A heat flow and physical properties package for the surface of Mercury

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.     

Photometry and bulk physical properties of Solar System surfaces icy analogs: The Planetary Ice Laboratory at University of Bern

We have designed and constructed an original facility to characterize the VIS–NIR Bidirectional Reflectance Distribution Function (BRDF) and some complementary bulk physical properties of planetary analog samples containing water ice. The central part of the facility is a highly accurate gonio-radiometer (PHIRE-2) operating in the VIS–NIR spectral range (400–1100 nm) installed in a large laboratory freezer. Its development was based on the experience gained on the gonio-radiometer PHIRE-1 (Gunderson et al., 2006). The PHIRE-1 design was modified to permit operations at sub-zero temperatures and to optimize the performance of the instrument. The photometric measurements are complemented by a detailed simultaneous characterization of the physical state and possible temporal evolution of the samples using a combination of macro- and micro-imaging, thermal, electrical and sample mass measurements. The modified design will support the interpretation of current and future remote sensing and in-situ datasets on icy planetary objects with a special emphasis on cometary nuclei, Martian polar regions and Jovian satellites.     

Simulating Martian regolith in the laboratory

Regolith and dust cover the surfaces of the Solar Systems solid bodies, and thus constitute the visible surface of these objects. The topmost layers also interact with space or the atmosphere in the case of Mars, Venus and Titan. Surface probes have been proposed, studied and flown to some of these worlds. Landers and some of the mechanisms they carry, e.g. sampling devices, drills and subsurface probes (“moles”) will interact with the porous surface layer. The absence of true extraterrestrial test materials in ample quantities restricts experiments to the use of soil or regolith analogue materials. Several standardized soil simulants have been developed and produced and are commonly used for a variety of laboratory experiments. In this paper we intend to give an overview of some of the most important soil simulants, and describe experiments (penetrometry, thermal conductivity, aeolian transport, goniometry, spectroscopy and exobiology) made in various European laboratory facilities.     

Duration and extent of lunar volcanism: Comparison of 3D convection models to mare basalt ages

It is widely accepted that lunar volcanism started before the emplacement of the mare fills ( b.p.) and lasted for probably more than 3.0 Ga. While the early volcanic activity is relatively easy to understand from a thermal point of view, the late stages of volcanism are harder to explain, because a relatively small body like the Earth's Moon is expected to cool rapidly and any molten layer in the interior should solidify rather quickly. We present several thermal evolution models, in which we varied the boundary conditions at the model surface in order to evaluate the influence on the extent and lifetime of a molten layer in the lunar interior. To investigate the influence of a top insulating layer we used a fully three-dimensional spherical shell convection code for the modelling of the lunar thermal history. In all our models, a partial melt zone formed nearly immediately after the simulation started (early in lunar history), consistent with the identification of lunar cryptomare and early mare basalt volcanism on the Moon. Due to the characteristic thickening of the Moon's lithosphere the melt zone solidified from above. This suggests that the source regions of volcanic rock material proceeded to increasing depth with time. The rapid growth of a massive lithosphere kept the Moon's interior warm and prevented the melt zone from fast freezing. The lifetimes of the melt zones derived from our models are consistent with basalt ages obtained from crater chronology. We conclude that an insulating megaregolith layer is sufficient to prevent the interior from fast cooling, allowing for the thermal regime necessary for the production and eruption of young lava flows in Oceanus Procellarum.     

Measuring Thermo-Mechanical Properties of Cometary Surfaces: In Situ Methods

Thermal and mechanical properties of cometary ices are closely associated with eachother. 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 comet46P/Wirtanen (Rosetta Lander) will for the first time measure these thermo-mechanical keyparameters in situ, using a hammering device, a drill, and anchors to be shot intothe ground by pyrotechnical means. Several of these components are associated to theexperiment MUPUS (MUlti-PUrpose-Sensors forsurface and sub-surface science). The development of this instrument has now reached amature state, as the flight model is already delivered and integrated with thespacecraft. We describe the main aspects of the experiment, outline the evaluationmethods, and show representative results from test measurements.