This study presents a strategy to produce artificial rocks, or simulants, designed to replicate boulders observed on the surface of asteroid Ryugu. The simulants are composed of a dust mixture with bulk composition and grain size distribution based on the analysis of particles returned from Ryugu by the Hayabusa2 mission. Two production methods, freeze-drying and dry-compression, were established to generate simulants with porosities between 45% and 80%. Five key parameters were used to characterise the simulants and to compare them with Ryugu particles: the bulk composition of the dust mixture, the size and shape distribution of the individual components, the simulant microstructure, i.e. the internal distribution of material and void spaces, and the interaction between the grains within the simulant. These parameters were assessed using scanning electron microscopy, laser diffraction, helium gas pycnometry, and micro-tomographic analysis. Even though some discrepancies in composition and grain size distribution remain, these can be addressed in future updates of the simulant dust mixture. It was generally found that freeze-dried simulants capture the microstructure and grain interactions of Ryugu particles better than the dry-compressed simulants. In a next step, thermal and mechanical properties of the simulants will be measured to support the interpretation of remote sensing observations of Ryugu’s surface.

Context. Water ice in micro-granular form is the most common volatile in comets, and its behaviour when approaching the Sun must be understood before cometary activity can be properly modelled. Aims. To assess the properties of granular water ice, we investigated its evolution under illumination in a cryogenic high-vacuum environment. Methods. We produced a sample of water ice consisting of micrometre-sized particles, placed it inside a thermal vacuum chamber, and exposed it to high-intensity visible/near-infrared (VIS/NIR) illumination. Due to the energy absorption within the NIR bands of the ice, the sample is locally heated, which causes evaporation close to the surface. The total mass loss of the irradiated sample was measured using a scale and the surface temperatures were recorded with an infrared camera. Furthermore, we used several cameras to observe surface changes and ejected solid particles. Results. We derived the mass loss due to water-ice sublimation from the spatially resolved surface temperatures. This mass loss amounts to 68%-77% of the total mass loss. The remaining fraction (between 23% and 32%) of the mass is ejected in solid particles, which can be seen by the naked eye. Conclusions. The self-ejection of water-ice grains can be explained by a geometrical model that describes the sublimation of the icy constituents of the sample, taking into account the size distribution of the water-ice particles and the volume filling factor (VFF) of the sample. According to this model, solid ice particles are emitted when they (or the particle cluster they belong to) lose contact with the sample due to the faster evaporation of a smaller connecting ice grain. We discuss the possible relevance of this process for cometary dust activity.

Observations of the diurnal variations of the surface temperature of asteroid (162173) Ryugu from orbit and on the surface were performed by the Haybusa2 spacecraft and MASCOT lander. A low thermal inertia of the boulders on Ryugu was derived from these temperature variations and interpreted as the consequence of high porosity. Samples of Ryugu returned to Earth by Hayabusa2 showed higher thermal inertia when investigated by microscopic thermography. Here, we apply a simple thermal model, considering a horizontal fracture interrupting the heat flow into the surface, and investigate whether the low thermal inertia of Ryugu's boulders might be caused by fractures rather than high porosity. We find that the diurnal temperature variations on Ryugu observed by MARA can be partially explained by introducing a single horizontal crack at 9 mm depth below the surface observed by MARA.

