Session 40P. Comets I, II, III
Contributed Poster Session, Wednesday, October 14, 1998, 5:10-6:10pm, Hall of Ideas

## [40P.09] Investigating Strength and Possible Chemical Heterogeneity of Active Regions on Comet Halley

L. M. Carter (U. Illinois), N. H. Samarasinha, M. J. S. Belton (NOAO), W. H. Julian (NMSU)

As part of a larger study aimed at understanding the properties of active regions on Comet 1P/Halley (Belton {\em et al.} 1998, this meeting), we are investigating the size and relative composition of the five active regions on the nucleus identified by Belton {\em et al.} (1991, {\em Icarus}, {\bf 93}, 183). The model and observed water production rates are used to determine the strength (area) of individual active regions. We use a thermal model (Julian {\em et al.} 1998, {\em Icarus}, submitted) to compute the water production rate per unit area from each active region. The OH production rates derived by Schleicher {\em et al.} (1998, {\em Icarus}, {\bf 132}, 397) are used to calculate the total water production of the comet. We then use these observed and modeled water production rates in a least-squares fitting routine to derive the sizes of individual active regions. We will discuss the results and possible improvements to the procedure. We will also show how we can use these derived areas to search for variations in chemical composition between the active regions.

This research was supported through the NSF Research Experience for Undergraduates program.

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