The water production rate of Rosetta target Comet 67P/Churyumov–Gerasimenko near perihelion in 1996, 2002 and 2009 from Lyman α observations with SWAN/SOHO

Abstract We report here the observations of the hydrogen cloud in Lyman alpha emission of Comet 67P/Churyumov–Gerasimenko at the last three passages through its perihelion, in 1996, 2002 and 2009. This comet became the target of ESA space mission Rosetta in 2003, and is therefore of particular interest. The data were collected with the SWAN instrument on board SOHO, the main mission of which is to record all-sky images of interplanetary neutral hydrogen, in order to monitor the solar wind latitude distribution. For the 2009 perihelion, a dedicated campaign was implemented and allowed to collect 26 smaller and more refined images around the position of the comet, from which a unique series of H2O production rates could be derived by comparison with a model, for the period from 2 to 50 days after perihelion. To our knowledge, these are the only determination of H2O production rate for 2009. In addition, we could retrieve the H emission at the two previous perihelia in 1996 and 2002, thanks to serendipitous observations of comets as part of the all-sky monitoring program: 4 and 10 respectively for 1996 and 2002. While the perihelion distance to sun decreased continuously (1.300, 1.292, 1.246 AU respectively for 1996, 2002, 2009), the average production Q(H2O) just after perihelion did not increase accordingly: 1.30×1028, 1.70×1028, and 5.65×1027 mol s−1. Comparison with 1982 IUE measurement of 6×1027 mol s−1 suggests no rapid aging of the comet, and we may expect a similar level of activity at the next perihelion in August 2015. The production rate in 2009 showed a peak around 16.4 days post-perihelion, with a suggestion of a second peak at ~40 days, and a somewhat reduced rate in between (though SWAN measurements are incomplete). These measurements may help in planning of Rosetta activities around the next perihelion.

[1]  M. Berthé,et al.  LYMAN-ALPHA OBSERVATIONS OF COMET HYAKUTAKE WITH SWAN ON SOHO , 1998 .

[2]  J. Worden,et al.  Improved solar Lyman α irradiance modeling from 1947 through 1999 based on UARS observations , 2000 .

[3]  Jean-Loup Bertaux,et al.  The Shadow of Comet Hale–Bopp in Lyman-Alpha , 2002 .

[4]  J. Bertaux,et al.  SOHO/SWAN OBSERVATIONS OF SHORT-PERIOD SPACECRAFT TARGET COMETS , 2011 .

[5]  Robert L. Millis,et al.  The ensemble properties of comets: Results from narrowband photometry of 85 comets , 1995 .

[6]  G. Bourgois,et al.  Observations at Nançay of the OH 18-cm lines in comets - The data base. Observations made from 1982 to 1999 , 2002 .

[7]  M. Combi,et al.  Temporal deconvolution of the hydrogen coma I. A hybrid model , 2005 .

[8]  P. Feldman,et al.  Observations of Comet 67P/Churyumov-Gerasimenko with the International Ultraviolet Explorer at Perihelion in 1982 , 2004 .

[9]  Karoly Szego,et al.  The Shadow of Comet Hale-Bopp in Lyman-Alpha , 2002 .

[10]  D. K. Prinz,et al.  Validation of the UARS solar ultraviolet irradiances: Comparison with the ATLAS 1 and 2 measurements , 1996 .

[11]  R. Lallement,et al.  SWAN: A study of Solar Wind Anisotropies on SOHO with Lyman alpha sky mapping , 1995 .

[12]  Eric Quémerais,et al.  SOHO/SWAN Observations of the Structure and Evolution of the Hydrogen Lyman-α Coma of Comet Hale–Bopp (1995 O1) , 2000 .

[13]  Rita Schulz,et al.  Rosetta target comet 67P/Churyumov-Gerasimenko: Postperihelion gas and dust production rates , 2004 .

[14]  W. McClintock,et al.  Solar–Stellar Irradiance Comparison Experiment II (Solstice II): Instrument Concept and Design , 2005 .

[15]  Donald Fenna,et al.  The Data Base , 1978 .

[16]  T. Pulkkinen,et al.  Comets in full sky L alpha maps of the SWAN instrument. I. Survey from 1996 to 1998 , 2001 .

[17]  M. Combi,et al.  Monte Carlo particle-trajectory models for neutral cometary gases. II: The spatial morphology of the Lyman-alpha coma , 1988 .

[18]  J. Bertaux,et al.  LYMAN-ALPHA OBSERVATIONS OF COMET 46 P/WIRTANEN WITH SWAN ON SOHO: H2O PRODUCTION RATE NEAR 1997 PERIHELION , 1999 .

[19]  D. Schleicher.  Compositional and physical results for Rosetta's new target Comet 67P/Churyumov–Gerasimenko from narrowband photometry and imaging , 2006 .