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The detection and characterization of lunar resources, including water ice, is a key area of interest for a new generation of lunar missions. The electrical properties of water ice in the extremely low frequency (ELF) range support its detection by means of in-situ permittivity measurements. A new type of miniaturized subsurface permittivity sensor is presented, which is under development for the PROSPECT package on the Luna-27 lander mission. Here, the sensor concept is described, key design features are presented and possible operations modes are introduced. The expected accuracy for measurements of the relative permittivity along the borehole is ~10-15% and depends mainly on the accuracy of borehole geometry models. Laboratory test results from a prototype sensor on a water ice / simulant mixture at cryogenic temperatures are presented, demonstrating the capability to detect water ice at 125 K. The improved capabilities of the flight design are discussed, operational modes are explained and alternative electrode configurations for lunar landers and rovers are proposed.

Planetary sciences is an exciting part of astronomy, and even though space missions are nowadays providing high-quality data from remote and in-situ measurements of the planets, asteroids and comets, ground-based observations are still yielding exciting results by providing crucial data sets for a better understanding of the diverse bodies in the Solar System. The discovery of thousands of exoplanetary systems during the last few decades further enhances the need for ground-based observations, collaboration between small telescope facilities and for strengthening the contribution of amateur astronomers to planetary sciences. Access to the Europlanet Telescope Network As part of the recently launched Europlanet 2024 Research Infrastructure (EPN 2024 RI; https://bit.ly/2Z1XA8u), a new collaboration between telescopes around the world has been started for providing coordinated observations and rapid responses in support of space missions and in following-up of new events. The so-called Europlanet Telescope Network (https://bit.ly/37SCiyj) will thereby provide professional scientists and amateur astronomers with access to an initial set of 16 telescope facilities (see Fig. 1) up to 2 m in diameter. While the network plans to draw in additional facilities and to build new collaborations, particularly in regions that are currently under-represented in planetary sciences, scientists and amateurs can now apply to visit those facilities that are already participating in the network and have their expenses reimbursed for the time needed to make their observations. This also comprises the possibility of remote observations since the network includes some robotic or remotely operated facilities. The Call for Observations (see website: https://bit.ly/2Br5LDt) runs from June 2020 until the end of 2023, and is coordinated through EPN 2024 RI, which is funded by the European Commission’s Horizon 2020 program. Fig. 1: The Europlanet Telescope Network (see also Section The Telescopes). Supporting Amateur Astronomers Besides fostering collaboration and providing access to small telescope facilities, the Europlanet Telescope Network also plans to support the integration of amateur astronomers into planetary sciences, since their observations can be of crucial importance for several scientific areas. Planetary atmospheres, for instance, is a field that benefits intensively from amateur astronomers. Their regular observations at high-spatial resolution are used by researchers to perform detailed studies of the atmosphere dynamics of Jupiter and Saturn and surveys of atmospheric activity on Neptune. They also provide excellent coverage of dust storms on Mars and complementary observations of Venus to space missions that observe over different viewing geometries. The accumulated observing time provided by amateurs makes it likely that unexpected events (such as convective storms on Jupiter and Saturn; impacts on Jupiter) are discovered by amateurs faster than by orbiting spacecraft or regular ground-based observation programs. Many amateurs supply their data to public data repositories that cover multiple planets like ALPO-Japan (http://alpo-j.sakura.ne.jp) or PVOL (http://pvol2.ehu.es/pvol2) on a daily basis, resulting in extremely fast follow-ups of interesting events. Space missions like NASA’s Juno keep excellent interactions with amateur astronomers that provide a large amount of observations to the mission through a dedicated website (https://www.missionjuno.swri.edu/junocam) used by Juno’s scientists to target some of their high-resolution observations. Advanced asteroid studies by using the GaiaGOSA web service (gaiagosa.eu) is another important example on how amateur observers can help planetary scientists. The photometric observations of asteroids provided by amateurs are essential for the determination of rotation periods. Data gathered from a few oppositions allow to determine detailed physical parameters that are crucial for determining the nature of these particular objects such as spin axis orientation, shape, and size, but also for verifying our understanding of the history of the Solar System. Recently, the data gathered by amateur observers helped to determine more precise shapes and volumes of 13 asteroids (Podlewska-Gaca et al., 2020, A&A, id.A11; see also Fig. 2) and to reveal the true nature of asteroid (10) Hygiea, which turned out to be a perfect candidate for a dwarf planet rather than an asteroid (Vernazza et al., 2020, Nature Astr., 136-141). Fig. 2: The shape of (68) Leto asteroid determined with help of GaiaGOSA observers. The Telescopes (Fig. 1): Pic du Midi Observatory, France: 1.06-m telescope Moletai Astronomical Observatory, Lithuania: 1.65-m and 35/51-cm telescopes Kryoneri Observatory, Greece: 1.2-m telescope Skalnate Pleso Observatory, Slovakia: 1.3-m and 61-cm telescopes Faulkes Telescope Project: two 2-m, nine 1-m, and ten 40-cm robotic telescopes Tartu Observatory, Estonia: 1.5-m and 60-cm telescopes, and 30-cm robotic telescope Danish 1.54-m telescope at La Silla Observatory, Chile: 1.54-m telescope Beacon Observatory, UK: 42-cm telescope Observatorie del Teide, Spain: 82-cm and 45-cm telescopes Calar Alto Observatory, Spain: 1.23-m telescope Lisnyky Observation Station, Ukraine: 70-cm telescope Chuguev Observatory, Ukraine: 70-cm telescope Terskol Peak Observatory, Ukraine: 2-m and 60-cm telescopes Konkoly Observatory, Hungary: 1-m and 80-cm telescopes Ussuriysk Astrophysical Observatory, Russia: 25-cm and 50-cm telescopes Rozhen Observatory, Bulgaria: 2-m, 60-cm, and 50/70-cm telescopes Further information available at https://bit.ly/2Br5LDt. Acknowledgements: Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

