SB11
In the context of the upcoming Japanese led MMX mission, to be launched in autumn 2026, this session invites scientific presentations providing new findings with respect to Phobos and Deimos, or comparative studies with respect to other small bodies of the solar system currently visited by other space missions.
Contributions from various scientific disciplines are invited, including remote sensing, laboratory experiments, numerical modeling, and mission science, to investigate the physical and compositional properties of the Martian moons. Topics of interest include, but are not limited to, spectroscopic observations, surface morphology, regolith properties, internal structure, orbital dynamics, and space weathering processes. A goal is to further understand the needs and requirements for upcoming observations and to discover interdisciplinary aspects of interest. Special attention will also be given to recently acquired datasets from spacecraft observations, as well as to new mission concepts and instrument developments designed to explore these two bodies. The session seeks to advance our understanding of Phobos and Deimos, providing new insights into their origin.
The Martian Moons eXploration (MMX) mission, scheduled for launch in 2026, will conduct the first comprehensive exploration of the Martian moons and return samples from Phobos to Earth in 2031. The mission aims to determine the origin of Phobos and Deimos and to clarify the evolution of the Martian system as a key interface in the inner Solar System.
A major component of MMX is its global remote sensing campaign, which will characterize the composition, geology, and physical properties of the Martian moons. After arrival, the spacecraft will perform multi-year observations of Phobos and Deimos, with particular emphasis on systematic surveys of Phobos from quasi-satellite orbits. Operating at altitudes of ~10–190 km, these observations will provide near-global coverage at progressively higher spatial resolution, enabling characterization of surface heterogeneity and identification of candidate sampling sites.
The remote sensing payload includes high-resolution imaging (TENGOO), multiband visible imaging (OROCHI), near-infrared spectroscopy (MIRS), laser altimetry (LIDAR), and elemental measurements by a neutron and gamma-ray spectrometer (MEGANE). Together, these instruments will map surface morphology, mineralogy, and elemental composition, including the distribution of hydrated materials and hydrogen, which are key indicators of formation processes. In addition, the CNES/DLR-built IDEFIX rover will perform in situ investigations of the Phobos surface, characterizing regolith mechanical, thermal, and mineralogical properties through imaging, radiometry, and Raman spectroscopy, while also supporting landing site assessment for the main spacecraft. In parallel, MMX will observe the Martian atmosphere and circum-Martian environment, linking surface processes with dust transport, volatile cycling, and atmospheric escape. These datasets will provide key constraints to distinguish between competing formation scenarios, such as primitive asteroidal capture versus formation through a giant impact involving Martian material.
Complementing the remote sensing observations, sample return from Phobos will provide ground truth for orbital observations and enable laboratory analyses at high precision, including potential access to Martian ejecta preserved in Phobos regolith. Within this framework, remote sensing plays a central role in establishing global context and guiding the interpretation of returned materials.
Through the integration of remote sensing, in situ observations, and sample analyses, MMX will deliver a comprehensive understanding of the Martian moons and the evolution of the Martian system, providing new insights into planetary formation, volatile evolution, and material transport processes in the inner Solar System.
How to cite: Kuramoto, K., Michel, P., Usui, T., and Kawakatsu, Y. and the MMX International Science Board: Constraining the origin of the Martian moons through global remote sensing and sample return: the MMX mission at launch, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-298, https://doi.org/10.5194/epsc2026-298, 2026.
Introduction: JAXA’s Martian Moon eXploration (MMX) mission is dedicated to study the two Martian moons Phobos and Deimos with the goal on shedding light on their origin and evolutionary history [1,2]. For in-situ mineralogical analysis on the martian moon Phobos with the MMX IDEFIX rover [3], a highly compact Raman spectrometer [4] was developed under the lead of DLR with contributions from international partners: Instituto Nacional de Tecnica Aerospacial (INTA), University of Valladolid (UVa), JAXA and University of Tokyo. MMX will be launched in fall 2026, arrive in the Mars system in summer 2027 and the IDEFIX rover will be released to the surface of Phobos between late 2028 and early 2029 for a surface operations phase of 100 (Earth) days [5]. Orbital observations with the main MMX spacecraft and in-situ science on Phobos with the IDEFIX rover are going to be complemented by returning surface samples (>10 g) from Phobos to Earth, which shall arrive in 2031.
The RAX Raman spectrometer: By characterizing in-situ the mineral composition of Phobos’ surface, the RAman spectrometer for MMX (RAX) directly contributes to the top-level goals of the MMX mission. Different mineral phases can be associated with different formation scenarios (e.g. captured asteroid or major impact) and to surface alteration processes on Phobos. Next to providing ground truth, the mineralogical information obtained with RAX can also support sampling decisions with the main spacecraft and be compared with data obtained from the returned samples and in-situ data from the surface of Mars.
RAX is located on the underside of the 24 kg rover and is characterized by its extremely compact design, a mass of only 1.5 kg and a volume of about 1 dm³. It contains a spectrometer with a miniaturized and highly sensitive optical assembly. The optical design of RAX was driven by A.) the tight constraints of volume and mass available on the small MMX rover and B.) optimizing the collection and detection capabilities of the Raman signal from a sample at several centimeters distance below the rover’s body. Raman excitation (continuous wave with λ = 532 nm) is achieved through a separate laser module based on the Raman Laser Spectrometer (RLS) laser developed for the ExoMars mission’s Rosalind Franklin rover [6]. To focus the laser onto Phobos’ surface beneath the rover, the spectrometer is equipped with an opto-mechanical autofocus subsystem that allows fine-tuning of the focus position at a working distance of approximately 8 cm, within a range of 13 mm and to an accuracy of 50 µm. Raman measurements on Phobos will be done during Phobos night. The rover’s locomotion system is needed for the main height adjustment: the rover will gradually lower its height until the RAX instrument is within its working range. After autofocusing, dark spectra (without the laser) and Raman spectra will be measured from a footprint of 50 µm from what is exposed in the RAX field-of-view beneath the rover.
To demonstrate the functionality of the RAX instrument after launch and to monitor its performance, a Verification Target (VT) is part of the payload. The VT is a pellet made of deuterated polyethylene terephthalate (PET) specifically developed for this mission [7]. The VT is placed in the field of view of the RAX instrument and can be measured during the cruise and while in orbit until the rover separates from the MMX spacecraft for landing on Phobos in late 2028.
Status: The flight model of the IDEFIX rover was delivered to JAXA/MELCO and integrated into the main spacecraft for qualification and functional testing. Operational sequences, e.g. defining the interaction between locomotion and science instruments, are currently being prepared and tested [8]. RAX checkout activities are being prepared and tested for the MMX cruise phase after launch. RAX surface measurements are being prepared with laboratory studies with the RAX development model in a vacuum chamber at low temperatures, see Fig. 1 B and [9], and in combination with the rover’s locomotion system using the MMX IDEFIX rover model Prototypix in the testbed of DLR in Oberpfaffenhofen [10].
Figure 1 A: RAX flight model. B: RAX development model in vacuum chamber for reference measurements.
References:
[1] T. Usui, K. Bajo, W. Fujiya et al., Space Sci. Rev. 2020, 216, 49.
[2] Y. Kawakatsu, K. Kuramoto, T. Usui et al., Acta Astronaut. 2023, 202, 715.
[3] S. Ulamec, P. Michel, M. Grott et al., Acta Astronaut. 2023, 210, 95.
[4] T. Hagelschuer, U. Böttger, M. Buder et al., Internat. Astronautical Congress (IAC): 18-22 September, 2022, Proceed. 2022, IAC-22-A3.4A.8.
[5] S. Ulamec, P. Michel, N. Murdoch et al., PEPS 2025, 12, 97.
[6] F. Rull, S. Maurice, I. Hutchinson et al., Astrobiology 2017, 17, 627.
[7] A. G. Moral, J. Mora, O. Prieto-Ballesteros et al., J. Raman Spectrosc. 2023, 54, 1268.
[8] C. Krause, C. Delmas, D. Arrat et al., SpaceOps 2025, ID #29.
[9] N. Krybus, F. Seel, S. Schröder et al., EPSC-DPS 2025, ID #1669.
[10] F. Buse, L. Burkhard, N. Borgsmüller et al., iSpaRo 2025,454-460.
