HR: 11:40h
AN: P42A-05    [Abstracts]
TI: New Chandra Observations of Comets, 2003 - 2005.
AU: * Lisse, C M
EM: carey.lisse@jhuapl.edu
AF: JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 United States
AU: Christian, D J
AF: Queens University, Belfast, Department of Pure and Applied Physics, Belfast, NI BT7 1NN United Kingdom
AU: Dennerl, K
AF: Max-Planck-Institut f�r extraterrestrische Physik, Postfach 1603, Garching, 85740 Germany
AU: Wolk, S J
AF: Chandra X-Ray Center, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AU: Bodewits, D
AF: Rijkuniversiteit Groningen, KVI atomic physics Zernikelaan 25, Groningen, AA 9747 Netherlands
AU: Hoekstra, R
AF: Rijkuniversiteit Groningen, KVI atomic physics Zernikelaan 25, Groningen, AA 9747 Netherlands
AU: Combi, M R
AF: University of Michigan, Department of Atmospheric, Oceanic, and Space Sciences University of Michigan 2455 Hayward St., Ann Arbor, MI 48109 United States
AU: Makinen, T
AF: Finnish Meteorological Institute, Space Research, P.O. Box 503, Helsinki, FIN 00101 Finland
AU: Weaver, H A
AF: JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 United States
AU: Sassen, T
AF: Physics Department, University of California, Santa Barbara, CA 93016 United States
AU: Hurwitz, M
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AB: The highly favorable perigee passage of the well studied comet 2P/Encke in late 2003 and the very active comet 2001 Q4 (NEAT) in early 2004 provided an excellent opportunity to use Chandra's high spatial, spectral, and temporal resolution to study cometary x-ray emission in the low neutral target density, low x-ray flux regime and the opposite, collisionally thick, high flux regime. X-ray emission from comet Encke was found only in a small, asymmetric region between 1500 km - 40,000 km from the nucleus. The Encke ACIS-S3 200 -- 1000 eV spectrum shows many of the same x-ray emission lines previously observed from comets (C⁺⁵, O⁺⁶,O⁺⁷), including confirmation of several emission lines in the 800 to 1000 eV range. However, the Encke spectrum shows very different line ratios in the 200 - 700 eV range than any previous comet. A lightcurve with peak-to-peak amplitude of 20% and period 11.7 hours was found over the 15 hour observing period, similar to that reported by Belton et al. (2004) and Fernandez et al. (2004) for the comet. Comparing the observations to contemporaneous measurements of the coma and solar wind made by other means, we find the combination of a low density, collisionally thin (to charge exchange) coma and a post-massive X-flare, high temperature, moderate density solar wind can explain our unusual Encke x-ray observations. X-ray emission from 2001 Q4 was highly extended and very bright. The image morphology was similar to the hemispherical shape seen for other bright comets, as was the spectrum. New to the study of comets was the contemporaneous observations of the comet by the CHIPS spacecraft in the 47 - 134 eV energy range, sensitive to emissions from Fe, Mg, Si, and S. We present our preliminary results on the analysis of the Q4 observations. The Deep Impact spacecraft. launched in January 2005, is set to rendezvous with comet 9P/Tempel 1 on July 4, 2005. An 380 kg impactor will hit the comet at 10.2 km sec^-1 at a set time with known kinetic energy, creating a hypervelocity explosion with impact flash, ejected surface material, and non-equilibrium plasma from the vaporized impactor. We have obtained 300 ksec of Chandra time to observe the comet before, during, and after thee impact. Here we describe our planned observations and expectations for the encounter.
DE: 2152 Pickup ions
DE: 6025 Interactions with solar wind plasma and fields
DE: 6035 Orbital and rotational dynamics
DE: 6060 Radiation and spectra
DE: 6061 Remote sensing
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly