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MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) observations suggest that sulfur‐bearing minerals are key components of Mercury's surface. These minerals have been proposed to explain the strong concave downward curvature between 300 and 600 nm in MESSENGER reflectance spectra of the hollows. We investigated the spectral curvature of the entire surface of Mercury and its relationship with surface temperature. High spectral curvatures map the youngest terrains: hollows, bright spots and very bright craters within the Mercury cold poles. These results demonstrate that freshly exposed materials are spectrally similar to hollows‐forming material and sulfides. High spectral curvature is muted by thermal processing near Mercury's hot poles. The optical effect of thermal weathering that we observed on Mercury are consistent with laboratory measurements on weathered CaS and includes a flattening of the reflectance in the visible. This suggests Mercury's crustal composition to be rich in sulfur‐bearing minerals. Plain Language Summary Reflectance measurements are used to investigate the composition, alteration and physical properties of planetary surfaces. On Mercury, spectroscopic observations from previous missions lack asbsorption features to identified minerals. However, the overall shape of the spectrum in the near‐ultraviolet to near‐infrared is used to differentiate the different terrains types and spectral units. Here, we investigated the spectral curvature—that is, the concavity ‐ of Mercury in the near‐ultraviolet to visible. We found that the temperature and aging of the surface strongly alter this spectral property previously related to surface composition only. Key Points The highest values of spectral curvature between 300 and 600 nm map the youngest geological features of Mercury The spectral curvature on Mercury is well preserved near the cold poles and affected by thermal weathering near the hot poles

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.

Launched onboard the BepiColombo Mercury Planetary Orbiter (MPO) in October 2018, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is on its way to planet Mercury. MERTIS consists of a push-broom IR-spectrometer (TIS) and a radiometer (TIR), which operate in the wavelength regions of 7-14 μm and 7-40 μm, respectively. This wavelength region is characterized by several diagnostic spectral signatures: the Christiansen feature (CF), Reststrahlen bands (RB), and the Transparency feature (TF), which will allow us to identify and map rock-forming silicates, sulfides as well as other minerals. Thus, the instrument is particularly well-suited to study the mineralogy and composition of the hermean surface at a spatial resolution of about 500 m globally and better than 500 m for approximately 5-10% of the surface. The instrument is fully functional onboard the BepiColombo spacecraft and exceeds all requirements (e.g., mass, power, performance). To prepare for the science phase at Mercury, the team developed an innovative operations plan to maximize the scientific output while at the same time saving spacecraft resources (e.g., data downlink). The upcoming fly-bys will be excellent opportunities to further test and adapt our software and operational procedures. In summary, the team is undertaking action at multiple levels, including performing a comprehensive suite of spectroscopic measurements in our laboratories on relevant analog materials, performing extensive spectral modeling, examining space weathering effects, and modeling the thermal behavior of the hermean surface.

C-type asteroids are among the most pristine objects in the Solar System, but little is known about their interior structure and surface properties. Telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. This includes observations of C-type asteroid (162173) Ryugu1–3. However, on arrival of the Hayabusa2 spacecraft at Ryugu, a regolith cover of sand- to pebble-sized particles was found to be absent4,5 (R.J. et al., manuscript in preparation). Rather, the surface is largely covered by cobbles and boulders, seemingly incompatible with the remote-sensing infrared observations. Here we report on in situ thermal infrared observations of a boulder on the C-type asteroid Ryugu. We found that the boulder’s thermal inertia was much lower than anticipated based on laboratory measurements of meteorites, and that a surface covered by such low-conductivity boulders would be consistent with remote-sensing observations. Our results furthermore indicate high boulder porosities as well as a low tensile strength in the few hundred kilopascal range. The predicted low tensile strength confirms the suspected observational bias6 in our meteorite collections, as such asteroidal material would be too frail to survive atmospheric entry7.The MASCOT lander observed a boulder on the surface of asteroid Ryugu up close. The boulder’s low thermal inertia is closer to fine regolith or comets rather than stony boulders, indicating high porosity and low tensile strength. Orbit measurements confirm that Ryugu’s surface is covered with similar boulders.

Solar System bodies undergo to daily and periodical variations of temperature that mainly depend on their closeness to the Sun. It is known that mineral expansion and contraction due to such variations modify the thermal infrared spectra acquired on solid surfaces. Therefore, it becomes crucial to know the best temperature range at which the acquisition itself should be carried out to get reliable information on the mineralogy of such bodies. Here we provide the thermal expansion of olivine between 20 and 298 K determined by X-ray diffraction. Our data reveal the non-linear behaviour of silicates that undergo to low temperatures, where volume variations appear positively correlated with temperatures. Subtle bond-length variations occurring at low temperatures are then expected to minimally affect vibrational absorption positions. We suggest that thermal infrared spectra of those Solar-System surfaces that are not exceeding 300 K provide reliable information about not only the silicate mineral identification but also on their chemical composition, regardless of the instantaneous temperature.

