Gas Production
to 7 AU !!!
� CO - the dominant observed species r > 4 AU - ejected from dayside and fast (T>>Tsublimation) (Jewitt et al. 1996)
� Water became the dominant species only at r ~ 3.5 AU inbound
� CH3OH and H2CO have �different� variation at large r
and have different velocity than CO
=> produced from an extended source - H2CO (Eberhardt et al. 1987)
� Models for nucleus activity (Bockel�e-Morvan & Rickman 1998; Flammer et al. 1997, Capria et al. 1997 ; Enziean et al. 1998; Prialnik et al. 1998)
- distant activity is not controlled by sublimation of surface CO
Possible ideas: - heated in a porous & poorly-conducting layered structure
- heated in the inner, dense dust coma - and/or CO released at depth in the water
amorphous to crystalline phase transition (T ~ 100-120K)
� HNC is produced as an extended source in the coma probably
from ion-neutral chemistry (Rogers and Charnley 1998; Irvine et al. 1998)
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