New Chandra Observations of Comets, 2003 - 2005.

Details New Chandra Observations of Comets, 2003 - 2005. New Chandra Observations of Comets, 2003 - 2005.

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p42a..05l&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #P42A-05

Other

2152 Pickup Ions, 6025 Interactions With Solar Wind Plasma And Fields, 6035 Orbital And Rotational Dynamics, 6060 Radiation And Spectra, 6061 Remote Sensing

Scientific paper

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.

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