Hi Richard and everyone on this list! I'm the author of
Spaceweather.com, and I have been following your discussion to help me
report on the latest eruption of 12P.

Richard, thank you for inviting me to join. I have a question about
something you said in an earlier email:

"Just checked on JPL Horizons, comparing the direction of the linear
features in the July and October outburst comae with the direction an
ion tail or the dust trail would be expected at these two epochs. Turns
out that neither fit the observed directions."

Approximately how big was the mismatch between the direction of 12P's
horns and the expected ion/dust tails?

Also, you speculated that "the direction has been imposed by the
cryo-eruption ... in the sense of a shadow of the expanding dust shell.
" Do you mean that the comet's core is physically blocking material from
flowing into the gap?

--Tony Phillips

> Just checked on JPL Horizons, comparing the direction of the linear features in the July and October outburst comae with the direction an ion tail or the dust trail would be expected at these two epochs. Turns out that neither fit the observed directions. So that means the direction has been imposed by the cryo-eruption but in the sense of a shadow of the expanding dust shell. (A bit like the Pac-Man feature we see sometimes when 29P has an energetic outburst). So that means the eruption is in the OPPOSITE direction to the line of symmetry through the linear features.
>
> R.