How to cite: Schröder, S., Cho, Y., Hübers, H.-W., Prieto-Ballesteros, O., Buder, M., Bunduki, Y., Dietz, E., Hagelschuer, T., Krause, C., Krybus, N., Moral Inza, A. G., Peter, G., Rammelkamp, K., Säuberlich, T., Seel, F., Ulamec, S., Usui, T., and Weber, I.: The RAX Raman Spectrometer on the MMX IDEFIX Rover for in-situ Mineralogical Analysis on Phobos , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-872, https://doi.org/10.5194/epsc2026-872, 2026.
It has been suggested that Phobos and Deimos are fragments of a common progenitor—likely a planetary embryo—that was disrupted either through a collision with Mars or with another planetary embryo (Canup & Salmon 2018; Bagheri et al., 2021). We tested the viability of this scenario by calculating the probability of its occurrence during the formation of terrestrial planets. Using extensive numerical simulations of the late stage of terrestrial planet formation, where planetary embryos undergo giant impacts while submerged in an ocean of small planetesimals, we found that within simulations producing Mars-analogs, the probability of the required Mars-embryo or embryo-embryo collisions is less < 3%. Within these systems, the probability of producing fragments with the specific size characteristics of Mars’ satellites is even smaller. Conversely, our simulations reveal that Saturn’s secular resonance efficiently scatter a large quantity of planetesimals into the Martian region where they can be potentially captured. Given this strong scattering effect and the low probability of a common progenitor disruption, we argue that the capture of asteroid-belt objects represents a more viable pathway for the origin of Mars’ satellites. We detail our simulations framework and discuss the implications of their results.
How to cite: Haghighipour, N. and Sudol, J.: Assessing the likelihood of Phobos and Deimos being captured fragments of a disrupted planetary embryo , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-301, https://doi.org/10.5194/epsc2026-301, 2026.
Introduction: The formation of the Martian moons, Phobos and Deimos, remains a long-standing problem in understanding the formation and early evolution of Mars. Their small masses, irregular shapes and relatively low-albedo reflectance spectra suggest that they are captured objects (Burns 1992). However, their orbital characteristics, i.e., their low eccentricities and inclinations, are very difficult to reconcile with capture (Burns 1992) and suggest that they formed in-situ from orbiting debris. The giant impact (GI) scenario proposes that Phobos and Deimos accreted from circum-planetary disk formed in a large collision and is currently the most successful in-situ formation scenario that can explain their dynamical properties (Rosenblatt et al. 2011; Craddock 2011). Prior work used 3D smoothed particle simulations to model the impact (Rosenblatt et al. 2016, Hyodo et al. 2017, Canup & Salmon 2018) but was very limited in resolution and modeled the materials as ideal fluids neglecting the effect of material strength. However, recent studies (Kurosawa & Genda 2018, Emsenhuber et al. 2018, Ballantyne et al. 2023, Ballantyne et al. 2024, Denton et al. 2025) suggest that the rheology can play a key role in modelling such intermediate scale impacts, significantly influencing the thermal, chemical and compositional history of the colliding bodies. These properties are crucial for generating accurate predictions of the GI scenario, including the resulting chemical composition and volatile inventory, which are key to interpreting data returned by the Martian Moons eXploration (MMX) mission.
Methods: We revisit the two impact scenarios proposed by Hyodo et al. (2017; H17) and Canup & Salmon (2018; C18) using the novel Smoothed Particle Hydrodynamics (SPH) code pkdgrav3 (Potter et al. 2018, Meier et al. 2026, Meier et al. submitted). The effect of material strength is incorporated via a pressure-dependent shear strength model (Jutzi 2015), following the approach by Emsenhuber et al. (2018) and Ballantyne et al. (2023). Mars and the impactor are assigned the same masses and compositions as in previous studies, and iron and rock are represented using the ANEOS equations of state (Thompson & Lauson 1972; Melosh 2007) for iron and forsterite from Stewart et al. (2019, 2020). The impact velocity ranges from ∼ 6 to 7 km/s, while the impact angle varies between 15° and 75°. Compared to previous studies, we increase the numerical resolution by three orders of magnitude and adapt the minimum resolution for each impact such that the circumplanetary disk mass predicted in earlier work is resolved with at least ∼1000 particles. Prior to the impact both bodies are placed ten mutual radii apart to allow for tidal deformation before the impact. For each combination of impact angle and velocity we perform a simulation with a fluid and solid (intact: luni and fully damaged: lund) rheology and determine the disk mass, composition and thermal state.
Results: For both rheological models, we find that the disk mass depends on the impact angle. However, the disk masses and impact angle where most debris is ejected differ substantially between the fluid and solid rheology (see Figure 1). Also, the inferred disk composition (Martian vs. impactor material) and thermal state are very different. While all disks in the fluid case contain a substantial fraction of Martian material, the disks in the solid case are dominated by impactor material. Overall, the compositional difference between the two rheological models is approximately 20%. Successively increasing the simulation resolution reveals that the disk mass decreases substantially, whereas the disk composition remains largely unaffected (see Figure 2). The thermal state of the disk is substantially colder than found in previous studies (see Figure 3). In all cases, the majority of the material remains below the melting point of rock, although for a solid rheology up to ∼20% of the material may experience melting, implying significantly less thermal processing than previously assumed.
Conclusions: Our work shows that rheology and numerical resolution play key roles in modeling the formation of Phobos and Deimos from an impact-generated debris disk. The inferred disk mass and composition depend strongly on the assumed rheology and are very different from those found in previous studies, while the thermal state remains consistently colder and less thermally processed than previously suggested. Furthermore, we observe that increasing the numerical resolution results in lower disk masses but does not substantially alter the disk’s composition and thermal state. Taken together, our findings suggest that the impact scenarios proposed in prior work may need to be revised and that realistic modeling of the rheology is crucial for making accurate predictions for the giant-impact scenario, including the chemical composition and volatile content, that are required to interpret data returned by the MMX mission.
Figure 1: for a fluid (solid line), solid intact (dashed line) and solid damaged (dotted line) rheology. The impact velocity in all simulations is ∼6 km s-1 . The disk mass and composition (Martian: red versus impactor: blue) is strongly influenced by the rheology. Whereas a fluid rheology, as assumed in previous studies, yields a disk containing a substantial fraction of Martian material, accounting for shear strength in the solid phase results in a disk composed primarily of impactor-derived material. Rheology therefore plays a critical role in the interpretation of MMX samples.
Figure 2 : The disk mass (left panel) and composition (right panel) versus impact angle obtained assuming a fluid rheology and different numerical resolution (3×106: solid, 3×107: dashed and 3×108: black dot). The impact velocity in all simulations is ∼6 km s-1 . The inferred disk mass decreases with increasing numerical resolution, while the disk composition remains nearly constant.
Figure 3: The temperature distribution (left: count, right: cumulative) in the disk after an impact occurring at 45° and ∼6 km s-1 for different rheologies and a resolution of 3×106 particles. The disk material is substantially colder than inferred in previous studies and all disks have median temperatures of ∼900 K, so most of the material remains below the melting point. The hottest disks are obtained for a solid rheology where ∼20% of the material may experience melting.
How to cite: Reinhardt, C., Jutzi, M., and Meier, T.: The impact origin of Phobos and Deimos revisited, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-483, https://doi.org/10.5194/epsc2026-483, 2026.
Introduction
Laboratory measurements in the NIR range allow the detection of spectral signatures, which depend on the structural arrangement and composition of the mineral. In this spectral range, the reported absorption bands indicate vibrational modes (bending, stretching and combination of harmonics) in the minerals [1]. In the case of carbonates and organics, the distinction between those classes can become difficult as their overtones overlap in the 3.2 – 3.6 µm range [2], [3]. The goal of this study is to investigate the relevance and ability of spectral analyses that would provide the contribution of each component and distinguish one from another on the spectra.
Moreover, in the context of the JAXA Martian Moons eXploration (MMX) mission which will be launched in autumn 2026 to investigate on the Martian moons, those minerals are potential candidates of their composition and could then be observed by the MMX Infrared Spectrometer (MIRS) operating in the 0.9 – 3.6 µm range. Their presence would provide important information on the moons’ composition and help constraining their origin [4]. The engineering model of MIRS (EM1) is available at the LIRA – Paris Observatory to support the mission and ground calibration. The EM1 will also be part of the instruments used for this study. This work will help to prepare and optimize the future observations.
