MITM3
This session explores the critical synergies between the three pillars of planetary defense:
- Observations: We’ll discuss the latest advancements in ground-based surveys and space-borne telescopes tasked with finding and tracking potentially hazardous objects and virtual impactors.
- Modelling: We will cover the computational physics of impact effects, orbital mechanics, and the structural analysis of rubble-pile versus monolithic asteroids.
- Space missions: We will review lessons learned from recent missions, such as DART/LICIACube, and look forward to the next generation of spacecrafts, such as Hera, OSIRIS-APEX, RAMSES and DESTINY+.
The ESA Hera mission [1] is the European contribution to the first asteroid deflection test with the NASA DART mission. The DART probe successfully impacted Dimorphos, the small moon of the binary asteroid Didymos, on September 26, 2022. The orbital period modification of Dimorphos around Didymos, measured by ground-based observatories, was reduced by 33 minutes from its original value of 11h 55 min. The Italian LICIACube obtained some images of Dimorphos within the first few minutes following impact. However, we still do not know Dimorphos' final properties, modified by this impact, because no other spacecraft remained long enough in close proximity to collect such observations. Is there a crater on Dimorphos' surface, and if so, what are its properties? Or, was Dimorphos entirely reshaped? Answers to these questions are crucial for numerical simulations of the DART impact, required to reproduce these final properties to be validated as well as for our general understanding of the impact response of such objects in low-gravity regimes.
Hera will, therefore, perform the investigation starting in November 2026 for at least 6 months. Although we already have images of Dimorphos before impact thanks to DART, we are confident that the images that Hera will take of the same body will have little similarity with those already obtained. This is because an impact with likely global effects took place. Furthermore, Didymos, the primary of the binary system may also look very different compared to pre-DART impact images. It is expected that some fraction of the ejecta from Dimorphos impacted Didymos, which may have modified its morphology and surface properties. Hera will, therefore, reveal an entirely new world, transformed by an event aimed at protecting us from an incoming asteroid, allowing us to assess the efficiency of the kinetic impactor technique. Thanks to its main spacecraft and its two cubesats, we will have detailed knowledge of the system, from the surface to the interior of the two components, including the composition and thermal properties through a spectrometer and a JAXA-contributed thermal infrared imager.
So far, all newly obtained data of asteroids from previous missions have revealed some surprises [2]. Two months before arrival, we can expect Hera to also surprise us and challenge our understanding of these small worlds.
Acknowledgments: The authors acknowledge support from ESA, ASI, CNES, DLR, JAXA, NASA.
References
- Michel P., et al., Planetary Science Journal 2022, 3, 160-180.
- Michel P., et al., Space Science Reviews 2025, 221, 270.
How to cite: Michel, P., Küppers, M., Fitzsimmons, A., Green, S., Lazzarin, M., Ulamec, S., Abell, P., Sugita, S., and Carnelli, I.: The ESA Hera mission: two months before arrival to the binary asteroid Didymos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-204, https://doi.org/10.5194/epsc2026-204, 2026.
The ESA–JAXA RAMSES (Rapid Apophis Mission for Space Safety) mission has been designed to investigate the near-Earth asteroid (99942) Apophis during its exceptionally close encounter with Earth on 13 April 2029. During this event, Apophis will pass at a distance of about 32,000 km from Earth’s surface, well within the geostationary orbit region, providing a unique natural experiment to observe how a small body responds to strong planetary tidal forces.
RAMSES will rendezvous with Apophis several weeks before the closest approach and monitor the asteroid before, during, and after the encounter. This temporal coverage will enable the first direct investigation of tidal-induced modifications affecting the asteroid’s rotation state, surface morphology, internal structure, and physical properties.
The mission concept builds upon the heritage of ESA’s Hera mission and includes a main spacecraft supported by two CubeSats, enabling a distributed measurement strategy that combines remote sensing and in-situ observations.
From a scientific perspective, the Apophis encounter represents a key opportunity to address fundamental questions on the mechanical behavior of rubble-pile bodies. In particular, RAMSES will assess whether tidal forces can trigger surface processes such as landslides, regolith mobilization, and exposure of fresh material, as well as possible internal reorganization.
A major strength of the mission lies in its ability to combine complementary measurements. High-resolution imaging and spectroscopy will detect compositional and mineralogical changes, while a low-frequency radar will probe the internal structure. Radio science experiments will provide precise constraints on Apophis’ mass, gravity field, and rotational state. For the first time on an asteroid, a lander carrying a seismometer will attempt in-situ measurements, providing unique constraints on mechanical properties and internal response to tidal forcing. In addition, a plasma spectrometer and a magnetometer will investigate the interaction of Apophis with the solar wind and Earth’s magnetospheric environment. These measurements, coupled with dust detection and analysis by one of the CubeSats, will offer a new perspective on dust activity and surface–environment coupling during the encounter.
In parallel, the Apophis 2029 encounter will be observed within a broader international framework. The JAXA DESTINY+ mission, launched on the same H3 rocket provided by JAXA, will perform a flyby of Apophis before the arrival of RAMSES, while NASA’s OSIRIS-APEX mission will rendezvous with the asteroid after the encounter. This coordinated international effort will provide a unique multi-mission temporal coverage.
How to cite: Lazzarin, M., Michel, P., Kueppers, M., Green, S., Tortora, P., Ulamec, S., Vincent, J. B., Abell, P., Sugita, S., and Martino, P.: The ESA -JAXA RAMSES Mission to Apophis: Investigating Asteroid Response to Planetary Tidal Forces, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-828, https://doi.org/10.5194/epsc2026-828, 2026.
1. Introduction
The 2029 Earth Close Approach (ECA) of the near-Earth asteroid (99942) Apophis presents a once-in-a-millennium opportunity to witness the real-time physical and dynamical evolution of a rubble-pile body under terrestrial tidal forces. During this encounter, Apophis will pass closer to Earth than geostationary orbit, providing a rare natural experiment for investigating how planetary tides modify the surface, spin state, and internal structure of a potentially hazardous asteroid. Although catastrophic disruption is not expected, the encounter may trigger localized surface changes, including regolith/boulder motion, fresh-material exposure, and seismic-related resurfacing.
International flagship missions such as ESA’s RAMSES and NASA’s OSIRIS-APEX are planned to provide comprehensive characterization of Apophis before and after the encounter. However, the scientific community would benefit from geometrically complementary, high-cadence datasets captured during the peak dynamic window around ECA. Here we present the Student-led Threatening Asteroid Reconnaissance of Tsinghua (START) mission, a low-cost, rapid-response SmallSat designed to observe Apophis from a geocentric perspective during its closest approach to Earth.
2. Geocentric Flyby Architecture and Science Return
START is a 200-kg SmallSat mission under active development at Tsinghua University in collaboration with commercial space partners. Operating within a low-cost mission framework of ~.8M USD, START leverages commercial components, private investment, and rideshare launch opportunities to demonstrate a scalable mission architecture. Rather than undertaking a conventional multi-year interplanetary cruise, START exploits the fact that Apophis itself will pass through near-Earth space during the 2029 encounter. The spacecraft is planned to launch as a rideshare payload into Low Earth Orbit in early 2028 and use a 60-mN xenon-based solar electric propulsion system to autonomously transfer over approximately 150 days to a 31,600-km-altitude circular mission orbit, matching Apophis’s ECA altitude.
Near Apophis’s Earth closest approach, START will perform a high-speed intercept with a relative velocity of 8.74 km/s and a closest approach distance of 7 km. The mission trajectory adopts a 55° inclination orbit to balance flyby velocity, nodal precession, and commercial launch accessibility. This design allows START to maximize launch opportunities while maintaining favorable observing geometry during the encounter. The spacecraft also requires enhanced attitude control capability to maintain stable target tracking during the high-speed flyby, with angular accelerations up to 0.608°/s².
The payload suite includes a high-resolution narrow-field camera, a wide-field navigation camera, and dual visible-to-near-infrared hyperspectral imagers covering 0.4–2.5 μm. During the flyby, START is expected to achieve a peak spatial resolution of approximately 8 cm/pixel, enabling the detection of tidally induced surface modifications such as localized mass flow, boulder displacement, and seismic-related resurfacing. The hyperspectral imagers will measure surface spectral properties and search for compositional variations associated with freshly exposed material.
START has completed system-level design and is now in the detailed design phase, with spacecraft manufacturing and integration planned to begin in late 2026. During Apophis’s closest approach, START will provide an independent close-range observing perspective that complements international flagship missions and contributes to the global Apophis campaign, while demonstrating a scalable, cost-effective architecture for future planetary-defense and small-body-exploration missions.
Fig1. START Mission Overview
References
Giorgini, J. D., Benner, L. A. M., Ostro, S. J., ... & Busch, M. W. (2008). Predicting the Earth encounters of (99942) Apophis. Icarus, 193(1), 1-19.
DellaGiustina, D. N., Nolan, M. C., Polit, A. T., ... & Wolner, C. W. V. (2023). OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis. The Planetary Science Journal, 4(10), 198.
Morelli, A. C., Mannocchi, A., Giordano, C., ... & Topputo, F. (2024). Initial Trajectory Assessment of a low-thrust option for the RAMSES Mission to (99942) Apophis. Advances in Space Research, 73(8), 4241-4253.
Binzel, R. P., Morbidelli, A., Merouane, S., ... & Tokunaga, A. T. (2010). Earth encounters as the origin of fresh surfaces on near-Earth asteroids. Nature, 463(7279), 331-334.
How to cite: Wu, Y., Li, Y., Wang, Z., Wang, T., Li, J., Baoyin, H., and Cheng, B. and the START mission team of Tsinghua University: Progress Updates on the START Mission: Geocentric Reconnaissance of the 2029 Apophis Encounter in Support of Planetary Defense, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1083, https://doi.org/10.5194/epsc2026-1083, 2026.
Space weathering (SW) consists of the solar wind component dominated by ~1 keV H+ ion irradiation, and the micrometeorite bombardment caused by hypervelocity impacts of sub-mm dusty grains. Both SW components are simulated in the laboratory independently by distinct agents. Proton bombardment is used to simulate the solar wind and pulse laser irradiation is used to simulate the microimpacts. The total energy deposited during the laboratory simulations is then converted to an equivalent exposure time in interplanetary environment for a given heliocentric distance. Here we present the spectral changes for equivalent exposure time at 1 au designated as EET. The proton bombardment simulations cover typically 10-103 years EET, while the laser irradiation cover longer time scales of 107-1010 years EET with a time gap of 104-106 years EET not sufficiently covered by SW experiments. This time gap causes difficulty to predict EET from reflectance spectra within this time interval [1]. [2] conducted both proton and pulse laser irradiation experiments on identical olivine and orthopyroxene samples and characterized related material and reflectance spectra changes. Results indicate that proton irradiation-related spectral changes saturate around 103 EET in both minerals (meaning that increased irradiation does not result in additional significant spectral changes) while laser irradiation starts to produce detectable spectral changes only around 108 EET.
