We conducted an intensive observational campaign of Comet 2P/Encke in late 2003, obtaining 16 nights of imaging over a 2 month interval. While Encke was near opposition, observations were focused on acquiring a nucleus rotational lightcurve. The near total lack of small dust grains in Encke's coma permits the direct detection of the nucleus even while the comet is active, by using narrowband continuum filters which avoid the extensive gas emission, leaving only the nuclear signal. Photometric extractions yield viable phased lightcurves only at a period of 11.07+/-.01 day (single-peaked) and simple multiples of this value; no signature from complex rotation, as proposed by Belton et al. (2005; Icarus 175,181), is evident.A second goal of our observations was to detect sufficient structure in the long-known pre-perihelion sunward gas fan to follow changes induced by rotation and outward motion, and we successfully detect the presence of a diffuse side-ways spiral or corkscrew in the CN emission band frames. The position angle of the center of the corkscrew (and fan) was used to derive the 3-D orientation of the rotation axis, with a resulting obliquity of 58o and orbital longitude of 48o (in the comet's frame of reference), with an uncertainty of less than 2o. Preliminary modeling of the corkscrew with time places the source near a latitude of 70o, and implies that the true period is 11.07 hr rather than twice this value, even though this solution requires either an unusually shaped nucleus to yield a single-peaked lightcurve or that the lightcurve shape is dominated by significant albedo variations. These and the results of ongoing analyses to model the outward motion of the corkscrew and intercompare the various gas species will be presented. This research is supported by NASA's Planetary Astronomy Program.
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007