Cintia Panizza Wrote:
-------------------------------------------------------
> DougWeller Wrote:
> -------------------------------------------------------
> > This also looks good.
> >
> [aacimotaatiiyankwi.org]
>
>
> I found your link extremely interesting, but the
> theory of an airbust explosion of a comet might
> have destroyed the Hopewell it is not very clear
> to me, although the arguments on the article are
> pretty good. What happened in Tunguska being an
> airbust explosion of a comet is a pretty good
> explanation but it is not the consensus. The
> Tunguska region iridium was already found like in
> the Hopewell region. This explosion is considered
> to be capable of destroying a large metropolitan
> area
> [pt.m.wikipedia.org]
> The consensus on Tunguska is that an asteroid
> actually hit the ground, so the comet theory was
> dismissed. I have my doubts yet on the comet
> theory destroying the Hopewell and being the cause
> of the explosion in Tunguska, or being the cause
> of the dinosaurs extinction.
> I have to add a little humor saying that is so hot
> in Brazil in this past week and specially today
> that talking about heat it is a no good subject
> for today.
>
> Cintia Panizza
> —————————————

Actually, the scientific consensus is that the Tunguska event was an airburst event. The prime evidence is the lack of a crater in explosion region, implying that the impactor did not make it to the ground intact. What did reach the ground was the shock wave from the object exploding, blowing down over 2000 square kilometres of forest, with the trees falling radially to the the epicentre of the explosion. Recent modelling using data obtained from the 2013 Chelyabinsk airburst suggests that the object was a stony object of around 50 to 80 metres in size, and exploded around 10 to 14 kilometres in altitude with a energy equivalent to 5-10 Megatons of TNT. It is of these parameters that there is no clear consensus, and is still actively debated.

There is debate over the composition of the impactor; was it a comet fragment, or a stony or iron asteroid, and thus what was the object's size and velocity. This in turn has implications for the objects size, and the height of the explosion. This then all feeds into the debate over the event's energy yield. Some analysis suggests that the impact energy was of the order of 15-30 Megatons (based upon extrapolation of nuclear weapon tests), whilst some studies suggest 10-15 Megatons. There is even a model in which the impact energy is much less, around 3 to 5 Megatons, and that most of the damage was caused by excess forward momentum imparted to the blast wave from the objects pre-explosion trajectory, causing a kind of focusing phenomenon, meaning an increased energy density at the surface, i.e. a smaller energy event could cause much greater damage than expected due to this momentum "focusing".

About 15 years ago, there was a suggestion that part of the object survived the explosion, and this surviving fragment impacted the surface creating Lake Cheko (which lies roughly in the trajectory of the orginal object). More recent studies suggest that the lake is at least 280 years old (based on varve counting of lake sediment cores, similar to counting annual tree rings on a tree), and thus too old to have been caused by the Tunguska event.

In summary, there is still much we do not know for certain about the nature of the Tunguska impactor, but the scientific consensus is that it was an airburst event of an object between 40 and 100 metres in size, occurring around 5-15 kilometres in height, with an energy range of between 3 and 30 Megatons, all depending upon model parameters.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup