Hi, Mark - glad to have debate on this issue!

In reply:

LJ: 2. Trees were blown down in a non-spherical pattern, and some of the blow-down was rotated. An air-burst would produce a perfectly spherical shock wave.

Mark: The butterfly pattern has been simulated by using a specific trajectory. This statement is flat out false.

LJ: I may have misinterpreted his points about the pattern, but I still think he has a strong case against a space body explosion due to the blow down pattern. The rotation of fall direction would seem to me hard to explain by a point-source (more or less) explosion. Just out of interest (not wanting to start a flame war) have you read his article?

LJ: 3. Trees show evidence of being burned after they were broken, that is, the heat arrived after the shock wave, which is inconsistent with a high-energy air burst.

Mark: I have heard the reverse. They were burned for only a brief period of time as if lit then blown out. This is consistant with ignition by radiant heat followed by a shockwave blowing out.

LJ: "The presence of broken and burnt tree branches show that the shock wave arrival preceded the high-temperature explosion products, and this is characteristic of chemical explosions only. " From: http://www-th.bo.infn.it/tunguska/abstr3.html

LJ: 4. Some trees near the supposed epicenter survived. With a 40 megaton air burst, everything near the epicenter should have been incinerated.

Mark: This has also been simulated. Appealing to common sense versus published experiment makes ones research suspect. A little more thoughtful common sense would reveal that a force directly downward is unlikely to push something sideways.

LJ: OK, you can't have trees being ignitied at great distances by radiant heat and still have those at the epicenter survive. I understand what you are saying about a vertical force, but this isn't just a big wind, it's high power radiation we're talking about. Vertical or not, the trees should have been ashes.

LJ: 6. No significant fragments or dust have been found, which is important even to the comet theory, as comets have a considerable solid component (probably chondritic-type material).

Mark: Totally ignores the heat and resulting melting involved in such an explosion

LJ: What do you mean by that? There should have been evidence of dust and/or particel deposition in the area, regardless of heat or melting factors. That's a lot of material not to leave any trace.

LJ: 7. An unusualy sky-glow was noted in Siberia and many other areas for several days before the event. A comet tail would be too tenuous to produce such effects, especially if the comet were not visible prior to the exposion.

Mark: The glow was after the fact not before.

LJ: According to the article (one of his references: http://www-th.bo.infn.it/tunguska/abstr3.html) the glow appeared a week before the event, then disappeared quite quickly afterwards - sooner than would be expected from an 8 km altitude air burst of that size, which should have left dust in the atmosphere for weeks or months.

Do you have some links to more definitive sites regarding Tunguska? As I mentioned, most of the ones I've looked at seem to have a lot of large holes in them.