Method
To investigate the effects of the contribution of each component, we prepared three series of mixtures of carbonates (dolomite), organics (mix of acids containing aliphatic and aromatic chains), serpentine (antigorite) and dark component (synthetic iron oxide) at INAF – Arcetri Observatory (Italy).
The first series OCS (Organics Carbonates Series) consisted in varying carbonates and organics mixed with a fixed quantity of serpentine to evaluate the bands position depending on the minerals’ interaction. The second series SDS (Serpentine Dark component Series) consisted in mixing fixed and identical amount of carbonates and organics with varying quantities of serpentine and dark component to evaluate the influence of the darkening of a sample on the band depth. The last one SENS (SENsitivity Series) was to mix small quantities of organics and carbonates with serpentine to evaluate the sensitivity of the EM1 and its ability to detect those components. We measured the mixtures and endmembers with three instruments; Bruker VERTEX 70v at INAF, the Bruker Invenio R and EM1 both in LIRA. In this work, we present the results from the VERTEX 70v spectrometer.
For the band analysis, based on the principle that one absorption band can be represented by a gaussian function, or the sum of several gaussian functions [5], we used a Gaussian fitting band program to retrieve the parameters of the absorption bands for each mineral and each mixture. The amplitude, standard deviation and mean of the gaussian function would correspond to the depth, the width, and the centre of the band, respectively. We first applied the method to the endmembers helped by literature [2], [3], [6], [7], then to the mixtures. We used chi-squared method and Z-test to compare the parameters found between the mixtures and the well-known pure endmembers.
Results
The obtained spectra are presented in Figure 1. We retrieved the overtones got from the fit for each mixture. We focus here on the OCS series also displayed on Figure 2, where it shows a non-linear evolution in the spectra, with a possible lower level of sensitivity for the organics than for the carbonates. We focused on the location of the bands to perform the fits and we show one example on the OCS-MIX05 corresponding to a composition of 100% carbonates and 0% organics.
Figure 1: spectra of the OCS (up, left), SDS (up, right), and SENS (down) series. The region of interest (3.2 – 3.6 µm) is shown with red dashed lines. The spectra were obtained in Arcetri.
Figure 2: normalized spectra in the 3.2 – 3.6 µm range of the OCS series (left), using the same colour code as in Figure1 and gaussian fit on the normalized spectrum of OCS-MIX05 (right).
Our first results indicate complex interactions between multiple absorptions in this wavelength range. The complete analysis will be presented and discussed.
Acknowledgements
MIRS is built at Paris Observatory in collaboration with CNES and close collaboration with JAXA and MELCO. MMX is developed and built by JAXA, with contributions from CNES, DLR, ESA and NASA. We thank the MMX JAXA teams for their efforts and CNES for the financial support.
Bibliography
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[4] M. A. Barucci et al., « MIRS: an imaging spectrometer for the MMX mission », Earth Planets Space, vol. 73, no 1, p. 211, déc. 2021, doi: 10.1186/s40623-021-01423-2.
[5] J. M. Sunshine, C. M. Pieters, et S. F. Pratt, « Deconvolution of mineral absorption bands: An improved approach », J. Geophys. Res., vol. 95, no B5, p. 6955‑6966, mai 1990, doi: 10.1029/JB095iB05p06955.
[6] R. N. Clark, T. V. V. King, M. Klejwa, G. A. Swayze, et N. Vergo, « High spectral resolution reflectance spectroscopy of minerals », J. Geophys. Res., vol. 95, no B8, p. 12653‑12680, août 1990, doi: 10.1029/JB095iB08p12653.
[7] V. Vinogradoff et al., « Laboratory Investigations Coupled to VIR/Dawn Observations to Quantify the Large Concentrations of Organic Matter on Ceres », Minerals, vol. 11, no 7, p. 719, juill. 2021, doi: 10.3390/min11070719.
How to cite: Chaudesaygues, C., Barucci, A., Merlin, F., Poggiali, G., Yumoto, K., Alberini, A., and Sultana, R.: Laboratory measurement in the 3.2 – 3.6 µm range of carbonates – organics to investigate their contribution., Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-109, https://doi.org/10.5194/epsc2026-109, 2026.
We present results of our efforts co-registering data from High Resolution Stereo Camera (HRSC) (1) on Mars Express to existing shape models of Phobos (2,3). There are numerous challenges when trying to align this data set with the derived topography. Nonetheless, the correct geometric alignment is of importance for the photometric analysis that is to follow.
HRSC is a line scanning stereo camera with angular separation between the forward- or backward-looking channels of up to 18.9 degrees (1) with respect to the nadir direction.
For the co-registration we use a classic photogrammetric approach that requires homologous points across several images. Other than on Mars where the single channels observe the surface at the same time providing additional geometric constraints, Phobos is too small and usually each channel observes the surface at a different epoch. The quality of homologous points is thus of great importance to geometrically stabilize the adjustment problem.
HRSC observes Phobos approximately every 5 to 6 months from a close distance due to orbit geometries of both Phobos and the Mars Express S/C. Flyby observations occur at irregular distances, and thus image pixel resolutions, and under a wide range of illumination conditions. Though important for the photometric analysis it constitutes an obstacle when it comes to finding homologues points between different flybys. To automate the matching process, we used the pre-trained deep learning models SuperPoint (4) for feature extraction and LightGlue (5) for feature matching. Before matching, Phobos is segmented in all input images, followed by contrast enhancement to help account for invariances across the observations. The nadir observations are matched pairwise across the whole dataset of different flybys. Thereby, all matching pairs undergo an outlier removal to improve robustness of the point correspondences. Finally, we used the same techniques to identify features correlating with confirmed matches in each associated channel, supported by least-squares matching (6) for a dense keypoint grid within one flyby observation.
A classic photogrammetric adjustment approach was used to achieve the alignment between the shape model and the image data. As the HRSC is a line scanning camera, the applied software (7) establishes virtual orientation points and interpolates the s/c trajectory and attitude between these orientation points. Co-registration with respect to existing shape models is achieved by introducing several landmark coordinates extracted from the shape models as ground control points in the adjustment problem. First tests show that a co-registration with an average accuracy below 1 meter can be achieved while the accuracy of the homologous points ranges within +/- 35m on average. This is a satisfying result showing that the co-registration to an existing reference works very well. The remaining error of the homologous points is in agreement with the average pixel resolution of the contributing images.
We will report on the progress and further results during the meeting.
Acknowledgements: A. Schriever is partially funded by the Deutsche Forschungsgemeinschaft (DFG) – Project 528586639. The authors thank the HRSC Experiment teams for their successful planning and acquisition of data as well as for making processed data available to the HRSC team.
(1) R. Jaumann et al., The high-resolution stereo camera (HRSC) experiment on Mars Express: Instrument aspects and experiment conduct from interplanetary cruise through the nominal mission. Planetary and Space Science 55, 928–952 (2007). (10.1016/j.pss.2006.12.003).
(2) M. Ernst et al., High-resolution shape models of Phobos and Deimos from stereophotoclinometry. Earth, Planets and Space 75, 103 (2023). (10.1186/s40623-023-01814-7).
(3) Willner, X. Shi, J. Oberst, Phobos' shape and topography models. Planetary and Space Science 102, 51–59 (2014). (10.1016/j.pss.2013.12.006).
(4) DeTone, D., Malisiewicz, T., & Rabinovich, A. (2018). SuperPoint: Self-supervised interest point detection and description. Proceedings of the IEEE conference on computer vision and pattern recognition workshops(pp. 224-236). (1109/CVPRW.2018.00060)
(5) Lindenberger, P., Sarlin, P. E., & Pollefeys, M. (2023). LightGlue: Local feature matching at light speed. Proceedings of the IEEE/CVF international conference on computer vision(pp. 17627-17638). (11109/ICCV51070.2023.01616)
(6) Gwinner, K., et al. (2009) Derivation and Validation of High-Resolution Digital Terrain Models from Mars Express HRSC Data. PE&RS 75(9), 1127-1142. (14358/PERS.75.9.1127)
(7) Spiegel. (2007), Kombinierte Ausgleichung der Mars Express HRSC Zeilenbilddaten und des Mars Global Surveyor MOLA DGM, München 2007, ISBN 3 7696 5049 2
How to cite: Schriever, A. and Willner, K.: Co-Registering MEX HRSC Image Data to Existing Shape Models for Photometric Analysis, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-322, https://doi.org/10.5194/epsc2026-322, 2026.
