally processed into line intensity profiles. An ablation simulation, based on Bayesian statistics using a Markov-Chain Monte-Carlo method, allows to determine a parameter space, including the ablation temperatures, chemical elements and their corresponding line intensities, to fit against the line intensity profiles of the observed meteor spectra. The algorithm is presented in this talk. Several hundred spectra have been processed and will be made available through the Guest Archive Facility of the Planetary Science Archive of ESA.

The Canary Island Long-Baseline Observatory (CILBO) is a double-station meteor camera setup located on the Canary Islands operated by ESA's Meteor Research Group since 2010. Observations of meteors are obtained in the visual wavelength band by intensified video cameras from both stations, supplemented by an intensified video camera mounted with a spectral grating at one of the locations. The cameras observe during cloudless and precipitation-free nights, and data are transferred to a main computer located at ESA/ESTEC once a day. The image frames that contain spectral information are calibrated, corrected, and finally processed into line intensity profiles. An ablation simulation, based on Bayesian statistics using a Markov chain Monte Carlo method, allows determining a parameter space, including the ablation temperatures, chemical elements, and their corresponding line intensities, to fit against the line intensity profiles of the observed meteor spectra. The algorithm is presented in this paper and one example is discussed. Several hundred spectra have been processed and made available through the Guest Archive Facility of the Planetary Science Archive of ESA. The data format and metadata are explained.

Anghel, S., et al., The increase in detector sensitivity and availability in the past three decades has allowed us to derive knowledge of the meteoroid flux and impact energy into the Earth's atmosphere. We present the multi-instrument detected 2018 December 22 fireball over Western Pyrenees, and compare several techniques aiming to obtain a reliable method to be used when measuring impacts of similar scale. From trajectory data alone, we found a bulk density of 3.5 g cm-3 to be the most likely value for the Pyrenean meteoroid. This allowed to further constrain the dynamic mass, which translated into a kinetic energy of 1 ton TNT (4.184 × 109 J). For the second energy derivation, via the fireball's corrected optical radiation, we obtained a more accurate empirical relation measuring well-studied bolides. The result approximates to 1.1 ton TNT, which is notably close to the nominal dynamic result, and agrees with the lower margin of the seismic-based energy estimation, yet way lower than the infrasound estimate. Based on the relation derived in this study, we consider the nominal estimate from both the dynamic and photometric methods to be the most accurate value of deposited energy (1 ton TNT). We show that the combination of these two methods can be used to infer the meteoroid density. Among the methods presented in this paper, we found that the optical energy is the most reliable predictor of impact energy near the ton TNT-scale., S. Anghel and D. A. Nedelcu were supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0226/16PCCDI/2018, within PNCDI III. EP-A and JMT-R acknowledge funding from PGC2018-097374-B-I00 (MCI-AEI-FEDER, EU). M. Birlan work was partly supported by SEEING-IEA CNRS program. R. Hueso and A. Sánchez-Lavega were supported by Diputación Foral de Bizkaia and Gobierto Vasco IT1366-19.

The NEO Coordination Centre (NEOCC) is one of the key components of ESA’s Planetary Defence activities. Among its goals, it has a mandate to coordinate, collect and analyse telescopic observations of NEOs. To reach this objective, we developed a wide network of observational assets. In this contribution, we discuss some of the latest results obtained thanks to this unique global network. In the recent years, ESA has strengthened its network of follow-up telescopes. It now has direct access to the Optical Ground Station (Tenerife, Spain) and the Calar Alto Schmidt telescope (fully dedicated to NEOCC activities - Spain). Via dedicated contracts, it also has allocated time in the LCO network, as well as telescopes in Australia (Zadko), Namibia (6ROADS), Reunion and India. Scientific collaboration & agreements granted time with ESO’s VLT and Korean’s BOAO and SOAO facilities. Regarding future observational means, ESA is currently continuing the construction of the Flyeye telescope. This is a 1-meter class telescope with an ultra-wide field of 7º by 7º that will be installed on top of Monte Mufara (Italy). The Flyeye will be a remote-controlled telescope, while data will be automatically analysed by a dedicated pipeline, with the overall objective of reducing to a minimum the human intervention. The mentioned observational assets available to our observers are used for a variety of observations. The main goal is of course the acquisition of follow-up observations, both on short notice and at the faint end of an object's observability window. We employ our smaller but geographically-distributed telescopes to quickly react to discoveries of possible new high-priority objects, such as imminent impactors. Larger assets, such as VLT, are instead routinely scheduled to obtain astrometry of risk list objects, down to magnitude ~27. With some specific telescopes we are also focusing on twilight and low-elongation observations, which are essential to track and characterize specific classes of objects, such as Atiras or Earth Trojans. In addition to these regular observations, we also use some of the telescopes to attempt challenging or innovative observation techniques. For example, we are experimenting with the possibility to use modest sub-meter-size telescopes to obtain detections of important objects down to magnitude ~24, by observing the same target for an entire night and then stacking hundreds of frames on the motion of the object. These capabilities are made possible by recent advancements in GPU processing, which are also opening the way to new image analysis modes, such as synthetic tracking. We are also pioneering the so called "negative recovery" technique, using targeted non-detections of risk list objects to exclude their impact solutions, even without recovering the object itself. Finally, we are active players in international campaigns dedicated to specific NEOs or observational challenges. This includes both our participation in internationally-led efforts, such as those managed by IAWN, and the organization of our own campaigns, such as a recent one dedicated to the astrometric coverage of the Earth fly-by of BepiColombo as a proxy to test the observational capabilities of our network on very close approachers. All those observations are supplemented by the operations of our own orbit determination and impact monitoring software system (so-called AstOD) that allows constraining with the best possible accuracy the orbits of the observed objects and the possible impact chances with the Earth in the next 100 years. In what regards the threat monitoring over imminent impactors, we count on the Meerkat tool, which bases its automated operation on the use of systematic ranging and allows detecting and warning our staff of those cases, as recently occurred with 2022 EB5.

Increasing our knowledge of the orbits and compositions of Near-Earth Objects (NEOs) is important for a better understanding of the evolution of the Solar System and of life. The detection of serendipitous NEO appearances among the millions of archived exposures from large astronomical imaging surveys can provide a contribution which is complementary to NEO surveys. Using the AstroWISE information system, this work aims to assess the detectability rate, the achieved recovery rate and the quality of astrometry when data mining the ESO archive for the OmegaCAM wide-field imager at the VST. We developed an automatic pipeline that searches for the NEO appearances inside the AstroWISE environment. Throughout the recovery process, the pipeline uses several public web-tools to identify possible images that overlap with the position of NEOs, and acquires information on the NEOs predicted position and other properties (e.g., magnitude, rate and direction of motion) at the time of observations. We have recovered 196 appearances of NEOs from a set of 968 appearances predicted to be recoverable. It includes appearances for three NEOs which were on the impact risk list at that point. These appearances were well before their discovery. The subsequent risk assessment using the extracted astrometry removes these NEOs from the risk list. We estimate a detectability rate of 0.05 per NEO at an SNR>3 for NEOs in the OmegaCAM archive. Our automatic recovery rates are 40% and 20% for NEOs on the risk list and the full list, respectively. The achieved astrometric and photometric accuracy is on average 0.12 arcsec and 0.1 mag. These results show the high potential of the archival imaging data of the ground-based wide-field surveys as useful instruments for the search, (p)recovery and characterization of NEOs. Highly automated approaches, as possible using AstroWISE, make this undertaking feasible., 13 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

In the course of the NEar real-time MOnitoring (NEMO) project an information system for bright fireballs on a global scale has been developed. It analyses and combines as much available data as possible from different sources to monitor fireball events, from witness reports via meteor networks to infrasound data. One of near real-time monitoring system's main goals is to deliver information about events in near real-time. For this purpose, the project is supplemented by an alert system. This system is based on Social Media, predominantly on Twitter. Its detection procedure and working principle are presented in this study.

