[X] My Assistant

[Guest_paulanderson_*]

This is the first source I've come across for this, an interview with Carey Michael Lisse, member of the Deep Impact Science Team and Principal Investigator for the Chandra X-Ray and Spitzer telescope Deep Impact spectrometer results:

http://www.earthfiles.com/news/news.cfm?ID...ategory=Science

Interesting results, including 50% + water ice, limestone-like carbonates and amino acid precursors, just presented at the 9th International Asteroids, Comets and Meteors Conference in Brazil.

[edstrick]

There's a <deleted>-load about comets we don't know..but there's a lot we do know which gives us pieces of the puzzle.

There has never been a meteor photographed as part of a comet's meteor shower that lasted long enough and penetrated low enough into the atmosphere to have been a rock that could have survived entry. Decades ago, shower meteors were described as "having the mechanical strength of cigarette ash".... which makes loads of sense if they're bits of dessicated <well.. devolatilized> cosmic dust-bunnies.

Small comets like a comet Linear a couple years ago can disintegrate all on their own with nothing left other than dissipating dust clouds big enough for Hubble to see. Clearly, those objects don't have melted-and-refrozen slushball cores.

The parent object of the Kreutz <sp?> Sungrazer comets is believed to have been a monster to have split into so many substantial comets... Bigger than Hale-Bopp which was big.... Maybe it had a core that last rounded the sun in Cro-Magnon time and isn't coming back for another 5000 years, but the pieces it broke up into don't seem to have any more guts than Shoemaker Levy did. Kuiper Belt objects 200.. 500 km across proabaly did heat up inside, but how much is model dependent.. and a big unknown in the model is if any of the short lived radio-isotopes in the early solar system were still around when they accreted.

We have almost no idea how fine the ice grains in comet insides are, below any "rind" or "mantle" heated when a comet is in short period orbits. We have almost no idea of vapor transport within the comet.. barely know how volatile some of the ices are since we don't have any real inventory of the volatiles.... the Deep Impact flash data, and the plume data, both from the spacecraft and remote observations are telling us a lot.

Some of the ices may even be explosive. Take simulated Triton surface ices.. Water/Nitrogen/Methane frosts... Irradiate the mix with charged particles, it turns yellow with new compounds..... and it explodes when heated. There are crackpot therories of exploding asteroid/comet parent planets or ice-moons, with electrolytic chemical products in their interior making them timebombs waiting to go off... The theories overall are crackpot, but bits and pieces of them may well be valid. If we ever do get a cryogenic core sample return from a comet's interior, there's lab safety reasons to be sure it stays cold, besides science-value reasons!