The Martian moons, Phobos and Deimos, have debated origins. The JAXA mission Martian Moon eXploration (MMX) aims to clarify their origins through remote sensing observations of both moons and a sample return from Phobos. The mission will launch in October 2026. The MMX landing sites, from which samples will be collected, must be carefully selected to ensure that the sampled material is representative of Phobos while also having grain size and porosity compatible with the sampling mechanism. The compositional and physical properties of the regolith inferred from photometric observations [1] can help assessing the suitability of each landing site candidate. High-resolution images of Phobos have been acquired during Mars Express (MEx) flybys for more than 20 years and were recently calibrated [2]. In this study, we intend to use these images to analyze the regional photometry of the potential landing sites, as a global analysis of Phobos had already been done [3].
We analyzed data taken by the Super Resolution Channel (SRC) of the High-Resolution Stereo Camera (HRSC). HRSC is a push broom camera with nine filters in total, five being panchromatic and four color filters (blue, green, red, and infrared), and the photometric analysis of Phobos data was already done and published by a previous study [2]. SRC is a framing camera made of one panchromatic filter centered covering the 400 - 900 nm region. [4,5]. We have analyzed the photometry of 10 potential landing sites identified so far by JAXA on the basis of landing feasibility and safety for the MMX spacecraft. For each landing site, the SRC data cover a wide phase angle range (0.5-90°), including the opposition effect. The spatial resolution ranges between 7 and 65 m/px, and with an average value of 42 m/px.
We first simulate the observation conditions for each image, meaning the incidence, emission, and phase angle, as well as the longitude and the latitude. Then, we coregister the images using ElastiX python library [6]. The coregistration was a difficult process as with the higher resolution of the images, there was a slight rotation difference between the observations and simulations, hence the need for a non-linear translation. The coregistration algorithm computes two transformations based on the original image. The first one is a rigid transform to a translation and rotation to the image. Then, a similarity transformation for a more precise rotation. Once those transformations are applied, we extract a displacement map for individual pixels and we apply this map to simulations.
Our next step is to apply disk-resolved Hapke model [7] for the different landing sites investigated. From the derived photometric parameters, such as the opposition surge amplitude and width, and single-scattering albedo, we will infer surface properties including brightness, roughness, and surface porosity for each candidate landing site analyzed and we will compare their properties to those derived from the global analysis of Phobos [3]. This study will help MMX team in the selection of the final landing site.
Acknowledgment: This work has received support from France 2030 through the project named Académie Spatiale d'Île-de-France (https://academiespatiale.fr/) managed by the National Research Agency under bearing the reference ANR-23-CMAS-0041, as well as the Centre National d’Etude Spatial (CNES).
Reference:
[1] Sato et al. (2014), JGR, 119(8)
[2] Wargnier et al. (2025), A&A, 703, A289
[3] Fornasier et al. (2024), A&A, 686, A203
[4] Jaumann et al., PSS, 55, 928-952
[5] Oberst et al. PSS, 56, 473-491
[6] Klein et al. (2010), 19, 1, 196-205
[7] Hapke (2012), Cambridge University Press
How to cite: El-Bez-Sebastien, N., Teissieres, T., Yumoto, K., Fornasier, S., Wargnier, A., and Barnouin, O.: MMX landing sites photometric properties using Mars Express SRC observations, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-884, https://doi.org/10.5194/epsc2026-884, 2026.
Airless bodies experience significant space weathering from solar wind, galactic cosmic rays, and micrometeorites bombardments [1]. However, the biggest Martian moon, Phobos, is peculiar in the Solar System because, due to its proximity with its host planet, its surface is also altered by Martian heavy atmospheric escaping oxygen ions. Because Phobos is tidally locked the sub-Martian hemisphere is strongly affected by these ions and a strong hemispheric dichotomy on Phobos might be expected. To characterize the expected modifications caused by oxygen irradiation and compared it with solar wind irradiation, we investigated in laboratory the spectroscopic, photometric, physical, and chemical modifications of various ion irradiated samples.
To represent the surface of Phobos, several samples based on their mineralogical composition and/or spectroscopic properties were selected, including two Phobos simulants (UTPS, OPPS) [2,3], olivine, phyllosilicate (saponite), coal (anthracite and DECS-19 from the Penn State Coal Bank), and iron sulfide. This study investigated the spectro-photometric variations induced by space-weathering with spectroscopic measurements ranging from 0.4 to 3.6 µm with different geometry of observations. Additionally, mid-infrared (MIR) reflectance spectra (1.25 – 18 µm) were also obtained to study the modifications of shape and positional shifts of two key MIR features for mineralogical interpretation: the Christiansen feature (CF) and the Reststrahlen band (RB). Modifications of the physical properties were investigated through scanning electron microscopy (SEM) and atomic force microscopy (AFM). Chemical variations were monitored by using Raman spectroscopy with 532 nm and 248.6 nm laser excitations, and energy-dispersive X-ray (EDX) spectroscopy. In addition, we prepared plasma focused ion beam (pFIB) sections and subsequently performed Transmission Electron Microscopy (TEM) analysis to study the microstructural, chemical, and mineralogical changes induces by space-weathering inside the samples.
We irradiated the various samples with 7 keV O+ ions, reaching a maximum fluence of 6.1015 ions.cm-2, representing about 103 years of irradiation on Phobos’ surface. To represent the light and heavy solar wind ions contribution, we irradiated the same samples with 36 keV He2+ and 126 keV Ar7+ ions, respectively. The irradiation experiments were performed using the ARIBE beamline at the large heavy ion national accelerator (GANIL, France), under ultra-high vacuum (P ~ 10-7–10-9 mbar) and at ambient temperature.
We explored the spectroscopic modifications induced by space-weathering, with a specific focus on the evolution of the spectral slope and of some key absorption bands such as the 2.7 µm O-H feature and the 3.4 µm C-H aliphatic and aromatic features. We found no modification of the 2.7 µm feature after O+ ion irradiation in saponite and Phobos simulants. However, a small decrease of 10% in the C-H absorption band depths was observed in the DECS-19 sample. This decrease in the C-H feature may be consistent with the partial amorphization observed through Raman spectra associated with this sample. Regarding spectral slope and reflectance level, most of the samples do not exhibit variations, except OPPS for which a darkening and reddening is observed after O+ irradiation, and DECS-19 with a slight bluing in the visible. In the MIR, for all samples, no modifications are observed for both CF and RB feature(s). New transmission electron microscopy (TEM) imaging results will also be presented. Unlike O+ irradiation, He2+ and Ar7+ irradiations led to significant spectral modifications for most of the samples, in terms of spectral slope and reflectance level, for example with a strong bluing and brightening for UTPS.
This study shows that oxygen irradiation from Martian atmospheric ions might have a limited effect on the spectroscopic properties due to their low energy, and hence their low projected range in the regolith grains. On the contrary, solar wind ions may significantly alter the surface of Phobos. However, Phobos returned samples from the JAXA Martian Moons eXploration (MMX) mission [4] – which will be launched in autumn 2026 – may exhibit traces of alteration at the submicron scale by these oxygen ions, which may be important to understand the history of the Martian system.
Acknowledgements: The authors acknowledge the Centre National d’Études Spatiales (CNES) for the continuous support, and the Grand Accélérateur National d'Ions Lourds (GANIL, France) for the time allocated on the ARIBE beamline for ion irradiation experiments under proposals P1377_23 and P1402_24.
References: [1] Pieters and Noble (2016), JGR Planets, 121, 10 [2] Wargnier et al. (2024), Icarus, 421, 3 [3] Miyamoto et al. (2021), EPS, 73, 214 [4] Kuramoto et al. (2022), EPS, 74, 12
How to cite: Wargnier, A., Moingeon, A., Gautier, T., Quirico, E., Nakamura, T., Takase, T., Enokido, Y., Beck, P., Yumoto, K., Poggiali, G., Caminiti, E., Poch, O., Domaracka, A., Rothard, H., Boduch, P., and Tatsumi, E.: Simulating space-weathering on Phobos: He2+, Ar7+, and O+ ion irradiation of simulants, minerals, and organics, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-107, https://doi.org/10.5194/epsc2026-107, 2026.
