[meteorite-list] Re: Rubble pile asteroids

From: Maurizio Eltri <eltri_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:31 2004
Message-ID: <5.0.2.1.1.20020925220014.00a28c30_at_mail.tin.it>

If possible, I would be pleased to get your opinions about my hypothesis
concerning the possible structure of some asteroids.
My idea is following :

I formulated this hypothesis after observing a fireball which occurred
during the 12th of August, 1998, during the maximum activity of perseids:
its apparent magnitude was comparable to that of the moon during the
first quarter, and it was observed throughout almost all of Italy as well as
Croatia.
After analyzing the trajectory, I am sure I can assert that this fireball
didn't belong to the perseids meteor shower. What struck me were not
only its great luminosity and its chromatic properties, but, above all,
probably depending on being in the right position of observation, was that
beginning from the central part of its trajectory and going on for many
degrees, its nucleus seemed to be constituted by five or six very bright and
separate spots.
This probably implies that the fragmentation process began in the very high
atmosphere, and this could give many relevant informations about its
structure that can be summarized mainly in two points:

1.a non-aerodynamic shaped meteoroid, or one with fractures that started
its fragmentation process, from the highest part of the atmosphere, and after
its fragments should have acquired such an aerodynamic shape by an
ablation process so as better to resist atmospheric friction.

2. the meteoroid was most likely made of a rocky conglomerate, as a sort of
ordinary chondritic material kept together by a friable and lighter material
probably of cometary origin, I suppose it was porous and carbonaceous.

By the means of the last hypothesis, even if it is not so easy to show, we can
explain the meteoroid fragmentation in the upper atmosphere in terms of the
disruption of the friable parts (such as soft clay minerals which hold the
somewhat harder material together) by attrition, and only the most resisting
parts can survive and reach the lower regions of the atmosphere and maybe
impact on the Earth.
What is interesting is that if such asteroids do exist, they may be generated by
a sort of soft anaelastic collision between an outgassed cometary nucleus and
an asteroid. After this collision, an accretion process would make these rocky
fragments stick together.
                                     
Greetings,
Maurizio Eltri.
 
Received on Wed 25 Sep 2002 04:15:09 PM PDT