The implication of this observation is that the SW evolution is non-linear with an interval of 104-106 years EET where SW does not produce significant changes in reflectance spectra. In Fig. 1 we present an example of combined solar wind – microimpact SW spectral evolution of olivine and orthopyroxene. First, rapid evolution of solar wind induced spectral changes concentrated mainly at 0.5-1.5 µm is observed within initial thousand years of exposure. This is followed by microimpact induced SW spectral attenuation over broader 0.5-2.5 µm range becoming noticeable only at ~107 years EET.
Figure 1: SW spectral evolution of olivine (left) and orthopyroxene (right). Solar-wind dominated SW is indicated at timescales of 50-500 years (from upper to lower blue curve) and microimpact dominated SW at timescales of 108-1010 (from upper to lower red curve). The unaltered pristine spectrum is green.
ASPECT is a flexible hyperspectral imager based on tunable Fabry-Perót interference filter [3]. It consists of three independent Vis-NIR imaging channels, one single-point SWIR spectrometer, and a dedicated data processing unit (DPU) based on Xiphos Q7 (Table 1). ASPECT is the prime payload of Milani CubeSat carried by ESA Hera mission [4] to binary asteroid Didymos-Dimorphos.
The spectral range of ASPECT, especially the range 0.7-1.6 µm of the imaging Vis-NIR1/2 channels, cover the key spectral area of 0.5-1.5 µm where the abovementioned rapid SW onset occurs on timescales 10-103 years EET. ASPECT will conduct global hyperspectral mapping of the target asteroids with a resolution of 1 m/px from 5 km and will be able to detect resurfacing on both asteroids either excavation of fresh material caused by DART spacecraft impact or deposition of fallback ejecta.
Table 1: ASPECT parameters.
How to cite: Kohout, T. and Palamakumbure, L.: Detection of a rapid onset of the space weathering and its non-linear temporal evolution with ASPECT hyperspectral imager of the ESA Hera / Milani mission, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-191, https://doi.org/10.5194/epsc2026-191, 2026.
Our knowledge of the internal structure of asteroids relies entirely on inferences from remote sensing observations of the surface and theoretical modeling. Is the body a monolithic piece of rock or a rubble-pile, and how high is the porosity? What is the typical size distribution of the constituent blocks? Are these blocks homogeneous or heterogeneous? Direct measurements of an asteroid’s deep interior structure are needed to better understand asteroid accretion and their dynamic evolution for science, planetary defense and exploration. In orbit Radars sounding is the most mature instruments capable of achieving the objective of characterizing the internal structure and heterogeneity [1].
This is the goal of JuRa, the Juventas radar, onboard the ESA HERA mission. JuRa is a monostatic radar, BPSK coded at 60MHz carrier frequency and 20MHz bandwidth [2], [3], [4]. The main objective of JuRa is to characterize the asteroid interior, to identify internal geological structure such as layers, voids and sub-aggregates, to bring out the aggregate structure and to characterize its constituent blocks size distribution from sub-metric to global scale. The second objective is to estimate the average permittivity and its spatial variation to retrieve information on its composition and porosity.
In less than a year, the JuRa radar will begin probing the internal structures of Dimorphos and Didymos. The instrument is in good shape, and observation strategies are currently under development. In parallel, data retrieval and tomographic processing methods are being developed within the JuRa instrument team.
In addition to radar signal compression and radiometric calibration, a crucial aspect of preprocessing is signal co-registration. The final processing is performed in the body-fixed frame, and the goal is to perform this geometric transformation precisely in order to ensure the phase coherence of the signal required for any radar processing. In other words, this involves determining not only the trajectory but also the system’s dynamic state (position of the spin axis, precession, etc.) with a precision better than 1 meter (lambda = 5m). Different radar processing techniques allow for refinement of the geometric information, such as autofocus, which tests phase coherence within a single acquisition sequence, or interferometric methods, which quantify the phase difference between sequences [5]. These techniques for classical Earth observation need to be adapted to the specific observational geometry of a binary asteroid.
The main processing step is SAR synthesis, which corresponds to signal backpropagation. The backpropagation in a vacuum, which does not account for differences in permittivity within the asteroid, is fast and useful for co-registration and geometric correction, but its performance remains remain limited for imaging the interior [6]. Full tomographic processing is needed to inverse the interior and consist in an iterative minimization under the constraints of a direct problem [7], [8].
Geometry correction and tomography are currently undergoing development and validation. To this end, we have developed a scaled experiment using analog models. Different models on the scale of an asteroid were produced using 3D printing with materials of controlled permittivity. These ~15 cm models were then characterized in an anechoic chamber over the 3–18 GHz frequency range. This chamber covers virtually the entire range of observation geometries at a fixed distance ~1.5m. The measured signals can then be used to validate the JuRa processing chain [9], [10].
In this presentation, we will first review the current status of the instrument, followed by a focus on the development and validation of the processing.
[1] A. Herique et al., « Direct observations of asteroid interior and regolith structure: Science measurement requirements », Advances in Space Research, vol. 62, no 8, p. 2141‑2162, oct. 2018, doi: 10.1016/j.asr.2017.10.020.
[2] P. Michel et al., « The Hera Space Mission in the Context of Small Near-Earth Asteroid Missions in the Past, Present and Future », Space Sci Rev, vol. 221, no 5, p. 70, juill. 2025, doi: 10.1007/s11214-025-01195-1.
[3] H. Goldberg et al., « The Juventas CubeSat in Support of ESA’s Hera Mission to the Asteroid Didymos », 2019, 33rd Annual AIAA/USU Conference on Small Satellites, SSC19-WKIV-05
[4] A. Herique, « JuRa: The Juventas Radar on Hera mission to probe internal structure of Didymos and Dimorphos asteroids. », SSR submitted. .
[5] W. Carrara, Spotlight synthetic aperture radar. in Signal Processing Algorithms. Artech House, 1995.
[6] O. Gassot, A. Herique, Y. Rogez, W. Kofman, S. Zine, et P.-P. Ludimbulu, « SPRATS: a versatile Simulation and Processing RAdar ToolS for planetary missions », in 2020 IEEE Radar Conference (RadarConf20), Florence, Italy: IEEE, sept. 2020, p. 1‑5. doi: 10.1109/RadarConf2043947.2020.9266488.
[7] A. Dufaure, C. Eyraud, L.-I. Sorsa, Y. O. Yusuf, S. Pursiainen, et J.-M. Geffrin, « Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data - I. The frequency domain approach », A&A, vol. 674, p. A72, juin 2023, doi: 10.1051/0004-6361/202244777.
[8] Y. Berquin, A. Hérique, Y. Rogez, W. Kofman, et S. Zine, « Internal structure imaging of Didymos with JuRa using homogeneous asteroid models », Copernicus Meetings, EPSC-DPS2025-788, juill. 2025. doi: 10.5194/epsc-dps2025-788.
[9] L.-I. Sorsa, C. Eyraud, A. Hérique, M. Takala, S. Pursiainen, et J.-M. Geffrin, « Complex-structured 3D-printed wireframes as asteroid analogues for tomographic microwave radar measurements », Materials & Design, p. 109364, déc. 2020, doi: 10.1016/j.matdes.2020.109364.
[10] T. Pajala, C. Eyraud, A. Hérique, J.-M. Geffrin, et S. Pursiainen, « Rubble pile asteroid radar analogue model for Dimorphos — The asteroid moon of 65803 Didymos », Acta Astronautica, vol. 246, p. 462‑476, sept. 2026, doi: 10.1016/j.actaastro.2026.04.027.
How to cite: Herique, A., Plettemeier, D., Berquin, Y., Eyraud, C., Geffrin, J.-M., Haynes, M., Kofman, W., Pajala, T., Pursiainen, S., Rogez, Y., and Virkki, A.: JuRa Radar on HERA: tomography processing development and validation using scaled measurements on asteroid analog models., Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-798, https://doi.org/10.5194/epsc2026-798, 2026.
The Seismic Instrument for Asteroids (SIA) will be deployed to the surface of asteroid 99942 Apophis by the ESA–JAXA RAMSES mission prior to the asteroid’s closest approach to Earth to measure its seismic response to tidal forces [1,2]. SIA will monitor the seismic activity continuously from three hours before to six hours after perigee - this is the critical window when peak tidal-induced seismic activity is expected [1]. Before and after this critical window, periodic SIA measurements will support seismic background noise assessment and allow for monitoring other natural sources such as micrometeoroid impacts and thermal cracking [3–5]. The SIA measurements will be used to constrain the seismicity of Apophis and probe the asteroid’s subsurface and internal structure.
SIA is a compact seismometer (Fig. 1) specifically designed to be integrated into a small asteroid surface package (the Ramses CubeSat-2) and to operate under the harsh conditions at the surface of Apophis without requiring leveling. The instrument includes a three-axis accelerometer and three single-axis geophones along with dedicated custom-built low-noise electronics and is designed to achieve an instrument noise level below 1.0 × 10⁻⁹ m/s/√Hz over the 5 - 200 Hz band. Both the sensor assembly and the electronic stack (Fig. 1) are integrated into a common mechanical assembly with outer dimensions of 190 x 98 x 54 mm. At the instrument level, SIA has successfully passed a vacuum thermal balance test, qualification-temperature burn-in thermal cycles, and Electromagnetic Compatibility (EMC) tests. The performance tests have demonstrated that the electronic, sensor and integrated instrument noise levels meet the science requirements. The Engineering Model is expected to be delivered mid-2026 with the Flight Model delivery early 2027.
This presentation will provide an update on the SIA science objectives, planned operations and the instrument development in preparation for the 2028 RAMSES launch.
Figure 1: A photo of the electronic stack and the sensor assembly of the SIA instrument. Both parts are integrated into a common mechanical assembly.
Acknowledgements
SIA is being developed at ISAE-SUPAERO with support from the French Space Agency (CNES) and the European Space Agency (ESA), in collaboration with IPGP.
References
[1] DeMartini, J. et al. (2025) Planetary Science Journal, 6:263.
[2] Ballouz et al., (2025) Planetary Science Journal, 5:251.
[3] Murdoch, N. et al., (2017) Planetary and Space Science, 144, 89-105.,
[4] Murdoch, N. et al., (2015) Asteroids IV, University of Arizona Press Space Science Series.
[5] Compaire, N., et al. (2022). Geophysical Journal International, 229(2), 776-799.
How to cite: Carpi, P., Murdoch, N., Garcia, R. F., Cadu, A., Sournac, A., Wilhelm, A., Lavigne, T., Torrent-Duch, A., Boudjemaa, L., DeMartini, J., Robert, O., Piou, V., Melac, L., Moussi, A., Loubies, M., and Bousquet, P.: The Seismic Instrument for Asteroids (SIA) for the RAMSES mission to asteroid Apophis, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-522, https://doi.org/10.5194/epsc2026-522, 2026.