In October 2026, the Martian Moons eXploration (MMX) mission [1] will depart for the Martian system. Its primary objective is to unveil the origins of Phobos and Deimos, distinguishing between two possible scenarios: either the moons were captured asteroids or they formed from the debris of a giant impact on Mars.
Onboard MMX, the MMX InfraRed Spectrometer (MIRS) [2] will map the surfaces of Phobos and Deimos in the 0.9–3.6 µm range to search for weak spectral signatures of hydrated minerals (at 2.7 µm) or organics (at 3.3–3.4 µm), which would indicate an asteroidal origin. Thanks to its high signal-to-noise ratio and continuous spectral coverage, MIRS will fill the gaps in existing data from CRISM, OMEGA, and PFS. Previous analyses of CRISM data have revealed a weak signature of hydrated minerals around 2.7 µm [3] leading to an asteroidal capture, but the instrument’s limitations prevent definitive conclusions.
To prepare for the MMX mission and calibrate its instruments, spectral analogues for the surface of Phobos have been developed, namely OPPS [4] and UTPS-TB [5]. Although these analogues reproduce the spectral properties of Phobos, they are based on the asteroidal capture scenario (D-type asteroid for OPPS and Tagish Lake C2 chondrite for UTPS-TB) and incorporate organic materials and hydrated minerals.
In this work, we are developing a new simulant to test the post-impact scenario. The objective is to reproduce the near-infrared (NIR) spectral properties (reflectance level and spectral slope) of Phobos without incorporating any materials (such as organics or hydrated minerals) that would have been likely decomposed or evaporated by the impact [6].
To develop this simulant, we used a Hawaï lava tube basalt grinded in an Retsch PM100 planetary grinder and sieved the resulted powders into several categories (<50 µm, 50-100 µm, 100-300 µm). The choice of lava tube basalt was motivated as a proxy for a rapid melting and solidification, which minimizes the presence of large mineral grains and try to preserve mostly amorphous material, thus reducing potential absorption features from silicates (olivine, pyroxenes) [7]. As a darkening agent, we added up to 50 vol% magnetite.
The mixtures were then measured in the visible (VIS), near-infrared (NIR) and mid-infrared (MIR) using a Bruker Invenio-R FTIR coupled with the BOROMIR goniometer available at LIRA spectroscopy facility. To enable direct comparison with CRISM observations of Phobos from October 23, 2007 [8], we performed measurements replicating the observation geometry. We set the goniometer to match the geometry at the central region of the Phobos disk in the CRISM data, with an illumination angle of 30° and an emergence angle of 15°.
Figure 1 shows the spectral measurements of our samples compared to CRISM data under similar geometry. With the 50–50 vol% mixture, we obtained a red slope devoid of any spectral bands between 1.4 and 4 µm, although a weak adsorbed water feature around 2.8 µm is visible due to laboratory humidity. The slope and reflectance level of this mixture are consistent with those of Phobos’ red unit and almost perfectly overlap the observations. For similar geometry of observation for OPPS and UTPS-TB (incidence at 30° emergence at 20°), their spectra are much brighter despite sharing similar red slopes.
Figure 1: Spectra of Phobos from CRISM data, OPPS, UTPS, and this works simulant.
This preliminary work therefore demonstrates the possibility of reconciling the post-impact scenario with the spectral properties observed on Phobos.
As an improvement for this post-impact simulant, we are aiming at melting basalt around 1700K and cool the lava quickly under a reducing atmosphere as an extension to the work of [9].
We hope to produce a dark glass to reduce the amount of darkening component in the simulant and increase the amount of amorphous material to reduce the bands around 1 µm. The ongoing laboratory experiments and results will be presented and discussed
[1] Kuramoto et al., 2022, Earth, Planets and Space, 10.1186/s40623-021-01545-7
[2] Barucci et al., 2021, Earth, Planets and Space, 10.1186/s40623-021-01423-2
[3] Fraeman et al., 2014, Icarus, 10.1016/j.icarus.2013.11.021
[4] Wargnier et al., 2023a, Monthly Notices of the Royal Astronomical Society, 10.1093/mnras/stad2132
[5] Miyamoto et., 2021, Earth Planets and Space, 10.1186/s40623-021-01406-3
[6] Craddock, 2011, Icarus, 10.1016/j.icarus.2010.10.023
[7] Pisello et al., 2022, Icarus, 10.1016/j.icarus.2021.114801.
[8] Pajola et al., 2018, Planetary and Space Science, 10.1016/j.pss.2018.02.016
[9] Moroz et al., 2009, Icarus, 10.1016/j.icarus.2009.02.007
How to cite: Sultana, R., Hedjal, C., Yumoto, K., Chaudesaygues, C., Millan, M., Fornasier, S., Gautier, T., and Barucci, A.: Testing experimentally the post-impact formation scenario of the areolian moons: development of a new Phobos spectral simulant, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-963, https://doi.org/10.5194/epsc2026-963, 2026.
Remote sensing visible to near-infrared (VNIR) reflectance spectroscopy measurements of a surface are influenced by its composition, physical properties, and interactions with the environment, including temperature variations. Laboratory measurements are used to isolate the effects of temperature variations from other phenomena. Temperature changes induce variations in the intrinsic absorption properties of common rock-forming minerals such as olivine and pyroxene (Singer and Roush, 1985; Roush and Singer, 1986; Schade and Wäsch, 1999). These changes result in modification of the position, depth, width, and shape of absorption bands. The surface temperature variations across small bodies and planetary surfaces must thus be considered for an optimal interpretation of spatially resolved observations. Several meteorites have been investigated at low temperature, however, due to their low reflectance, less has been done for carbonaceous chondrites (CCs). Laboratory studies focusing on spectral modifications induced by cryogenic temperatures in the VNIR are mostly limited to 2.5 µm, which prevents investigation of the hydroxyl and molecular water absorption band around 3 µm. In this work, we report a comparative analysis of temperature-dependent spectral modifications on a panel of nine meteorites over the 0.5-4 µm spectral range. We study CCs from four different class (CI, CM, CV, and CO) as well as an ungrouped one (UCC), an ordinary chondrite (OC), and a diogenite. We analyze a temperature range from ~280 K to ~70 K and detail the importance of spectral changes for the MMX mission.
Low-temperature reflectance spectroscopy measurements were acquired at IPAG (France) using the bidirectional reflectance spectro-gonio-radiometer SHINE (SpectropHotometer with variable INcidence and Emergence) (Brissaud et al., 2004). SHINE was coupled with the double environmental chamber CarboN-IR (Beck et al., 2015). Spectra were acquired from 0.5 to 4 µm with an incidence angle of 0° and an emission angle of 30°. We performed measurements from about 280 K to a minimum of 70 K with several intermediate levels. The temperature error is estimated to be 1 K. Measurements were performed under secondary vacuum (P~10-6 mbar), preventing effects of oxidation by ambient air. All of our samples were in the form of unsieved powder. We use the position, depth, and width of the absorption bands (0.7, 1, 2, and 3 µm) to characterize spectral modifications induced by low temperatures. We also investigate interband peaks and average slopes.
There is a significant evolution of spectral properties of OCs, CCs, and diogenites with low temperatures in the visible to near-infrared. This includes changes in the position, depth (Figure 1), and width of the absorption bands at about 0.7, 1, 2, and 3 µm, as well as changes in the position of the interband peaks at around 0.55, 0.7, and 1.5 µm. The spectral slope is also modified. Spectral changes induced by low temperatures can influence the interpretation of the composition and degree of hydration of meteorites and planetary bodies.
The MMX InfraRed Spectrometer (MIRS) (Barucci et al., 2025) instrument onboard MMX will perform a spectral characterization of the Martian system between 0.9 and 3.6 mm. Although the specific mineralogy of the moons is currently difficult to determine, due to the lack of a strong absorption band in the VNIR, possible weak bands have been discussed and CCs have been highlighted as potential analogs (Rivkin et al., 2002b; Fraeman et al., 2012; 2014). If absorption bands are observed, the effects of low temperatures on their properties must be considered. In fact, surface temperatures on Phobos could vary between 100 K and 320 K (Giuranna et al., 2011; Sultana et al., 2025). With a spectral resolution of <32 nm, the instrument will be sensitive to the band’s position shifts as well as changes in the amplitude and width. MMX will also observe the Martian moons using the Optical RadiOmeter composed of Chromatic Imagers (OROCHI) instrument using seven spectral bands between 0.39 and 0.95 µm (Kameda et al., 2021). If the 0.7-µm absorption band is observed, low temperature effects must be considered for an optimal interpretation of the spectral band (Figure 2). MMX will return Phobos samples to Earth in 2031. We encourage to consider the effects of low temperature on spectral properties when comparing the future sample studied in the laboratory with remote sensing data. This work extends beyond the Martian moons and the MMX mission, and several other missions such as Hera (ESA), Lucy (NASA), Tianwen-2 (CNSA) and EMA (UAE) are concerned.
Figure 1: Spectral modifications induced by low temperatures on the band depth (BD) of the absorption band around 1 mm for three CCs.
Figure 2: Simulated MMX OROCHI spectra of Murchison (CM) meteorite, converted from laboratory reflectance measurements
References:
- Barucci et al., Prog. Earth Planet. Sci. 12.1, 69 (2025).
- Beck et al., Icarus 257, 471–476 (2015).
- Brissaud et al., Appl. Opt. 43.9, 1926–1937 (2004).
- Fraeman et al., Icarus 229, 196–205 (2014).
- Fraeman et al., JGR Planets 117.E11, (2012).
- Giuranna et al., Planet. Space Sci. 59.13, 1308–1325 (2011).
- Kameda et al., EPS 73.1, 218 (2021).
- Rivkin et al., Icarus 156.1, 64–75 (2002).
- Roush & Singer, JGR 91.B10, 10301–10308 (1986).
- Schade & Wäsch, Adv. Space Res. 23.7, 1253–1256 (1999).
- Singer & Roush, JGR 90.B14, 12434–12444 (1985).
- Sultana et al., A&A 701, A46 (2025).
How to cite: Caminiti, E., Beck, P., Wargnier, A., Bonal, L., Schmitt, B., and Usui, T.: Low-temperature reflectance spectra of meteorites: implications for the MMX mission, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-175, https://doi.org/10.5194/epsc2026-175, 2026.
Martian Moon eXploration (MMX) mission will launch in October 2026 to investigate the Martian system, notably the moons, Phobos and Deimos, in order to uncover their origins. Among the instrumentation, the MMX InfraRed Spectrometer (MIRS) is a spectro-imager which covers the 0.9 - 3.6 μm range. It will permit to detect several minerals and compounds including hydrated minerals between 2.6 and 2.8 m and organics in the 3.3 - 3.5 μm region, with high Signal to Noise Ratio (SNR). MIRS will play a key role in selecting the landing site, as well as improving our understanding of the composition of Phobos and Deimos. It is expected to measure thousands of spectra. To facilitate the processing of these data, we adapted and improved an existing code called Spindex, which was originally developed in IRL for the OVIRS instrument on the OSIRIS-REX mission [1].
The original code used a catalogue comprising over 100 potential spectral bands, each of which was associated with spectral parameters that are used in a set of 21 different equations (depending on the band form) to compute the spectral band depth (see Fig. 1). If this depth was above 5%, then the spectral band was considered to be detected. The code also computes the spectral slope over seven different regions of interest.
Figure 1: Example of the spectral parameterls, band depth and error associated equations used by Spinmirs.
In our version, called Spinmirs, we have slightly reduced the number of potential bands, grouping the different types of olivine bands in the 0.9 - 1.3 μm region together, as this lead to several false detections. This also reduced the number of equations to 19. Furthermore, we have introduced an additional quality criterion. Each band depth is associated with an error, if the band depth is less than twice the error, the band is considered ‘potentially detected’ rather than ‘detected’, as this indicate a low SNR in the area where it is locate. The final change we made was adjusting the threshold of 5% to each mineral if it were over- or under-detected.
Figure 2: Example of Spinmirs output on a terrestrial sample available on RELAB.
Spinmirs has been tested on the RELAB dataset, as well as Bennu spectra taken by OVIRS and gives promising results (see Fig. 2), as most of the band detected are indeed appearing on the spectra. There are a few case of false detection, notably with the biotite at 1.30 μm. The average computation time for one spectra is of 0.31 seconds. It will be a valuable tool to treat and interpret future MIRS spectra.
Acknowledgement : This work has received support from France 2030 through the project named Académie Spatiale d'Île-de-France (https://academiespatiale.fr/) managed by the National Research Agency under bearing the reference ANR-23-CMAS-0041, as well as the Centre National d’Etude Spatial (CNES).
References :
[1] Kaplan et al. (2020), M&PS, 55, 4, 744-765
How to cite: El-Bez-Sebastien, N., Fornasier, S., and Lely, L.: Spectral bands detector tool for future MIRS/MMX data, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-416, https://doi.org/10.5194/epsc2026-416, 2026.
The Martian Moons eXploration (MMX) mission is a JAXA-led sample return mission scheduled for launch in 2026, aiming to reveal the origin and evolution of the Martian moons, Phobos and Deimos. In particular, detailed proximity observations of Phobos are planned. Our objective is to precisely determine the orbit of the MMX spacecraft and the gravity field of Phobos using radiometric tracking, laser ranging, and landmark observations, and ultimately to estimate the internal density structure of Phobos based on these results.
After arriving in the Martian system, the MMX spacecraft will be inserted into a Quasi-Satellite Orbit (QSO) around Phobos, from which detailed observations will be conducted. To ensure spacecraft safety, mission operations begin from a high-altitude QSO and gradually transition to lower-altitude QSOs while updating operational parameters required for navigation and observation. In this study, based on the planned mission profile, we investigate a strategy for stepwise gravity field estimation of Phobos during the gradual orbital descent of the MMX spacecraft.
The proposed approach sequentially updates the gravity field solution at each orbital altitude using all observational data accumulated up to that stage, enabling the estimation of the best available gravity field and spacecraft orbit solutions before entering lower-altitude operational phases. This is particularly important because low-degree gravity coefficients, which contribute most strongly to the gravity acceleration, can be progressively refined during the early mission phases, thereby improving the estimation of higher-degree gravity terms from lower-altitude observations with greater sensitivity. Such a sequential strategy is expected to enhance both the robustness and stability of gravity field recovery.
To evaluate this concept, numerical simulations were performed using predefined “true” shape and internal density structure models of Phobos. The nominal true shape model was based on Ernst et al. (2023), modified so that the center of figure coincides with the center of mass. A geometrically similar model with a slightly different scale was also used to simulate scale factor estimation. For the internal density structure, we assumed a model containing a density anomaly beneath Stickney crater, from which the corresponding gravity field was computed and used to propagate the spacecraft trajectory. Simulated Doppler, LIDAR (Light Detection and Ranging), and landmark observation data were generated from the resulting “true” trajectory, with random Gaussian noise added to each observation type to represent realistic measurement errors.
Gravity field coefficients and spacecraft orbit parameters were estimated from the simulated observations using initial values of the spacecraft state vectors, shape model scale factor, gravity coefficients, and libration amplitude that were intentionally offset from the true solution to reproduce realistic operational uncertainties. The simulations were performed using the GINS software package developed by CNES.
The results show that the proposed stepwise gravity field estimation approach is significantly more effective than a non-sequential estimation method. In simulations without the stepwise approach, the gravity field estimation tended to diverge, whereas the sequential estimation strategy provided stable and convergent solutions throughout the gradual orbital descent. These results demonstrate that the stepwise approach is essential for robust gravity field recovery during MMX operations around Phobos.
Reference
Ernst, C. M., et al.: High-resolution shape models of Phobos and Deimos from stereophotoclinometry, Earth Planets Space, 75, 103, https://doi.org/10.1186/s40623-023-01814-7, 2023.
How to cite: Yamamoto, K., Matsumoto, K., Ikeda, H., Laurant-Varin, J., Marty, J.-C., and Araki, H.: Simulation of Stepwise Gravity Field Estimation for Phobos in MMX QSO Operations, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-855, https://doi.org/10.5194/epsc2026-855, 2026.
