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The Heat Flow and Physical Properties Package HP 3 for the InSight mission will attempt the first measurement of the planetary heat flow of Mars. The data will be taken at the InSight landing site in Elysium planitia (136  ∘ E, 5  ∘ N) and the uncertainty of the measurement aimed for shall be better than ±5 mW m −2 . The package consists of a mechanical hammering device called the “Mole” for penetrating into the regolith, an instrumented tether which the Mole pulls into the ground, a fixed radiometer to determine the surface brightness temperature and an electronic box. The Mole and the tether are housed in a support structure before being deployed. The tether is equipped with 14 platinum resistance temperature sensors to measure temperature differences with a 1- σ uncertainty of 6.5 mK. Depth is determined by a tether length measurement device that monitors the amount of tether extracted from the support structure and a tiltmeter that measures the angle of the Mole axis to the local gravity vector. The Mole includes temperature sensors and heaters to measure the regolith thermal conductivity to better than 3.5% (1- σ ) using the Mole as a modified line heat source. The Mole is planned to advance at least 3 m—sufficiently deep to reduce errors from daily surface temperature forcings—and up to 5 m into the martian regolith. After landing, HP 3 will be deployed onto the martian surface by a robotic arm after choosing an instrument placement site that minimizes disturbances from shadows caused by the lander and the seismometer. The Mole will then execute hammering cycles, advancing 50 cm into the subsurface at a time, followed by a cooldown period of at least 48 h to allow heat built up during hammering to dissipate. After an equilibrated thermal state has been reached, a thermal conductivity measurement is executed for 24 h. This cycle is repeated until the final depth of 5 m is reached or further progress becomes impossible. The subsequent monitoring phase consists of hourly temperature measurements and lasts until the end of the mission. Model calculations show that the duration of temperature measurement required to sufficiently reduce the error introduced by annual surface temperature forcings is 0.6 martian years for a final depth of 3 m and 0.1 martian years for the target depth of 5 m.

The physical properties of cometary nuclei observed today relate to their complex history and help to constrain their formation and evolution. In this article, we review some of the main physical properties of cometary nuclei and focus in particular on the thermal, mechanical, structural and dielectric properties, emphasising the progress made during the Rosetta mission. Comets have a low density of 480 ± 220 kg m − 3 and a low permittivity of 1.9–2.0, consistent with a high porosity of 70–80%, are weak with a very low global tensile strength < 100  Pa, and have a low bulk thermal inertia of 0 – 60 J K − 1 m − 2 s − 1 / 2 that allowed them to preserve highly volatiles species (e.g. CO, CO 2 , CH 4 , N 2 ) into their interior since their formation. As revealed by 67P/Churyumov-Gerasimenko, the above physical properties vary across the nucleus, spatially at its surface but also with depth. The broad picture is that the bulk of the nucleus consists of a weakly bonded, rather homogeneous material that preserved primordial properties under a thin shell of processed material, and possibly covered by a granular material; this cover might in places reach a thickness of several meters. The properties of the top layer (the first meter) are not representative of that of the bulk nucleus. More globally, strong nucleus heterogeneities at a scale of a few meters are ruled out on 67P’s small lobe.

Thermal and mechanical material properties determine comet evolution and even solar system formation because comets are considered remnant volatile-rich planetesimals. Using data from the Multipurpose Sensors for Surface and Sub-Surface Science (MUPUS) instrument package gathered at the Philae landing site Abydos on comet 67P/Churyumov-Gerasimenko, we found the diurnal temperature to vary between 90 and 130 K. The surface emissivity was 0.97, and the local thermal inertia was 85 ± 35 J m −2 K −1 s -1/2 . The MUPUS thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength. A sintered near-surface microporous dust-ice layer with a porosity of 30 to 65% is consistent with the data.

