During May 2014, comet 67P/Churyumov-Gerasimenko will be in full view of Rosetta. And thus continues the fascinating adventure of the European space probe as it chases its target.
From March 23rd to May 4th 2014, the imaging system OSIRIS began to photograph the comet at distances ranging from five to two million km.
Pictures acquired from April 30th to May 4th show not only a luminous nucleus, but also the brighter surrounding structures.
These first pictures bear witness to the birth of the dust coma of 67 P, which extends out to about 1 300 km in space. The nucleus, with a size of about 4 km, is not yet resolved.
In contrast to ground based instruments, those on board Osiris were able to detect the presence of a cometary coma even though the comet was at a heliocentric distance of over 600 million kilometers ; it is not obvious that so far out from the Sun, the comet should be so active.
The OSIRIS pictures enable the light curve of the comet, i.e. the variation of its luminosity as its rotates, to be measured, and hence to find the rotation period of its nucleus, which turns out to be 12,4 heures, 20 minutes shorter than the period found previously using ground based data.
This information is required in order to be able to program observations using Rosetta’s various instruments.
The various scientific teams which have helped create the imaging system, and in particular scientists from the Paris Observatory, are delighted with these first results. Composed of two cameras, the Narrow Angle Camera (NAC) and the Wide Angle Camera (WAC), OSIRIS is a vital component for the success of the Rosetta mission.
OSIRIS will furnish essential data on the nature of cometary nuclei, and more generally on cometary physics (the gas and dust coma). The pictures it will send will also play a key role in the local and global characterization of the nucleus, and in the choice of the landing site of the Philae lander which will try to land there in November 2014.
Observations start when cometary activity has only just begun. They will continue until December 2015, 4 months after the comet has passed its perihelion (1.37 AU).
Three scientists from the Laboratory for Space Instruments and Research at the Paris Observatory are members of the Osiris team : Maria Antonietta Barucci, Fornasier Sonia and Cédric Leyrat.
The OSIRIS imaging system was built by a consortium led by the Max Planck Institute for Solar System Research (MPS, Germany), together with the CISAS, Padova University (Italy), the Marseille Astrophysics Laboratory (France), the Instituto de Astrofísica de Andalucia, CSIC (Spain), the science support office of the European Space Agency (ESA-Holland), the Instituto Nacional de Técnica Aeroespacial (Spain), the Universidad Politéchnica de Madrid (Spain), the Department of Physics and Astronomy of Uppsala University (Suède), and the Institute of Computer and Network Engineering of Braunschweig (Germany). OSIRIS was financed by the space agencies DLR (Germany), CNES (France), ASI (Italy), MEC (Spain), SNSB (Sweden) and by ESA