NOAO >   Observing Info >   Approved Programs >   2008B-0470

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Proposal Information for 2008B-0470


PI: Beatrice Mueller, Planetary Science Institute, muller@psi.edu
Address: 1700 E. Ft. Lowell, Suite 106, Tucson, AZ 85719, U.S.A.

CoI: Yanga Fernandez, University of Central Florida
CoI: Nalin Samarasinha, NOAO and PSI

Title: Decoding the Secrets of Comet Encke's Spin State

Abstract: We propose to determine how the rotation state of Comet 2P/Encke changes from orbit to orbit. We are asking for two observing runs, at least three weeks apart between late August and early October 2008, while the comet is just pre-aphelion. The observations will be used to investigate if the dominant periodicity has changed from that measured around a previous aphelion, in 2001-2002, which was two apparitions ago. Comparison of data from the 1980s and 2001-2002 suggests that the dominant periodicity is decreasing by a few minutes per orbit, but we need much more detailed coverage than what was obtained in the 1980s to confirm a period change. The proposed observations will also be used to check if the comet is in a non-principal axis spin state as was claimed by Belton et al. (2005). Jets emanating from the nucleus can provide a reaction torque to change the spin state of the nucleus (e.g. Whipple 1950, Samarasinha et al. 2004). Such a phenomenon must be taken into account if we are to understand Encke's rotation state. Furthermore this could be used to ultimately derive the comet's mass, density, and even the product of the shear modulus and the quality factor (structural parameters), fundamental properties that are poorly constrained among cometary nuclei.


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