The Lunar Meteoroid Impact Observer (LUMIO) is a CubeSat mission at the Earth-Moon Lagrangian point 2 (L2) designed to observe, quantify, and characterize the meteoroid impacts by detecting their flashes on the Lunar farside. LUMIO can be deployed as one of the payloads in the NASA Commercial Lunar Payload System or from Artemis-2 mission to a low Lunar orbit and to demonstrate autonomous navigation capabilities to reach its operational orbit around the Earth-Moon L2. From there, its scientific mission to map and investigate the spatial and temporal characteristics of meteoroids impacting the Lunar surface will start and is expected to last for one year. LUMIO is a 12U CubeSat including a dedicated camera to monitor impact flashes in the visible and near-infrared spectrum, and also allows estimating the impact of temperature and energy. Optical navigation using the payload camera will also demonstrate increased on-board autonomy and drastically reduced mission costs. Navigation validation will be carried out using standard ground-based radiometric techniques enabled by a miniaturized X-band coherent transponder on-board. LUMIO can also use an inter-satellite link for telemetry and control via a commercial Lunar data relay system, providing a redundant communication system and lowering the need for high-gain ground stations for routine operations. The satellite bus derives from a commercial version designed for Low Earth Orbit and it will feature several improvements to operate in the Lunar environment, including a more advanced thermal control and radiation shielding. Commercial Off-The-Shelf systems will require a radiation screening and this will contribute to maintain the mission budget low and aim at a launch date in 2024.

1. Introduction The ESA-Roscosmos ExoMars 2022 Mission [1] will deliver the Rosalind Franklin Rover and Kazachock Surface Platform to the Oxia Planum landing site on Mars [2, 3]. The launch window opens on 20 September 2022 with a corresponding Mars arrival on 10 June 2023. The Rover’s mission objectives are to search for signs of life and characterise the shallow subsurface. During its 211 sol nominal mission ‘Rosalind Franklin’ will accomplish its objectives using its ‘Pasteur’ Payload of 9 instruments, plus a drilling system capable of extracting samples from down to 2m for analysis. 2. Mission Status Tests and reviews to confirm overall spacecraft readiness are proceeding, including a campaign of High Altitude Drop Tests (HADTs) on the parachute system. Activities at the Rover Operations Control Centre (ROCC) —located at ALTEC, Turin (IT)— are ramping up. Software systems used during the mission for planning are being tested and refined, and the Control and Science Teams are working together to train for the day-to-day operations environment. 3. Spacecraft Control The ROCC can be considered an Activity Plan factory for the Rosalind Franklin rover. The ROCC is designed to support ESOC (European Space Operations Centre) during the launch, LEOP (Launch and Early Orbit Phase), when conducting periodic checkouts of the rover and instruments in interplanetary cruise, and to perform rover mission operations on Mars. A partner facility in Moscow, the Surface Platform Payload Operations Control Centre (SPOCC), controls the Kazachok Surface Platform. The Science Team and the rover Control Team work together at the ROCC (including by remote connection) to conduct two parallel and connected processes. The Strategic process, performed during office hours, is the top-level process to plan rover activities. It proceeds via daily structured work and meetings. Strategic planning aims to achieve the rover mission objectives and maximize scientific return, and it is dynamic; adjusting to new scientific findings and interpretations. Strategic planning is done on 3 timescales: short term (next sol), medium term (within the current mission phase), and long-term (the next major mission phase plus objectives that could be addressed further in the future). The Tactical process is the sequence of events triggered by the downlink of rover data to ROCC following an orbiter pass. It ends with uplink of validated activity plans to the rover for execution. Tactical planning is done on a schedule synchronised with downlink and uplink via Mars orbiters. Figure 1: Illustration of scheduling strategic and tactical processes. 4. Strategic Plan The Strategic Plan provides traceability from the top-level mission science objectives to individual rover activities. It provides the scientific context and background for how the mission science is organised. The Rover Science Operations Working Group (RSOWG) is building the Strategic Plan for the rover via 3 main tasks: Define scientific questions elaborated from the mission objectives. From these questions, construct corresponding hypotheses that are testable by rover instruments at the Oxia Planum landing site. Prepare preliminary instrument command sequences and potential targets to test the hypotheses. Upon landing, the Strategic Plan will be ‘initialised’ at the landing point by the Science Team. They will interpret new data, assess locations to perform initial activities, and set long-term objectives. 5. Science Targets The ‘Science Target Scheme’ has been conceived for use in daily science operations in order to harmonize the description of the places and features observed by the Rosalind Franklin rover during the mission, and the links between them. It is integrated into software tools running at the ROCC, and the data submitted to ESA’s Planetary Science Archive (PSA). It is a hierarchical schema of 10 classes representing objects at spatial scales relevant to Rover science, from areas identified in orbital data, down to spots on crushed samples analysed by instruments in the Rovers’ Analytical Laboratory Drawer, ALD [see 1]. A concept showing use of several target types used during the Post-Landing-To-Egress (PLTE) mission phase is shown in Figure 2. Figure 2: Concept for use of science targets in the PLTE mission phase (expected to last ~10 sols). 6. Team Simulations During 2021-2023 a programme of simulations is being performed for training and certification of the team for operations. A subset of simulations in the programme are planned and run by the RSOWG. These allow the Science Team to test and refine their processes, for example to perform decision-making in the time-limited operations environment, and to rehearse several designated roles (e.g. Journal Keeper, Long Term Planner). RSOWG simulations are planned by a dedicated Simulations Planning Group composed of science, project and industrial team representatives. They use inputs from all Rover instrument teams, and lessons learned from analogue campaigns [e.g. 4] and other information, to design the scenarios determined to be most fruitful for maturing scientific processes. 7. ‘Micro’ and ‘Macro’ working groups The RSOWG has chartered the ‘Micro’ and ‘Macro’ sub-working groups with a broad mandate to prepare for and optimise aspects of science operations at those spatial scales. For example, the Micro group works on the protocol for assessment of sample analyses, and builds knowledge of sample types using terrestrial analogues. While the Macro group, for example, provides a detailed morphostratigraphic map of the landing site as input to building the strategic plan [5], and prepares the geospatial data layers used in operations. Both groups also work together on important topics that span orbital to sample spatial scales, such as interpreting orbital spectroscopic and geomorphological data to set and refine mineralogical expectations for mission samples. Acknowledgements The authors wish to sincerely thank the ExoMars 2022 Science Team and Industrial Teams for their continuing tireless efforts to ensure readiness for operations. References [1] Vago, J. L. et al., (2017) Astrobiology 17 (6–7), 471–510, doi:10.1089/ast.2016.1533 [2] Quantin-Nataf, C. et al., (2021) Astrobiology 21 (3), doi:10.1089/ast.2019.2191 [3] Mandon, L. et al., (2021), Astrobiology 21 (4), doi:10.1089/ast.2020.2292. [4] Balme, M. R. et al., (2019) Planet. Space Sci. 165, 31–5. [5] Sefton-Nash, E. et al., (2021) in LPSC 52, #1947.

