Solar Orbiter’s encounter with the tail of comet C/2019 Y4 (ATLAS): Magnetic field draping and cometary pick-up ion waves

¹ Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
e-mail: l.matteini@imperial.ac.uk
² Physics Department, University of California, Berkeley, CA 94720-7300, USA
³ Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
⁴ Swedish Institute of Space Physics (IRF), Uppsala, Sweden
⁵ Space and Plasma Physics, Department of Physics and Astronomy, Uppsala University, Uppsala 75120, Sweden
⁶ UCL Mullard Space Science Laboratory, Holmbury St. Mary, Dorking RH5 6NT, UK
⁷ The Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK
⁸ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁹ LPP, CNRS, Ecole Polytechnique, Sorbonne Université, Observatoire de Paris, Université Paris-Saclay, Palaiseau, Paris, France
¹⁰ LPC2E, CNRS, 3A avenue de la Recherche Scientifique, Orléans, France
¹¹ Université d’Orléans, Orléans, France
¹² CNES, 18 Avenue Edouard Belin, 31400 Toulouse, France
¹³ Technische Universitat Dresden, Wurzburger Str. 35, 01187 Dresden, Germany
¹⁴ Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czech Republic
¹⁵ Space Research Institute, Austrian Academy of Sciences, Graz, Austria
¹⁶ Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic
¹⁷ Department of Space and Plasma Physics, School of Electrical Engineering and Computer, Uppsala, Sweden
¹⁸ Radboud Radio Lab, Department of Astrophysics, Radboud University, Nijmegen, The Netherlands
¹⁹ Institut für Experimentelle und Angewande Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
²⁰ Johns Hopkins University, Applied Physics Laboratory, Laurel, MD, USA
²¹ Universidad de Alcalá, Dpto. de Física y Matemáticas, Space Research Group, 28805 Alcalá de Henares, Spain
²² Institut de Recherche en Astrophysique et Planétologie, CNRS, Université de Toulouse, CNES, Toulouse, France
²³ INAF-Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
²⁴ Southwest Research Institute, 6220 Culebra Road, San Antonio TX 78238, USA
²⁵ European Space Agency, ESAC, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Canada, Madrid, Spain
²⁶ European Space Agency, ESTEC, PO Box 299 2200 AG Noordwijk, The Netherlands

Received: 30 April 2021
Accepted: 6 October 2021

Abstract

Context. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft’s first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU.

Aims. This study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet ATLAS, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. This encounter provides us with the first opportunity of addressing such dynamics in the inner Heliosphere and improving our understanding of the plasma interaction between comets and the solar wind.

Methods. We analysed data from all in situ instruments on board Solar Orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted.

Results. We identified a magnetic field structure observed at the start of 4 June, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. The cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. Inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities.

Conclusions. Solar Orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We suggest that this corresponds to the magnetotail of one of the fragments of comet ATLAS or to a portion of the tail that was previously disconnected and advected past the spacecraft by the solar wind.