Contribution Invited Talk
The volatile inventory of comet 67P/Churyumov-Gerasimenko from Rosetta/ROSINA
- Léna LE ROY
- Léna LE ROY (university of Bern, Physic Institute)
- Kathrin ALTWEGG (university of Bern, Space Research and Planetary Sciences)
- Jean Jacques BERTHELIER (LATMOS)
- André BIELER (Department of Atmospheric, Oceanic and Space Science, University of Michigan)
- Christelle BRIOIS (LPC2E)
- Ursina CALMONTE (University of Bern, Space Research and Planetary Sciences)
- Mike R. COMBI (Department of Atmospheric, Oceanic and Space Science, University of Michigan)
- Johan DE KEYSER (Space Physics Division, BIRA-IASB)
- Björn FIETHE (Institute of Computer and Network Engineering, TU Braunschweig)
- Stephen A. FUSELIER (Southwest Research Institute & University of Texas at San Antonio)
- Sébastien GASC (Space Research and Planetary Sciences, University of Bern)
- Myrtha HÄSSIG (Southwest Research Institute & Space Research and Planetary Sciences, University of Bern)
- Annette JÄCKEL (Space Research and Planetary Sciences, University of Bern)
- Chia-Yu TZOU (Space Research and Planetary Sciences, University of Bern)
- Tamas I. GOMBOSI (Department of Atmospheric, Oceanic and Space Science, University of Michigan)
- Frederik DHOOGHE (Space Physics Division, BIRA-IASB,)
- Martin RUBIN (Space Research and Planetary Sciences, University of Bern)
Comets are believed to belong to the most pristine bodies in the solar system. The study of their composition can therefore give us important clues about the processes that occurred during the solar system formation .
The composition of cometary atmospheres has been investigated remotely and by in situ spacecraft measurements. Until now more than twenty molecules have been identified .
The European Space Agency’s Rosetta mission gives us a unique chance to probe and study the composition in the inner coma of comet 67P/Churyumov-Gerasimenko (67P/CG). Rosetta is the first mission to orbit a comet and to land a module on its surface . The Rosetta orbiter follows the comet from ~3.5 AU through perihelion and out again to ~3.5 AU over a time-span of more than 2 years.
On board the Rosetta spacecraft several instrument aim to study the composition of 67P/CG (atmosphere and/or nucleus). Among them, the ROSINA (Rosetta Orbiter Sensor for Ion and Neutral Analysis) experiment  is dedicated to study the composition and the dynamics of 67P/CG’s coma. ROSINA consists of a suite of three instruments: a pressure sensor (COPS: COmetary Pressure Sensor) and two mass spectrometers: the Reflectron Time of Flight mass spectrometer (RTOF) and the Double Focusing Mass Spectrometer (DFMS). The two sensors are complementary. RTOF has a large mass range and can record mass spectra at high time resolution; whereas DFMS has a high mass resolution (m/dm = 9000 at FWHM at 28 u/e). DFMS is a traditional mass spectrometer that combines an electrostatic analyzer for energy analysis with a magnet for momentum analysis. To date, DFMS is the highest mass resolution mass spectrometer in space. It is able to resolve CO from N2 at m/q= 28 u/e or 12CH and 13C at m/q= 13 u/e . This allows to measure many isotopes in different molecules, such as the deuterium and oxygen isotopes in water .
Since August 2014, ROSINA is monitoring the volatiles in 67P/CG’s coma [5, 6, 7, 8]. In October 2014, to prepare for the lander delivery, the Rosetta spacecraft flew in terminator orbits at an unprecedented close distance (10 km) from the nucleus during roughly two weeks. The total neutral density was high during these measurements, which enabled the detection of minor species in the coma. In March 2015 the spacecraft performed a close flyby with closest approach at 8 km from the center of the nucleus. During this period, we observed even higher densities but for a very short time and numerous neutral species have been detected for the first time in comets. In our presentation we will present some of these molecules and compare our results with the composition in the interstellar medium.
References  Irvine W.M. & Lunine J.I. (2004) In Comets II, pp25-31. University of Arizona Press  Bockelee-Morvan et al (2004) In Comets II, pp391-423. University of Arizona Press  Glassmeier, K.H. & al. ( 2007) Space Science Reviews 128(1), pp1 - 21  Balsiger H.,et al. 2007, Sp. Sci. Rev., 128, 745.  Altwegg et al. 2015, Science, 347  Hässig et al. 2015, Science, 347  Rubin et al, 2015, Science, 348, pp232-235  Le Roy et al, 2015, A&A submitted