1. Introduction The AIDA international collaboration, which includes the DART (NASA) and Hera (ESA) missions, aims to test the technology of deflection by a kinetic impactor and to enhance our understanding of small bodies in general. In the context of these missions, a spacecraft, DART, will impact the secondary of the 65803 Didymos system, Dimorphos, at the end of October 2022 [1]. The impact will eject asteroid material from the target surface, leading to a measurable change in the orbital period of the binary. A second, follow-up spacecraft, Hera, will arrive at the system several years after the impact to characterize the system and the impact consequences [2]. The objective of this study, which is conducted in the context of the NEO-MAPP project, is to model the collision of the kinetic impactor with Dimorphos and to predict the outcome of the impact with respect to parameters that are measurable by spaceborne and in-situ instrumentation provided by the Hera mission. We model the impact using two different numerical schemes: a continuum approach using iSALE-2D/-3D & a smooth particle approach using Bern SPH. Although all codes solve similar forms of conservation equations and use similar constitutive models, different numerical schemes can produce systematically different results. Hence, as a first step, accurate validation tests against laboratory experiments are conducted to improve the reliability of results from numerical modelling.2. MethodiSALE-2D/-3D [3, 4] is a grid-based arbitrary Eulerian Lagrangian (ALE) code and is best suited to study crater formation and the propagation of shock waves from a high velocity impact into targets with a variety of different properties. On the other hand, Bern's grid-free Smooth Particle Hydrodynamics (SPH) [5, 6] is most appropriate to study the ejection of material and processes where the entire target body is involved. Both codes include the simulation of material compaction (iSALE: ε-α model; SPH: P-α model) and different strength models. In this study, we employ the Drucker-Prager and the Lundborg rheology models to describe the strength of the material. For both codes, the ejection behaviour is analysed as described in [7,8,9], and the ejection data is used to determine the momentum transferred to the target for deflection (momentum enhancement factor β = ejecta + impactor momentum / impactor momentum). This approach was used previously for systematic parameter studies [9] and benchmarking studies [10]. To validate our shock physics codes, we compare our results against observations from a recent laboratory study [11], where PVC projectiles with a mass of ~25 mg were accelerated to velocities of 1-2 km/s, impacting glass beads, sand and regolith simulant targets. In a second step, we continue the benchmarking work done by the Hera impact working group [12] to detect, assess and remove deviations between two different numerical schemes, iSALE (in 2D and 3D) and Bern SPH at the scale of the DART impact. 3. Validation We have simulated the crater formation in glass beads and regolith simulant with iSALE-2D at impact speeds of 2.4 km/s and 2.2 km/s, respectively. The glass beads target was modelled using a Drucker-Prager criterion with a coefficient of internal friction, f = 0.5 and an initial porosity of 35%. The regolith simulant used f ~ 0.8 and an initial porosity of 42%. We determine β-values of 2.9 and 1.4, which agree well with experimentally determined values of 2.7 and 1.3, respectively. In the glass beads target laboratory experiment, at ~0.5-1 ms after the impact, the ejecta curtain made an angle of 50-60°. In the case of the regolith simulant, at ~0.5 ms after the impact, the ejecta curtain angle was 30-40°. From our numerical models, we determined ejecta curtain angles 0.5 ms after the impact as 48° (glass beads) and 30° (regolith, Fig. 1). Both results agree with the lower bound of the experimental constraints. 4. Benchmark The first benchmark study focuses on the influence of target properties on the efficiency of the momentum transfer from the DART impact, β, for materials similar to the regolith simulant. The 600 kg projectile impacts targets with varying porosities, between 10 and 50%, and cohesions from 1 to 100 kPa, at a velocity of 6 km/s. The second benchmark study focuses on the influence of the impact angle on β for the 20% porosity case with 10 kPa cohesion at an impact velocity of 7 km/s. In previous studies, we found generally good agreement between the results derived with iSALE and SPH [12, 13, 14]. However, for certain porosities the deviations between the results were larger (e.g., 20% porosity and 1 kPa cohesion), which may have been the result of discrepancies in the details of the crush curve used in each model. As a result, here we conducted new models with more consistent crush curves (Fig. 2). Varying the impact angle for a specific impact scenario and set of target properties shows a remarkably good agreement between the two codes (Fig. 3). 5. SummaryOur joint modelling and experimental approach to study the efficiency of asteroid deflection by a kinetic impactor shows that there is generally a good agreement between different numerical approaches and experimental work. The benchmark studies show that the results from the grid based iSALE (-2D/-3D) and the meshless SPH can deviate for similar initial porosities when the crush curves are not consistent, but they produce similar results when the same impact conditions are considered. AcknowledgementsWe gratefully acknowledge the developers of iSALE (www.isale-code.de). This work has received funding from the European Union’s Horizon 2020 research and innovation programme, NEO-MAPP, grant agreement No. 870377.References[1]A.F.Cheng et al.,P&SS157(2018)104-115.[2]P.Michel et al.,AdvSpaceRes.62(2018)2261-2272.[3]K.Wünnemann et al.,Icarus180(2006)514–527.[4]D.Elbeshausen et al.,Icarus204(2009)716–731.[5]M.Jutzi et al.,Icarus198(2008)242–255.[6]M.Jutzi,P&SS107(2015)3–9.[7]M.Jutzi&P.Michel,Icarus229(2014)247-253.[8]R.Luther et al.,M&PS53(2018)1705–1732.[9]S.D.Raducan et al.,Icarus329(2019)282–295.[10]A.Stickle et al.,Icarus338(2020)113446.[11]S.Chourey et al.,P&SS194(2020)105112.[12]R.Luther et al.,EPSC-DPS2019-1776(2019).[13]S.D.Raducan et al.,52th LPSC(2021)#2548id1908.[14]R.Luther et al.,7th PDC(2021)#122.

Drolshagen, E., et al., [Context] In meteor physics, the luminous efficiency τ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, a lack of sufficiently accurate verification methods or adequate laboratory tests mean that discussions around this parameter are a subject of controversy. [Aims] In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein. [Methods] Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required. [Results] We find τ-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10-6-100 kg. The derived τ-values have a median of τmedian = 2.17%. Most of them are of the order of 0.1-10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of τ on the pre-atmospheric velocity of the meteor, ve, is noticeable with a relation of τ = 0.0023 ve2.3. Furthermore, a dependence of τ on the initial meteoroid mass, Me, is found with negative linear behaviour in log-log space: τ = 0.48 Me-0.47. [Conclusions] The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of τ on Me implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.

著者人数: 69名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 吉川, 真), Number of authors: 69 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Yoshikawa, Makoto), Accepted: 2019-02-14, 資料番号: SA1190045000

Space capabilities play a crucial role in ensuring human security. One of the threats coming from space is the possible damage to our assets by an asteroid or comet impact. As demonstrated by the object entering the Earth's atmosphere over Chelyabinsk, Russia, in February 2013, the threat of an asteroid or comet impact is a real and global issue demanding development of an international response. Addressing such a hazard, by first identifying those objects that pose a threat to enable planning a corresponding mitigation campaign, require international coordination. The United Nations Member States, especially those with capabilities to engage in a possible planetary defence mission, already share a number of common activities in this field. This paper outlines the progress made in the implementation of recommendations for an international response to the NEO impact threat, as agreed under the auspices of the United Nations (UN) Committee on the Peaceful Uses of Outer Space (COPUOS) and welcomed by the UN General Assembly in its resolution 68/75 of December 2013. The recommendations provide for a coordinated international response to a possible NEO threat. They aim at ensuring international information-sharing in discovering, monitoring and physically characterizing potentially hazardous NEOs with a view that all countries, in particular developing countries with limited capacity in predicting and mitigating a NEO impact, are aware of potential threats. They emphasize the need for an effective emergency response and disaster management in the event of a discovered NEO impact threat. The International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG), which are the two entities established in 2014 as a result of the UN-endorsed recommendations, are important mechanisms at the global level for strengthening the coordination in the area of planetary defence. The United Nations Office for Outer Space Affairs (UNOOSA) acts as secretariat to SMPAG and works with both IAWN and SMPAG in addressing this global issue. In the event of a credible impact prediction, warnings would be issued by the IAWN, the SMPAG would propose mitigation options and implementation plans for consideration to the Member States. The goal is the global protection of the eco-system, of human beings and their properties on Earth, and of the civilization of humankind from a devastating asteroid impact. The current paper outlines the work of the IAWN and the SMPAG towards a road-map for planetary defence at the global level, including agreements on initial criteria and thresholds for impact threat response actions, consideration of mitigation mission types and technologies and mapping of threat scenarios to mission types as well as developing a plan for action in case a credible threat is discovered. The paper also reflects on how to convey information about the NEO impact warnings and associated impact probabilities to the public and governmental decision-makers as part of the agreed communications guidelines, which are another important pillar in the work of the IAWN.