The NASA InSight Mission is expected to be launched in 2018 after the initial date of the launch in 2016 had to be postponed due to technical problems. The major tasks of the InSight Mission will be to investigate the appearance of tectonic activity, as well as to obtain more accurate information on the interior structure of Mars and the detection of the inner heat flow that is created by the core. Therefor, a seismometer (SEIS) and a heat flow probe (HP3) will be placed by the InSight lander onto the surface of the planet. The HP3 will penetrate 3 - 5 metres deep into the ground of Mars to avoid the influence of the solar radiation on the heat flow measurement and to allow measurement of the temperature gradient using thermal sensors on the trailing cable at different depths. The penetration process will be used additionally to investigate the mechanical behaviour of the soil by measuring the displacement of the probe after a set of strokes. The dynamics of the hammering mechanism and its penetration performance is dependent on the soil behaviour. Therefore, a coupled simulation of the hammer mechanism and the soil response is used to investigate the behaviour of the soil and the performance of the HP3. The simulation is done by the use of the Discrete Element Method (DEM) which allows to simulate both the hammering and penetration in one model, where the coupling is done by velocity and force exchange. The simulation model is used to investigate the densification of the soil due to the dynamic penetration process, to determine the displacement of the probe and to investigate the influence of confining boundaries, which are unavoidable in laboratory tests. The use of the DEM allows to investigate the behaviour at the particle level, so that the simulations provide insights in the soil behaviour at micro-scale, e.g. the force chains transmitting the applied load to the soil or the track of the particles during the penetration.

The NASA InSight mission will provide an opportunity for soil investigations using the penetration data of the heat flow probe built by the German Aerospace Center DLR. The Heat flow and Physical Properties Probe (HP^3) will penetrate 3 to 5 meter into the Martian subsurface to investigate the planetary heat flow. The measurement of the penetration rate during the insertion of the HP3 will be used to determine the physical properties of the soil at the landing site. For this purpose, numerical simulations of the penetration process were performed to get a better understanding of the soil properties influencing the penetration performance of HP^3. A pile driving model has been developed considering all masses of the hammering mechanism of HP^3. By cumulative application of individual stroke cycles it is now able to describe the penetration of the Mole into the Martian soil as a function of time, assuming that the soil parameters of the material through which it penetrates are known. We are using calibrated materials similar to those expected to be encountered by the InSight/HP^3 Mole when it will be operated on the surface of Mars after the landing of the InSight spacecraft. We consider various possible scenarios, among them a more or less homogeneous material down to a depth of 3–5 m as well as a layered ground, consisting of layers with different soil parameters. Finally we describe some experimental tests performed with the latest prototype of the InSight Mole at DLR Bremen and compare the measured penetration performance in sand with our modeling results. Furthermore, results from a 3D DEM simulation are presented to get a better understanding of the soil response.

