Characterization of the Nucleus of 103P/Hartley 2 for the EPOXI Mission

Meech, Karen Jean; Hainaut, O.; Weaver, H. A.; Snodgrass, C.; Pittichova, J.; Pittichova, J.; Riesen, T.; Vilas, F.; A'Hearn, M. F.; Licandro, J.; Gulbis, A.; Lowry, S.
Bibliographical reference

American Astronomical Society, DPS meeting #41, #20.07

Advertised on:
9
2009
Number of authors
12
IAC number of authors
1
Citations
0
Refereed citations
0
Description
With the recovery of comet 103P/Hartley 2, the target of the EPOXI mission, we have begun the characterization of the nucleus necessary for the mission. Observations from past apparitions of this comet show that it typically begins activity while far from the sun, near r = 4 AU (about 450 days pre-perihelion). This makes obtaining information about the nucleus very challenging, because the comet is small and thus faint (near mag 25) just before activity begins. The comet was recovered using the VLT with FORS2 during 2008 using observations obtained at 4 epochs when the comet was between 5.7-5.5 AU (Snodgrass et al.). Deep composite images showed evidence of dust, possibly evidence of the dust trail. To ensure that we could obtain adequate information about the rotation period for the mission, an international observing campaign was undertaken with 8-10 m telescopes from March-July 2009. Ten hours were awarded on the LBT telescope, 28 hours of time on the Gemini N and S telescopes, 2 nights on the VLT 8m, 7 hrs on the GTC 10.4m and 20 hrs on the SALT telescope in S. Africa. In addition we received 12 orbits of HST time, spanning a clock time of 1 day. The comet was very faint in the HST images, and data were averaged by orbit to create the light curve. Data from Gemini N and S were obtained on 3 consecutive nights, under excellent conditions. A preliminary analysis of the Gemini data suggests a double peaked light curve with a nucleus rotation period near 16.6 hrs, which is consistent with the HST observations. The light curve shape has uneven maxima and sharp minima, suggesting the nucleus shape deviates from a triaxial ellipsoid.