Introduction: The JAXA Hayabusa2 sample return mission investigated asteroid (162173) Ryugu via remote sensing (Tsuda et al., 2013, Watanabe et al., 2019), deployed the DLR/CNES MASCOT (Ho et al., 2021), performed an artificial impact experiment (Arakawa et al., 2020) and returned samples to Earth (Yada et al., 2022). Ryugu is a rubble-pile asteroid with similarities to aqueously altered carbonaceous chondrites, in particular CI chondrites (Kitazato et al., 2021, Hamm et al., 2022, Nakamura et al. 2022, Yokoyama et al., 2022). One of the biggest surprises was the prevalence of boulders and dm-sized pebbles on the surface and the deficiency of smaller particles (Jaumann et al., 2019, Sugita et al., 2019). Such finer particles were expected to dominate the surface based on thermal inertia estimates from telescopic infrared observations (Müller et al., 2011). The MASCOT radiometer MARA and the main spacecraft’s TIR infrared imager confirmed the thermal inertia estimates from telescopic observations despite the boulder-dominated surface (Grott et al., 2019, Okada et al., 2020). The low thermal inertia was confirmed to be an intrinsic property of the boulders themselves (Grott et al., 2019, Hamm et al., 2020, Sakatani et al., 2021, Hamm et al., 2022). More specifically, the presence of a layer of dust masking the thermophysical properties of the boulder was limited to small patches of thin dust layers, or no dust at all (Biele et al., 2019, Hamm et al., 2023). In contrast to these in-situ results, the analysis of sample fragments by lock-in thermography resulted in a much higher thermal inertia more comparable to that of meteorites samples (Ishizaki et al., 2023). In this study we attempt to reconciliate the results from spacecraft observations and laboratory analysis by expanding our thermophysical mode to incorporate horizontal fractures. This procedure has been proposed by Elder et al., 2022. We investigate if it is possible to explain the MARA observations with a fracture boulder of higher bulk thermal inertia. This work has implication on the regolith gardening on asteroids like Ryugu as weak and porous boulders would respond to impacts of micro-meteorites differently than fracture boulders with low porosity (Cambioni et al., 2021).Methods: We start from the 1D-thermal model as used in Hamm et al., 2020. The heat conduction equation is solved for a 1D grid of N points from x0 = 0 to xN . At the lower boundary condition, the flux is set to zero. The upper boundary condition is given by the energy balance. Illumination is calculated by averaging over those DEM-facets of the boulder shape model within the MARA field of view. The emissivity of the surface reduced by thermal reradiation as described in Hamm et al., 2023. Here we modify the model such that the heat conduction equation is given by:ρcp ∂T/∂t = σ(T4(xd,t)- T4(xu,t))For xu

CoPhyLabLaboratory experiments are of major importance to understand the activity of comets and to support future space missions. However, past comet simulation experiments were performed under the assumption that comets are mainly composed of water ice with only a limited amount of dust. In the past years, however, the Rosetta mission has shown that cometary nuclei consist primarily of dust and less volatile materials are present than previously thought. Hence, it is high time to set up a new series of laboratory experiments with the aim to investigate the physics of realistic cometary analogue materials. This task is currently addressed by the CoPhyLab (Comet Physics Laboratory) which is a joint project among different partner institutions. This laboratory aims at studying the physics of cometary analogue materials. This task is approached by firstinvestigating isolated physical properties in so-called small experiments (S experiments). In a next step, the experiment’s complexity is increased step-by-step by either adding further components to the sample, or by studying several physical properties under different conditions (large experiments, which will be performed in the L chamber). S1: the tensile strength of organic materialsThe knowledge of the tensile strength of the cometary surface is of key importance to better understand the activity of comets. The tensile strength determines the strain required to detach material from the surface. As organic materials are ubiquitous in space, they could have played an important role during the planet formation process and are most likely incorporated into cometary nuclei. This S experiment campaign provides new measurements on the tensile strength of various granular organic materials. These materials are investigated by the Brazilian Disc Test and the measured values are normalised to a grain size of one micrometer and a volume filling factor of 0.5 for better comparability. The experiments show that the tensile strength of organic materials ranges over four orders of magnitude. Graphite and paraffin have much higher tensile strengths values compared to silica, whereas the tensile strength of coals is very low. This work demonstrates that organic materials are not generally stickier than silicates, or water ice.S2: gas permeability of analogue materials The cometary nucleus is made of water ice, organics and silicateous dust and the ice is trapped inside the matrix of non-volatiles. Hence, the evolving gas has to stream away from its originating region inside the surface layers towards the surface. This work package has the aim to investigate the gas transport mechanisms through porous cometary analogue materials. Therefore, gas flow measurements are performed to investigate the permeability of several materials, which are chosen to mimic cometary surface properties. With these measurements, the gas permeability and the Knudsen diffusion coefficient of the sample materials are obtained. These simulants are tested with respect to different filling heights, packing properties and grain shapes. The gas flow experiments show that the grain size distribution and the packing density of the samples are primarily influencing the permeability of the sample. S3: thermal conductivity of analogue materialsMeasurements of the thermal properties of analogue materials are essential in interpreting remote sensing data and the findings of in-situ instruments. The thermal properties of the subsurface layers determine the surface temperature of asteroids and comets. The temperature stratification inside planetary object is a key parameter to understand the processing of their interior. This experiment campaign is dedicated to measure the thermal properties of analogue materials. In preparation for these measurements we have set up a small vacuum chamber equipped with an infrared camera and temperature sensors. The samples are illuminated for a short duration by a laser. We then compare the measured temperature profiles with the predictions of a thermophysical model to determine the thermal conductivity of the samples.S4: ejection of materialWhen comets approach the Sun, the sublimation pressure will be reached inside the material. If the tensile strength is exceeded by the evolving pressure, the particles can be ejected from the cometary surface and are accelerated. However, the details of the dust dynamics close to the surface are not understood in detail. The idea of this S experiment campaign is to develop an experimental routine to track ejected particles from a sample composed of granular water ice. Therefore, we recorded the power of the illumination, the temperature of the sample and measured the particle trajectories with an high speed camera. Furthermore, the experiments are also simulated by a thermophysical model. Our experiments show that samples composed of pure granular water ice can eject water-ice particles by the pressure build up of water vapour in their interior. Compressed samples posses an higher activity level (ejection events per second) compared to uncompressed samples. The ejected particles have a non-zero initial velocity which is most probably caused by a very fast acceleration of the particles before the first data point is recorded by the camera.The L chamberThe core of this project is the realisation of a comet simulation chamber which will be capable to utilise multiple instruments to monitor and measure the sample properties before, during and after the experiment campaigns. This chamber will be used to perform long duration experiments at low temperatures and low pressures. At this stage (end of June, 2020), the chamber is already installed in place and is vacuum tight, the cooling shield is assembled and the sample carrier cart as well as the self-made glove box are ready to use. The next steps comprise the integration of the cooling shield and the main cooling system. We foresee to run the first experiments in approximately six weeks from now. During the EPSC conference we will provide a technical overview of the chamber and we will present the first experiments performed in the L chamber.AcknowledgementsThis work was carried out in the framework of the CoPhyLab project funded by the D-A-CH programme (GU 1620/3-1 and BL 298/26-1 / SNF 200021E 177964 / FWF I 3730-N36). DB and JB thank the Deutsches Zentrum f\"ur Luft- und Raumfahrt for support under grant 50WM1846.