Several planetary lander missions conducted in the past and planned for the near future have instruments on board, which are dedicated to the determination of various material properties, among them mechanical properties of the surface like material strength and penetration resistance. In this paper two instruments are considered in more detail: (i) the MUPUS penetrator, a device aboard the Lander Philae of ESA׳s Rosetta mission, and (ii) the Mole HP 3 , which is part of the payload of NASA׳s next Discovery mission InSight , due for landing on Mars in 2016. Both devices are driven by hammering mechanisms designed to work under low or micro-gravity conditions and blaze themselves a trail into the subsurface of their respective target bodies. Naturally the speed with which this process takes place and if penetration is possible at all depends on the mechanical properties of the soil. However, a quantitative evaluation of soil mechanical parameters from measured depth-versus-time data is not a straightforward task. In this paper we apply an old technique, originally developed for modelling the driving of a pile into the ground, to describe the performance of penetrators and Moles developed for planetary applications. The numerical pile driving model of Smith (1962) is scaled and adapted for this purpose and used to predict the penetration behaviour of these instruments in dependence of their internal construction and the properties of the soil they are driven in. The model computes the permanent set of the surrounding soil in response to one hammer blow cycle as well as the oscillations and waves excited inside the devices and in the surrounding soil. Both the penetration resistance of the tip and the resistance caused by friction of the penetrator along the cylindrical side wall are calculated. By comparing the modelling results with previous laboratory measurements it is demonstrated that the models produce realistic results and can be used both as tools for proper design of future penetration devices and for the evaluation of soil-mechanical properties from measured penetration data. The most sensitive soil parameter controlling penetration progress per stroke is the ultimate static bearing capacity of the ground. Although the method used for our calculations is essentially the same as that applied by Smith (1962) for describing the behaviour of long and heavy piles in geotechnical engineering, it is found that the penetration process for such small and light weight systems takes place in a quite different way. While for the former secondary oscillations are irrelevant for the determination of the permanent set caused by one stroke, in the latter the penetration in response to one hammer stroke takes place in many small increments, until a stable depth is reached. Our model describes the full dynamic behaviour of the system over an arbitrary time span and has the potential to be adapted to systems with other geometrical dimensions and masses, as long as the diameter/length ratio of the probe remains reasonably small.

European Space Agencies fifth cornerstone mission BepiColombo includes a ‘Surface Element’ to land a scientific payload on the surface of Mercury. The current strawman payload includes a heat flow and physical properties package (HP3), focussing on key thermal and mechanical properties of the near-surface material (down to a depth of 2– 5 m ) and the measurement of heat flow from Mercury's interior, an important constraining parameter for models of the planet's interior and evolution. We present here an overview of the HP3 experiment package and its possible accommodation in a self-inserting ‘mole’ device. A mole is considered to be the most appropriate deployment method for HP3, at least in the currently-assumed case of an airbag-assisted soft landing architecture for the Mercury Surface Element.

In the years 2011–2013 the ESA mission Rosetta will explore the short period comet 46P/Wirtanen. The aims of the mission include investigation of the physical and chemical properties of the cometary nucleus and also the evolutionary processes of comets. It is planned to land a small probe on the surface of the comet, carrying a multitude of sensors devoted to in situ investigation of the material at the landing site. On touchdown at the nucleus, an anchoring harpoon will be fired into the surface to avoid a rebound of the lander and to supply a reaction force against mechanical operations such as sample drilling or instrument platform motion. The anchor should also prevent an ejection of the lander due to gas drag from sublimating volatiles when the comet becomes more active closer to the Sun. In this paper, we report on the development of one of the sensors of the MUPUS instrument aboard the Rosetta Lander, the MUPUS ANC-M (mechanical properties) sensor. Its purpose is to measure the deceleration of the anchor harpoon during penetration into the cometary soil. First the test facilities at the Max-Planck-Institute for Extraterrestrial Physics in Garching, Germany, are briefly described. Subsequently, we analyse several accelerometer signals obtained from test shots into various target materials. A procedure for signal reduction is described and possible errors that may be superimposed on the true acceleration or deceleration of the anchor are discussed in depth, with emphasis on the occurrence of zero line offsets in the signals. Finally, the influence of high-frequency resonant oscillations of the anchor body on the signals is discussed and difficulties faced when trying to derive grain sizes of granular target materials are considered. It is concluded that with the sampling rates used in this and several other space experiments currently under way or under development a reasonable resolution of strength distribution in soil layers can be achieved, but conclusions concerning grain size distribution would probably demand much higher sampling rates.

