In the eye of the storm: Inner coma remote sensing of three Jupiter family comets

NASA Solar System Observations Program

Subaward to PSI from University of Arizona

PI: Walter Harris (University of Arizona)

Start Date: 05/01/2016
Project #: 1476
End Date: 04/30/2021
Award #: 323982

PSI Personnel

Project Description

Earth-based remote sensing of comets relies strongly on the coma for determination of the volatile composition and activity. The large-scale characteristics of the coma are the emergent property of active regions and diffuse surface production combined, in some cases, with a near-nucleus icy halo. This environment is spatially, compositionally, temporally and hydro-dynamically variable, with dependencies on rotational state, seasonal illumination patterns, overall gas production, and outburst activity. The transition from the collisional near nucleus region to the ballistic coma plays out over a narrow range of cometocentric distance that is also comparable to the scale lengths of many volatile species.

Several visits to comet nuclei have revealed an extraordinary diversity in the processes driving inner coma activity that is reflected only ambiguously in the large-scale characteristics of the coma. This limits our ability to understand acceleration processes, dust-gas interaction, and production mechanisms from remote sensing except for the few cases where the orbit of a nucleus brings it close enough to Earth that the small distance scales where these processes develop can be spatially resolved.

We propose a wide-ranging study of Jupiter family comets (JFCs) 45P/Honda-Mrkos- Pajdusakva (HMP), 41P/Tuttle-Giacobini-Kresek (TGK), and 46P/Wirtanen. All three objects will have close perigee passages ranging from 0.078 to 0.148 AU between 2017 & 2018. Such a clustering of close approaches is rare and will provide a unique opportunity to obtain detailed information of inner coma processes from objects with different overall patterns. The significance of this opportunity is magnified by the subsequent drought of JFC close approaches that follows. After 46P/Wirtanen, the next comparable opportunity will not occur for nearly two decades.

The primary aims of this study will be to employ proven observational approaches, image enhancement techniques, and coma models to

1) Investigate the rotational state of each nucleus to better understand the diurnal and seasonal patterns of surface activity and how they shape its physical evolution.
2) Map the species-specific morphology and bulk outflow velocity of the inner coma to trace the photochemical evolution of sublimated volatiles.

3) Measure the species-specific gas production rates, along with the locations and extent of active regions and icy-halo sources.
4) Characterize the size, shape, and major surface features of the nucleus, along with the amount and size distribution of debris surrounding the nucleus.

5) Monitor all processes for changes due to rotation, season, and outburst activity.

Broad and narrow band visible filters will be combined with radar observations of the nucleus shape, rotation, and dust to characterize the inner coma of each comet. Complementary 18-cm OH measurements will be used to monitor the velocity structure and hydrodynamic state of the coma. Observations of 41P/TGK and 45P/HMP will be combined in a campaign from February-June 2017, while 46P/Wirtanen will be monitored from October 2018 to February 2019. In all cases the targets are available for 4-8 hours at low airmass for all nights of the observing periods. The visible imaging observations will be obtained primarily using the telescopes at the University of Arizona, while radar and OH measurements will be obtained at the Arecibo and Greenbank radio telescopes. These resources will be leveraged through coordination with collaborating institutions and through access to community facilities in both hemispheres. The data obtained through this program will be reduced and archived with the NASA PDS, with the initial results published.

Dr. Mueller will participate in observations of comets 41P/Tuttle-Giacobini-Kresak, 45P/Honda- Mrkos-Pajdusakova, and 46P/Wirtanen. She will further be involved in the reduction, analysis, archival and dissemination of these data. During the first year, she will help observe comets 41P and 45P and reduce the data. In the second year, she will be involved with more observations and reductions of comets 45P, as well as with the analysis, interpretation and publication of the results of comets 41P and 45P. She will also be responsible for archiving the data into PDS. In the last year, she will help observe comet 46P/Wirtanen. She will reduce the data and will be involved in analyzing, interpreting and publishing of the data and the results. She will archive the data of 46P into PDS.

Dr. Samarasinha will be leading international campaigns to obtain coma morphological observations of comets 41P/Tuttle-Giacobini-Kresak, 45P/Honda-Mrkos-Pajdusakova, and 46P/Wirtanen in addition to his own participation in observations. He will also be involved in the image enhancement, analysis, interpretation and publication of results based on these data. During the first two years, his efforts will be concentrated on comets 41P/TGK and 45P/HMP. In the third year, he will observe comet 46P/Wirtanen and be involved in the analysis, interpretation and publication of the results.

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