The MErcury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) is part of the payload of the Mercury Planetary Orbiter spacecraft of the ESA-JAXA BepiColombo mission. MERTIS combines an imaging spectrometer covering the wavelength range of 7-14 μm with a radiometer covering the wavelength range of 7-40 μm. The instrument will map the whole surface of Mercury with a spatial resolution of 500 m for the spectrometer channel and 2 km for the radiometer channel. The compositional map of Mercury provided by MERTIS will allow unique insights into the evolution of the least explored terrestrial planet and will directly address questions raised by the NASA MESSENGER mission. For example, MERTIS will be able to provide spatially resolved compositional information on the hollows and pyroclastic deposits and answer the question whether hollows are actually predominately composed of sulfide. MERTIS will also provide spatially resolved temperature maps inside the permanently shadowed craters, thereby potentially constraining the stability of water ice deposits in those craters.BepiColombo is currently in the final part of its 7-year journey to Mercury. The interplanetary cruise includes in total nine flybys for gravitational assists: one at Earth, two at Venus and six at Mercury. MERTIS could obtain so far observations during the Earth flyby in April 2020, the first Venus flyby (FB1) in October 2020 and the second Venus flyby (FB2) on August 10, 2021. The recently published results for FB2 show that MERTIS performed well beyond requirements and provided new insights into the long-term stability of the Venusian atmosphere.

Diurnal and seasonal variations in soil and surface temperature measured with the HP3 thermal probe and radiometer of NASA's InSight Mars mission are reported. At a representative depth of 10-20 cm, an average temperature of 217.5 K was found, varying by 5.3-6.7 K during a sol and by 13.3 K during the seasons. From the damping of the temperature variation with depth and the phase shift, a thermal diffusivity of (3.93 +/- 0.39) x 10 8 m2/s was derived for the upper similar to 10 cm from the diurnal temperature variation and of (3.63 +/- 0.53) x 10 8 m2/s for the similar to 40 cm depth range of the mole from the annual temperature variation. Using published thermal conductivity and inertia values together with the diffusivities, soil densities of 1,470 and 1,730 kg/m3 were derived for these depths. The temperatures allow the deliquescence of thin films of brine, the efflorescence of which may explain the cemented duricrust observed.