People worldwide are becoming aware of the necessity of Planetary Defense after the Chelyabinsk meteorite air burst event in 2013. Later, the kinetic impact experiment using the NASA Double Asteroid Redirect Test (DART) to asteroid Dimorphos was successfully performed in 2022, whose efficiency will be verified by the ESA Hera mission in 2026 to 2027. A close encounter to Earth of the asteroid Apophis in 2029, and the ESA-JAXA joint mission RAMSES (Rapid Apophis Mission for Space Safety) will continuously observe the asteroid during the flyby in 2029. A recent discovery of asteroid 2024YR4 was found, which was considered potentially impacting Earth in 2032. Therefore, physical properties of asteroids are essential for planetary defense studies concerning the nature of asteroids, the effect of asteroid deflection by a kinetic impact of spacecraft, and a degree of disaster caused by an asteroid impact to Earth.
Thermal infrared imaging of asteroids from spacecraft is a useful method to characterize the target bodies during flyby and rendezvous to provide their thermophysical and compositional properties, as was proven in the Hayabusa2 mission. Here we present the Therma InfraRed Imager (TIRI) instrument[1,2] and future observation plans in Hera and RAMSES missions. The instrument is based on an uncooled micro-bolometer array of 1024 x 768 pixels and has a field of view of 13° x 10° and an angular resolution of 0.23 mrad/pixel. It takes images at 25 Hz. In addition, an 8-position filter wheel is equipped with a wide band (8-14 µm) filter to be used for thermal imaging, and six narrow band (centered at 7.8, 8.6, 9.6, 10.6, 11.6, and 13.0 µm, with approximately 1 µm width) to be used for multi-band imaging in comparison with laboratory experiments for meteorites and rocks at thermal infrared wavelengths.
The instrument has proven its in-flight performance during the Earth-Moon system imaging just after the Hera launch in October 2024, and during the imaging of Mars and Deimos (and Phobos). The performance tested during the calibration campaign using the TIRI flight spare will be briefly shown.
References
- Okada T. et al. SSR (2025) 221, 104.
- Okada T. et al. Acta Astronautica (2026) 240, 888-892.
How to cite: Okada, T., Tanaka, S., Sakatani, N., Shimaki, Y., Arai, T., Senshu, H., Demura, H., Sekiguchi, T., Kouyama, T., Kanamaru, M., Ishizaki, T., Vilardell-Belles, R., Furukawa, S., Karatekin, O., Blommaert, J., and Titus, T.: Thermal Infrared Imaging Instruments for Planetary Defense Missions: Hera and RAMSES, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-730, https://doi.org/10.5194/epsc2026-730, 2026.
The ESA Hera spacecraft was sucessfully launched on October 7, 2024, with the aim of studying binary asteroid (65803) Didymos [1]. The moonlet of the system, named Dimorphos, was impacted by the NASA DART spacecraft on September 26, 2022, as part of the first test of a kinetic impactor deflection technology. DART impact changed the orbital period of Dimorphos around Didymos, generating a huge cloud of dust and debris observable from the Earth. Asteroid Didymos has been extensively observed in the visible to near-infrared (vnir) using ground-based telescopes [2,3,4]. It is classified as an S-type, dominated by mafic silicates, mostly pyroxene and olivine, that show two very characterisic absorption bands at 1 and 2 mm. Band center and depth, together with spectral slope, can be used to infer compositional information on the surface of the asteroid. In addition, space weathering (sw) effects in such surfaces inlcude decrease in albedo and band depth and reddening in the slope.
Hera is expected to arrive to Didymos in October 2026, when the spacecraf will progressively reduce its distance to the system, getting as close as ~1 km to the surface of Dimorphos at the final stage, in June-July 2027. One of the instruments onboard is HyperScout-H (HSH), a hyperspectral imager operating in the 650-950 nm wavelength range that provides spectral and spatial information simultaneously [5]. Its wavelength coverage allows to measure several spectral parameters, like the position of the minimum and the maximum of the 1 mm absorption band (i.e. an estimation of its depth), and the spectral slope (Fig. 1, Bottom). These parameters will be used, in combination with the information provided by the other instruments onboard the spacecraft, to create compositional and space weathering maps (high-level products) of the surfaces of the two asteroids through all the mission phases. In this work we present what we expect to measure with HSH at the arrival to the system, including different potential scenarios regarding Dimorphos status after the DART impact. We use as a reference the collection of Didymos vnir spectra (Fig. 1, Top) obtained with XSHOOTER at the 8.2m VLT (ESO, Chile), right before and after the DART impact, to measure several spectral parameters and to compare with meteorite spectra. These measurements will define the compositional and space weathering space where to locate HSH measurements.
Figure 1. Top: visible to near-infrared spectrum of (65803) Didymos obtained with XSHOOTER at VLT on the nigtht of September 27, 2022, after the DART impact. The blue region indicates the wavelength range covered by the HSH instrument onboard the Hera spacecraft. Bottom: visible spectrum of Didymos (in blue) as seen by HSH (orange circles), and different spectral parameters measured.
References
[1] Michel, P., et al. Planet. Space Science 2022, 3, 160-181, [2] de León, J., et al. Astron. Astrophys. 2010, 517, 23-48, [3] Polishook, D., et al. Planet. Space Science 2023, 4, 229-24, [4] Lazzarin, M., et al. Nat. Comm. 2026, 17, id.551, [5] Popescu, M., et al. Space Sci. Rev. 2025, 221, id.112
How to cite: de Leon, J., Prodan, G., Popescu, M., Opitom, C., and Migliorini, A.: Compositional characterization of asteroid Didymos from ground-based spectra in preparation of the arrival of the ESA Hera mission, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-440, https://doi.org/10.5194/epsc2026-440, 2026.
Introduction. The Nancy Grace Roman Space Telescope (hereafter Roman) is NASA’s next flagship astrophysics mission, with launch currently planned for late August or early September 2026. The primary instrument on Roman is the Wide Field Instrument (WFI), which provides broad-band imaging in the near-infrared (0.48 – 2.3 μm) over a large 0.281 deg2 field of view. Roman’s primary goals are to study dark energy and dark matter, evaluate the expansion rate of the universe via observations of supernovae, and push the limits of exoplanet detection. To achieve these goals, Roman must look out through our own solar system, creating an opportunity to study foreground solar system small bodies. In particular, Roman will be capable of providing photometric and astrometric observations of near-Earth objects (NEOs) for both scientific and planetary defense applications. Such observations can be combined with those from other facilities which are beginning to come online, including the Vera C. Rubin Observatory (Ivezić et al. 2019) and NEO Surveyor (Mainzer et al. 2023), to improve orbits, determine sizes, and constrain bulk compositions for some of the smallest and fastest-moving NEOs. The results presented here were published in Holler et al. (2025).
Observe smaller NEOs. The Roman Core Community Surveys are not designed with the necessary combination of coverage and cadence to discover new NEOs; that task is left to Rubin’s Legacy Survey of Space and Time (LSST) and NEO Surveyor. However, using the WFI and the wide bandpass F146 filter, Roman can detect NEOs with diameters smaller than 20 meters at the 5-σ level over a wide range of expected angular rates of motion. This diameter is roughly a third the size of the “city killer” asteroid 2024 YR4 (Rivkin et al. 2025) and comparable in size to the Chelyabinsk meteoroid that exploded in the atmosphere in 2013, leading to widespread injuries and property damage. The ability to reliably detect objects of this size does not currently exist.
Improve orbits. The ability to observe very small, potentially fast-moving asteroids is a boon for planetary defense initiatives. The first task when any new object is discovered, and particularly for NEOs on Earth-crossing orbits, is to determine the orbit and begin to evaluate risk. NEO Surveyor is designed with the cadence to allow orbit computation for previously unidentified NEOs: two sets of four observations in a 6 – 9-hour period spaced ~13 days apart. We find that adding a single additional astrometric data point with Roman, which has a pixel scale ~30 times finer than that of NEO Surveyor (0.11” vs 3”), a week after the second NEO Surveyor measurement (for a total time baseline of only ~3 weeks) can decrease the orbital uncertainties by 95 – 99% up to a year into the future.
Determine sizes. A full assessment of an object’s risk to the Earth also includes an estimate of the diameter. Only Roman and NEO Surveyor can observe the smallest NEOs. NEO Surveyor operates in the mid-infrared in two wavelength windows, 4.0 – 5.2 μm and 6.0 – 10.0 μm, where thermal emission is strongest (Mainzer et al. 2023). Roman’s wide-band filters span the near-infrared from 0.48 – 2.3 μm, where reflected light peaks. Individually, neither facility is capable of simultaneously constraining albedo and diameter, but together, the combination of near- and mid-infrared photometric measurements can recover the albedo and diameter to high-precision (>10-σ). Constraining a potentially hazardous NEO’s orbit and diameter to high-precision provides the necessary information for more detailed risk assessment and mitigation planning.
Constrain bulk compositions. The diameter of an NEO provides a first-order approximation for the impact assessment, but what is more valuable is an estimate of the mass, which requires constraints on the composition. Information on the spectral type, and thereby composition, provides a crucial delta that can lead to a more accurate mass measurement. The Roman broad-band filters provide sufficient spectral leverage to differentiate between C-, S-, and X-type asteroids in the Bus-DeMeo system (DeMeo et al. 2009). These are the most common asteroid spectral types and represent three different bulk compositions: carbonaceous, silicate-rich, and metal-rich, respectively. Each type is associated with a range of densities, which when combined with a diameter leads to an improved mass estimate.
Roman calibration pipeline enhancements. At the time of abstract submission, none of the measurements described above could actually be performed. This is because the Roman default calibration pipeline as constructed treats moving objects, especially fast-moving objects like NEOs, similar to cosmic rays and removes them from images. We will provide an update on efforts to recover moving target streaks, fit the streaks to extract photometry and astrometry, and make that information available to the larger community.
Acknowledgements. We recognize financial support from the STScI Director’s Research Funds (DRF).
References
DeMeo, F. E., et al. (2009). Icarus 202, 160.
Holler, B. J., et al. (2025). PASP 137, 105004.
Ivezić, Z., et al. (2019). ApJ 873, 111.
Mainzer, A. K., et al. (2023). PSJ 4, 224.
Rivkin, A. S., et al. (2025). RNAAS 9, 70.
How to cite: Holler, B., Cosentino, R., Schultz, W., Brandt, T., Masiero, J., Sharkey, B., Bernardinelli, P., and Holt, C.: NASA’s Nancy Grace Roman Space Telescope as a planetary defense asset, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-712, https://doi.org/10.5194/epsc2026-712, 2026.