Bilobate comets—small icy bodies with two distinct lobes—are a common configuration among comets, but the factors shaping these bodies are largely unknown. Cometary nuclei, the solid centres of comets, erode by ice sublimation when they are sufficiently close to the Sun, but the importance of a comet’s internal structure on its erosion is unclear. Here we present three-dimensional analyses of images from the Rosetta mission to illuminate the process that shaped the Jupiter-family bilobate comet 67P/Churyumov–Gerasimenko over billions of years. We show that the comet’s surface and interior exhibit shear-fracture and fault networks, on spatial scales of tens to hundreds of metres. Fractures propagate up to 500 m below the surface through a mechanically homogeneous material. Through fracture network analysis and stress modelling, we show that shear deformation generates fracture networks that control mechanical surface erosion, particularly in the strongly marked neck trough of 67P/Churyumov–Gerasimenko, exposing its interior. We conclude that shear deformation shapes and structures the surface and interior of bilobate comets, particularly in the outer Solar System where water ice sublimation is negligible. The shape and internal structure of bilobate comet 67P is controlled by shear deformation inducing mechanically driven erosion along shear fracture networks, according to a 3D analysis of images from the Rosetta mission.

We present a search for precovery observations of asteroid 2017 XO2, a previously high-rated possible impactor, as an ideal example of how archival searches can be used to clarify, either directly or indirectly, the danger posed by objects whose orbits are poorly known or even lost. In particular, we explore how images which should (but do not) contain the position corresponding to an impacting orbit can provide an indirect way to exclude the impacting solution even in the case of asteroids that are currently lost and therefore not directly observable again.

We present the results of our ground-based astrometric observation campaign of BepiColombo during its Earth fly-by on 2020 April 10. The observational circumstances induced by the fly-by geometry made this event an excellent proxy for a close fly-by or an imminent impact of a natural body with a diameter of a few meters, with the added benefit of having a ground-truth orbit (from radio tracking) to compare with our purely optical orbit determination., The work of TSR was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This work was supported by the MINECO (Spanish Ministry of Economy) through grantRTI2018-095076-B-C21 (MINECO/FEDER, UE).

The advancement in the acquisition of spectral data from meteors, as well as the capability to analyze meteoritic entries in ground testing facilities, requires the assessment of the performance of software tools for the simulation of spectra for different species. The Plasma Radiation Database, PARADE, is a line‐by‐line emission calculation tool. This article presents the extensions implemented for the simulation of meteor entries with the additional atomic species Na, K, Ti, V, Cr, Mn, Fe, Ca, Ni, Co, Mg, Si, and Li. These atoms are simulated and compared to ground testing spectra and to observed spectra from the CILBO observatory. The diatomic molecules AlO and TiO have now been added to the PARADE database. The molecule implementations have been compared to the results of a simple analytical program designed to approximate the vibrational band emission of diatomic molecules. AlO and TiO have been identified during the airborne observation campaigns of re‐entering man‐made objects WT1190F and CYGNUS OA6. Comparisons are provided showing reasonable agreement between observation and simulation.

Context. Fireballs are particularly bright meteors produced by large meteoroids or small asteroids that enter the Earth’s atmosphere. These objects, of sizes from some tens of centimetres to a few metres, are difficult to record with typical meteor detection methods. Therefore, their characteristics and fluxes are still not well known. Infrasound signals can travel particularly well through the atmosphere over large distances. Impacting meteoroids and asteroids can produce those signals, as well as space-detectable optical signatures. Aims. This paper aims to study and compare fireball data from the Geostationary Lightning Mappers (GLMs) on board the two Geostationary Observational Environmental Satellites (GOES-16 and GOES-17) and the data from the infrasound stations of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organisation (Vienna, Austria). The overall goal is a more accurate energy estimation of meteoroids and asteroids as well as a better understanding of both methods. Methods. The data consist of the brightest 50 events in the GLM database, as identified by recorded peak energy. For 24 of those fireballs, a significant signature could be identified in infrasound data. The data are supplemented by, if available, optical fireball data based on US government sensors on satellites provided by NASA’s Center for Near-Earth Object Studies (CNEOS). Results. The energies as computed from the GLM data range from 3.17 × 107 J up to 1.32 × 1012 J with a mean of 1.65 × 1011 J. The smallest meteoroid recorded by infrasound had an energy of about 1.8 × 109 J, the largest one of about 9.6 × 1013 J, and the mean energy is 5.2 × 1012 J. For 19 events, data were simultaneously available from all three data sources. A comparison between the energy values for the same event as determined from the different data sources indicates that CNEOS tends to give the lowest energy estimations. Analysis of infrasound data results in the largest derived energies. Conclusions. The energies derived using the three methods often deviate from one another by as much as an order of magnitude. This indicates a potential observational bias and highlights uncertainties in fireball energy estimation. By determining the fireball energy with another independent method, this study can help to better quantify and address this range of uncertainty.

There is currently no metric to discern the relative importance of an asteroid close approach with the Earth from the rest. This typically leads to communication media releasing information on close approach events under undefined criteria. This further means that, on many occasions, they inform about events that lack relevance or are publicised to levels which are not justified in terms of objective considerations. The evaluation of that relevance is further complicated by the fact that there are many factors that play a role in this subject, as asteroid size, minimum close approach distance, close approach velocity, actual NEO population, etc. In this paper, we establish an objective criterion to evaluate the expected frequency for the close approach of an NEO, based on the current estimates of the population of such objects, the object absolute magnitude and the parameters of the close approach. In addition, we propose a scalar close approach index that can be used to discriminate the relevance of an NEO close approach with the Earth, and we apply it to the current list of close approaches reported in ESA’s NEO Coordination Centre web portal.

Various meteor and fireball networks exist worldwide. Most data sets which include ground-based observational data of meteors are affected by biases. The larger and faster the entering meteoroid, the brighter is the produced meteor. Hence, small and slow objects often stay undetected. This bias of meteor observations towards faster meteoroids is a challenge if quantitative population and flux models are derived. In this work the velocity distribution of objects in space is analysed by using different data sets that are not affected by this velocity bias since they include only large objects, like the near-Earth object (NEO) risk list of ESA’s (European Space Agency) SSA (Space Situational Awareness) near-Earth object Coordination Centre (NEOCC), and the fireballs in NASA’s (National Aeronautics and Space Administration) CNEOS (Center for near-Earth object Studies) JPL (Jet Propulsion Laboratory) fireball database. Additionally, when only the largest objects recorded with the CILBO (Canary Island Long-Baseline Observatory) camera setup were analysed, a very similar distribution was shown. These velocity distributions are in good agreement with a widely used velocity distribution for smaller sporadic meteoroids in free space which was adopted as reference by the ECSS (European Cooperation for Space Standardisation) Space Environment Standard.