Introduction: With the return of mankind to the Moon in the frame of NASA's Artemis program comes the need for detailed analyses of ambient conditions and resources like e.g. water ice in possible landing regions. There are several hints to water ice deposits within permanently shadowed regions (PSRs) in the Moon's south pole area. Some of these regions might have sufficiently low temperatures to allow the presence of water ice over geological timescales [1-4] . In fact, the LCROSS experiment showed the presence of water ice within at least one of these PSR's [5]. Intuitive Machines' first mission (IM-1) recently landed successfully in Malapert crater 300 km from the south pole. Its follow-up mission IM-2 is planned to land on the Shackleton-de Gerlache connecting ridge close to the south pole in late 2024. There, IM-2's main lander Nova-C will deploy the NASA-funded Polar Resources Ice-Mining Experiment-1 (PRIME-1) - consisting of a drill and a mass spectrometer - to search for ice deposits below the surface. [6, 7]. Nova-C will also carry a smaller vehicle, the Micro-Nova hopper, which will perform a series of short flights across the surface and land in a PSR. The hopper's payload consists of a set of cameras, a neutron spectrometer (PLWS), and the Lunar RADiometer (LRAD).The LRAD Instrument: The Lunar Radiometer's purpose is to measure the surface brightness temperature inside a PSR, thus providing ground truth for thermophysical models of the south polar region. Specifically, LRAD measures the radiative flux in the thermal infrared range [8, 9, 10]. To that end it houses six thermopile sensors, equipped with individual IR-filters to fulfill specific scientific measurement goals. These are: Determination of surface brightness temperature in the illuminated and shadowed terrain. Determination of the mm to cm-scale surface roughness. Determination of surface thermal inertia. The thermopile sensors are situated inside the sensor head having a radiation shield, reflective coating and heaters for temperature control. To decouple the sensor head thermally from the rest of the hopper, the head is attached to the hopper using PEEK brackets. (Fig. 1) A low-thermal conductivity flex harness connects the sensor head to the avionics box. Figure 1: LRAD's components during a vibration test. Left: Sensor head and PEEK mounting brackets. Right: Avionics box. Sensor head and avionics box are connected via a low-thermal conductivity flex harness. (© DLR (CC BY-NC-ND 3.0))Calibration: We describe the relation between target temperature T and the signal voltage U by a form of the Sakuma-Hattori interpolation equationU = R * exp(- c2 /(A*T+B)) - R * exp(- c2 /(A*TS +B)) + SH*PH + Uoffwhere c2 is the second radiation constant while R, A, B, SH and Uoff are adjustable parameters. PH is the heating power used to stabilize the sensor head at the chosen setpoint, and the factor SH corrects for the instrument background radiation slightly varying with PH.LRAD underwent radiometric calibration in a small vacuum chamber equipped with a He-cooled cold head (Fig. 3 and 4). The sensor head was placed inside a temperature-controlled aluminum box representing the thermal environment while viewing a blackbody mounted to the cold head. By varying the blackbody temperature from 70-330 K and the box temperature between 200 K and 280 K the five calibration coefficients could be fitted for each thermopile channel. The estimated uncertainty of the brightness temperature measurement (using the longpass filters), including systematic disturbances, is 10 K for a target temperature of 80 K and 5 K for a target temperature of 100 K.Figure 2: Brightness temperatures inverted during calibration and deviation from blackbody temperature.Summary: As part of Intuitive Machines' second mission IM-2, LRAD will measure the brightness temperature of regolith near the lunar south pole, thus performing the first in-situ temperature measurements within a PSR. Here we report on the calibration of the instrument. Acknowledgements: LRAD is supported by the German Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by the German Bundestag. Grant: 50OW2103References: [1] Feldman, W.C., et al. (1998) Science, 281, 5382, 1496-1500[2] Hayne, P.O., et al. (2015) Icarus, 255, 58-69[3] Rubanenko, L. et al., (2019) Nat. Geosci,12, 597-601[4] Hayne, P. O., et al. (2021). Nat. Astr., 5, 169[5] Colaprete, A., et al. (2010) Science, 330, 6003, 463-468[6] Atwell, M., et al., (2020). Lunar Surface Science Workshop 2020, 6011[7] Voosen, P., et al., (2021). Science, 373, 6560, 1188-1192[8] Spohn, T., et al. (2007). Space Sci. Rev., 128, 339[9] Grott, M., et al., (2017). Space Sci Rev., 208, 413[10] Spohn, T., et al. (2018). Space Sci. Rev., 214, 96.

