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We describe thermal effects on the nucleus of comet 67P. Due to the overall low thermal inertia of the nucleus surface, the surface temperature is essentially dominated by the instantaneous value of the solar incidence angle and the heliocentric distance. However, for each location, the smallest achievable value of insolation angle depends on the season and topography. Given the substantial obliquity of comet 67P, seasons are such that the northern hemisphere is mainly illuminated at aphelion while the southern hemisphere receives most insolation soon after perihelion. In addition, the heliocentric distance strongly affects the surface temperature, all other parameters being equal. This is a larger effect in comets than in asteroids, due to the wide range of heliocentric distance values spanned by comets. When Rosetta started its global mapping observation campaign, in early August 2014, hyperspectral images acquired by the VIRTIS imaging spectrometer onboard the Rosetta Orbiter covered only the northern regions of the cometary surface, and the equatorial belt became gradually unveiled, while the southern region has been revealed from 2015 onwards. In parallel, the comet’s heliocentric distance has been decreasing from 3.6 AU down to 1.24 AU, the distance at which the perihelion passage occurred on 13 August 2015. By relating surface temperatures as measured by VIRTIS to three variables: solar incidence angle, true local solar time and heliocentric distance, we aim to separate the relative contributions due to season and to the heliocentric distance. To do this, we use both VIRTIS-M data (namely data from the mapping spectrometer covering the 1-5 µm range, available up to April 2015, i.e. before the failure of the IR cryocooler) and VIRTIS-H data (namely data from the high-resolution point spectrometer covering the 2-5 µm range), and we focus in particular on three regions: one in the northern hemisphere, one in the equatorial region and one in the southern hemisphere. These three regions are chosen so as to be relatively smooth at the spatial resolution that is achieved from a distance of about 100 km (25 m/px for VIRTIS-M, 50x150 m/px for VIRTIS-H), in order to limit the effects of large-scale surface roughness. Acknowledgements: The authors would like to thank the following institutions and agencies, which supported this work: Italian Space Agency (ASI - Italy), Centre National d’Etudes Spatiales (CNES- France), Deutsches Zentrum für Luft- und Raumfahrt (DLR-Germany), National Aeronautic and Space Administration (NASA-USA) Rosetta Program, Science and Technology Facilities Council (UK). VIRTIS has been built by a consortium, which includes Italy, France and Germany, under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which guides also the scientific operations. The VIRTIS instrument development has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES, and from DLR. The computational resources used in this research have been supplied by INAF-IAPS through the DataWell project.

The scope of these tests is to study the performance and eventually to identify any possible degradation of the dichroic after the radiation tests. The sample has been exposed at a total electron dose of 100 krad in two steps. The electron dose has been obtained at the e-LINAC, a facility of the Azienda Ospedaliera di Terni” (AOT). The tests have been performed on May 17th 2015 and June 6th 2015. The optical performances of the dichroic has been measured by using a Fourier Transform InfraRed (FT-IR) spectrometer and a Perkin Elmer Lamda. The spectral transmittance and reflectance was obtained in the spectral range of interest from 0.3 to 8 μm.

In the past few years several authors have reported detection of a very small amount of methane in the martian atmosphere. Suggested hypotheses for this methane production can be linked either to geological or biological activities, and in both cases our perspective on the planet evolution would require a major revision. It has been suggested that methane is heterogeneously distributed in the atmosphere, but its temporal and spatial variability is still unknown. Our goal is to describe the distribution of the methane concentration in the martian atmosphere and its temporal evolution, providing insight into its sources and constraining its sinks. Using the extensive data set of the thermal emission spectrometer onboard Mars Global Surveyor and a statistical clustering technique, here we tracked the gas evolution over three martian years using the ν4 Q-branch methane band at 1306 cm−1. We identify three localized sources, corresponding to Arabia Terrae, well known for the high content of underground water, and to the two main volcano provinces, Tharsis and Elysium. Our analysis suggests a seasonal cycle of the methane distribution, as well as interannual variations. This discovery potentially constrains the lifetime of the methane molecule in the martian atmosphere to

After a 10-year cruise, the Rosetta spacecraft began a close exploration of its main target, comet 67P/Churyumov-Gerasimenko, in July 2014. Since then, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS) acquired hyperspectral images of the comet’s surface with an unprecedented spatial resolution. VIRTIS data are routinely used to map the surface composition and to retrieve surface temperatures on the dayside of the comet. The thermal behavior of the surface of comet 67P is related to composition and physical properties that provide information about the nature and evolution of those materials. Here we present temperature maps of comet 67P that were observed by Rosetta under different illumination conditions and different local solar times.