Introduction In recent years, interest in predicting the consequences of the encounter of a NEO with Earth has increased. Most studies focus on rocky or cometary objects [1-3]. However, in the most frequent size range of the smallest objects, the effects of iron objects are more severe than for equal-sized rocky objects. Indeed, most small craters on Earth have been formed by iron objects, which penetrate the atmosphere more efficiently than stony asteroids. Intact meteoroids form single craters (e.g. Kamil), fragmented meteoroids form crater/meteorite strewn fields (e.g. Morasko), and larger asteroids fragment and form a single crater (e.g., Barringer). The atmospheric entry and cratering generate shock waves, which can cause damage on the ground. In this project, we combine different approaches in a knowledge-base to predict the outcome of such events with sufficient accuracy in a fast way. Such a tool is highly desirable for ESA's Planetary Defence Office to release impact warnings and inform emergency response agencies. Method We describe the behaviour of iron objects of few metres in size up to ~50 m in diameter. We assume that their strength follows a typical Weibull power law. In order to simulate the atmospheric entry of an iron object, we follow different approaches: 1) small (i.e. ~1 m sized) meteoroids that are strong enough to avoid fragmentation in the atmosphere are subject to ablation and deceleration, 2) slightly larger asteroids (i.e. few metres) are described by a separate fragment model [e.g. 4,5], and 3) the largest asteroids are described by the pancake model [e.g. 6]. The effect of atmospheric shock waves (i.e. overpressure and wind speeds on the ground) are calculated based on fits to nuclear explosion data [1,7], which yield circular-symmetric results. For cases that are not accurately described by simple parameterisation, we use the shock physics code SOVA [8] to simulate the evolution of shock waves based on pre-calculated energy release curves. Tracer gauges measure the pressure and velocity distribution over time in atmosphere and store the maximum values. Results Distinction between individual fragments and a homogenous cloud of fragments: The fragmentation of an iron meteoroid/asteroid and the altitude at which such an event occurs depends on the initial parameters (velocity, entry angle, size). Large objects typically have a lower strength than smaller ones and fragment earlier in the atmosphere. Once fragmented, the individual pieces separate from each other with a lateral dispersion velocity, which depends on the absolute velocity of the object [4]. To decide which parameterisation to use, we compare the total cross- sectional area of all fragments with their separation distance (similar approach has been used in [9]). As long as the cross-sectional area of all fragments is larger than the corresponding size of the expanding fragment cloud (estimated from the dispersion velocity), the pancake model can be applied. This condition is expressed by the following equation (assuming equal-sized fragments): with the initial size R, separation velocity constant C, air density ρair, asteroid density ρasteroid, Weibull exponent αW, atmospheric scale height H, number of fragments N and entry angle ϑ. The altitude of fragmentation (and, thus, the atmospheric density at fragmentation) depends on the initial parameters, which is why the equation cannot be solved analytically. The dependence is shown in Figure 1. A meteoroid of the size of the Morasko event (~3 m radius, [5]) falls into the regime where the separate fragment model is applied. An asteroid like the one that formed the Barringer crater (~25 m radius) can be modelled with the pancake model. We also apply this approach to fragments with exponential size-frequency distribution, and the results are essentially the same. Figure 1: Expansion radii (colour lines) versus initial radius of a meteoroid (X-axis and grey line). Iron density is 7800 kg/m³, the reference strength for a 1kg sample is 440 MPa, αW=0.2. If the coloured lines are below the grey line, the pancake model is valid (separation distance is smaller than the maximum radius of the compact body). If the coloured lines are above the grey line, the separate fragment model is applicable (fragments are well-separated when the second fragmentation occurs). Colours represent different number of fragments: black – 10; blue – 100; green – 1000; and red – 106. Overpressure: We show results for two size classes of objects, which represent the size of the Kamil and the Barringer cratering events (Figure 2). For the Kamil event (initial radius of ~ 1.5 m), the outcome depends on modelling parameters (e.g. strength) and can vary between the formation of a single crater or a strewn field. However, overpressure distributions show little variation with and without a fragmentation event. For larger objects, the strength is less important. Overpressures are caused mostly by the crater formation and to some part by the atmopsheric entry. Figure 2: Overpressure caused by the entry of two different sized objects. Top: 1.5m radius, 20km/s, 45° entry angle, different strength parameters, Bottom: 23m radius, 18km/s, 30°- 45° entry angle (green, and red & blue, respectively). The red line represents a ten times weaker reference strength. Results based on nuclear explosion data [7] are shown in black. Discussion and Conclusion Shock physics codes give most reliable results for the prediction of overpressures. However, for a range of input parameters, the usage of parameterisation in combination with nuclear explosion data produces reliable estimates much faster (cf. Figure 2). In this project, we use a combination of both approaches. For small iron objects, overpressures are low apart from a small range near the crater, and damage is localised within a few crater radii. Acknowledgements We acknowledge the funding by ESA SSA-NEO, contract code P3-NEO-VIII. References [1]Collins G.S., Melosh H.J. and Marcus R.A. (2005)M&PS,40(6),817-840. [2]Wheeler et al. (2018)Icarus,315,79-91. [3] Artemieva N. and Shuvalov V. (2019)M&PS,54(3),592-608. [4] Artemieva N. and Shuvalov V. (2001)JGR,106,3297-3309. [5] Bronikowska et al. (2017)M&PS,52(8),1704-1721. [6] Chyba C.F., Thomas P.J. and Zahnle K.J. (1993)Nature,361,40-44. [7] Collins et al.(2017)M&PS,52(8),1542-1560. [8] Shuvalov V.V. (1999)ShockWaves,9,381-390. [9] Svetsov V.V., Nemtchinov I.V., and Teterev A.S. (1995)Icarus,116,131-153.

Fireballs are very bright meteors with magnitudes of at least -4. They can spark a lot of public interest. Especially, if they can be seen during daytime over populous areas. Social Media allows us to be informed about almost everything, worldwide, and in all areas of life in real-time. In the age of intensive use of these media, information is freely available seconds after the sighting of a fireball.This is the basis of the alert system which is part of NEMO, the NEar real-time MOnitoring system, for bright fireballs. It uses Social Media, mainly Twitter, to be informed about a fireball event in near real-time. In addition, the system accesses various data sources to collect further information about the detected fireballs. The sources range from meteor networks, the data from weather satellites or lightning detectors to the infrasound data of the IMS (International Monitoring System) operated by the CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organisation).Since large meteoroids or asteroids can be detected by these infrasound sensors when they enter the Earth's atmosphere, this network provides the possibility to detect fireballs worldwide and during day and night. From the infrasound data the energy of the object that caused the fireball can be determined and hence, its size and mass can be calculated. By combining all available information about the fireball from different data sources the amount of scientific knowledge about the event can be maximized.NEMO was under development for about 2.5 years. Since the beginning of the year the system is in operation at the European Space Agency, as part of its Space Safety Programme. In this presentation we will give an overview about NEMO, its working principle and its relation to the IMS.

‘Oumuamua (1I/2017 U1) is the first known object of interstellar origin to have entered the Solar System on an unbound and hyperbolic trajectory with respect to the Sun1. Various physical observations collected during its visit to the Solar System showed that it has an unusually elongated shape and a tumbling rotation state1–4 and that the physical properties of its surface resemble those of cometary nuclei5,6, even though it showed no evidence of cometary activity1,5,7. The motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing8. Because non-gravitational accelerations are at least three to four orders of magnitude weaker than gravitational acceleration, the detection of any deviation from a purely gravity-driven trajectory requires high-quality astrometry over a long arc. As a result, non-gravitational effects have been measured on only a limited subset of the small-body population9. Here we report the detection, at 30σ significance, of non-gravitational acceleration in the motion of ‘Oumuamua. We analyse imaging data from extensive observations by ground-based and orbiting facilities. This analysis rules out systematic biases and shows that all astrometric data can be described once a non-gravitational component representing a heliocentric radial acceleration proportional to r−2 or r−1 (where r is the heliocentric distance) is included in the model. After ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from ‘Oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that ‘Oumuamua has thermal properties similar to comets.

ESA's SMART-1 mission to the Moon achieved record firsts such as: 1) first Small Mission for Advanced Research and Technology; with spacecraft built and integrated in 2.5 years and launched 3.5 years after mission approval; 2) first mission leaving the Earth orbit using solar power alone; 3) most fuel effective mission (60 L of Xenon) and longest travel (13 months) to the Moon!; 4) first ESA mission reaching the Moon and first European views of lunar poles; 5) first European demonstration of a wide range of new technologies: Li-Ion modular battery, deep-space communications in X- and Ka-bands, and autonomous positioning for navigation; 6) first lunar demonstration of an infrared spectrometer and of a Swept Charge Detector Lunar X-ray fluorescence spectrometer; 7) first ESA mission with opportunity for lunar science, elemental geochemistry, surface mineralogy mapping, surface geology and precursor studies for exploration; 8) first controlled impact landing on the Moon with real time observations campaign; 9) first mission supporting goals of the International Lunar Exploration Working Group (ILEWG) in technical and scientific exchange, international collaboration, public and youth engagement; 10) first mission preparing the ground for ESA collaboration in Chandrayaan-1, Chang’ E1 and future international lunar exploration. We review SMART-1 highlights and new results that are relevant to the preparation for future lunar exploration. The technology and methods had impact on space research and applications. Recent SMART-1 results are relevant to topics on: 1) the study of properties of the lunar dust, 2) impact craters and ejecta, 3) the study of illumination, 4) radio observations and science from the Moon, 5) support to future missions, 6) identifying and characterising sites for exploration and exploitation. On these respective topics, we discuss recent SMART-1 results and challenges. We also discuss the use of SMART-1 publications library. The SMART-1 archive observations have been used to support the goals of ILEWG. SMART-1 has been useful to prepare for Kaguya, Chandrayaan-1, Chang'E 1, the US Lunar Reconnaissance Orbiter, the LCROSS impact, future lunar landers and upcoming missions, and to contribute towards objectives of the Moon Village and future exploration.