Red clover leaves accumulate high levels (up to 1 to 2% of dry matter) of two caffeic acid derivatives: phaselic acid (2- O -caffeoyl-L-malate) and clovamide [ N -caffeoyl-L-3,4-dihydroxyphenylalanine (L-DOPA)]. These likely play roles in protecting the plant from biotic and abiotic stresses but can also help preserve protein during harvest and storage of the forage via oxidation by an endogenous polyphenol oxidase. We previously identified and characterized, a hydroxycinnamoyl-coenzyme A (CoA):malate hydroxycinnamoyl transferase (HMT) from red clover. Here, we identified a hydroxycinnamoyl-CoA:L-DOPA hydroxycinnamoyl transferase (HDT) activity in unexpanded red clover leaves. Silencing of the previously cloned HMT gene reduced both HMT and HDT activities in red clover, even though the HMT enzyme lacks HDT activity. A combination of PCR with degenerate primers based on BAHD hydroxycinnamoyl-CoA transferase sequences and 5′ and 3′ rapid amplification of cDNA ends was used to clone two nearly identical cDNAs from red clover. When expressed in Escherichia coli , the encoded proteins were capable of transferring hydroxycinnamic acids ( p -coumaric, caffeic, or ferulic) from the corresponding CoA thioesters to the aromatic amino acids L-Phe, L-Tyr, L-DOPA, or L-Trp. Kinetic parameters for these substrates were determined. Stable expression of HDT in transgenic alfalfa resulted in foliar accumulation of p -coumaroyl- and feruloyl-L-Tyr that are not normally present in alfalfa, but not derivatives containing caffeoyl or L-DOPA moieties. Transient expression of HDT in Nicotiana benthamiana resulted in the production of caffeoyl-L-Tyr, but not clovamide. Coexpression of HDT with a tyrosine hydroxylase resulted in clovamide accumulation, indicating the host species’ pool of available amino acid (and hydroxycinnamoyl-CoA) substrates likely plays a major role in determining HDT product accumulation in planta. Finally, that HDT and HMT proteins share a high degree of identity (72%), but differ substantially in substrate specificity, is promising for further investigation of structure-function relationships of this class of enzymes, which could allow the rational design of BAHD enzymes with specific and desirable activities.

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. Spectral characteristics can be used to link asteroid and meteorite materials. Here, the authors show in-situ mid-infrared data of a boulder on asteroid Ryugu, compared with laboratory spectra of various meteorites, indicate that Ryugu experienced strong aqueous alteration prior to dehydration.

The MASCOT radiometer MARA is a multi-spectral instrument which measures net radiative flux in six wavelength bands. MARA uses thermopile sensors as sensing elements, and the net flux between the instrument and the surface in the 18 ∘ field of view is determined by evaluating the thermoelectric potential between the sensors’ absorbing surface and the thermopile’s cold-junction. MARA houses 4 bandpass channels in the spectral range of 5.5–7, 8–9.5, 9.5–11.5, and 13.5–15.5 μm, as well as one long-pass channel, which is sensitive in the > 3 μm range. In addition, one channel is similar to that used by the Hayabusa 2 orbiter thermal mapper, which uses a wavelength range of 8–12 μm. The primary science objective of the MARA instrument it the determination of the target asteroid’s surface brightness temperature, from which surface thermal inertia can be derived. In addition, the spectral bandpass channels will be used to estimate the spectral slope of the surface in the thermal infrared wavelength range. The instrument has been calibrated using a cavity blackbody, and the temperature uncertainty is 1 K in the long pass channel for target temperatures of > 173 K . Measurement uncertainty in the spectral bandpasses is 1 K for target temperatures above 273 K.

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. Plain Language Summary A soil's ability to transport heat is a fundamental parameter that holds information on quantities like soil bulk porosity, composition, grain size, and the state of cementation or induration. In the soil, heat is transported through grain‐to‐grain contacts as well as through the pore filling CO2 gas. The heat flow and physical properties package (HP3) of the InSight Mars mission measured soil thermal conductivity at the landing site repeatedly over the course of a martian year. As atmospheric pressure changes between seasons due to the redistribution of CO2 across the planet, we found that soil thermal conductivity also changes. Thermal conductivity increased for increased atmospheric pressure, a behavior typical for unconsolidated material. This implies that the amount of cement or induration of the sampled soil must be minimal. Key Points We measured thermal conductivity of the martian soil and found that its conductivity strongly correlates with atmospheric pressure We conclude that heat conduction through the pore‐filling gas is significant and that cementation of the soil must be minimal Our data show that the atmosphere directly interacts with the top most meter of material on Mars