Introduction: Phobos’ formation remains uncertain, with two main hypotheses: accretion of debris following a high-energy impact between Mars and an asteroid [1] or capture of a primitive asteroid [2]. To solve this, JAXA’s Martian Moons eXploration (MMX) mission aims to return samples from Phobos by 2031 [3]. The characterisation of these samples will determine the origin of Phobos.
Current observations of Phobos are limited to remote measurements that are interpreted without direct mineralogical ground-truth. In this study, we have characterised the infrared (IR) reflectance spectra and mineralogy of meteorites considered good analogues for materials likely to be present on the surface of Phobos. These measurements provide a link between remote sensing data and physical sample analysis by building a spectral-mineralogical reference catalogue using powdered meteorites. This catalogue will help interpret the initial remote observations (prior to landing on Phobos’ surface) of the upcoming MMX mission, inform sampling site choices, and then help evaluate the later returned sample spectra to ultimately constrain the origin of Phobos. In addition, the mineralogical-spectral correlations can be referred to for future spectral calibration across other small bodies in the Solar System.
Methods: We have characterised the mineralogy and spectral properties of six CM (Mighei-like) carbonaceous chondrites, Tarda (C2-ung), the CO (Ornans-like) chondrite Kainsaz, CRs (Renazzo-like) NWA 801 and 1567, a range of shock darkened ordinary chondrites (mostly falls) including L4-6 and H5-6, four ureilites, Martian meteorites Nakhla and Tissint (shergottite), and a Tagish Lake (C2-ung) based simulant created by the University of Tokyo, known as UTPS-TB [5].
We performed FTIR and XRD measurements on the same powder (~50 mg, grain size <40 μm) to reduce variability in the results from differences in grain size and potential sample heterogeneity. This ensures that the mineralogy determined by XRD can be directly correlated with the spectral features. Such a controlled, internally consistent dataset allows us to isolate the effects of mineralogy on the spectra [e.g. 6], which are critical parameters when interpreting remote spectra from Phobos.
Diffuse reflectance spectra (1.6 - 25 μm) of powders were collected using a Bruker VERTEX 70V FTIR spectrometer under vacuum. Spectra were calibrated at the start of each measurement day and between measurements of samples using a gold standard.
XRD patterns were collected using an INEL X-ray diffractometer with a position-sensitive detector. Each sample was measured for 16 hours to achieve good signal-to-noise. Measurements of well-characterised standard minerals were collected for 30 minutes and compared with meteorite patterns to identify minerals and quantify their abundance in the sample [e.g. 7].
Results & Discussion:
Figure 1: PSD-XRD modal mineralogy in volume % for Phobos-analogue meteorites.
Figure 1 shows the modal mineralogy of the Phobos analogues, presenting a range of aqueous and thermal alteration, with significant variation in composition between the classification groups. The carbonaceous chondrites studied (except CO Kainsaz) all have phyllosilicate minerals, varying from 10 to 92 vol.%. In contrast, the Martian meteorites’ composition are almost entirely anhydrous silicates; Nakhla’s composition was 77 vol.% pyroxene and 10 vol.% olivine, and Tissint was composed of 45 vol.% olivine and 28 vol.% pyroxene.
Figure 2: Comparison of spectral features with mineralogy determined by XRD . (a) OH feature band depth vs volume of phyllosilicates serpentine and smectite (combined). (b) CF centre position vs volume of olivine, with Phobos’s CF centre position (8.82 microns) as determined by [8].
We find a positive correlation between the 3-micron band depth and abundance of phyllosilicates. As the 3-micron feature is present due to the stretching of OH (which phyllosilicates contain), the depth of the feature is proportional to the abundance of phyllosilicate. MMX’s MIRS instrument will operate in the region where the 3-micron feature is present [9]. So far, a possible 3-micron feature has been observed in Phobos’s spectrum, but the MMX instrument will be searching for it as aqueous alteration could indicate a captured primitive asteroid origin.
The CF feature is a key region of study as the miniRAD radiometer on MMX’s rover will investigate the position of the feature as a first order mineralogical characterisation [10]. The position of the feature varies in relation to the meteorites’ mineral composition; in the case of Figure 2b the centre of the CF has a negative correlation with the mineral abundance of olivine as samples with lover olivine abundances (like carbonaceous chondrites) contain more phyllosilicates which have CFs at shorter wavelengths. The remotely observed position of the CF (8.82 microns) is plotted and falls closely to the CF of carbonaceous chondrite samples, implying that Phobos’ composition is close to that of the primitive carbonaceous.
Based on this data it may be possible to infer the abundance of phyllosilicate from the band depth of the 3-mircon feature, especially when used in combination with the CF position. Increasing aqueous alteration leads to more phyllosilicate and less olivine abundance. The 3-micron band depth and CF position combined could therefore be a powerful tool for interpreting the surface mineralogy of Phobos.
Conclusion: Carbonaceous chondrites are the closest spectral match to Phobos from the samples studied according to the position of their CF. These results support the interpretation that Phobos is composed of primitive material, likely of outer solar system origin, which favour a capture scenario over a collisional formation from Martian ejecta, and further demonstrates the importance of the MMX mission sample return for solving the mystery of their origin definitively.
References: [1] R. Citron et al. (2015) Icarus 252:334-338. [2] M. Pajola et al. (2013) The Astrophysical Journal 777:127. [3] K. Kuramoto et al. (2022) Earth, Planets and Space 74:12. [4] K. D. Pang et al. (1978) Science 199(4324):64-66. [5] H. Miyamoto et al. (2021) Earth, Planets and Space 73:1-17. [6] H. C. Bates et al. (2023) Meteoritics & Planetary Science 1-23. [7] G. Cressey et al. (1996) Powder Diffraction 11:35-39. [8] Wargnier et. al (2024) Icarus 421 116216. [9] M. Barucci et al. (2025) Progress in Earth and Planetary Science 12:69. [10] J. Knollenberg et al. (2025) Progress in Earth and Planetary Science 12:53.
How to cite: Branagan-Harris, E., Bates, H., Shirley, K., King, A., Bowles, N., and Russell, S.: Spectral–Mineralogical Correlations in Meteorite and Simulant Analogues: Implications for the Composition and Origin of Phobos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-650, https://doi.org/10.5194/epsc2026-650, 2026.
Introduction
Continuous astrometric observations of the Martian satellites are essential for refining their ephemerides. Of particular value are the so-called mutual event observations, that is, images showing not only one of the moons but also a second reference object. When the ephemeris of that object is well known, its measured position in the frame can be used to correct the spacecraft’s pointing, thereby enabling more accurate determinations of the moon’s location. Alternatively, the pointing-independent angular separation between the two objects can be extracted.
Mars Express/SRC images
In earlier studies we have processed SRC frames that show Phobos or Deimos and the Jupiter system or Saturn, as well as images in which both Martian moons appear simultaneously [1]. In addition, we have analysed HERA/AFC observations of Deimos with Mars in the background that were acquired during HERA's Mars fly-by in March 2025 [2].
Here, we report on the analysis of images that depict either of the moons and one or several stars (Figure 1). We also evaluate images showing one of the moons and the Jovian system (Figure 2) in the background. Because of their great distance, the Galilean satellites appear as point-like sources. Consequently they look indistinguishable from stars, and we process these images using almost the same methodology. The SRC images are affected by a complex point spread function (PSF) owing to which stars as well as the Galilean moons appear as triangular objects with diffuse edges (Figure 1).
Fig 1: Phobos with stars in the background (Orbit 12563 [ESA/DLR/FU Berlin]). Due to the rather complex point spread function SRC images show stars as triangular objects with diffuse edges.
Fig 2.: Mutual event observation of Phobos and Jupiter with the Galilean satellites (Orbit 12515, [ESA/DLR/FU Berlin]). In addition a star was observed.
Methods: The measurement consists of determining the image coordinates of each body’s centre of figure (COF). For Phobos and Deimos we generate a synthetic image with the NAIF SPICE toolkit, incorporating the moons’ ephemerides, shape and rotation models, the Mars Express trajectory, and the SRC’s nominal pointing and camera parameters. The surface reflectance is modeled using the parameter-free Akimov disk function. Because the COF is known a priori in the simulated image, its pixel location in the observation can be determined with sub-pixel accuracy once a satisfactory match between the observation and the simulation is achieved [1].
