Cometwatch from Earth: peak brightness and coma gases

The latest update from the professional ground-based observing campaign of Comet 67P/Churyumov-Gerasimenko, with inputs from astronomers Colin Snodgrass, Alan Fitzsimmons, Cyrielle Opitom and Emmanuel Jehin. While Rosetta made a far excursion 1500 km from the comet to get a view of the wider coma and plasma environment during late September/early October, Earth-based observers have also been continuing to monitor the comet – from even greater distances! The image below was taken on 30 September, the same day that Rosetta reached its furthest distance from the comet during this excursion. To help put things into perspective, the image is also shown with two red dots: the right hand dot marks the centre of the nucleus, while the left hand one lies roughly 1500 km in the sunward direction, showing approximately where Rosetta was at the time the ground-based observations were made. Peak brightness Meanwhile, the ground-based astronomers have been analysing the comet’s brightness following perihelion – the comet’s closest approach to the Sun along its orbit – on 13 August. Based on measurements made by the 60-cm diameter TRAPPIST telescope located at the La Silla observatory in Chile, the comet appeared to show the peak in brightness at the end of August. Indeed, data obtained by the TRAPPIST telescope on 31 August indicated a dust production rate at the nucleus corresponding to approximately 1000 kg per second. The peak brightness on the same day was recorded as magnitude 12 (roughly 250 times dimmer than the faintest stars visible to the unaided naked eye, and thus decent-sized telescopes are needed to study the comet). Since the peak dust production rate measured on 31 August, the overall activity has reportedly been declining steadily, following the trend anticipated from observations made of 67P/C-G during previous perihelion passages (see Snodgrass et al 2013). How much mass is […]

from Rosetta - ESA's comet chaser » Rosetta - ESA's comet chaser http://ift.tt/1S9kLTH
via IFTTT