AbstractDiurnal and seasonal variations in soil and surface temperature measured with the thermal probe and radiometer of NASA's InSight Mars mission are reported. At a representative depth of 10–20 cm, an average temperature of 217.5 K was found, varying by 5.3–6.7 K during a sol and by 13.3 K during the seasons. From the damping of the temperature variation with depth and the phase shift, a thermal diffusivity of (3.93 0.39) × /s was derived for the upper 10 cm from the diurnal temperature variation and of (3.63 0.53) × /s for the 40 cm depth range of the mole from the annual temperature variation. Using published thermal conductivity and inertia values together with the diffusivities, soil densities of 1,470 and 1,730 kg/ were derived for these depths. The temperatures allow the deliquescence of thin films of brine, the efflorescence of which may explain the cemented duricrust observed.

Introduction: The MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) is an instrument to study the mineralogy and temperature distribution of Mercury’s surface in unprecedented detail [1]. During the nominal mission, MERTIS will map the whole surface at 500 m scale, combining a push-broom IR grating spectrometer (TIS) with a radiometer (TIR) sharing the same optics, instrument electronics, and in-flight calibration components for the whole wavelength range of 7-14µm (TIS) and 7-40µm (TIR) [1]. MERTIS successfully completed its planned tests of the Near-Earth Commissioning Phase (NECP) in November 2018 and several checkouts, collecting thousands of measurements of its internal calibration bodies and deep space. Those data show a performance comparable with ground-based measurements. Scientific data will arrive well before the 2025 arrival at Mercury. MERTIS observed the Moon on in April 2020 producing ~12k TIS observation with ~3k measurements of the Moon at various angles. Even if the Moon is 7000 farther away and half maximum temperature than Mercury during nominal operation, the signal is clearly visible and shows the excellent MERTIS TIS sensor. MERTIS archival data are stored in Planetary Data System v4 format (PDS4) [2] format, that actually describe 2 physical formats for each MERTIS channel. Each channel will be stored in Flexible Image Transport System (FITS) [3] and in pure ASCII. The Mission and the Instrument: BepiColombo [2] is a dual spacecraft mission to Mercury that has been launched in October 2018 and is jointly carried out by the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA). The spacecraft comprises two separate orbiters: the Mercury Planetary Orbiter (MPO), focused on observations of the surface and internal composition, and the Mercury Magnetospheric Orbiter (MMO), which will study the particle science in the extreme thermal environment. In addition to a suite of instruments complementary to the NASA MESSENGER mission, BepiColombo will be able to observe both the northern and southern hemispheres at high spatial resolution. BepiColombo uses an innovative solar electric propulsion system and its trajectory toward Mercury is a combination of low-thrust arcs and flybys at Earth, Venus, and Mercury. This will allow us to reach Mercury with low relative velocity. The spacecraft was successfully launched on the 20th of October 2018, 01:45 UTC, from the ESA Guiana Space Centre using an Ariane 5 rocket and will reach its mappings orbit at Mercury in 2026. The MERTIS instrument was proposed in 2003 as payload of the Mercury Planetary Orbiter spacecraft of the ESA-JAXA BepiColombo mission and the final Flight Model (FM) was delivered in 2013. MERTIS is an innovative and compact spectrometer, that combines a push-broom IR grating spectrometer (TIS) with a radiometer (TIR) with only 3kg of mass and an average 10 W power consumption [1,4]. TIS operates between 7 and 14 μm and will record the day-side emissivity spectra from Mercury, whereas TIR is going to measure the surface temperature at the day- and night side in the spectral range from 7-40 μm corresponding to temperatures from 80- 700 K. TIR is implemented by an in-plane separation arrangement, while TIS is an imaging spectrometer with an uncooled micro-bolometer array. The optical design of MERTIS combines a three-mirror anastigmatic lens (TMA) with a modified Offner grating spectrometer. A