The study of Near-Earth Objects (NEOs) is essential for several reasons. From a scientific perspective, these objects may have played a role in delivering organic material and water to Earth [1,2] while also preserving information about their origin and evolution from the early Solar System. From a planetary defense perspective, NEOs can pose a non-negligible threat to Earth. Several events in Earth’s history (e.g. K-Pg event and the Chelyabinsk meteor in February 2013) demonstrate that such objects can cause significant material damage and, in extreme cases, mass extinctions. In particular, previous studies have shown that even relatively small objects (10-100m in diameter) can produce regional-scale damage [3]. It is therefore essential to characterize these potential hazards by providing key information to support civil protection and mitigation efforts.
To address these scientific and operational challenges, the NEO Physical Observations and Properties Simulation (NEOPOPS) project was funded by the European Union and implemented by the European Space Agency (ESA). In particular, the Rapid Response work package (WP6) aims to enable the comprehensive characterization of potentially hazardous objects within a short time after discovery. Due to their small size, these objects are typically bright enough for detailed observations for only a few weeks. After this period, they generally become unobservable until their next predicted close approach or potential impact date.
2025 FA22 was discovered by the Pan-STARRS-2 survey on March 29, 2025. With an estimated diameter between 120 and 290 m, it was originally classified as a virtual impactor with a Torino Scale [4] rating of 1, due to a low but non-zero probability of impact in 2089. This initial risk classification triggered high-priority follow-up astrometry, which rapidly refined the orbit and conclusively ruled out any impact threat, leading to its removal from global risk lists. On September 18, 2025, 2025 FA22 passed safely by Earth at a distance of approximately 8.42 x105 km (about 2.19 lunar distances). It was therefore selected as a primary target for a global, coordinated observing campaign under the auspices of the International Asteroid Warning Network (IAWN).
The campaign was specifically designed to stress-test the global planetary defense infrastructure, treating the object, for the purposes of the exercise, as a hypothetical virtual impactor. This opportunity also enabled the collection of extensive astrometric and physical characterization data. We successfully conducted a coordinated observational campaign, including astrometry, photometry, spectroscopy, radar and polarimetry, within just a few weeks of the initial alert. This rapid response demonstrates the capability to transition from discovery to a detailed physical characterization within the tight operational windows required for planetary defense.
In this presentation, we report the results of this extensive multi-technique observing campaign [5,6], providing a comprehensive set of physical parameters for 2025 FA22.
Acknowledgments : The NEOPOPS observations contract is funded by the Horizon Europe Programme of the European Union and implemented by ESA (agreement No. 4000147191/25/D/MRP). The observations with the 0.65m Mayer telescope were supported by the Praemium Academiae award from the Academy of Sciences of the Czech Republic, grant no. AP2401.
References
-
Morbidelli A., Chambers J., Lunine J. I., et al., M&PS, 2000, vol. 35, p 1309-1320
-
Marty B., Avice G., Sano Y., et al., E&PS, 2016, letters, vol. 441, p. 91-102
-
Perna D., Barucci M.A., Drube L. et al., P&SS, 2015, 118, P. 311-317
-
Binzel R., P&SS, 2000, vol. 48, p. 297-303
-
Rivet J.P., Bagnulo S., Bendjoya P., et al., arXiv, 2026.
-
Ieva S., Bourdelle de Micas J., Farina A., et al., in prep
How to cite: Bourdelle de Micas, J., Ieva, S., Dotto, E., Pravec, P., Barucci, A., Birlan, M., Lazzarin, M., Bagnulo, S., Cano, J. L., Devogèle, M., Mazzotta Epifani, E., Farina, A., Fatka, P., Frank, E., Ferri, F., Fulchignoni, M., La Forgia, F., Perna, D., and Sonka, A. and the collaborators: Characterization of the virtual impactor by the NEOPOPS team: the case of 2025 FA22, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-934, https://doi.org/10.5194/epsc2026-934, 2026.
Introduction: Near-Earth Asteroids (NEAs) are asteroids with perihelion distances smaller than 1.3 AU. They represent a key population for the study of small bodies, Solar System evolution, and the possible delivery of water and organic molecules to the early Earth (Kokhirova et al. 2023)]. A subset of NEAs, the Potentially Hazardous Asteroids (PHAs), follows orbits that can approach the Earth and includes objects large enough to produce significant damage in the event of an impact. At present, about 2500 PHAs are known, including objects such as Didymos and Apophis. For these reasons, the physical characterization of NEAs, and in particular PHAs, is an important task for both Solar System science and planetary defence.
The NEOPOPS project: Space missions provide detailed information on selected targets, but ground-based observations remain the main tool for the rapid physical characterization of newly discovered NEAs. As of May 2026, more than 41,000 NEAs are known, with an average discovery rate of about 3000 new objects per year. The NEO Physical Observations and Properties Simulation project (NEOPOPS) is funded by the Horizon Europe Programme, implemented by ESA and led by INAF–OAR. The project started in February 2025 and will continue until August 2028. Its goal is to improve the physical characterization rate of NEAs through complementary techniques, including photometry, spectroscopy, and polarimetry, with particular attention to rapid response observations of newly discovered objects and possible impactors.
Observations: In this work, we present the first results from the first two years of the spectroscopic survey of NEAs carried out at the Asiago Observatory within Work Package 4, dedicated to spectroscopy, and Work Package 6, dedicated to rapid response observations. The observations were obtained with the 1.22 m Galileo Telescope equipped with the Boller & Chivens spectrograph, and with the 1.82 m Copernico Telescope equipped with the AFOSC spectrograph. These facilities allow low-resolution visible spectroscopy in the approximate range 0.45–1.0 μm, depending on the telescope and instrumental setup. Since the beginning of the project, 75 NEAs have been observed, including recently discovered objects, PHAs, and targets with available light-curve information.
Analysis and results: The spectral analysis includes taxonomic classification based on the DeMeo et al. (2009) system, comparison with laboratory meteorite spectra (DeMeo et al. 2022), and the study of spectral slopes and absorption features. The observed sample is dominated by S-complex objects, followed by X- and C-complex asteroids. For each object, the taxonomic classification is also used to estimate the size when no direct measurement is available, assuming a representative albedo for the assigned taxonomic class. We also investigate the distribution of the observed NEAs as a function of absolute magnitude, estimated size, and orbital parameters, including perihelion distance, aphelion distance, eccentricity, inclination, and semi-major axis. This allows us to compare the spectroscopic properties of the sample with its dynamical distribution and to distinguish between NEAs and PHAs.
A preliminary analysis of the phase reddening effect was also performed by studying the spectral slope as a function of phase angle in two wavelength intervals, 6000–7000 Å and 5500–9000 Å. This analysis allows us to search for possible trends between surface spectral properties and observing geometry. Several objects were observed on different nights or over a significant fraction of their rotation, allowing us to test possible spectral variability. Among them, the binary asteroid 1999 HF1 was observed over two full rotations. We also obtained twelve spectra of the PHA 2025 FA22, classified as an X-type object, which show a largely homogeneous surface over about 2.3 hours of rotational coverage.
Conclusions: These first results show the role of regular spectroscopic monitoring from Asiago within the NEOPOPS project. The survey provides taxonomic and compositional information for a growing sample of NEAs, supports the rapid characterization of newly discovered objects, and allows the study of spectral variability in selected targets. The continuation of the survey will increase the statistical value of the sample and improve our knowledge of the physical properties of NEAs and PHAs.
Acknowledgments: The NEOPOPS observations contract is funded by the Horizon Europe Programme of the European Union and implemented by ESA, agreement No. 4000147191/25/D/MRP.
References
[1] Kokhirova et al. (2023), Solar System Research, 57, 487–495.
[2] DeMeo et al. (2009), Icarus, 202, 160–180.
[3] DeMeo et al. (2022), Icarus, 380, 114971.
How to cite: Farina, A., Lazzarin, M., La Forgia, F., Ferri, F., Mura, A. C., Ieva, S., Bourdelle de Micas, J., Dotto, E., Pravec, P., Mazzotta Epifani, E., Perna, D., Bagnulo, S., Cano, J.-L., and Devoggele, M.: First results from the first two years of NEA spectroscopic observations within the NEOPOPS project at Asiago Observatory , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-870, https://doi.org/10.5194/epsc2026-870, 2026.
Introduction:
In collisional physics, a target body is said to be ‘catastrophically disrupted’ when the largest fragment is equal to half of the original target mass [e.g., Benz & Asphaug 1999]. The specific energy, Q, required to result in that disruption is known as Q*D. Q*D is known to be sensitive to the interior properties and strength of an object [Holsapple & Housen 1999, Raducan et al. 2022, Ballouz et al. 2026]. Here, we present results of high-speed impacts at the catastrophic disruption threshold on “designer asteroids”: impact targets with well characterized strength and interior properties.
Background:
Knowledge of Q*D is important for planetary defense as it sets a limit at which an earth-bound asteroid may be mitigated through impulsive techniques, such as kinetic impacts [e.g., Daly et al. 2023]. Specifically, kinetic impacts that result in catastrophic disruption may do more harm than good as the resulting fragments may still be sufficiently large as to remain a hazard to Earth. In such a scenario, other mitigation options may become more favorable, such as slow-pull/push mitigation through gravity tractor or ion-beam deflection [OWL 2022].
Methodology:
In this work, we created target materials out of a variety of dental plasters, each with distinct strengths (12 to 117 MPa), densities (1.1 to 2 kg/m3), and porosities (15 to 51%). The target categories included 1) homogeneous targets made of a single type of dental plaster, and 2) “rubble pile” targets made up of a matrix of dental plaster binding loose granular material.
Targets that were 4” and 6” were prepared for impact experiments at NASA’s Ames Vertical Gun Range (AVGR). Projectile sizes of ⅛” to ¼” were launched at the targets at a 15° angle from the horizontal at speeds between 1.72 and 4.65 km/s.
Results:
Figure 1 show images of one our disrupted targets, a rubble pile composed of aquarium gravel with a ‘mounting plaster’ matrix. This 4” target disrupted after a 2.4 km/s impact of ¼” diameter Pyrex projectile.
Figure 1: 4" Rubble Pile (Mounting Plaster with Aquarium Gravel) after disruption from 2.4 km/s impact. Not pictured: additional smaller fragments.
Table 1 summarizes this and the additional experimental outcomes that resulted in disruption: 2 homogeneous mounting plaster targets, one 4” and one 6”, and another 4” rubble pile target with different rubble material.
Table 1: Disrupted Target/Shot Parameters. Largest fragment mass is less than half of the original mass of the target.
Discussion:
Q for impacts were calculated using Equation 1:
Figure 2 shows this Q as a function of target mass for the various targets we impacted, regardless of whether they were disrupted or deflected. Triangular data points with <0.5 fragment mass fraction are those that were decidedly ‘disrupted.’ The disrupted target in each target type typically had the highest Q values. An exception is target RP3, a mounting plaster and lava rock rubble pile mixture. For this same target, an impact with a higher Q value, but a very similar mass did not disrupt. We continue to work towards understanding why this was the case. Plausible culprits that we are exploring include small differences in the internal structure of the target, impact angle relative to the surface normal, and impact velocity.
