[meteorite-list] Russian meteor: Stefan Geens' research updates - part 3

From: Robin Whittle <rw_at_meteoritecentral.com>
Date: Fri, 22 Feb 2013 15:23:09 +1100
Message-ID: <5126F2AD.9070809_at_firstpr.com.au>

Here is my 3rd set of highlights from the emailed updates I get for:

http://ogleearth.com/2013/02/reconstructing-the-chelyabinsk-meteors-path-with-google-earth-youtube-and-high-school-math/


There's an extensive and apparently continually updated page:

  http://meteorites.ru/menu/press-e/yuzhnouralsky2013-e.php


A photo with the very tail-end of the smoke trail clearly visible, after
some movement due to winds:

  http://s18.postimage.org/a9wyibt3t/7_Mvu4yml_Bg4.jpg

>From an aircraft:


http://i54.fastpic.ru/big/2013/0215/66/1d6cc8d2b2e95609ad9e4ca3ad9ff066.jpg


Is this an meteorite?:

  http://www.youtube.com/watch?v=5tF5f1kLpQ4
  http://www.youtube.com/watch?v=ymt_3AZa-ww


"Started another map, based on sound delay:"
  http://goo.gl/pNxPh


A most interesting backwards and forwards analysis of the video I
referred to previously, which has not yet appeared in MikeG's "Chebarkul
Videos - Choice Selections to Watch" messages:

   This video was mentioned for its sounds, but for me the most
   interesting aspect of it is that it is the only video I have
   seen which shows at least two smaller objects following the
   main mass after the main part of the smoke trail. I suggest
   switching to full-screen and starting the player at 4:30:

     http://www.youtube.com/watch?v=gQ6Pa5Pv_io

This is an animated GIF which goes back and forwards continually.

   http://postimage.org/image/zdzm79g95/

Most interesting! I can now see a smaller body going ahead of a larger
body, with two smaller bodies trailing. Closer examination reveals a
fifth small luminous moving object between the two trailing objects. I
assume this is due to a solid object, rather than being just a bunch of
previously heated and still-radiating gas which is moving at such high
speeds in the smoke trail due to momentum or general movement of gas
along the path of the previous objects.

I think this shows the glowing gas around four or more bodies at least
which were separate at this point, surviving the main conflagration and
deceleration. They are being cooled by radiation and contact with the
now-denser cool atmosphere, and must be moving at a velocity which
doesn't cause more heating than cooling, since they stop glowing within
a second or so. They are on somewhat different paths - they have been
pushed sideways or up-and-down by the contact with the atmosphere
creating extreme stresses on the original object.

With their different sizes, they decelerate at different rates. The
smaller body which is initially ahead is on a different path to the
larger object behind it, and the smaller object which is ahead
decelerates more rapidly, so it ceases to be visible as distinct from
the larger glow surrounding the larger object.

The objects themselves would be too small to see with a camera with this
resolution. However, we see their surrounding incandescent gas for as
long as they are going fast enough to generate this.

My guess is that any object which survives as a single body to this
point is unlikely to suddenly explode into many tiny fragments further
down, since after this point it is getting slower and slower and is not
being heated so much. I guess they are still supersonic, but in just
these two seconds of this remarkable video, I can see how much these
bodies are slowing down.

Kinetic energy is proportional to the mass multiplied by the velocity
squared. At the end of these two seconds those bodies have far less
kinetic energy than they had at the start. I guess the velocity has
dropped a factor of at least 4, so the kinetic energy would have dropped
by a factor of at least 16.

I would expect that one or more of these bodies would survive its
further travel through the atmosphere. So I would not be surprised if
there much larger chunks fall to the ground than have been reported so
far (as far as I know - and everything of interest I wrote to this list).

I have never understood how some experts state that an entire bolide can
burn up in the air, leaving nothing to fall to Earth. I guess this is
intended to reassure people that rocks won't drop on their heads.
However, this does not make sense to me.

Surely, once the object is in small enough pieces, some or most of those
pieces slow down within a fraction of a second, without being vaporised,
to a velocity where there is little further heating and low-enough
aerodynamic stress so that there is no further fragmentation. Those
fragments would fall to Earth.

As to what size those fragments would be . . . surely it depend on the
material, with solid metal or high-metal-content objects surviving in
larger chunks than rocky objects or comet-like material. I once read
that comets have the density of cigarette ash, but I don't entirely
believe this. How could such a body remain intact with either
mechanical binding and/or gravitational attraction over thousands of
years in even the diffuse solar wind. Some of them are destroyed on
their only recorded passage near the Sun. Others make repeated passes
near the Sun and survive with only a minor loss of material.

 - Robin
Received on Thu 21 Feb 2013 11:23:09 PM PST