As mentioned above, the SRC images are characterised by a complex PSF that renders stars as triangular objects with diffuse edges. Instead of generating a full synthetic image, we employ the PSF model presented in [3] to detect both stars and the Galilean moons and to extract their precise positions. The identified stars are cross‑matched with the Gaia catalogue [4, 5].
MMX/TENGOO
While MMX moves about Phobos in a quasi-satellite orbit, the TENGOO camera will have the chance to capture mutual event images of Deimos against a stellar background. Here we consider the epoch from 1 July 2028 to 30 September 2028. The observing windows for mutual events are spread throughout the epoch, with multiple opportunities sometimes occurring on a single day. Because downlink bandwidth is limited, not every opportunity can be exploited. Consequently, one must prioritize those instances that offer the most favorable observing conditions - i.e., the ones that will yield the highest-quality astrometric measurements of Deimos. These are related to
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Apparent size: Deimos should occupy as many pixels as possible; we therefore prefer images in which the satellite spans ≥ 70 pixels.
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Illumination geometry: A phase angle ≤ 90° is preferred to ensure adequate illumination without excessive shadowing.
Moreover, observations should be well-distributed in Deimos’ mean anomaly so that the entire orbit around Mars is sampled. Figure 3 illustrates the mean anomaly, the phase angle and the apparant size of Deimos for the mutual event opportunities.
Fig. 3: Mean anomaly, phase angle and apparent size of Deimos for the mutual event opportunities spanning 1 July 2028 - 30 September 2028.
Covering the entire set of six 60° anomaly sectors can be achieved only if we include observations with phase angles ≤ 115°. When we impose the requirement that Deimos occupies an apparent size larger than 70 pixels and restrict the phase angle to ≤ 90°, no viable windows remain for anomaly values between 60° and 240°. If we relax the size constraint to a minimum of 50 pixels while still limiting the phase angle to ≤ 90°, the only remaining gap lies between 120° and 180° anomaly. Additionally, the only opportunities that fall within the 60°–90° anomaly range occur in September 2028.
Summary
We described the reduction of mutual events observations by Mars Express/SRC. The new observations complement the previous data set and enable maintaining the ephemerides of the Martian satellites. In addition, we outlined MMX/TENGOO imaging opportunities that could record Deimos together with background stars.
References:
[1] Ziese, R., Willner, K. (2018). A&A, 614, A15.
[2] Ziese, R., Willner, K., Vincent, J.-B., and Oberst, J. (2025). EPSC-DPS Joint Meeting 2025, EPSC-DPS2025-1965.
[3] Duxbury, T. et. al. (2011). HRSC Team Meeting 2011. Technical Note.
[4] Gaia Collaboration, T. Prusti, J.H.J. de Bruijne, et al. (2016). A&A 595, A1.
[5] Gaia Collaboration, A. Vallenari, A. G. A. Brown, et al. (2023). A&A 674, A1.
Acknowledgements:
This project is supported by the Deutsche Forschungsgemeinschaft (DFG), research grant number 528586639. It also relies on work done in an earlier project, suppported by DFG, grant number OB 1 24/1 4-1.
How to cite: Ziese, R., Willner, K., Matz, K.-D., Matsumoto, K., and Oberst, J.: Mutual event observations of the Martian moons with Mars Express/HRSC and MMX/TENGOO, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-670, https://doi.org/10.5194/epsc2026-670, 2026.
Doppler tracking of planetary missions is crucial for science objectives related to understanding, among others, solar system interiors and evolution. These analyses conventionally rely on closed-loop Doppler data from networks such as ESTRACK and the DSN. The Planetary Radio Interferometry and Doppler Experiment (PRIDE) can provide complementary data by extracting open-loop Doppler and VLBI observables from spacecraft radio signals recorded by radio-astronomical telescopes [1,2,3]. These (three-way) observables are generated using the existing downlink from the spacecraft and therefore generated concurrently with the typical (usually two-way) closed-loop tracking data. While PRIDE data of planetary missions have been used for various applications, their direct use in a full orbit-estimation problem had not yet been demonstrated. Here, we report on the first end-to-end PRIDE-based orbit estimation of a planetary mission, using PRIDE Doppler data.
We use the 2013 Mars Express flyby of Phobos, for which both conventional closed-loop Doppler data and PRIDE open-loop Doppler (EVN experiment GR035, PI: Pascal Rosenblatt) data are available [4]. Using the open-source TU Delft Astrodynamics Toolbox (Tudat) [5,6], we independently estimate the Mars Express trajectory and the gravitational parameter of Phobos from the closed-loop and open-loop datasets. The solutions are cross-validated against the Mars Express orbit computed by the Royal Observatory of Belgium (ROB) team from closed-loop Doppler data using the GINS software.
The closed-loop solution gives RMS position differences with respect to the ROB Mars Express ephemerides of approximately 0.27 m radial, 17 m along-track, and 130 m cross-track, consistent with the expected uncertainty of the reference solution. For the PRIDE open-loop Doppler data, we form 27 different three-station combinations of PRIDE datasets, with one station on each of three continents, such that each combination spans the full tracking interval. From each combination, we estimate an independent orbit of Mars Express, leading to separate orbit estimates, each of comparable quality to those derived from closed-loop data, as quantified by the difference with respect to the ROB reference. The estimated gravitational parameter of Phobos is likewise consistent between the open-loop and closed-loop analyses and with reference values from the literature.
To further quantify the uncertainty of the PRIDE-based orbit estimates, we compute the RMS dispersion of the 27 station-combination solutions at each point along the estimated trajectory. This dispersion peaks at approximately 0.4 m radial, 15 m along-track, and 100 m cross-track. Its temporal behaviour closely matches the difference between our closed-loop solution and the ROB reference ephemeris, indicating that the spread between PRIDE station-combination solutions provides a measure of the true orbit-estimation error that is comparable to the difference with respect to an external reference solution. This is a key advantage of PRIDE’s multi-station redundancy: it enables an internal assessment of solution uncertainty, without relying exclusively on formal covariance estimates, which are often too optimistic, or on comparison with an external reference solution, which is not always available.
Assessing the true uncertainty of radio-tracking-based estimation is crucial for robustly using estimated parameters (for instance the gravitational parameter of Phobos) to improve our understanding of planetary interiors and Solar System evolution. PRIDE observations are particularly valuable for selected tracking intervals of high scientific interest, where the multi-station redundancy can provide validation and error quantification beyond what is available from conventional tracking alone. For events such as flybys of the Galilean moons [3], PRIDE Doppler data can therefore provide a complementary source of information for assessing the reliability of orbit and parameter estimates. Future work will include the processing of PRIDE Doppler data during the JUICE flyby of Venus, and spacecraft orbit estimation using a combination of open- and closed-loop tracking data.
[1] Duev, D.A., et al. "Spacecraft VLBI and Doppler tracking: algorithms and implementation." Astronomy & Astrophysics 541 (2012): A43.
[2] Molera Calvés, G., et al. "High spectral resolution multi-tone Spacecraft Doppler tracking software: Algorithms and implementations." Publications of the Astronomical Society of Australia 38 (2021): e065.
[3] Gurvits, L.I., et al. "Planetary radio interferometry and Doppler experiment (PRIDE) of the JUICE mission." Space Science Reviews 219.8 (2023): 79.
[4] Bocanegra-Bahamón, T.M., et al. "Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos Flyby: II. Doppler tracking: Formulation of observed and computed values, and noise budget." Astronomy & Astrophysics 609 (2018): A59.
[5] Dirkx, D., et al. "The open-source astrodynamics Tudatpy software–overview for planetary mission design and science analysis." EPSC2022 EPSC2022-253 (2022).
[6] Gisolfi, L, et al. "Open-Source High-Fidelity Orbit Estimation for Planetary Science and Space Situational Awareness Using the Tudat Software." arXiv preprint arXiv:2510.23179 (2025).
How to cite: Sánchez Rodríguez, A., Dirkx, D., Bocanegra, T., Molera Calvés, G., Cimò, G., Fayolle, S., Gisolfi, L., Gurvits, L. I., and LeMaistre, S.: Orbit determination and error quantification of planetary missions using PRIDE open-loop Doppler data: Application to the Mars Express flyby of Phobos, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-166, https://doi.org/10.5194/epsc2026-166, 2026.