Figure 2: Q of select AVGR Experimental Data is for the target categories in which disruption was observed. MP = mounting plaster, RP1 = rubble pile made of MP matrix and aquarium gravel, RP3 = rubble pile made of MP matrix and lava rocks.
In Figure 3, we present preliminary analysis to estimate Q*D for three types of designer asteroids. These cases had sufficient data to determine Q*D = 1040 ± 208 J/kg (MP), 1006 ± 116 J/kg (RP1), and 2200 ± 413 J/kg (RP3). The scatter in data for a given target type is likely due to the variation in impact speeds (a factor of ~3) across the different cases presented here, as Q*D is known to depend on impact velocity [e.g., Holsapple & Housen 1999]. The larger value of Q*D of RP3 (by a factor of ~2) may be due to the large porosity of the embedded lava rocks which increases the resistance of the target to disruption as the interior is able to compact in response to an impact.
Figure 3: Q of select AVGR Experimental Data is for the target categories in which disruption was observed, and sufficient data was collected to estimate Q*D.
To gain a better understanding of our measurement, we intend to fully characterize the interior structure and strengths of our rubble pile targets, as well as other homogenous targets that were not readily disrupted. We have already measured the density and porosity of the matrix plasters used in our target. In many instances, we have made x-ray CT scans of target samples before impact, and the fragments generated after. These remain to be analyzed in detail. We have also begun analyzing efforts to characterize the static and dynamic strength of these targets. Through these measurements, we anticipate to get a better understanding of what factor contribute to the disruption of our rubble pile targets. Our findings will be critical for developing the right sort of strategies to deflect asteroids, without disrupting them involuntarily.
Acknowledgements: This project was funded by NASA Grant 80NSSC21K1139 to A. Stickle under the NASA Yearly Opportunities for Research in Planetary Defense (YORPD). We thank Freddy Perez, Chuck Cornelison, and JP Weins at the NASA Ames Vertical Gun Range for supporting these experiments.
References: Benz, W., & Aphaug, E. (1999) Icarus 142, 5-20. Housen, H. & Holsapple, H. (1999) Icarus, Volume 142, Issue 1, pp. 21-33. Raducan, S. D., et al. (2022) Astronomy & Astrophysics, Volume 665, id.L10, 12 pp. Ballouz, R.-L., et al. (2026) The Planetary Science Journal, Volume 7, Issue 4, id.87, 30 pp. Daly, R.T., et al. (2023) Nature 616, 443. National Academies of Sciences, Engineering, and Medicine. (2022). Origins, worlds, and life: a decadal strategy for planetary science and astrobiology 2023-2032.
How to cite: Meier, R., Stickle, A., Barnouin, O., and Ballouz, R.: Designer Asteriods: Investigating the dependence of the catastrophic disruption threshold on target interior properties, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-715, https://doi.org/10.5194/epsc2026-715, 2026.
Several techniques may be appropriate for deflecting a threatening asteroid on a collision course with Earth. Slow-push techniques, such as gravity tractors, require long lead times. Fast-push techniques such as nuclear standoff bursts require much less lead time but come with a host of additional issues. Kinetic impactors are an alternative fast-push technique that can be used on small-to-medium hazards with moderate warning time. The Double Asteroid Redirection Test (DART) mission demonstrated the kinetic impactor technique when it successfully changed the orbital period of Dimorphos in 2022; however, questions still remain about the efficiency of momentum transfer with this technique. Modeling work performed in support of DART suggests that properties such as material strength, porosity, crush properties, asteroid internal structure, and inherent flaw distribution, can significantly affect the deflection that will be caused by a kinetic impactor. Here, we undertake a set of experiments to better constrain how material strength and target structure affect the outcomes of kinetic impactor asteroid deflection. In this study, we focus on hypervelocity (>1km/s) kinetic impactor results.
We constructed “designer asteroids” with varying internal structures, from coherent asteroids to rubble piles, and performed impact experiments at the Johns Hopkins Applied Physics Laboratory (APL) Impact Lab (IL) and the NASA Ames Vertical Gun Range (AVGR) to evaluate the momentum transfer efficiency following impact. In this study, we report on impacts ranging from 1-5 km/s undertaken at the AVGR. A separate companion study focuses on the lower speed impact undertaken at the IL.
Near-spherical targets were created using a range of well understood plaster materials of varying strengths, at three different sizes (e.g., Figure 1). Rubble piles were created using plaster matrix material surrounding either aquarium gravel or porous pumice. All these plasters have well characterized strength properties ranging from 12 to 117 MPa. The internal structure of the targets was evaluated using X-ray Computed Tomography (XCT) scans (e.g., Figure 2), the shape and volume of the craters and resulting deformation was tracked, and a ballistic pendulum was used to track deflection.
Thirty-seven shots were performed at the NASA AVGR into 7 different target types, with 2 different target sizes (10 and 15-cm diameter spheres). Impact speeds ranged from ~ 1 km/s to ~5 km/s. Four separate plasters were used to create homogenous targets, with varying strength and porosity properties (Table 1).
High-speed videos were used to measure the impact location and angle and to determine the displacement and rotation of the target following impact. We use particle and object tracking algorithms to compute the horizontal, vertical and lateral displacements, and the rotations of the pendulum to determine post-impact momentum. We also measure the ejection speed and direction of target ejecta to understand the origin of any momentum enhancement, and characterize the shape and mass of the largest individual ejecta. Finally, fragments are collected following the impact and basic fragment analysis is performed to generate fragment size frequency distributions.
Figure 1. A “family portrait” of example impact targets at three different sizes. (left) 5-cm diameter sphere, (middle) 10-cm diameter sphere, (right) 15-cm diameter sphere. The medium and large targets are “rubble pile” targets, with aquarium gravel visible just below the surface.
Table 1. Summary of target materials and number of hypervelocity experiments performed on each different target type. The strength and bulk porosity for the rubble pile targets is in the process of being measured.
The XCT scans can be used to evaluate internal structure in more detail as well as post-impact damage patterns. In the AVGR experiments, impact-induced fracturing is seen below the craters and throughout the targets. For rubble pile targets, damage patterns are significantly affected by pre-impact structure, with fractures largely concentrated in the plaster matrix material and curving around gravel and pre-existing large voids. In rare cases, the fractures are seen through the aquarium gravel (Figure 3).
Differences in momentum enhancement are seen across velocity and target structures. We find that more porous targets generate less ejecta and the impacts likely cause less momentum change, consistent with findings in the literature. At the time of writing, other factors, like impact angle and strength differences, are still being evaluated for our hypervelocity impact experiments. Rubble pile targets behave noticeably different than homogenous targets regardless of impact speed.
Our experiments show that there are variations in experimental outcomes across the replicates of the same target type (e.g., “RP1” or “RP3”), but experimental outcomes vary more when we compare across the different target structures. Targets with higher initial porosity also tended to have deeper craters, while targets with lower initial matrix/plaster strength had larger craters overall compared to those with stronger matrix or plaster strength. The internal rubble structure did also affect crater size and shape.
In this presentation, we will describe the initial experiments, results, and discuss internal structure effects on deflection and damage patterns in our hypervelocity impact experiments.
Figure 2. Examples of post-impact XCT images for 6 different target types. All targets are 4” spheres. (MP2): Homogenous “mounting plaster” target, impact velocity = 0.98 km/s; (SR1) Homogenous “silky rock” target, impact velocity = 1.62 kms; (PR1) Homogenous “prima rock” target, impact velocity = 2.17 km/s; (RP1_1) “Rubble Pile 1” target, impact velocity = 1.72 km/s; (RP2_2) “Rubble Pile 2” target, impact velocity = 1.95 km/s; (RP3_1) “Rubble Pile 3” target, impact velocity = 2.12 km/s. Black arrows show examples of areas of density variation or large voids that naturally result from the manufacturing process. Light blue arrows highlight post-impact fracturing; green arrows highlight post-impact compression of material beneath the point of impact.
Figure 3. Example of impact-induced fracturing from a “rubble pile 2” target. Impact velocity = 1.95 km/s. Most fractures are concentrated in the matrix and pass around, or truncate on, pre-existing gravel or large voids. For sufficiently energetic impacts, the aquarium gravel can also become fractured (e.g., white stone, left).
How to cite: Stickle, A., Barnouin, O., Meier, R., and Ballouz, R.: Designer Asteroids: Hypervelocity impact experiments to track internal structure effects on deflection by kinetic impactors, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-630, https://doi.org/10.5194/epsc2026-630, 2026.
How to cite: Hirabayashi, M., Hayakawa, M., Mimasu, Y., Hirata, N., Iwaki, T., Kamata, S., Kitazato, K., Kouyama, T., Sakatani, N., Yumoto, K., Fujiwara, M., Takeuchi, H., Saiki, T., Senshu, H., Shimomura, S., Suetsugu, R., Yokota, Y., Nakazawa, S., Tanaka, S., and Yoshikawa, M. and the Hayabusa2# mission team: JAXA’s Hayabusa2#: Flyby observations and characterizations of Asteroid (98943) Torifune, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-177, https://doi.org/10.5194/epsc2026-177, 2026.
Near-Earth asteroids that penetrate the atmosphere deposit energy along their flight path, generating shock waves that decay into infrasound, sub-audible acoustic waves below 20 Hz that propagate efficiently over hundreds to thousands of kilometers with minimal attenuation. Infrasound is frequently among the few geophysical observables captured from bolide events at regional to global distances. Infrasound signal periods can be used to recover the blast radius and, through it, the energy deposited per unit path length (the source function) along the trajectory, a quantity that informs impact-hazard assessments, bolide flux calibrations, and post-event characterization for planetary defense. However, the weak-shock models used in this source-function recovery have not previously been benchmarked against a hypersonic source with independently known parameters, leaving a poorly quantified systematic uncertainty in source-function estimates derived from natural impactors.
The OSIRIS-REx Sample Return Capsule (SRC) reentry on 24 September 2023 offers an opportunity to reduce this uncertainty. The SRC is a rigid, effectively non-ablating hemisphere whose geometry, trajectory, and velocity at each emission point are constrained from mission data and ray tracing, reducing source-side ambiguity associated with ablation and fragmentation that complicates natural meteoroid analyses. Infrasound was recorded at 39 ground stations deployed in Nevada and Utah, each sampling a different emission point along the trajectory at source altitudes of 44 to 62 km, providing a controlled, multi-station calibration dataset for weak-shock theory applied to a hypervelocity atmospheric source (Fig. 1).
