Evening Nick,

Although I am mainly talking about 29P, we do have the 2023 11 14 lightcurve
for a strong outburst of 12P that you obtained really early on in the
eruption plus later data from Pepe Chambo, and this too fits being a
cryovolcanic eruption that shut down very quickly.

You ask, " Can you explain to us non-chemists why the standard professional
model of crystalline-amorphous ice phase change just can't explain what we
observe."

I'll be quick but I can expound further as this is supposed to be a comet
discussion group and am very happy to discuss questions such as this one.

I could list a few things but let's start with one important one.
The amorphous ice is theorised to have been deposited when the cometary body
first formed in a cooling nebula in which H2O molecules in the gas phase
accumulated on a growing cometesimal at vey low temperature (<50K say). So
by definition such accumulations are pristine or seen temperatures much
higher than 50K. They are therefore undifferentiated and so are distributed
throughout a comet nucleus in some unknown fashion. When the amorphous ice
was laid down at even lower temperatures (20K say) then CO ice and other
hypervolatile ices were mixed with it and it is the release of these
hypervolatiles when the nucleus is heated that is supposed to drive a strong
cometary outburst.

So far, so good. We might also suppose that the hypervolatiles release leads
to some gas pressure which builds up and ruptures some sort of crust.
The question now is what would you then expect in terms of the ejection rate
of material over time once an outburst starts?

There are two elements to this:
One concerns the nature of the onset of such an outburst and how quickly the
ejection rate can reach a maximum
The second is the way in which an outburst terminates

With various deposits of amorphous ice and a weak crust, you would expect a
rather complicated and drawn-out process of the ejection rate building up
then fluctuating in intensity as gas and dust find their way to the surface.
This would mean there would be various probability distributions in the
release rate dependent on the amount and depth locations of these deposits.
So the rate at which material escapes into space would fluctuate, rising and
falling depending on the supply rate of gas and dust being transported from
some depth where the deposits are located and reaching the surface.

For much stronger crusts, more pressure could build up before an eruption
occurs and so you might then see a short-lived single rise to peak ejection
rate but then the model would be similar to a chamber expelling the gas that
was stored there under pressure. The ejection rate would decrease
exponentially or monotonically until it reached zero and this would take
quite some time for it to stop. Once an amorphous-ice driven eruption
starts, I see no mechanism that could seal the fissure very quickly and shut
down the release like we observe for 29P and 12P.

There are other serious problems with the amorphous-ice hypothesis to do
with the thermochemistry and the potential amount of energy available but
I'll leave describing those for another time!

Cheers,
Richard

-----Original Message-----
From: baa-comet@simplelists.com <baa-comet@simplelists.com> On Behalf Of
Nick James
Sent: Wednesday, March 27, 2024 12:01 AM
To: baa-comet@simplelists.com
Subject: Re: [BAA Comets] A link between the size and composition of comets

Richard,

We now have multiple instances of catching these outbursts in progress for
29P and 12P. As you say, the shape of the outburst lightcurves strongly
indicate an impulsive release of material which then expands into the
vacuum. The latest example for 29P is a really good example of this.

Can you explain to us non-chemists why the standard professional model of
crystalline-amorphous ice phase change just can't explain what we observe.

Scientific theories develop an inertia all of their own but eventually they
have to be abandoned if they don't fit the facts.

Nick.

PS - Jeremy - Thanks for posting these papers. They are often very
interesting and, like this one, are good starting points for other
discussions.

On 26/03/2024 22:03, rmiles.btee at btinternet.com (via baa-comet list)
wrote:
>   The model described
> in the above paragraph goes nowhere near explaining this behaviour.

To unsubscribe from this list please go to
https://www.simplelists.com/confirm/?u=aR5jVcAm0PpxqWzIIDZTQWdURWgNdCOC