pointing device allows viewing the planet (through the planet-baffle), deep space (through the space-baffle), and two internal black bodies at 300 K and 700 K temperature, respectively. MERTIS was developed at DLR in collaboration with the Westfälische Wilhel-Universität Münster and industry partners. The MPO operational plan foreseen a 2.3 hour low eccentricity orbit that allows MERTIS to achieve its 500 meters global mapping scientific goal. As confirmed by the NASA MESSENGER mission, due to the iron-poor nature of the surface the thermal infrared is the most useful wavelength range to study Mercury’s surface composition. Silicates as well as sulfides have characteristic spectral features in this range that MERTIS can map with high signal-to-noise ratio. The MERTIS spectrometer aims to capture data on the mineralogy whereas the radiometer surveys the thermal inertia of the planet. Flyby Results: MERTIS nominal nadir viewing port (Planet View) is obstructed by the MTM (Mercury Transfer Module) during the whole cruise to Mercury, while the Space View port is unobstructed and normally used for calibration purpose. We trick MERTIS nominal observation cycle (Internal reference Blackbodies, Space, multiple Space) to acquire only from the Space port. We collect ~12k TIS observation, with more than 3000 spectra from the Moon. The acquisition campaign was split in 8 “observation”, that describe different modes of the instrument. During the Flyby the only TIS sensor binning was change to test different acquisition modes. A typical observation crossing the Moon is in Fig.1. The spectra radiance values are sharply decaying towards the Moon edges. The Moon is a much colder target than Mercury (around 400K max vs. 700K) and is it farther than the planned target distance during the nominal mission at Mercury (700.000 km vs ~1000 km ). The signal from the Moon is nevertheless clearly discernible from the background. The PI Team at DLR and Münster University is currently testing the calibration procedures and geometrical registration and on the verge to deliver the first calibrated data acquired in space to the CoI team. The final data format is still to be defined, but the data container will be the same as in the RAW level data [6] available on ESA PSA website[7]. References: [1] Hiesinger, H. and Helbert, J., Planet. Space Sci. 58, (2010). [2] NASA Planetary Data System, pds.nasa.gov [3] FITS Support Office, fits.gsfc.nasa.gov [4] Instrument User Manual (FM), MER-DLR-MA-001 (2017). [5] Python PDS4 Tools, SBN sbndev.astro.umd.edu/wiki [6] D’Amore et al, LPSC 2020, 2020LPI....51.1438D [7] European Space Agency's Planetary Science Archive (PSA) archives.esac.esa.int/psa Fig.1 left: Calibrated spectra radiance in W/(m² µm sr). right: Same spectra as in the first panel, as produced from TIS sensor (y is spatial direction , x is reversed spectral direction).

The Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is part of the ESA-JAXA BepiColombo science payload en-route to Mercury. On April 10th 2020, BepiColombo flyby the Earth and obtained data from the Moon surface at a distance of around 700,000 km. The MERTIS thermal-infrared spectrometer (TIS) operating between 7 mu m and 14 mu m recorded more than 9,600 single hyperspectral observations of the Moon through its space baffle built for deep-space calibration. MERTIS has been designed to observe the surface of Mercury at a spatial resolution more than 1000 times better and at temperatures up to 2 times greater than that of the Moon. Therefore, lunar observations present a significant challenge for the instrument and the team. The standard acquisition procedure and the operations software were adapted to obtain data during the BepiColombo cruise phase. A specific calibration procedure and spatial binning have been developed to obtain the best radiometric data from the lunar surface. The calibrated data demonstrate the exceptional performance of the instrument, developed for a very different planetary object, comparable with ground-based measurements. The observations made during the cruise phase are very promising for future observations of Mercury with the space baffle during the fifth Mercury flyby scheduled for December 2024 and the nominal nadir viewing port (planet baffle) in orbit around Mercury.

