Context. Studying the coma environment of comet 67P/Churyumov-Gerasimenko (67P) is one of the primary scientific goals of the VIRTIS experiment on the ESA Rosetta mission. Aims. The distribution and variability of water vapour and carbon dioxide in the comet's coma are needed to estimate their production rate, abundances in the nucleus, and the spatial distribution of the active regions. Methods. Infrared emission lines from vibrational bands of water and carbon dioxide at 2.67 and 4.27 µm, respectively, were observed by the VIRTIS-M imaging channel and mapped from close to the nucleus up to ∼10 km altitude with a resolution of ∼40 m/px. A dataset consisting of 74 observations in the 1−5 µm spectral range acquired from 8 to 14 April 2015 when 67P was at a heliocentric distance of 1.9 AU is analysed in this work. A statistical correlation between the gas distribution and the surface's active regions was performed. Results. The maximum H 2 O emission is observed within 3 km from the nucleus and is mainly concentrated above two active regions, Aten-Babi and Seth-Hapi, while the CO 2 distribution appears more uniform with significant emissions coming from both the "head" and southern latitude regions. In the equatorial region, the column densities of both species decrease with altitude, although CO 2 decreases more rapidly than H 2 O. The calculated CO 2 /H 2 O column density ratios above Aten-Babi and Seth-Hapi are 2.4 ± 0.6% and 3.0 ± 0.7%, respectively. A value equal to 3.9 ± 1.0% is observed at equatorial latitudes in the region encompassing Imothep. Conclusions. VIRTIS-M has mapped the distribution of water vapour and carbon dioxide around the nucleus of 67P with unprecedented spatial resolution. The different water and carbon dioxide outgassing above the surface, seen in the VIRTIS-M data, might be indicative of a different thermal history of the northern and southern hemispheres of 67P.

Abstract. We present the results of our monitoring of comet 81P/Wild 2, the target of the S mission. Broad-band filter images and medium resolution spectra of this comet obtained along its pre-and postperihelion orbit between 1996 and 1998 were analysed in terms of coma morphology and activity. The morphological coma investigation revealed the presence of longlasting fan structures, which remained essentially unchanged for at least three months. The (B − V) and (V − R) colour indices were determined at three different positions along the orbit. The two-dimensional analysis showed a uniform colour over the entire coma. Hence, the material composing the structures is not different from that of the underlying coma. The distribution of coma brightness as a function of projected distance from the nucleus shows no peculiarities. The evolution of the comet's activity during the pre-and postperihelion phase appears to be asymmetric in that activity increases faster preperihelion than it decreases postperihelion. The production rates (or their upper limits in the case on a non-detection) of CN, C 2 , C 3 , and NH 2 were determined from the spectrophotometric observations and compared to other values published in the literature.

Infrared observations of the coma of 67P/Churyumov-Gerasimenko were carried out from July to September 2015, i.e., around perihelion (13 August 2015, with the highresolution channel of the VIRTIS instrument onboard Rosetta. We present the analysis of fluorescence emission lines of H 2 O, CO 2 , 13 CO 2 , OCS, and CH 4 detected in limb sounding with the field of view at 2.7-5 km from the comet centre. Measurements are sampling outgassing from the illuminated southern hemisphere, as revealed by H 2 O and CO 2 raster maps, which show anisotropic distributions, aligned along the projected rotation axis. An abrupt increase of water production is observed six days after perihelion. In the mean time, CO 2 , CH 4 , and OCS abundances relative to water increased by a factor of 2 to reach mean values of 32 %, 0.47 %, and 0.18%, respectively, averaging post-perihelion data. We interpret these changes as resulting from the erosion of volatile-poor surface layers. Sustained dust ablation due to the sublimation of water ice maintained volatile-rich layers near the surface until at least the end of the considered period, as expected for low thermal inertia surface layers. The large abundance measured for CO 2 should be representative of the 67P nucleus original composition, and indicates that 67P is a CO 2 -rich comet. Comparison with abundance ratios measured in the northern hemisphere shows that seasons play an important role in comet outgassing. The low CO 2 /H 2 O values measured above the illuminated northern hemisphere are not original, but the result of the devolatilization of the uppermost layers.

We present 2-5 µm spectroscopic observations of the dust coma of 67P/Churyumov-Gerasimenko obtained with the VIRTIS-H instrument onboard Rosetta during two outbursts that occurred on 2015, 13 September 13.6 h UT and 14 September 18.8 h UT at 1.3 AU from the Sun. Scattering and thermal properties measured before the outburst are in the mean of values measured for moderately active comets. The colour temperature excess (or superheat factor) can be attributed to submicrometresized particles composed of absorbing material or to porous fractal-like aggregates such as those collected by the Rosetta in situ dust instruments. The power law index of the dust size distribution is in the range 2-3. The sudden increase of infrared emission associated to the outbursts is correlated with a large increase of the colour temperature (from 300 K to up to 630 K) and a change of the dust colour at 2-2.5 µm from red to blue colours, revealing the presence of very small grains (≤ 100 nm) in the outburst material. In addition, the measured large bolometric albedos (∼ 0.7) indicate bright grains in the ejecta, which could either be silicatic grains, implying the thermal degradation of the carbonaceous material, or icy grains. The 3-µm absorption band from water ice is not detected in the spectra acquired during the outbursts, whereas signatures of organic compounds near 3.4 µm are observed in emission. The H 2 O 2.7-µm and CO 2 4.3-µm vibrational bands do not show any enhancement during the outbursts.

Abstract. We present the first results of BVRI photometry of Transneptunian Objects (TNOs) and Centaurs obtained through the ESO Large Program on physical studies of these icy bodies in the outer solar system. In total 28 objects were observed of which 18 are new measurements. Combining our new BVRI photometry with the data summary published by Hainaut & Delsanti (2002) results in a database of 94 objects: 45 Cubewanos, 22 Plutinos, 13 scattered disk objects, 14 Centaurs. The reddening range seems to be similar among the four dynamical classes (−5 to 55%/l00 nm) and only one outlier (1994 ES 2 ) exists. The spectral gradient distribution of the Cubewanos peaks between 25 to 35%/l00 nm, while for the three other types the maximum seems to fall below 20%/l00 nm. A clustering of red Cubewanos with perihelia beyond ∼41 AU in low eccentricity and low inclination orbit suggests that these objects are less affected by the physical processes that potentially produce neutral colors, i.e. resurfacing by collision and by intrinsic activity. For Cubewanos and scattered disk objects, the range of reddening increases with decreasing perihelion distance and with increasing orbital excitation. A correlation of the spectral slope with inclination is present for Cubewanos and scattered disk objects, and is non-existent for the other dynamical types. It is unclear whether these trends (or their absence) are discriminative for the correctness of the resurfacing scenarios. If intrinsic activity is responsible for resurfacing, the start of the effect inside ∼41 AU from the Sun may be indicative for the driving agent, while in the collision scenario the survival of the red Cubewano cluster in the central region of the Kuiper-Belt argues for the existence of a population of bodies the surface of which is heavily radiation processed without impact resurfacing.