Drolshagen, E., et al., [Context] The luminous efficiency, τ, can be used to compute the pre-Atmospheric masses of meteoroids from corresponding recorded meteor brightnesses. The derivation of the luminous efficiency is non-Trivial and is subject to biases and model assumptions. This has led to greatly varying results in the last decades of studies. [Aims] The present paper aims to investigate how a reduction in various observational biases can be achieved to derive (more) reliable values for the luminous efficiency. [Methods] A total of 281 meteors observed by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) are studied. The luminous efficiencies of the events are computed using an ablation-based model. The relations of τ as a function of the pre-Atmospheric meteoroid velocity, ve, and mass, Me, are studied. Various aspects that could render the method less valid, cause inaccuracies, or bias the results are investigated. On this basis, the best suitable meteors were selected for luminous efficiency computations. [Results] The presented analysis shows the limits of the used method. The most influential characteristics that are necessary for reliable results for the τ computation were identified. We study the dependence of τ on the assumed meteoroid's density, ρ, and include improved ρ-values for objects with identified meteoroid stream association. Based on the discovered individual biases and constraints we create a pre-debiased subset of 54 well-recorded events with a relative velocity change >80%, a final height

Using new data and recent models this paper derives a total combined flux model of the mass reaching Earth as interplanetary material. For the small sizes the interplanetary flux model by Grun et al. (1985) was used which describes the mass flux at 1 AU for meteoroids in the mass range 10 –21 kg to about 10 −1 kg. For the large objects the flux models by Brown et al. (2002) were used which were derived for bodies greater than 1 m and are based on sensor data of fireballs that entered the Earth atmosphere. For the intermediate size range interpolations and alternative models based on meteor and fireball data were used. All flux models were converted to an altitude of 100 km above the Earth surface to make them comparable. The total combined flux model covers more than 34 orders of magnitude in mass. Using recent measurements and alternative flux models the uncertainties of the obtained model were estimated. Recent measurements include in-situ impact data on retrieved space hardware and optical meteor and fireball data. Depending on the models and interpolation used the interplanetary material that enters the Earth atmosphere per day is in the range of 30−180 t with a best guess value of 54 t per day for an upper cut-off size of 1 km. If the upper size limit is placed at 0.5 m which is the largest size where statistically a daily impact is expected, the expected mass influx is slightly more than 32 t per day. The combined models with interpolations suggest deviations from a simple power law. The flux in the diameter range of 0.01–0.1 m appears not as large as suggested by a simple power law interpolation.

We have developed a new method to determine flux densities of meteoroids using optical double-station meteor observations. It is based on the assumption that the velocity distribution is constant for all mass bins. By comparing the observed velocity distribution with a model distribution we determine de-biasing factors to correct for meteors too slow to emit a detectable amount of light. We use this method to correct a dataset of about 20000 double-station meteoroids detected over a period of about 3.5 years with the Canary Island Long-Baseline Observatory (CILBO). The resulting cumulative flux density has a slope comparable to the model of Grun et al. (1985). The largest uncertainty is the luminous efficiency. Depending on which values for the luminous efficiency are assumed, the mass estimate deviates by about one to 1.5 orders of magnitude. Using the luminous efficiencies derived by Weryk et al. (2013) results in an excellent agreement of our data with the Grun data.

International audience; We used the OSIRIS camera system onboard the Rosetta spacecraft to monitor jet activity of comet 67P/Churyumov-Gerasimenko. With a monthly cadence, we covered an epoch from December 2014 to October 2015, thereby including the first equinox and the perihelion passage. Jet features were measured in individual images, which were used to perform a statistical inversion. The study provides maps for the locations of likeliest sources of jet activity on the comet’s surface as a function of time. The sources follow the sub-solar latitude, show clustering and a broadening of the activity band with time in the Northern hemisphere. On the Southern hemisphere they are not clustered but show a broader spread over all longitudes which is either related to the north-south dichotomy of the comet’s topography or due to a higher insolation during southern summer.

On 2016 July 03, several instruments onboard ESA's Rosetta spacecraft detected signs of an outburst event on comet 67P, at a heliocentric distance of 3.32 au from the Sun, outbound from perihelion. We here report on the inferred properties of the ejected dust and the surface change at the site of the outburst. The activity coincided with the local sunrise and continued over a time interval of 14-68 min. It left a 10-m-sized icy patch on the surface. The ejected material comprised refractory grains of several hundred microns in size, and sub-micron-sized water ice grains. The high dust mass production rate is incompatible with the free sublimation of crystalline water ice under solar illumination as the only acceleration process. Additional energy stored near the surface must have increased the gas density. We suggest a pressurized sub-surface gas reservoir, or the crystallization of amorphous water ice as possible causes.© 2015 The Authors., The support of the national funding agencies of Germany (DLR, grant 50 QP 1302), France (CNES), Austria, Finland and the ESA Technical Directorate is gratefully acknowledged.

Numerous water-ice-rich deposits surviving more than several months on comet 67P/Churyumov-Gerasimenko were observed during the Rosetta mission. We announce the first-time detection of water-ice features surviving up to 2 yr since their first observation via OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) NAC (narrow angle camera). Their existence on the nucleus of comet 67P at the arrival of the Rosetta spacecraft suggests that they were exposed to the surface during the comet's previous orbit. We investigated the temporal variation of large water-ice patches to understand the long-term sustainability of water ice on cometary nuclei on time-scales of months and years. Large clusters are stable over typical periods of 0.5 yr and reduce their size significantly around the comet's perihelion passage, while small exposures disappear. We characterized the temporal variation of their multispectral signatures. In large clusters, dust jets were detected, whereas in large isolated ones no associated activity was detected. Our thermal analysis shows that the long-term sustainability of water-ice-rich features can be explained by the scarce energy input available at their locations over the first half year. However, the situation reverses for the period lasting several months around perihelion passage. Our two end-member mixing analysis estimates a pure water-ice equivalent thickness up to 15 cm within one isolated patch, and up to 2 m for the one still observable through the end of the mission. Our spectral modelling estimates up to 48 per cent water-ice content for one of the large isolated feature, and up to 25 per cent water ice on the large boulders located within clusters.

International audience; Images of the nucleus and the coma (gas and dust) of comet 67P/Churyumov– Gerasimenko have been acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) cameras since 2014 March using both the wide-angle camera and the narrow-angle camera (NAC). We use images from the NAC camera to study a bright outburst observed in the Southern hemisphere on 2015 July 29. The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus. The heliocentric distance is 1.25 au and the spacecraft–comet distance is 186 km. Aiming to better understand the physics that led to the outgassing, we used the Direct Simulation Monte Carlo method to study the gas flow close to the nucleus and the dust trajectories. The goal is to understand the mechanisms producing the outburst. We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region. The outburst is in fact a combination of both gas and dust, in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas. We need a number of dust particles 7.83 × 1011 to 6.90 × 1015 (radius 1.97–185 μm), which correspond to a mass of dust (220–21) × 103 kg.

