Periodic Reporting for period 4 - CAstRA (Comet and Asteroid Re-Shaping through Activity)
Reporting period: 2021-11-01 to 2023-08-31
To study the motion of debris emitted from comet 67P, two algorithms have been developed to track the motion of individual dust particles or boulders flying in the coma in either a series of short exposures, or a single long exposure. This paved the way to studying the source regions and ejection circumstances of the material.
Telescope time on Hubble and the Very Large Telescope of the European Southern Observatory has been awarded to project members to observe several active asteroids and comets. A multi-year series of Hubble observations allowed us to constrain the mutual orbit of the binary main-belt comet 288P and identify its active component, which has led to the serendipitous discovery of a third component to this system. Hubble images of interstellar comet 2I/Borisov led us to conclude that activity in this object was subject to both a diurnal and a seasonal cycle, similar to Rosetta target 67P.
These results are published in peer reviewed articles, e.g.
Markkanen et al. (2018), ApJ, 868, L16.
Markkanen & Agarwal (2019), A&A, 631, A164.
Markkanen & Agarwal (2020), A&A, 643, A16.
Kim et al. (2020), ApJL 895, L34.
Agarwal et al. (2020), A&A 643, A152.
Pfeifer et al. (2022), A&A, 659, A171.
Lemos et al. (2023), MNRAS 519, 5775.
We find that the diurnal activity variation in interstellar comet 2I/Borisov is similar to that in Rosetta target comet 67P.
The main-belt asteroid 288P is likely a triple system. It probably formed by splitting of a precursor body whose rotation was driven to a critical frequency by asymmetric emission of thermal radiation, such that centrifugal forces exceeded gravity. However, we also find that this splitting likely was not the cause of the current sublimation of water ice that must have recently been excavated from deeper layers.