TESS Observations of Comet 67P/Churyumov-Gerasimenko

The Rosetta spacecraft orbited comet 67P/Churyumov-Gerasimenko (C-G) from 2014-2016, where it characterized the comet's behavior in detail.  Although the in situ mission is over, remote observations monitoring the comet's behavior should be continued, to reveal how the comet evolves over the course of subsequent apparitions.

The Transiting Exoplanet Survey Satellite (TESS) was designed to observe extrasolar planets by continuously staring at a wide-field (24° x 96°) sector of the sky for 27 days.  Comets occasionally pass through the TESS field of view, where high-cadence images are recorded for as long as the comet remains in the field.  We can use these images to study the long-term spatial and temporal behavior of the comet. TESS' excellent photometric qualities track the secular and rotational lightcurves of the comet to reveal how its activity changes with time.  The continuous, extended duration of the observations is also ideal for monitoring for outbursts and other spontaneous transient events.  The thousands of images obtained by TESS can also be registered on the nucleus and coadded to produce deep images that reveal faint morphological features.  This capability has made TESS an excellent tool for discovering and characterizing cometary dust trails and for characterizing comae in weak and distant comets.

Due to fortuitous circumstances, comet C-G was ideally placed for TESS observations during its 2021 apparition.  C-G passed through six consecutive sectors, where it was imaged almost continuously every 10 minutes for 159 days (21 Aug 2021 through 27 Jan 2022).  These observations bracketed perihelion (r=1.2 AU), with r ranging from 1.5 AU inbound to 1.6 AU outbound, and provide a record of the object's long-term behavior during this time period.  Preliminary analyses of the observations show activity levels that peaked about three weeks post-perihelion, with several small outbursts detected at random times.  C-G displays a moderate dust tail as well as a bright dust trail that extends several tens of degrees from the nucleus (see figure).