Monday

We present results from Solar Orbiter in situ observations of the crossing of the tail of comet C/2019 Y4 (ATLAS) during the first perihelion in June 2020 when the spacecraft was at a distance of approximately 0.5 AU from the Sun. Comet ATLAS fragmented during its last perihelion and this event provide then a unique opportunity for studying the interaction of a fragmented comet with the solar wind.
We have identified a magnetic field structure observed at the beginning of June 4th 2020, associated with a full magnetic field reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. We interpret this structure as magnetic field draping around a low-field and high-density object, as expected for a cometary magnetotail. Inside and around this large scale structure, several ion-scale fluctuations are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities.
We conclude that Solar Orbiter measurements are overall consistent with the crossing of a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We then propose 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.