Six blast-radius (R0) formulations and three weak-shock transition coefficients (C) were evaluated through systematic forward and inverse modeling. The Sakurai (1965) formulation achieves the lowest period residual (9% median absolute error) with near-zero bias, while the Mach-diameter approximation commonly used in bolide studies appears to overestimate the blast radius by a factor of approximately 3.4 for this non-ablating source (Fig. 2). The signal period is found to be a more operationally practical observable for constraining the source function than peak overpressure, which remains sensitive to propagation-model assumptions at these distances. A monotonic residual trend with source altitude suggests that constant-normalization blast-radius formulations may not fully capture the variation in energy coupling across the range of entry conditions sampled, an uncertainty that would map directly into source-function estimates for natural impactors.
These results contribute toward a calibrated performance baseline for infrasound-based source-function recovery from hypervelocity atmospheric sources and help quantify systematic uncertainties relevant to planetary-defense applications.
Figure 1: OSIRIS-REx SRC reentry trajectory and infrasound detection geometry. (a) Regional context map showing the projected SRC ground track and the 39 single-sensor infrasound stations deployed across three lines (A, T, C) in Nevada and Utah. (b) Three-dimensional view of the source-to-receiver geometry, with ray paths connecting ground stations to their raytracing-derived emission points (gold markers) along the trajectory at altitudes of 44 to 62 km.
Figure 2: Blast-radius overestimate factor for each of the six tested R₀ formulations, expressed relative to the Sakurai (1965) formulation (the best-performing for this non-ablating source). Each bar is annotated with the corresponding forward-model period median absolute percentage residual (MAPR) at C = 34.3. The top axis shows the approximate energy-per-unit-path-length overestimate.
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. Cleared for release.
How to cite: Silber, E.: Calibrating Infrasound-Based Energy Estimation for Atmospheric Impactors Using the OSIRIS-REx Reentry Benchmark, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-86, https://doi.org/10.5194/epsc2026-86, 2026.
The DART impact on Dimorphos caused the ejection from the asteroid of a large amount of debris of varying sizes, ranging from dust to large boulders [1]. A fraction of the low-velocity ejecta that remained in the binary system eventually re-impacted on Didymos as shown by [2] who studied the evolution of a population of large boulders ejected from Dimorphos. These re-impacts, termed sesquinary impacts, potentially altered the surface of Didymos and may have led to the formation of observable features.
In preparation for the Hera mission [3], following the identification of existing boulder tracks on Didymos and using statistical results on sesquinary impacts of ejecta debris combined with the shape model of Didymos, we investigate the fate of large boulders impacting the surface of Didymos at low velocity. We model the dynamics of the boulders after impact, driven by the topography and surface conditions of Didymos, including possible bouncing and assessing the conditions for ballistic lift-off. We statistically investigate the outcome of the sesquinary impacts by varying the key boulder-surface interaction parameters. We find that the displacement of boulders after the initial impact is possible and is driven by the rapid spin of the asteroid, leading to a preferential motion towards the equator and to the potential formation of new boulder tracks formed in the regolith-covered surface. The sesquinary impacts are likely to induce an accumulation of debris in the equatorial region, along with multiple low-velocity craters related to ejection or bouncing. The observation of boulder tracks is most likely from low to mid-latitudes, in the transition zone [4] characterised by low stability and high terrain slopes (Fig. 1). The presence of such surfaces features have the potential to inform on the surface mechanical properties, through interpretation of their location, density and dimensions. The length and starting latitude of tracks can be indicative of the surface friction and terrain stability. New observations by Hera, targeted on the predicted locations will be key to provide evidence supporting those processes and to gather data for subsequent interpretation.
We acknowledge funding support by the ERC GRAVITE project (Grant Agreement N°1087060).
Figure 1: Ground trajectories of impacting boulders on Didymos for three sets of parameters. The blue lines correspond to previously identified tracks [5].
References
[1] Li, J.-Y., Hirabayashi, M., Farnham, T. L., 2023, Nature, 616, 452-456.
[2] Langner, K., Marzari, F., Rossi, A., 2024, Astronomy and Astrophysics, 684, A151.
[3] Michel, P., Küppers, M., Bagatin, A. C., 2022, Sci. J., 3 160.
[4] Barnouin, O. S., Ballouz, R-L., Marchi, S., 2024, Nature Communications, 15, 6202.
[5] Bigot, J., Lombardo, P., Murdoch, N., 2024, Nature Communications, 15, 6204.
How to cite: Bigot, J., Murdoch, N., Rousseau, A., Rossi, A., Langner, K., Marzari, F., Barnouin, O., and Scheeres, D.: Modelling the fate of sesquinary DART ejecta debris impacting on Didymos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-96, https://doi.org/10.5194/epsc2026-96, 2026.
The Asteroid Framing Cameras (Vincent+2026) onboard ESA's Hera spacecraft (Michel+2026) are two identical panchromatic cameras with a field of view of 5.5 x 5.5 degree and an angular resolution of 93.7 micro-radians per pixel. Only one camera will be used at any time: nominally AFC1, with AFC2 serving as a redundancy instrument. Hereafter we use the acronym AFC to refer to the active camera.
The AFC design requirements were set to ensure a global mapping of both asteroids in the Didymos system down to a spatial scale of 0.5 meter per pixel, with 10 cm per pixel in selected regions of interest. The data is used for navigation and morphological characterization of the mission's targets. Figures 1 and 2 provide a summary of the expected distances and spatial scale, as well as sub-spacecraft latitude and phase angle.
By building a comprehensive visual characterisation of two Near-Earth Asteroids, the AFC contributes to Hera's Planetary Defense goal: to acquire the knowledge necessary for the deflection of a potentially hazardous object, when the time comes.
After Hera reaches the asteroids, the AFC baseline plan is to acquire one image every 15 min, within the operational constraints of the mission (typically 15h of observations followed by 8 hours of data transmission, with 1h margin, per day). This cadence guarantees sufficient redundancy and overlap between consecutive images to ensure a complete coverage of the surface of both asteroids. The outcome will be a new morphological map of Didymos and Dimorphos, documenting the changes induced by the DART impact in 2023 (see Barnouin+2024 for the pre-impact map).
The relatively rapid imaging is key to a precise measure of the rotational and orbital state of Dimorphos around Didymos. Analysis of fixed surface landmarks contributes to the Dimorphos mass determination, by measuring the subtle "wobble" motion it induces on the primary asteroid. High coverage of all regions will provide the multiple views of the surface necessary for shape reconstruction. The daily monitoring also enables detection of surface changes which may occur while Hera is orbiting the system.
In addition to this monitoring sequence, other activities are planned to support specific scientific objectives. AFC will for instance look for possible debris and satellites while approaching the system, and monitor the asteroids' limb for eventual dust ejection, as previously encountered by the OSIRIS-REX mission (Hergenrother+2019). Images are planned at multiple phase angles to establish a phase function of the asteroid surfaces and of dust in the system, if any. We will also dedicate observations to imaging the asteroids around zero phase angle in order to obtain a reliable measure of the albedo and photometric effects such as shadow-hiding and coherent backscattering.
AFC is also observing in synergy with other instruments, providing high resolution context images to the data acquired by Hyperscout (spectro-imager), TIRI (thermal imager) and PALT (laser altimeter), thus contributing to maximize the output of ESA's first Planetary Defense mission.
Figure 1: Planned trajectory for the first four phases of the mission after arrival at Didymos, ECP: Early Characterization Phase, PDP: Payload Deployment Phase, DCP: Detailed Characterization Phase, COP: Close Operations Phase. All dates are preliminary and may change during cruise
Figure 2: Sub-spacecraft latitude and phase angle on Didymos/Dimorphos in the first four phases of the mission after arrival at Didymos. All dates are preliminary and may change during cruise
How to cite: Vincent, J.-B., Sugita, S., Kueppers, M., Michel, P., Herique, A., Karatekin, Ö., Murdoch, N., Tortora, P., Pajola, M., Preusker, F., Kovács, G., and Guerbuez, C.: The Asteroid Framing Cameras on board ESA's Hera mission: planned activities in the asteroid phase, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-527, https://doi.org/10.5194/epsc2026-527, 2026.
Hera is an ESA mission currently en route to the Didymos, which it will reach in October 2026. The mission comprises a mothership, Hera, accompanied by two CubeSats, Juventas and Milani. Its primary scientific objectives include the detailed characterization of the binary asteroid system, and, in particular, the investigation of the internal structure of the asteroids, especially Dimorphos, the smaller member of the system. The key observables used to infer the interior properties of the asteroids are their mass, gravity field, moments of inertia, and rotation state, derived from the orbit determination of the three spacecraft. The internal properties of Dimorphos will be further constrained through radar and gravimetric observations acquired by the JuRa and GRASS instruments, respectively, before and after the landing of the Juventas CubeSat on Dimorphos.
The main objective of the Radio Science Experiment (RSE) is the precise reconstruction of spacecraft trajectories and the estimation of geodetic parameters characterising the bodies, using classical two-way Doppler and range direct-to-Earth measurements provided by the X-band Deep Space Transponder (X-DST), combined with inter-satellite link (ISL) S-band two-way range measurements between Hera and the CubeSats. In addition to these radiometric data, Hera’s orbit determination will benefit from the inclusion of LIDAR observations from the Planetary Altimeter (PALT) and optical images collected by the Asteroid Framing Cameras (AFC), both onboard the Hera spacecraft.
Among other quantities, the expected precision in the determination of asteroid mass, gravity field coefficients, and rotation parameters achievable by the mission was previously quantified by Gramigna et al. (2024) and Tortora et al. (2025) through multi-arc covariance analyses performed with NASA JPL’s orbit determination software MONTE. Here, we try to reproduce part of these simulations using CNES’s orbit determination software GINS, further adapted at the Royal Observatory of Belgium for planetary geodesy applications. In addition, we use GINS to analyze the real tracking data acquired by Hera during its Mars flyby in March 2025, thereby demonstrating its readiness for the processing of operational mission data. This work pursues a dual objective: independently validating the predicted scientific return of the Radio Science Experiment and preparing GINS for the analysis of the forthcoming Hera mission data.
How to cite: Le Maistre, S., Marty, J., Laurent-Varin, J., Gramigna, E., Lasagni Manghi, R., Zannoni, M., and Tortora, P.: Preparation of the GINS Software for the Hera Radio Science Experiment, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-680, https://doi.org/10.5194/epsc2026-680, 2026.
The NASA/DART mission demonstrated that a kinetic impact can successfully deflect a dangerous object by altering the orbital period of Dimorphos, the moonlet of the Near Earth, and Potentially Hazardous Asteroid Didymos, by approximately 33 minutes (Daly et al., 2023; Thomas et al., 2023). This significant change was amplified by the recoil of a massive ejecta plume, which transferred more momentum to the asteroid than the spacecraft hit itself (Cheng et al., 2023). As far as the debris are concerned, observations and theoretical simulations showed that while high-velocity particles escaped into heliocentric orbits, slower-moving fragments were subject to the complex gravitational environment of the Didymos system (Li et al., 2023). Over the long term, large boulders and cm-sized particles may remain trapped in the system for years, undergoing chaotic dynamical evolution due to solar radiation pressure and the irregular gravity fields of both asteroids (Rossi et al., 2022; Ferrari et al., 2023). Some of these particles are expected to eventually re-impact the surfaces or stabilize into a temporary, sparse debris disk. Small particles, mm-sized or smaller, have a highly transient survival time within the binary system itself, being heavily influenced by solar radiation pressure and the complex gravitational perturbations from both bodies. Therefore, very small grains in the ejecta cloud either escaped the system rapidly to form the extended dust tail or re-impacted the asteroids within days to weeks (Li et al., 2023; Langner et al., 2024; Langner et al., 2025). Nevertheless, small grains can always be present in the system as the product of ongoing secondary processes such as sesquinary impacts (Langner et al., 2024; Langner et al., 2025), rotational fission and mass shedding (Yu et al., 2019), and interplanetary dust impacts (Yu et al., 2024).
In December 2026 the ESA/Hera mission (Michel et al., 2022) is scheduled to arrive in the asteroidal system to analyse in detail the impact’s long-term effects and characterize the physics of the system itself. One way to infer the intimate nature (composition, shape, and size distribution) of remained small debris or, more generally, small dust particles present in the system, is inverting with theoretical scattering studies remote sensing data as the phase function of possible dust clouds obtained with the Hera/AFC instrument (Vincent et al., 2024). We present a set of theoretical simulations of scattering of sunlight by fractal and irregular particles consisting of asteroidal analogues to define the interpretative framework of future AFC’s phase function data. The simulations were performed with T-matrix and Discrete Dipole Approximation methodologies which allowed us to investigate the scattering behaviour of very small particles. Examples of dispersion properties of spherical larger particles, reaching the cm-sized geometric optics limit, were also performed with modified Mie theory codes.
Bibliographic References
- Cheng, A. F., et al. (2023). "Momentum Transfer from the DART Mission Kinetic Impact on Asteroid Dimorphos". Nature, 616(7957), 457–460.
- Daly, R. T., et al. (2023). "Success ful Deflection of Target Asteroid Dimorphos by DART Kinetic Impact". Nature, 616(7957),443–447.
- Ferrari, F., et al. (2023). "Long-term dynamics around the Didymos–Dimorphos binary asteroid of boulders ejected after the DART impact". Astronomy & Astrophysics, 671, L14.
- Langner et al. (2024). "Long-term dynamics around the Didymos-Dimorphos binary asteroid of boulders ejected after the DART impact". Astronomy & Astrophysics, 684, A151.
- Langner et al. (2025), "Secondary-impact debris in the Didymos system: What could be observed by Hera? ". Astronomy & Astrophysics, Volume 699, A123.
- Li, J.-Y., et al. (2023). "Ejecta from the DART-produced active asteroid Dimorphos". Nature, 616(7957), 452–456.
- Michel, P., et al. (2022). "The Hera mission: European component of the LICIACube and DART planetary defence investigation". The Planetary Science Journal, 3(7), 160. - Rossi, A., et al. (2022). "Dynamical Evolution of Ejecta from the DART Impact on Dimorphos". The Planetary Science Journal, 3(5), 118.
- Thomas, C. A., et al. (2023). "Orbital period change of Dimorphos due to the DART kinetic impact". Nature, 616(7957), 448–451. - Vincent, J.B., et al. (2024). "The Asteroid Framing Cameras on ESA’s Hera mission". EPSC2024-445.
- Yu et al. (2019). "The expansion of debris flow shed from the primary of 65803 Didymos", MNRAS 484,1.
- Yu et al. (2024). Nature Communications 15.
Acknowledgements
We thank the Italian Space Agency (ASI) within the ASI–UniBO agreements 2022-8-HH.0 and 2022-8-HH.1-2025.
How to cite: Bertini, I., Ferrigno, F., Ammannito, E., Cottini, V., and Vincent, J. B.: Small particles theoretical scattering simulations for the ESA/HERA mission, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-893, https://doi.org/10.5194/epsc2026-893, 2026.
Near-Earth Objects (NEOs) provide key insights for understanding the primordial structure of planetesimals and the compositional gradient of the solar nebula. They carry information about the processes that shaped the early Solar System as a function of heliocentric distance. Furthermore, NEOs may have been instrumental in delivering water and organic-rich material to Earth, potentially contributing to the emergence of life [1].
These objects can even pose a threat to our civilization. Terrestrial impact craters attest to the catastrophic effects of past asteroid collisions with our planet (e.g. the K-Pg event which occurred approximately 65 million years ago, attributed to the impact of an asteroid of about 10 km in size). Such events can produce changes in biodiversity, such as species extinction (or mass extinction) and drastic climate changes. More recently, the Chelyabinsk meteor event in February 2013 highlighted that even relatively small objects (less than 100m) can cause significant harm to human safety and infrastructure [2]. The blast created by this 20-m meteor's air burst produced extensive ground damage, and almost 1500 people sought medical attention because of the event. The overall majority of the injuries were caused by the secondary blast effects of glass which shattered and fell inward.
Accurate knowledge of a target's physical properties is essential for effective mitigation measures in any potential impact scenario, as this information is crucial for planning and successfully implementing appropriate response strategies. In this context, the NEO Physical Observations and Properties Simulation (NEOPOPS) was established, building on the success of previous international research programs dedicated to the study of NEOs (NEOShield, NEOShield-2, and NEOROCKS). NEOPOPS is an European project funded by the EU Horizon Europe Programme and implemented by ESA for the period 2025-2028. Its objectives are multiple:
- to efficiently organize follow-up astronomical observations of NEOs, to obtain high-quality data for deriving their physical properties, with priority given to the timely characterization of potentially hazardous objects;
- to significantly improve statistical analyses, modeling, and numerical simulations aimed at understanding the physical nature of NEOs, with a particular focus on small-sized objects, which are of paramount importance for designing effective mitigation measures both in space and on the ground;
- to foster European and international cooperation in NEO physical characterization, providing scenarios and roadmaps with the scale up the experience gained during the project to a global level;
- to collaborate with ESA to significantly improve public understanding and perception of the asteroid hazards, counteracting the spread of misinformation and unwarranted alarm.
Our team consists of six partners from four countries (Italy, France, the Czech Republic, and UK) employing diverse and complementary observational techniques to consolidate and further enhance physical characterization of NEOs. The team also contributes to rapid-response exercises aimed at characterizing newly discovered objects, thereby addressing the challenge posed by imminent impactors. In particular, we participated in recent observational campaigns to characterize 2024 YR4 [3] and 2025 FA22 [4].
The INAF-OAR is responsible for several working packages, including overall project coordination (WP1), spectroscopic observations (WP4) and rapid-response activities (WP6). In this presentation, we will describe the structure of NEOPOPS as well as its spectroscopic component. We will also present some recent results and statistics obtained during the first year of the project.
Acknowledgments: The NEOPOPS observations were funded by a program of the European Union and implemented by ESA (agreement No.4000147191/25/D/MRP)
References
- Bottke W.F., Cellino A., Paolicchi P., et al., 2002, Asteroid III, University of Arizona Press, p. 3-15, 2002.
- Perna D., Barucci M.A., Drube L., et al., 2015, P&SS, 118, P. 311-317
- Devogèle, M., Hainaut, O. R., Micheli, M. et al., 2026, JAnSc, 73, 31.
- Ieva, S., Bourdelle de Micas, J., Farina, A. et al., in preparation
How to cite: Ieva, S., Bourdelle de Micas, J., Dotto, E., Mazzotta Epifani, E., Pravec, P., Lazzarin, M., Bagnulo, S., Barucci, M. A., Cano, J. L., and Devogele, M. and the the NEOPOPS team: The NEO Physical Observations and Properties Simulation (NEOPOPS) project, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-572, https://doi.org/10.5194/epsc2026-572, 2026.
Asteroid (162173) Ryugu, visited by the JAXA Hayabusa2 mission, was extensively observed during the proximity phase with the NIRS3 near-infrared spectrometer (1.8 – 3.2 mm) [1,2]. The radiometric calibration of NIRS3 was initially obtained from ground-based measurements of a commercial blackbody. After the two touchdown (TD) maneuvers of the Hayabusa2 spacecraft, the instrumental response of the NIRS3 instrument was altered likely due to contamination by dust particles. Thorough analysis of all the Ryugu data obtained during the proximity phase showed systematic residual variations between data obtained during mission phases, indicating the need for further refinement of the radiometric calibration. The data obtained after TD1 were found to be about 5% brighter than the data before TD1, and the data after TD2 about 10% brighter. After improving the relative calibration of the NIRS3 dataset at the different mission phases, we also check and improve the absolute calibration of the instrument using the Moon observations acquired in December 2015 during the Hayabusa2 Earth gravity assist. Calibration method is as follows: (i) we used the photometrically-corrected radiance (i0=30 deg, e0=0 deg, α0=30 deg) lunar map derived from Kaguya/SP and Chandrayaan-1/M3 observations [4,5]; (ii) we applied the ROLO correction factor [3], which we updated to apply it to the SP data up to 2053 nm; (iii) from the NIRS3 footprint position on the Moon, we computed the average SP and M3 spectra and projected them to the NIRS3 observation geometries using their respective photometric model [4,5]; (iv) we finally derived a scale factor to match the two lunar models and the NIRS3 data in the wavelength range 1820 – 2053 nm. NIRS3 reflectance was underestimated by about 8% compared with the original calibration [1]. The updated calibration will support the future observations of the asteroids (98943) Torifune and 1998 KY26, the two targets of the Hayabusa2# extended mission.
These new radiometrically corrected data enabled us to derive updated global near-infrared photometric properties of Ryugu, using all data from the proximity phase acquired between June 2018 to November 2019. After removing observations acquired with extreme illumination/observation geometries (i, e > 70 deg) and performing a 3D averaging binning (i, e, α), we derived the global disk-resolved phase curves and fitted these phase curves with the Hapke IMSA model for all wavelength channels, hence obtaining the variations of the Hapke parameters with the wavelength. The obtained parameters with this full dataset are consistent with previous studies [6,7]. An east-west dichotomy of the phase ratio and phase reddening is observed, likely consistent with a higher surface roughness in Ryugu eastern hemisphere.
The photometric parameters are used to produce photometrically corrected (i0=30 deg, e0=0 deg, α0=30 deg) data. These radiometric and photometrically corrected NIRS3 data will be released through NASA PDS and JAXA DARTS.
Acknowledgments: This work is supported by the JAXA Hayabusa2# International Visibility Enhancement Project.