We report on the design of a new laboratory setup for testing the performance of optical and thermal sensors at temperatures ranging from 50 K to 350 K and pressures ranging from ambient atmospheric pressures down to 10-5 mbar. The system will be built around a closed-cycle cooled cryostat which houses the device under test. Optical stimuli will be provided by a calibrated selectable light source which provides collimated light from an integrating sphere or a cavity blackbody. Bandpass filters as well as imaging targets can be selected for determining the spectral response and modular transfer function. Data acquisition from the device under test will be accomplished using an automated test bench based on a custom-made FPGA interface adaption board.

The objective of this series of experiments was to support the data interpretation of short period changes in insolation of planetary bodies such as solar eclipses or transits. The temperature response of Martian regolith to the transit of Phobos has been observed by InSight and interpreted in terms of layering in the near surface [Mueller et al. 2021]. Current and future mission may observe similar transits if a suitable thermal infrared instrument is available. An opportunity to observe a similar event with the roles of Mars and Phobos switched may be the rover on the Martian Moons eXplorer (MMX) carrying the Mini-RAD radiometer [Ulamec et al. 2023]. The original mission plan did not foresee a landing on the Mars facing side, but in case the plan is revised due to the changing launch date there might be a chance. There are however open questions about the interpretation of such observations using 1D models of heat conduction [e.g. Mueller et al. 2021]. These models assume that the subsurface is a continuum, while in reality the material consists of particles that are not necessarily small compared to the characteristic depth scale (skin depth) of the material responding to the changes in insolation. The Planetary Ices Laboratory has the necessary equiment to recreate such events on Earth in form of a thermal vacuum chamber and a solar simulator (Fig. 1). The chamber walls can be cooled with liquid nitrogen and a window with mirror on the chamber ceiling allows illumination of an approximately 15 cm diameter spot by the solar simulator. For our test set-up we have placed a tray of about 38x18x2cm filled with regolith analogue material in the center of the chamber (Fig. 2) i.e. encompassing the illuminated spot. The radiometer is set up within the chamber on a rotary stage that allows to move the Field of View of the instrument along the long axis of the tray. The FoV is small enough to fall within the illuminated spot and the rotary stage allows adjustments within the running setup. A small TIR camera also observed the tray. This instrument has lower temperature resolution but provides data on temperature inhomogeneity of the sample. The general approach of simulating the eclipses was to first evacuate the chamber, either refill with 5 mbar CO2 or to leave at

Abstract The heat flow and physical properties package measured soil thermal conductivity at the landing site in the 0.03–0.37 m depth range. Six measurements spanning solar longitudes from 8.0° to 210.0° were made and atmospheric pressure at the site was simultaneously measured using InSight's Pressure Sensor. We find that soil thermal conductivity strongly correlates with atmospheric pressure. This trend is compatible with predictions of the pressure dependence of thermal conductivity for unconsolidated soils under martian atmospheric conditions, indicating that heat transport through the pore filling gas is a major contributor to the total heat transport. Therefore, any cementation or induration of the soil sampled by the experiments must be minimal and soil surrounding the mole at depths below the duricrust is likely unconsolidated. Thermal conductivity data presented here are the first direct evidence that the atmosphere interacts with the top most meter of material on Mars.

The Hayabusa2 mission provided a unique data set of asteroid Ryugu that covers a wide range of spatial scale from the orbiter remote sensing instruments to the returned samples. The MASCOT lander that was delivered onto the surface of Ryugu aimed to provide context for these data sets by producing in situ data collected by a camera (MasCam), a radiometer (MARA), a magnetometer (MasMag) and a spectrometer (MicrOmega). In this work, we evaluate the success of MASCOT as an integrated lander to bridge the gap between orbiter and returned sample analysis. We find that MASCOT’s measurements and derivatives thereof, including the rock morphology, colour in the visible wavelengths, possible meteorite analogue, density, and porosity of the rock at the landing site are in good agreement with those of the orbiter and the returned samples. However, it also provides information on the spatial scale (sub-millimetres to centimetres) at which some physical properties such as the thermal inertia and reflectance undergo scale-dependent changes. Some of the in situ observations such as the presence of clast/inclusions in rocks and the absence of fine particles at the landing site was uniquely identified by MASCOT. Thus, we conclude that the delivery of an in situ instrument like MASCOT provides a valuable data set that complements and provides context for remote sensing and returned sample analyses.