In this paper we discuss the objectives, the key technical aspects and the main results of AstroNet, a Web-controlled telescope that can be simultaneously operated by small groups of users (2-20 in turn), like in a real astronomical observatory. AstroNet is the outcome of a collaboration between the Astrophysics group and the DIDA-Lab of the University of Salento and has been developed to respond to the increasing number of re- quests coming from schools and families about astronomy lectures and sky observation tutorials. In the last year, AstroNet permitted to about 1000 young students to perform rich observation experiences from both school and home, with the same global effort previously needed to offer a similar experience to about 100 people. The recognition and the analysis of the main lunar geologic structures, the monitoring of the complex and diversified Jupiter atmosphere, the evolution of comets in proximity of perihelion are only some of the possible targets of observations and imaging sessions that are suitable to a great number of thorough analyses. Moreover, with the same instrumental equipment, even if with a more well-constructed approach, it is possible to start low cost scientific research projects in the field of asteroid photometry, variable stars or extrasolar planet transits.

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90– 120km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft1 and ground-based2–4 observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission1 owing to a lack of data and of an adequate observing geometry5,6. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 mm, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at 115 km and varies with solar zenith angle over a range of 10 km. This confirms previous modelling7, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96km61 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted8

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3–1 micron range), VIRTIS-M-IR (imaging spectrometer in the 1–5 micron range) and VIRTIS-H (aperture highresolution spectrometer in the 2–5 micron range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus’s chemical cycles. In particular, CO, H2O, OCS and SO2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 micron fundamental band of CO2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 micron, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation.

Because it is possible that Mars experienced an ancient climate warmer and wetter than the present one, it is reasonable to suppose that simple forms of life developed there, in the underground or at the surface, as in the terrestrial primitive biosphere. In this work we have performed infrared (IR) transmission spectroscopic analyses directed to examine the reaction to heat treatments of biotic (fresh and fossil materials) and abiotic particulate samples composed of calcium carbonate (aragonite or calcite). The aim is to check if IR spectroscopy can be a useful tool for discriminating between abiotic and biotic (fossil) carbonate samples collected on the martian surface, during in situ or sample-return missions. An important result we found is that, after thermal processing, it is possible to distinguish, by means of IR spectroscopy, abiotic aragonite from aragonite of recent biological origin. In addition we have found that the spectral behaviour of all the analysed fossil samples after heat treatment is the same as that of fresh biotic material irrespective of the original structure (whether aragonite or calcite).

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright ‘dipole’ feature surrounded by a cold ‘collar’ at its north pole. The polar dipole is a ‘double-eye’ feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus’ south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.

Atti curati da F. Forget, M.A. Lopez-Valverde, M.C. Desjean, J.P. Huot, F. Lefevre, S. Lebonnois, S.R. Lewis, E. Millour, P.L. Read e R.J. Wilson

Laser irradiation experiments have been performed on powdered silicates (othopyroxene, clinopyroxene, and olivine) using a nanosecond pulse UV excimer laser (193 and 248 nm) to simulate the effects of space weathering induced on minor bodies of the Solar System by micrometeorite bombardment. We have used different fluences (from 0.05 to 2 J/cm2) to weather the samples, experimenting below and above the ablation threshold. All the irradiated materials have shown reddening and darkening of their UV–vis-NIR reflectance spectra. In addition we have found that: (1) below ablation threshold, weathering effects increase with increasing number of laser pulses, and with increasing fluence, confirming that a thermal process is active; (2) above ablation threshold, weathering is much stronger and efficient than in the previous case, and is independent on the number of pulses.We show that astrophysical time-scales, i.e. times necessary to obtain similar effects on planetary objects, are of about 108 yr for both olivine and pyroxene in the case of ablation. The time grows up to 1010 yr in the case of thermal effects. We infer that micrometeorite bombardment can be rightly simulated by laser irradiation only considering congruent laser ablation.