If the x-rays are merely generated by collision with particles from the sun, wouldn't the coma's tail expand like an ideal gas in a vacuum, rather than remaining filamentary over solar distances (IE millions of miles?).

What if the x-rays are actually formed by synchrotron (cold) radiation from magnetically self-confined [circling/spiraling] charged particles? Would not that better explain both the confinement in a filament over stellar distances AND the x-ray emissions from the length of the coma in one fell swoop?

Also, how does a loose gas cloud stick to itself and get "bound?" Assuming the amount of gas is only equivalent to the mass of the asteroid, which seems insufficient for much mutual gravitation, let along enough to create gravitation strong enough to "pack" molecules together closely enough with enough force that they stick. Have we ever replicated gas clouds condensing under their own gravity in the lab? And wouldn't ideal gas laws expect gases to EXPAND in a vacuum rather than collapse? At what point does gravity overcome gas laws to "compact" nebulous material into a solid or semi-solid?

Also, I might note that many of the comets that broke up, did so not lightly drifting apart, but with violent breaks, spewing pieces all over...?

And I suppose I might also note: if it looks like a duck and quacks like a duck...

Comets and asteroids LOOK the same. so far I haven't seen any major differences in appearance between a comet and an asteroid from a close-up fly-by shot by a probe. They all LOOK like big ol' hunks of sharp and cratered rock, and not snow balls, or dust clouds, or mud (or whatever you prefer to call loosely bonded dust).

Many comets and moons also appear to have craters that should have shattered the body if it had been a ballistic impact onto a hard surface. And if it was a ballistic impact into a soft surface, one would think that they would have punched right through.

So, I'm still not entirely sold on the dust snowball motif. Especially when every picture shows them to be like giant boulders in space. Highly battered boulders at that. If they were just dust balls, one would expect that many significant impacts to have made the dust go "poof" by now, yeah?

And has anyone in a lab ever actually gotten two rigid bodies (or even two soft bodies) accelerated yo even a low impact speed to "congeal into one body." Or do the stresses ALWAYS shatter the hard bodies and make the soft bodies go "splat?" I'd be interested to see any research showing two or more bodies at mid to high impact velocities congealing rather than simply blowing apart due to all the forces and stresses involved. :)

Anywho, just my observations. If you really want I can track down a few pictures. Nasa's sites are usually good for that. Or the ESA sometimes.