Interior exploration using Seismic Investigations, Geodesy and Heat Transport's (InSight) seismometer package Seismic Experiment for Interior Structure (SEIS) was placed on the surface of Mars at about 1.2 m distance from the thermal properties instrument Heat flow and Physical Properties Package (HP3) that includes a self‐hammering probe. Recording the hammering noise with SEIS provided a unique opportunity to estimate the seismic wave velocities of the shallow regolith at the landing site. However, the value of studying the seismic signals of the hammering was only realized after critical hardware decisions were already taken. Furthermore, the design and nominal operation of both SEIS and HP3 are nonideal for such high‐resolution seismic measurements. Therefore, a series of adaptations had to be implemented to operate the self‐hammering probe as a controlled seismic source and SEIS as a high‐frequency seismic receiver including the design of a high‐precision timing and an innovative high‐frequency sampling workflow. By interpreting the first‐arriving seismic waves as a P‐wave and identifying first‐arriving S‐waves by polarization analysis, we determined effective P‐ and S‐wave velocities of vP=119−21+45 ${v}_{P}=11{9}_{-21}^{+45}$  m/s and vS=63−7+11 ${v}_{S}=6{3}_{-7}^{+11}$  m/s, respectively, from around 2,000 hammer stroke recordings. These velocities likely represent bulk estimates for the uppermost several 10s of cm of regolith. An analysis of the P‐wave incidence angles provided an independent vP/vS ratio estimate of 1.84−0.35+0.89 $1.8{4}_{-0.35}^{+0.89}$ that compares well with the traveltime based estimate of 1.86−0.25+0.42 $1.8{6}_{-0.25}^{+0.42}$ . The low seismic velocities are consistent with those observed for low‐density unconsolidated sands and are in agreement with estimates obtained by other methods.

The near-Earth asteroid (162173) Ryugu, the target of Hayabusa2 space mission, was observed via both orbiter and the lander instruments. The infrared radiometer on the MASCOT lander (MARA) is the only instrument providing spectrally resolved mid-infrared (MIR) data, which is crucial for establishing a link between the asteroid material and meteorites found on Earth. Earlier studies revealed that the single boulder investigated by the lander belongs to the most common type found on Ryugu. Here we show the spectral variation of Ryugu's emissivity using the complete set of in-situ MIR data and compare it to those of various carbonaceous chondritic meteorites, revealing similarities to the most aqueously altered ones, as well as to asteroid (101955) Bennu. The results show that Ryugu experienced strong aqueous alteration prior to any dehydration.

The Japanese MMX sample return mission to Phobos by JAXA will carry a rover developed by CNES and DLR that will be deployed on Phobos to perform in situ analysis of the Martian moon’s surface properties. Past images of the surface of Phobos show that it is covered by a layer of regolith. However, the mechanical and compositional properties of this regolith are poorly constrained. In particular, from current remote images, very little is known regarding the particle sizes, their chemical composition, the packing density of the regolith as well as other parameters such as friction and cohesion that influence surface dynamics. Understanding the properties and dynamics of the regolith in the low-gravity environment of Phobos is important to trace back its history and surface evolution. Moreover, this information is also important to support the interpretation of data obtained by instruments onboard the main MMX spacecraft, and to minimize the risks involved in the spacecraft sampling operations. The instruments onboard the Rover are a Raman spectrometer (RAX), an infrared radiometer (miniRad), two forward-looking cameras for navigation and science purposes (NavCams), and two cameras observing the interactions of regolith and the rover wheels (WheelCams). The Rover will be deployed before the MMX spacecraft samples Phobos’ surface and will be the first rover to drive on the surface of a Martian moon and in a very low gravity environment. Graphic Abstract

The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP$^3$ to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3--5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5-6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure - as was determined through an extensive, almost two years long campaign - was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign -- described in detail in this paper -- the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole finally reached a depth of 40 cm, bringing the mole body 1--2 cm below the surface. The penetration record of the mole and its thermal sensors were used to measure thermal and mechanical soil parameters such as the thermal conductivity and the penetration resistance of the duricrust and its cohesion. The hammerings of the mole were recorded by the seismometer SEIS and the signals could be used to derive a P-wave velocity and a S-wave velocity and elastic moduli representative of the topmost tens of cm of the regolith. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly consisting of debris from a small impact crater is inferred.