Lunar heat flow was determined in situ during the Apollo 15 and 17 missions, but some uncertainty is connected to the value of the regolith's thermal conductivity, which enters as a linear factor into the heat flow calculation. Different approaches to determine the conductivity yielded discordant results, which led to a downward correction of the obtained heat flow values by 30%–50% subsequent to the publication of the first results. We have reinvestigated likely causes for the observed discrepancies and find that neither poor coupling between the probe and regolith nor axial heat loss can explain the obtained results. Rather, regolith compaction and compression likely caused a local increase of the regolith's thermal conductivity by a factor of 2–3 in a region which extends at least 2–5 cm from the borehole wall. We conclude that the corrected lunar heat flow values, which are based on thermal diffusivity estimates sampling a large portion of undisturbed regolith, represent robust results. Future in situ measurements of regolith thermal conductivity using active heating methods should take care to both minimize regolith disturbance during probe emplacement and maximize heating time to obtain reliable results. We find that for the Apollo measurements, heating times should have exceeded at least 100 h, and ideally 200 h.

The miniRAD radiometer is one of the payloads of the Idefix rover on the MMX mission to Phobos. It is a multispectral instrument which measures the infrared radiative flux in six wavelength channels between 4.7 and 100 µm using single-element thermopile detectors. MiniRAD is equipped with optical filters, one centered at 5.5 µm, three narrow bandpass filters at 8.3 µm, 8.9 µm, and 9.5 µm and two longpass filters with cut-ons at 14–15 µm. One of the longpass filters made from boron nitride (BN) is especially optimized for very low flux, being sensitive in the very long wavelength region even beyond 50 µm. The main measurement objective of the miniRAD instrument is the determination of Phobos’ surface brightness temperature during nighttime, from which the thermal inertia of the surface can be derived. Secondary objectives are to provide constraints on the slope of the emissivity in the thermal infrared, the location of the Christiansen feature, and the surface roughness of Phobos. MiniRAD has been calibrated radiometrically under relevant environmental conditions using a cavity blackbody over the full expected range of object temperatures from 100 to 330 K. The predicted uncertainty of the brightness temperature is < 1 K at dayside temperatures > 270 K for all channels, while the BN filter uncertainty is < 5 K at the lowest calibration temperature of 100 K.

Diurnal and seasonal variations in soil and surface temperature measured with the HP3${\\mathrm{H}\\mathrm{P}}^{3}$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 ±$\\pm $  0.39) × 10−8${10}^{-8}$m2${\\mathrm{m}}^{2}$ /s was derived for the upper ∼${\\sim} $ 10 cm from the diurnal temperature variation and of (3.63 ±$\\pm $  0.53) × 10−8${10}^{-8}$m2${\\mathrm{m}}^{2}$ /s for the ∼${\\sim} $ 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${m}^{3}$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. Plain Language Summary Temperature is an important factor in understanding the physical properties of Martian soil. It determines how quickly physical processes and chemical reactions occur, including the transport of heat and materials. Temperature is crucial to astrobiology because it affects the habitability of the soil and the potential for water or brine to support microbial life. We measured the temperature in the soil during several Martian days and over a Martian year using the NASA InSight Mars mission's Heat Flow and Physical Properties Package. The average temperature was −56°C (217.5 K) over the depth extent of the thermal probe, which was about 40 cm. The temperature varied by 5–7° during the day, which is only a tenth of the daily surface temperature variation. It varied by 13° during the seasons. The temperature is subfreezing for water, but it allows the formation of thin films of salty brine for 10 hr or more during a Martian day. The solidification of the brine is a likely explanation for the observed few tens of centimeters thick duricrust, a layer of consolidated, cohesive sand, which is thought to have hampered the penetration to greater depth of the mission's thermal probe. Key Points We measured the temperature and its diurnal and annual variations in the top 40 cm of the Martian soil at the InSight landing site The soil thermal diffusivity was calculated from the diurnal and seasonal surface and soil temperature variations The soil temperature allows the formation of thin films of brine; their efflorescence may explain the formation of the observed duricrust