HST Observations of the Nucleus of Comet 41P/Tuttle-Giacobini-Kresak
Abstract
In early 2017, we discovered that comet 41P/Tuttle-Giacobini-Kresák (TGK), was spinning down at an incredibly rapid rate, with a rotation period that changed from 20 hours in early March (Farnham et al. CBET 4375, 2017) to 27 hours in late March (Knight et al. CBET 4377 2017) and >42 hours in early May (Bodewits et al. Nature 553, 186, 2017). These results indicate that the comet's rotation period decreased by 0.5 hr/day during this time period—the fastest changes ever observed in any comet. Thus, TGK is ideal for testing models of cometary dynamics, allowing us to investigate how the torques respond to changing production rates and illumination conditions. Furthermore, if the spin-down of TGK continues at this pace over the next apparition or two, it may be possible to document a comet's behavior as it transitions through a slow-rotation end state (e.g., will it enter a stage of complex rotation? Spin up in the opposite direction? Or will it exhibit some other response?). To follow up on this work, we were awarded 10 orbits of HST WFC3/UVIS time in December 2017 to observe the lightcurve of TGK. Our goal is to characterize the rotation state of the nucleus after its activity had subsided. Results from this work will not only provide a measurement of the "final" spin state achieved during the 2017 apparition, but will also define the initial state for future monitoring of any continuing changes over the next apparition. We can also take advantage of the high resolution of the HST images to separate the nucleus signal from that of any coma that is present. This allows us to constrain properties of the nucleus, including its general size and shape, that will be used in models of the comet's dynamical evolution. Although we requested our 10 orbits to be spaced over a 7-day baseline to cover any expected rotation period, scheduling constraints forced us to restrict our observational window to 3.5 days. This affects our ability to fully define the lightcurve, but otherwise our analyses will continue as planned. We will present results from this work, and will discuss how they might relate to the rapid evolution of the comet's dynamics.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5010605F