(meteorobs) Bolide size question

[Roberto G.]

>From: "Leo S." <l.stachowicz at btinternet.com>


> Hello all,
> 
> The recent Slovenian bolide, and its report on spaceweather.com has 
> brought up a couple of questions which I'm curious to find out the 
> answers to. Perhaps someone on this list could help me answer these 
> questions?
> 
> Firstly, on spaceweather.com it says that: "The July 25th fireball falls 
> into the category of superbolides--exploding meteors of magnitude -17 or 
> brighter. They are, essentially, small asteroids measuring a few to 10 
> meters in diameter and massing a few hundred metric tons"
> 
> Is it just me or does "a few to 10 meters in diameter" seem a little bit 
> of an exaggeration, even for an event of this magnitude? My 
> understanding of the subject would be that a -20 mag. could quite easily 
> be caused by a meteoroid of less that 1m diameter (with dense stony or 
> iron meteoroids), but perhaps I am mistaken! Would anyone here be 
> willing to speculate on the the size of this superbolide?

In general a bolid as full Moon (-12.6a) have 100 Kg of mass,
a bolid of 17.6 should have, we have not valid statistic on this class
of objects, a mass 100 biggest mass (10 Tn), an object of -20a
should have 5-10 more mass (then 50-100 Tn).
This usually, but there are tto many factors that can change this
mass but the number that I wrote before (50-100 Tn) show
the class where should be the object that fell the 25 July,
we must remember too that usually a meteoroid when fell
on our atmosphere has around 60 time more cinetic energy in 
mass that the same weight in TNT then this bolid should
display around 50-100 Tn x 60 = 3,000-6,000 Tn of TNT
= 3-6 Kilotons of power, Hiroshima was 20 Kilotons.
The 19 January 1993 fell in Northern Italy a bolid that
esplosed at 30 Km in height, it was biggest of this, it
was rekorded by 5 sismsic stations, 4 infrasound stations,
it was saw from 400 Km of distance (in Cecoslovacchia),
and by chance fell a night when all sk was clouded,
because if it fell with good weather or in dautime it
could do car accidents or other fatality, it esploxed
a 30 Km and it should too destroy the ozone layer
for a certain time.

>From this bolid now I remember that we prepare
for possible following bolid of the same class, it's
an idea of Korado Korlevic: in the day following
the dust of this bolid was dispersed in near half Europe,
the it's very important that many trap with adesive
surface are place in site with no industrial dusts,
the in the next day/wekk the dust of this bolid (25 July) 
shall be captured by this adesive surface.

> Secondly, assuming a stony or iron composition, and an entry angle of 45 
> degrees for sake of argument, what would be the approximate cut-off 
> point in terms of diameter for meteoroids to retain cosmic velocity all 
> the way down to the ground?

It's not a diameter but the mass, it's around 100 Tn, in this case
a residual cosmic speed of 2-3 Km/sec can to be conserved.

> 
> Best regards,
> Leo

Best greetings.
Roberto Gorelli