In recent years the exploration of planetary bodies by surface probes has entered a new phase of interest. The mechanical properties of the near-surface layers of cometary and planetary bodies, including their strength, texture and layering, are important parameters needed both for a proper physical understanding of these bodies and for the design of lander missions. The strength properties of such a surface can be determined either by measuring the penetration resistance encountered by a slowly penetrating tip (quasi-static penetrometry), or by impacting the surface with an artificial body whose mechanical properties and impact velocity are known. At low speeds (up to about 300 m s −1 ), it is often feasible to measure the force or deceleration during penetration (‘impact’ or ‘dynamic’ penetrometry). If the event is better described in terms of hypervelocity impact cratering than penetration, analysis of the resulting crater is performed instead. Other uses of artificial impacts include the generation of seismic waves to aid the calibration of seismometers and the formation of a crater and / or ejecta for analysis or sampling of the target body. Such methods feature in many recent, current and forthcoming planetary missions. Examples include: the Surface Science Package of the Huygens probe, the anchoring harpoon of the Rosetta Lander , various Mars penetrators and landers, NASA's Deep Impact mission and ESA's planned Mercury cornerstone mission BepiColombo . A short overview of missions (past, present, future) featuring penetrometry experiments or artificial impacts is given. The theory of impact penetration and methods to interpret deceleration profiles in terms of material strength are discussed and applied to data sets obtained from test shots performed with the Rosetta Lander anchoring harpoon.

Owing to the low surface gravity of the Rosetta target comet 46P/Wirtanen, a means of anchoring the Rosetta Lander to the cometary surface will be necessary. This task can be accomplished by firing an anchor into the cometary soil immediately after touchdown to prevent a rebound of the spacecraft from the surface or subsequent ejection by other forces, and to allow for mechanical activities (drilling, etc.) at the landing site. The rationale for anchoring is examined, based on estimates of the main forces likely to act on the spacecraft after landing. We report on the development of an anchoring device using a pyrotechnic gas generator as a power source and an instrumented anchor. In addition to the anchoring function, which is the primary purpose of this system, the integration of acceleration and temperature sensors into the tip offers the possibility to determine some important material properties of the cometary surface layer. The accelerometer is designed to measure the deceleration history of the projectile and is thus expected to give information on how the material properties (in particular strength) change within the penetrated layer(s), while the temperature sensor will measure temperature variations at the depth at which the anchor finally comes to rest. As the mechanical properties of the material are not known, it is difficult to predict the final depth of the anchor with any great certainty, but it may well be greater than that reached by any other of the lander's instruments. The instrumented anchor will be part of the MUPUS experiment, selected to form part of the Rosetta Lander payload. We report on results of laboratory simulations of anchor penetration performed at the Institut fur Weltraumforschung, Graz, and compare these with models of projectile penetration. The value of the results expected from the penetrometry experiment in the context of an improved understanding of cometary processes is discussed.

Thermal and mechanical properties of cometary ices are closely associated with each other. Both are largely determined by the texture (porosity, grain size distribution, grade of sintering) of the material. The surface probe of the Rosetta mission to comet 46P/Wirtanen (Rosetta Lander) will for the first time measure these thermo-mechanical key parameters in situ, using a hammering device, a drill, and anchors to be shot into the ground by pyrotechnical means. Several of these components are associated to the experiment MU PUS (MU lti-PU rpose-S ensors for surface and subsurface science). The development of this instrument has now reached a mature state, as the flight model is already delivered and integrated with the spacecraft. We describe the main aspects of the experiment, outline the evaluation methods, and show representative results from test measurements.