References: [1] Kitazato et al. (2019), Science, 364, 6437 [2] Iwata et al. (2017), SSR, 208 [3] Kouyama et al. (2016), PSS, 124 [4] Yokota et al. (2011), Icarus, 215, 2 [5] Besse et al. (2013), Icarus, 222 [6] Domingue et al. (2021), PSJ, 2:178 [7] Pilorget et al. (2021), Icarus, 355
How to cite: Wargnier, A., Tatsumi, E., Yumoto, K., Ichikawa, M., Murakami, S., Nagai, Y., Honda, K., Yokota, Y., Kouyama, T., Iwata, T., Matsuoka, M., Tanaka, S., and Kitazato, K.: Calibration update of the NIRS3 spectrometer and global near-infrared photometric properties of asteroid (162173) Ryugu: application for the Hayabusa2# extended mission, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-236, https://doi.org/10.5194/epsc2026-236, 2026.
The 2029 close encounter of asteroid (99942) Apophis with Earth will provide a unique natural experiment to investigate how tidal forcing, seismic shaking, and varying surface accelerations affect the mechanical response of a small body. ESA-JAXA’s RAMSES mission is designed to rendezvous with Apophis before the encounter and monitor its physical and geological evolution during the flyby, offering an unprecedented opportunity to detect surface reorganisation, slope failure, regolith transport, and possible mass shedding in real time.
Mass-wasting processes are expected to be particularly sensitive to the poorly constrained mechanical properties of asteroidal regolith. In this work, we introduce RAVEL (Regolith Astrodynamics in Variable Effective Low-gravity environments), a model particularly well suited to simulate potential motion of surface material on Apophis at closest approach to Earth. The model couples the instantaneous orbital configuration with the surface acceleration field and integrates the trajectories of massless Lagrangian tracers over the asteroid topography. These trajectories are interpreted as kinematic pathways of potential regolith mobilisation rather than as individual particle motions. Because the surface mechanical properties of Apophis remain largely unconstrained, we consider a cohesionless material and explore two end-member effective friction angles: ϕ = 20º and ϕ = 30º which bracket relatively high- and low-mobility regimes.
Our preliminary results show that Apophis may develop locally steep dynamical slopes during the encounter, with values reaching up to approximately 45º in some regions. Under the low-friction end-member, mobilisation is more spatially extensive and produces longer Regolith Migration Pathways (RMPs), indicating that surface material could be redistributed over significant distances and, in favourable locations, approach conditions potentially compatible with detachment or shedding. The higher-friction case strongly reduces the number and length of active pathways, but does not suppress mobilisation entirely: motion remains concentrated in the steepest and most dynamically perturbed regions. The comparison between both end-members suggests that the geometry of the main migration corridors is primarily controlled by the topography and encounter-induced acceleration field, whereas the assumed friction angle modulates the extent, runout, and efficiency of transport.
Our model, RAVEL, provides a predictive framework for interpreting RAMSES observations before, during, and after the 2029 flyby and will contribute to identify, prior to approach the regions where surface material is the most susceptible to be tidally displaced during the encounter. Conversely, comparison with RAMSES imaging and shape-model updates will allow the mechanical response of Apophis to be used as a constraint on regolith friction, cohesion, and near-surface structures. The determination of the Regolith Migration Pathways therefore offers a direct link between dynamical modelling and observable geomorphological change, contributing to the broader objective of using Apophis as a natural laboratory for asteroid geophysics and planetary defence.
Figure 1: a) Dynamical slope on the surface of Apophis at maximum Earth approach; b) Starting points for the RMPs with dynamical slope higher than 20º; c) RMPs for ϕ = 20º; d) RMPs for ϕ = 30º.
How to cite: Charnoz, S. and Herreros, I.: Regolith Migration Pathways on Apophis during the 2029 Earth close encounter: Implications for RAMSES observations, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-250, https://doi.org/10.5194/epsc2026-250, 2026.
Spacecraft observations (Thomas et al., 2001; Fujiwara et al., 2006; Barnouin et al., 2019; Sugita et al., 2019; Bierhaus et al., 2023; Barnouin et al., 2024) combined with theoretical models (Zhang et al., 2022) indicate that asteroids likely possess a wide range of internal structures. In many cases, asteroids may possess some degree of internal coherence or strength, while their uppermost surfaces are likely cohesionless (Arakawa et al., 2020; Barnouin et al., 2024; Lauretta et al., 2022).
Figure 1. Example of monolithic large boulders on Itokawa, Eros and Ryugu.
The presence of large boulders (Figure 1) on many asteroids (Thomas et al., 2001; Fujiwara et al., 2006; Barnouin et al., 2019; Sugita et al., 2019) with diameters between 50 and 100 m, suggests that some asteroids may be coherent monoliths. Objects of this size would be capable of causing substantial damage in the event of an Earth impact. The rapid spin rates observed for some small asteroids (Holsapple, 2007) also support the possibility of significant internal strength. Asteroids in this size range generally fall within the strength-dominated regime of commonly used Q* disruption scaling relationships.
To develop effective planetary defense strategies against such objects, it is important to understand the likely outcomes of deflection attempts involving asteroids with plausibly strong interior structures. Here, we investigate the effects of impacts into a variety of coherent targets with differing size, strength, porosity, and internal structure. This study is one of two investigations examining momentum transfer by kinetic impactor, focused on experiments conducted at the JHUAPL Impact Lab (IL) low (<0.5 km/s) impact velocities. A complementary investigation examines hypervelocity impacts (>1.0 km/s) conducted at NASA Ames.
In the IL, we fire ¼” Alumina projectiles into a range of well understood near-spherical targets that possess diameters of 6 to 10 cm The targets are hung from a string, like a ballistic pendulum (Figure 2). They are made of either uniform plasters of varying strength and porosity, or a mixture of these same plasters with aquarium gravel, or large porous lava rocks. The targets have well characterized porosity and strength properties; variations in their interior are understood using X-ray computed tomography (XCT) scans.
Figure 2. Example of shots at the JHUAPL Impact Laboratory (IL) used to measure momentum transfer.
During each experiment, we use two high speed (>1000f/s) cameras to measure the impact location and angle of the projectile, and directly measure the linear and angular displacement of the target as it swings following impact. The displacements provide estimates of the velocity changes experienced by the target, and its post-impact momentum. We then estimate the fraction of the momentum imparted by the projectile to the target. We also measure the ejection speed and direction of target ejecta, to understand the origin of any momentum enhancement, and characterize the shape and mass of the largest individual ejecta excavated during each impact.
Our preliminary findings indicate that impact angle is a major factor controlling the effectiveness of a kinetic impact in displacing an asteroid during low-speed impacts. More normal impacts produce greater displacement and result in more efficient transfer and enhancement of projectile momentum. Target porosity appears to be the next most important factor, as its presence tends to suppress ejecta production and spallation.
Although still under investigation, variations in target strength, which differ by as much as a factor of four in our experiments, may be among the least important factors influencing momentum transfer. In contrast, internal target structure, including the presence of cavities or strength heterogeneities, can have significant effects and lead to less predictable outcomes at the slower impact velocities considered here.
References: Arakawa, M., et al., 2020. Science 368, 67–71. https://doi.org/10.1126/science.aaz1701. Barnouin, O., et al., 2024. Nat Commun 15, 6202. https://doi.org/10.1038/s41467-024-50146-x. Barnouin, O.S., et al. 2019. Nature Geoscience 12, 247–252. https://doi.org/10.1038/s41561-019-0330-x. Bierhaus, E.B., et al., 2023. Icarus 115736. https://doi.org/10.1016/j.icarus.2023.115736. Fujiwara, A., et al., 2006. Science 312, 1330–1334. https://doi.org/10.1126/science.1125841. Holsapple, K.A., 2007. Icarus 187, 500–509. https://doi.org/10.1016/j.icarus.2006.08.012. Lauretta, D.S., et al., 2022. Science 377, 285–291. https://doi.org/10.1126/science.abm1018. Sugita, S., et al., 2019. Science 364, 252–252. https://doi.org/10.1126/science.aaw0422. Thomas, P.C., Veverka, J., Robinson, M.S., Murchie, S., 2001. Nature 413, 394–396. Zhang, Y., et al., 2022. Nat Commun 13, 4589. https://doi.org/10.1038/s41467-022-32288-y
How to cite: Barnouin, O., Stickle, A., Meier, R., and Ballouz, R.: Designer asteroids: Target interior effects on momentum transfer by slow (<1km/s) kinetic impactors., Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-540, https://doi.org/10.5194/epsc2026-540, 2026.
GRASS, the GRAvimeter for Small Solar System objects, will be the first gravimeter to perform in situ gravimetric measurements on an asteroid. It flies onboard ESA’s Hera spacecraft, currently en route to the binary asteroid system Didymos. Hera will arrive in late 2026 and deploy two CubeSats in early 2027, including Juventas, which carries the GRASS instrument.
After deployment, the Juventas CubeSat will land on the surface of Dimorphos, the secondary body of the system, where GRASS will measure the three-dimensional surface acceleration. The acceleration vector in its magnitude and direction, as well as its possible temporal variation, will help to constrain the local geological structure (mass anomalies, regolith depth and lateral variations) and the surface geophysical environment (tides, dynamic slopes, centrifugal forces).
We present here the latest status of the GRASS calibration, ground tests and in‑flight operations, including the checkout results obtained during the cruise phase. We also discuss the planned activities following the Juventas release, in the orbit of Dimorphos. CubeSat before landing as well as, expected measurement scenarios and signal characteristics on the surface of Dimorphos.
How to cite: Ritter, B., Karatekin, Ö., Tasev, E., Carrasco, J. A., Alavés Mañogil, H., Henry, G., Senel, C. B., and Tuzmen, N.: The GRASS instrument onboard Hera for Dimorphos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-808, https://doi.org/10.5194/epsc2026-808, 2026.
The Juventas 6U CubeSat is part of ESA's Hera mission, currently en route to the binary asteroid system Didymos. Hera will arrive at the end of 2026 and deploy Juventas in early 2027 to investigate the binary system. It will observe Dimorphos in particular in the aftermath of the kinetic impact delivered by NASA's Double Asteroid Redirection Test (DART) from Self-Stabilized Terminator Orbits (SSTOs) around the system, At the end of the mission, Juventas will leave the SSTO for a controlled descent and a ballistic landing on Dimorphos, followed by surface operations of nominal duration of two mutual orbital periods (~24 h). Following touchdown, the CubeSat is expected to undergo several bounces before reaching its final resting configuration.
We present the landing scenario and the planned operations during this complex and high-risk phase of the mission. The descent, touchdown, and surface phases will be monitored by a coordinated set of Juventas instruments including the laser altimeter, the navigation camera, and the Inertial Measurement Units (IMUs). The GRASS gravimeter will be operational as well. The landing event is expected to be observed by Hera and by the companion CubeSat Milani. We discuss the expected spacecraft–surface interactions during touchdown and bouncing and their implications for the operations and observations.
How to cite: Karatekin, Ö., Ritter, B., Moreno Villa, V. M., Domínguez Castillo, A., Sansalone, T., Tuzmen, N., Çelik, O., and Biele, J.: Landing Juventas on Dimorphos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-841, https://doi.org/10.5194/epsc2026-841, 2026.