Between August 2014 and September 2016, the ESA space mission Rosetta escorted comet 67P/Churyumov-Gerasimenko (67P) during its perihelion passage. The onboard OSIRIS Narrow Angle Camera (NAC) acquired high-resolution multispectral images of the cometary surface. These datasets allowed a characterization of the spectrophotometric variegation of the layering of the large lobe, correlated with the layer structural elevation. Aims. We perform a spectrophotometric characterization of the outcropping stratification of the small lobe of 67P as a function of its structural elevation, and consequently, a spectrophotometric comparison of the layered outcrops of the two lobes. Methods. We selected two sequences of post-perihelion OSIRIS NAC images (similar to 2.4 au outbound to the Sun), from which we built up two multispectral images, framing an extended geological section of the onion-like stratification of the small lobe. Then we classified the consolidated areas of the outcropping and the relative coarse deposits that were identified in the multispectral data with a two-class maximum likelihood method. For this, we defined the classes as a function of the structural elevation of the surface. Results. As a result, we identified a brightness variegation of the surface reflectance that is correlated with the structural elevation. The outer class, which is located at higher elevations, appears darker than the inner class. This fits previously obtained results for the large lobe. The reflectance values of the nucleus of 67P tend to decrease with increasing structural elevation. Conclusions. The observed spectrophotometric variegation can be due to a different texture as well as to a different content of volatiles and refractories. We suggest that the outer outcrops appear darker because they have been exposed longer, and the inner outcrops appear brighter because the surface has been more effectively rejuvenated. We interpret this variegation as the result of an evolutionary process.© ESO 2019, We are grateful to Andrea Longobardo for suggestions and corrections that improved our paper. OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, CISAS - University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged.

(Topical Collection: Cosmic Dust from the Laboratory to the Stars, Edited by Rafael Rodrigo, Jürgen Blum, Hsiang-Wen Hsu, Detlef Koschny, Anny-Chantal Levasseur-Regourd, Jesús Martín-Pintado, Veerle Sterken and Andrew Westphal); International audience; Interplanetary dust particles and meteoroids mostly originate from comets and asteroids. Understanding their distribution in the Solar system, their dynamical behavior and their properties, sheds light on the current state and the dynamical behavior of the Solar system. Dust particles can endanger Earth-orbiting satellites and deep-space probes, and a good understanding of the spatial density and velocity distribution of dust and meteoroids in the Solar system is important for designing proper spacecraft shielding. The study of interplanetary dust and meteoroids provides clues to the formation of the Solar system. Particles having formed 4.5 billion years ago can survive planetary accretion and those that survived until now did not evolve significantly since then. Meteoroids and interplanetary dust can be observed by measuring the intensity and polarization of the zodiacal light, by observing meteors entering the Earth’s atmosphere, by collecting them in the upper atmosphere, polar ices and snow, and by detecting them with in-situ detectors on space probes.

By using the Rosetta/OSIRIS-NAC data set taken in 2014 August, we focus on the neck region, called Hapi, located on 67P Churyumov-Gerasimenko's Northern hemisphere. The gravitational potential and slopes of Hapi, coupled with the geological unit identification and the boulder size-frequency distributions, support the interpretation that both taluses and gravitational accumulation deposits observable on Hapi are the result of multiple cliff collapses that occurred at different times. By contrast, the fine-particle deposits observable in the central part of the study area are made of aggregates coming from the Southern hemisphere and deposited during each perihelion passage. Both the consolidated terrains on the western part of Hapi, as well as the centrally aligned ridge made of boulder-like features, suggest that Hapi is in structural continuity with the onion-like structure of the main lobe of 67P. Despite the dusty blanket observable on Hapi, its terrains are characterized by water-ice-rich components that, once repeatedly and rapidly illuminated, sublimate, hence resulting in the strong jet activity observed in 2014 August.© 2019 The Author(s)., The support of the national funding agencies of Germany (DLR), Italy (ASI), France (CNES), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., A smooth deposit in the southern Khonsu region has been seen in ESA/Rosetta observations as active during the second half of 2015, when the southern summer coincided with the perihelion passage of 67P/Churyumov-Gerasimenko (67P). Image color sequences acquired by the OSIRIS instrument in the period of January 2015 to July 2016, pre- and post-perihelion, show the occurrence of several small transient events as well as three massive outbursts (-10 to 1500 tons). High spatial resolution images taken one year and a half apart allowed us to track a variety of sources: the formation of cavities that are 1.3-14 m deep, ice-enriched patches, scarp retraction, and a second 50 m-wide boulder. We then estimated their masses and the dust mass of their corresponding plumes and outbursts. In particular, the deformation left by that boulder and its lack of talus may provide evidence for the lifting and subsequent falling back to the surface of large blocks. We calculate that a minimum vapor production rate of 1.4 x 10(24) m(-2) s(-1) is required to lift such an object. The comparison of the masses that are lost in the new cavities to the dust mass of outbursts gives indirect evidence of highly volatile ice pockets underneath. The spectrophotometric analysis and boulder counting also provides evidence for cavities that formed only 30 m apart with different spectral slopes, two long-standing ice patches, and local variations in the boulder-size frequency distribution. All this points to sub-surface ice pockets with different degrees of depth. Finally, the total mass of the morphological changes compared to most recent calculations of the total released mass by activity on 67P is estimated to be between 1.5 and 4.2%. This means that as many as about 25 similar active zones across the nucleus would be enough to sustain the entire cometary activity.© P. H. Hasselmann et al. 2019, P.H.H. would like to thank Alice Bernard for her support. This work was funded by the DIM-ACAV project (Ile-de-France). OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, CISAS-University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We acknowledge the financial support from the France Agence Nationale de la Recherche (programme Classy, ANR-17-CE31-0004).

NELIOTA (NEO Lunar Impacts and Optical TrAnsients) is an ESA-funded lunar monitoring project, which aims to determine the size-frequency distribution of small Near-Earth Objects (NEOs) via detection of impact flashes on the surface of the Moon. A prime focus, high-speed, twin-camera system providing simultaneous observations in two photometric bands at a rate of 30 frames-per-second on the 1.2 m Kryoneri telescope of the National Observatory of Athens was commissioned for this purpose. A dedicated software processes the images and automatically detects candidate lunar impact flashes, which are then validated by an expert user. The four year observing campaign began in February 2017 and has so far detected more than 40 lunar impact events. The software routinely detects satellites, which typically appear as streaks or dots crossing the lunar disk. To avoid confusing these events with real flashes, we check different available catalogs with spacecraft orbital information and exclude spacecraft identifications., Comment: 12 pages, 17 figures. Proceedings of the "ESA NEO and Debris Detection Conference -Exploiting Synergies-", held in ESA/ESOC, Darmstadt, Germany, 22-24 January 2019

Remote sensing observations of dust particles ejected from comets provide important hints on the intimate nature of the materials composing these primitive objects. The measurement of dust coma backscattering ratio, BSR, defined as the ratio of the reflectance at phase angle 0 ◦ and 30 ◦ , helps tuning theoretical models aimed at solving the inverse scattering problem deriving information on the nature of the ejected particles. The Rosetta/OSIRIS camera sampled the coma phase function of comet 67P, with four series acquired at low phase angles from 2015 January to 2016 May. We also added previously published data to our analysis to increase the temporal resolution of our findings. We measured a BSR in the range ∼ [1.7-3.6], broader than the range found in literature from ground-based observations of other comets. We found that during the post-perihelion phase, the BSR is systematically larger than the classical cometary dust values only for nucleocentric distances smaller than ∼ 100 km. We explain this trend in terms of a cloud of chunks orbiting the nucleus at distances < 100 km ejected during perihelion and slowly collapsing on the nucleus over a few months because of the coma gas drag. This also implies that the threshold particle size for the dust phase function to become similar to the nucleus phase function is between 2.5 mm and 0.1 m, taking into account previous Rosetta findings. © 2018 The Author(s)., The support of the national funding agencies of Germany (DLR: Deutschen Zentrums fur Luft-und Raumfahrt), France (CNES: Centre national d' etudes spatiales), Italy (ASI: Agenzia Spaziale Italiana), Spain (MEC: Ministry of Education& Science), Sweden (SNSB: Swedish National Space Board), and the European Space Agency (ESA) Technical Directorate is gratefully acknowledged.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society., On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.© C. Tubiana et al. 2019, OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Daten-technik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. VIRTIS was built by a consortium, which includes Italy, France, and Germany, under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which also guides the scientific operations. The VIRTIS instrument development, led by the prime contractor Leonardo-Finmeccanica (Florence, Italy), has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES, and from DLR. We thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their support throughout all the phases of the mission. The VIRTIS calibrated data will be available through the ESA's Planetary Science Archive Website (www.rssd.esa.int) and is available upon request until posted to the archive. We thank the following institutions and agencies for support of this work: Italian Space Agency (ASI, Italy) contract number I/024/12/1, Centre National d'Etudes Spatiales (CNES, France), DLR (Germany), NASA (USA) Rosetta Program, and Science and Technology Facilities Council (UK).

