09/11 – Monday
8:50 - 9:40 Amazonia: The close links between water, biological activity and climate change (Paulo Artaxo)
9:40 - 10:30 Water in the Solar System: Results from ROSETTA (Fabrizio Capaccioni)
The Rosetta spacecraft has officially started its daily observations of the comet 67P/Churyumov-Gerasimenko in August 2014, although the first scientific observations were performed already since the previous March. The subsequent months were mainly spent mapping the comet nucleus, from distances ranging from 100km down to 10km, in support of the landing site selection, and on 12 November 2014 Philae successfully landed on the surface of the comet. Since completing its first science sequence, Philae has been in hibernation, while the Rosetta orbiter has embarked on the main phase of its mission: escorting the comet 67P/CG in its voyage through the inner Solar System.
The 10 experiments carried on-board are investigating the comet to retrieve the most accurate information ever on the composition of the nucleus and coma, on the nucleus morphology, physical structure and thermal properties and on the interaction of the nucleus with the solar wind (e.g., see Science Special Issue: Catching a comet. Science, 347, 2015).
The surface of the comet is very complex showing varied morphologies related to active processes. The peculiar bi-lobed shape as well as the evidence of extensive layering could help us understanding the formation modalities of cometary nuclei. Any interpretative model has also to explain the nucleus bulk density of 470 kg/m3 (Sierks et al, 2015). In fact, such a low density value implies an internal structure with porosity reaching up to 70% – 80%. The surface has a very low albedo (the value of 0.06 at 550nm has been reported, Sierks et al, 2015; Ciarniello et al, 2015) over a wide range of wavelengths from UV to IR, which describes a largely dehydrated surface, rich in organic compounds and opaque minerals but devoid of water ice and other solid ices (Capaccioni et al, 2015, Stern et al, 2015). Notwithstanding the absence of water ice directly on the surface of the cometary nucleus, activity due to sublimating gases has been observed since early June 2014, when the total H2O production rate was 1×1025 mol/sec. Already by August the gas production rate increased by a factor of 4 (Gulkis et al, 2015). The coma shows a large diurnal variability as well as a latitudinal heterogeneity with water vapour abundance varying by two orders of magnitude from north to south (Hässig et al, 2015). This is anticorrelated with the CO2 abundance which could either indicate seasonal variability or real heterogeneity in the spatial distribution of these molecules (Hässig et al, 2015, Bockelee-Morvan et al., 2015). The D/H ratio is 5.3×10-4 (Altwegg et al., 2015), much larger than any other comet for which the D/H has been measured. This value seems to preclude an origin of the Earth ocean water solely from Jupiter Family Comets. In the early activity phase the dust to gas mass ratio has been unusually high (4 ± 2) than generally assumed for comets (Rotundi et al, 2015).
The talk will summarise the scientific results obtained during the early Escort Phase and up to the perihelion passage (August 2015).