A Correction to this paper has been published: https://doi.org/10.1007/s11214-020-00780-w

The initial Spanish-american response to the crisis of the Spanish monarchy was one of loyalty to the king. It was also the beginning of an unknown number of uprisings, seditions, and conspiracies. Therefore, Peruvian historiography has highlighted the counterrevolutionary policy of Viceroy José Fernando de Abascal (1743-1821), a royal official who managed to consolidate the Peruvian viceroyalty as a realistic stronghold. However, the revolution in Cuzco, which began in August 1814, was a severe blow to the Peruvian fidelista authorities. Arequipa, a Peruvian city considered a royalist bastion, tried to resist the revolutionary attacks in Cuzco and, despite resisting, was militarily occupied by the revolutionary hosts of Cuzco for about a month. Therefore, the objective of this article is to describe the actions of the civil and military authorities during the monarchical restoration in the city from December 1814 to the first months of 1815. La respuesta inicial hispanoamericana frente a la crisis de la monarquía española fue de fidelidad al rey; asimismo, fue el inicio de un número indeterminado de levantamientos, sediciones y conspiraciones. En ese sentido, la historiografía peruana ha destacado la política contrarrevolucionaria del virrey José Fernando de Abascal (1743-1821), un funcionario real que logró consolidar al virreinato peruano como un bastión realista. Sin embargo, la revolución del Cuzco, que se inició en agosto de 1814, significó un duro golpe para las autoridades fidelistas peruanas. Arequipa, una ciudad peruana considerada como un bastión realista, intentó resistir los embates revolucionarios cuzqueños y, a pesar de presentar resistencia, fue ocupada militarmente por las huestes revolucionarias cusqueñas alrededor de un mes. El objetivo del presente artículo es describir la actuación de las autoridades civiles y militares durante la restauración monárquica en la mencionada ciudad desde diciembre de 1814 hasta los primeros meses de 1815.

Mercury's surface is thought to be covered with highly space-weathered silicate material. The regolith is composed of material accumulated during the time of planetary formation, and subsequently from comets, meteorites, and the Sun. Ground-based observations indicate a heterogeneous surface composition with SiO sub(2) content ranging from 39 to 57 wt%. Visible and near-infrared spectra, multi-spectral imaging, and modeling indicate expanses of feldspathic, well-comminuted surface with some smooth regions that are likely to be magmatic in origin with many widely distributed crystalline impact ejecta rays and blocky deposits. Pyroxene spectral signatures have been recorded at four locations. Although highly space weathered, there is little evidence for the conversion of FeO to nanophase metallic iron particles (npFe super(0)), or \"iron blebs,\" as at the Moon. Near- and mid-infrared spectroscopy indicate clino- and ortho-pyroxene are present at different locations. There is some evidence for no- or low-iron alkali basalts and feldspathoids. All evidence, including microwave studies, point to a low iron and low titanium surface. There may be a link between the surface and the exosphere that may be diagnostic of the true crustal composition of Mercury. A structural global dichotomy exists with a huge basin on the side not imaged by Mariner 10. This paper briefly describes the implications for this dichotomy on the magnetic field and the 3:2 spin:orbit coupling. All other points made above are detailed here with an account of the observations, the analysis of the observations, and theoretical modeling, where appropriate, that supports the stated conclusions.

Purpose - This purpose of this paper is to report about the temperature distribution in metal and ceramic powder beds during 3D printing. The differing powders are thoroughly characterized in terms of thermal conductivity, thermal diffusivity, emissivity spectra and density.Design methodology approach - The temperature distribution was measured in a 3D printing appliance (Prometal R1) with the help of thin thermocouples (0.25 mm diameter) and thermographic imaging. Temperatures at the powder bed surface as well as at differing powder bed depths were determined. The thermal conductivity, thermal diffusivity and emissivity spectra of the powders were measured as well. Numerical simulation was used to verify the measured temperatures.Findings - The ceramic powder heated up and cooled down more quickly. This finding corresponds well with numerical simulations based on measured values for thermal conductivity and thermal diffusivity as well as emissivity spectra. An observed color change at the metal powder has only little effect on emissivity in the relevant wavelength region.Research limitations implications - It was found that thermocouple-based temperature measurements at the powder bed surface are difficult and these results should be considered with caution.Practical implications - The results give practitioners valuable information about the transient temperature evolution for two widely used but differing powder systems (metal, ceramic). The paramount importance of powder bed porosity for thermal conductivity was verified. Already small differences in thermal conductivity, thermal diffusivity and hence volumetric heat capacity lead to marked differences in the transient temperature evolution.Originality value - The paper combines several techniques such as temperature measurements, spectral emissivity measurements, measurements of thermal conductivity and diffusivity and density measurements. The obtained results are put into a numerical model to check the obtained temperature data and the other measured values for consistency. This approach illustrates that determinations of surface temperatures of the powder beds are difficult.