We provide a detailed quantitative analysis of isolated boulder fields situated in three different regions of comet 67P/Churyumov-Gerasimenko: Imhotep, Hapi, and Hatmehit. This is done to supply a useful method for analyzing the morphology of the boulders and to characterize the regions themselves. Methods. We used OSIRIS Narrow Angle Camera images with a spatial scale smaller than 2 mpx(-1) and analyzed the size-frequency distribution and the cumulative fractional area per boulder population. In addition, we correlated shape parameters, such as circularity and solidity, with both the spatial and the size-frequency distribution of the three populations. Results. We identified 11 811 boulders in the Imhotep, Hapi, and Hatmehit regions. We found that the Hatmehit and Imhotep areas show power indices in the range of -2.3/-2.7. These values could represent a transition between gravitational events caused by thermal weathering and sublimation, and material formed during collapses that has undergone sublimation. The Hapi area is characterized by a lower power index (-1.2/-1.7), suggesting that those boulders have a different origin. They can be the result of material formed during gravitational events and collapses that has undergone continuous fragmentation. We calculated the cumulative fractional area (CFA) in order to investigate how the area is covered by boulders as a function of their sizes. The Hatmehit and Imhotep regions show a CFA that is well fit by a power law. In contrast, the Hapi area does not show the same trend. We analyzed the fractal distributions, finding that the populations seem to be fractal at all dimensions, except for the Hapi distribution, which shows a possible fractal behavior for small dimensions only. Finally, the average values of the shape parameters reveal solid and roundish boulders in all populations we studied.© ESO 2019, OSIRIS was built by a consortium of the Max-Planck Institut fur Sonnensystemforschung, in Guttingen, Germany, CISAS University of Padova, Italy, the Laboratoire de Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the ESA teams at ESAC, ESOC and ESTEC for their work in support of the Rosetta mission. We made use of Arcgis 10.3.1 software together with the Matlab, Java, and ImageJ software to perform our analysis. I thank Frederic Moisy for sharing the box-count work.

From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep-Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095 degrees and 62 degrees. Aims. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. Methods. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel-Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. Results. The Imhotep-Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature's nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 +/- 0.001%/100 nm/degrees at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Conclusions. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep-Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.© ESO 2019, OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, CISAS-University of Padova, Italy, Laboratoire d'Astrophysique de Marseille, France, Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, Universidad Politechnica de Madrid, Spain, Department of Physics and Astronomy of Uppsala University, Sweden, and Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES, and ASI. The SPICE libraries and PDS resources are developed and maintained by NASA. The authors thank the referee and editors for their questions, remarks, and advices for the improvement of this article.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society., The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9-10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences.© N. Masoumzadeh et al. 2019, OSIRIS was built by a consortium of the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany; the CISAS University of Padova, Italy; the Laboratoire d'Astrophysique de Marseille, France; the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain; the Research and Scientific Support Department of the ESA, Noordwijk, Netherlands; the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain; the Universidad Politechnica de Madrid, Spain; the Department of Physics and Astronomy of Uppsala University, Sweden; and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Operations Centre and the Rosetta Mission Operations Centre for the successful rendezvous with comet 67P/Churyumov-Gerasimenko. This research has made use of the USGS Integrated Software for Imagers and Spectrometers (ISIS). We gratefully acknowledge the developers of SPICE and NAIF/PDS resources. This research has made use of the scientific software shapeViewer www.comet-toolbox.com.L.K.acknowledges a support from the NASA SSW grant 80NSSC17K0731.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., The Rosetta space probe accompanied comet 67P/Churyumov-Gerasimenko for more than two years, obtaining an unprecedented amount of unique data of the comet nucleus and inner coma. This has enabled us to study its activity almost continuously from 4 au inbound to 3.6 au outbound, including the perihelion passage at 1.24 au. This work focuses identifying the source regions of faint jets and outbursts and on studying the spectrophotometric properties of some outbursts. We use observations acquired with the OSIRIS/NAC camera during July-October 2015, that is, close to perihelion. Methods. We analyzed more than 2000 images from NAC color sequences acquired with 7-11 filters covering the 250-1000 nm wavelength range. The OSIRIS images were processed with the OSIRIS standard pipeline up to level 3, that is, converted in radiance factor, then corrected for the illumination conditions. For each color sequence, color cubes were produced by stacking registered and illumination-corrected images. Results. More than 200 jets of different intensities were identified directly on the nucleus. Some of the more intense outbursts appear spectrally bluer than the comet dark terrain in the visible-to-near-infrared region. We attribute this spectral behavior to icy grains mixed with the ejected dust. Some of the jets have an extremely short lifetime. They appear on the cometary surface during the color sequence observations, and vanish in less than some few minutes after reaching their peak. We also report a resolved dust plume observed in May 2016 at a resolution of 55 cm pixel(-1), which allowed us to estimate an optical depth of similar to 0.65 and an ejected mass of similar to 2200 kg, assuming a grain bulk density of similar to 800 kg m(-3). We present the results on the location, duration, and colors of active sources on the nucleus of 67P from the medium-resolution (i.e., 6-10 m pixel(-1)) images acquired close to perihelion passage. The observed jets are mainly located close to boundaries between different morphological regions. Some of these active areas were observed and investigated at higher resolution (up to a few decimeter per pixel) during the last months of operations of the Rosetta mission. Conclusions. These observations allow us to investigate the link between morphology, composition, and activity of cometary nuclei. Jets depart not only from cliffs, but also from smooth and dust-covered areas, from fractures, pits, or cavities that cast shadows and favor the recondensation of volatiles. This study shows that faint jets or outbursts continuously contribute to the cometary activity close to perihelion passage, and that these events are triggered by illumination conditions. Faint jets or outbursts are not associated with a particular terrain type or morphology.© S. Fornasier et al. 2019, OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Goettingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, the Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. S.F. acknowledges the financial support from the France Agence Nationale de la Recherche (programme Classy, ANR-17-CE31-0004). The authors thank H. Campins for his comments that helped us improve this article. The authors would like to thank Andrew Cooper and Marco Parigi for spotting the inconsistencies in regional boundaried of Fig. 1 in the online preprint version of the paper.

International audience; Because of the diurnal thermal cycle and the irregular shape of the nucleus, gas outflow of comet 67P/Churyumov–Gerasimenko could be highly anisotropic as indicated by the colliminated dust jet structures on the sunlit side. Based on the OSIRIS imaging observations of the outgassing effect, a simple model of surface sublimation can be constructed by taking into account the dependence on the solar insolation. With preliminary information on the time variability of the global gas production rate, a sequence of gas coma models can be generated at different epochs before and after perihelion. We also investigate different patterns of dust particle dynamics under the influences of nuclear rotation and gas drag. From these considerations, a consistent picture of the spatial distribution of dusty materials across the surface of comet 67P as it moves around the perihelion can be developed. It is found that because of the redeposition of the ejected dust from the Southern hemisphere to the Northern hemisphere during the southern summer season the Hapi region could gain up to 0.4 m while the Wosret region would lose up to 1.8 m of dust mantle per orbit.