Rosetta’s far excursion to study the coma at large

Next week, on 23 September, Rosetta will depart on a three-week excursion that will take it up to 1500 km from the nucleus of Comet 67P/Churyumov-Gerasimenko, much farther than it has been since arriving at the comet in August 2014. The main science goal driving this course of action is to study the coma of 67P/C-G on a broader scale while the comet's activity is still high in the post-perihelion phase. While almost all instruments on Rosetta will be operating during the excursion, this exploration of the coma at large will be especially interesting to study the plasma environment of the comet with the Rosetta Plasma Consortium (RPC) instruments. In particular, scientists are aiming at detecting the bow shock, a boundary between the comet's magnetosphere and the ambient solar wind. The existence of a bow shock in a comet's environment around its activity peak was predicted in 1967 by Ludwig Biermann, and confirmed in the past decades by observations at comets 21P/Giacobini–Zinner, 1P/Halley, 26P/Grigg–Skjellerup and 19P/Borrelly. “Previous measurements that were performed during fly-bys only provided limited data points about the bow shocks of a handful of comets. Rosetta, instead, will take data over several days, monitoring the evolution of the plasma environment of 67P/C-G shortly after its perihelion,” says Claire Vallat, a Rosetta Science Ground Segment scientist at ESA's European Space Astronomy Centre (ESAC). Along the new trajectory, Rosetta will move away from the nucleus up to 1500 km in the direction of the Sun, where the bow shock is expected to be found. This maximum distance will be reached by the end of September, with the spacecraft returning to closer distances by mid-October. “While it may appear odd to depart from the nucleus at this time, these measurements are also key to understanding the comet's behaviour at large and […]

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