Distant activity of 67P/Churyumov-Gerasimenko in 2014: Ground-based results during the Rosetta pre-landing phase^⋆

¹ Planetary and Space Sciences, Department of Physical SciencesThe Open University, Milton Keynes, MK7 6AA, UK
e-mail: Colin.Snodgrass@open.ac.uk
² Max-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³ Institut d’Astrophysique et de Géophysique, Université de Liège, Sart-Tilman, 4000 Liège, Belgium
⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
⁵ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50 125 Firenze, Italy
⁶ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
⁷ University of Maryland, College Park, MD 20742, USA
⁸ Lowell Observatory, 1400 W. Mars Hill Rd, Flagstaff, AZ 86001, USA
⁹ Gemini Observatory, Recinto AURA, Colina El Pino s/n, Casilla 603, La Serena, Chile
¹⁰ Las Cumbres Observatory Global Telescope Network, 6740B Cortona Drive, Goleta, CA 93117, USA
¹¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹² Qatar Environment and Energy Research Institute (QEERI), HBKU, Qatar Foundation, Doha, Qatar
¹³ Centre for Astrophysics and Planetary Science, School of Physical Sciences, The University of Kent, Canterbury, CT2 7NH, UK
¹⁴ Institut UTINAM, UMR 6213 CNRS-Université de Franche Comté, 25000 Besançon, France

Received: 25 November 2015
Accepted: 28 January 2016

Abstract

Context. As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet.

Aims. We constrain the total activity level of the comet by photometry and spectroscopy to place Rosetta results in context and to understand the large-scale structure of the comet’s coma pre-perihelion.

Methods. We performed observations using a number of telescopes, but concentrate on results from the 8 m VLT and Gemini South telescopes in Chile. We use R-band imaging to measure the dust coma contribution to the comet’s brightness and UV-visible spectroscopy to search for gas emissions, primarily using VLT/FORS. In addition we imaged the comet in near-infrared wavelengths (JHK) in late 2014 with Gemini-S/Flamingos-2.

Results. We find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. The evolution of the total activity (measured by dust) followed previous predictions. No gas emissions were detected despite sensitive searches.

Conclusions. The comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that Rosetta results correspond to typical behaviour for this comet. The gas production (for CN at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits.