(meteorobs) Why do some meteors appear to zig-zag?

Marco Langbroek marco.langbroek at wanadoo.nl
Fri Jul 9 16:27:03 EDT 2004


> How many Pasamonte type fireballs do the
> professionals have to make a clear determination,
> I wonder.  Since that is the special case I support:
> bolide, high likelyhood to become meteorite, and
> perhaps more friable composition (see below):

Hello Doug,

There are more of such records in existence than you might think. The MORP
and EN networks photographed, and continue to photograph in the EN case,
quite a number of bolides which were highly suspect to have dropped
meteorites, which were not recovered for various reasons. The MORP project
alone published some 50 of such cases. And if you just look at meteors with
speeds <30 km/s, the number of recorded prof. quality multistation results
is close to 1300. So that is quite a lot.

I just made a search through the IAU photographic meteor database records. I
have the 1990 version and not yet the update with later orbits, so the
following detailed data are from photographs before 1990. The precision
files (there is also a file with less precision, graphically reduced Harvard
orbits), contain 1176 meteors with initial speeds < 30 km/s. Of these some
1000 are with speeds < 27 km/s, the approximate velocity boundary below
which a meteorite dropping becomes possible. 488 have speeds below 20 km/s
and 133 even below 15 km/s, which is very slow. Note that these are initital
speeds, before deceleration in the atmosphere. Quite a number of these slow
down to smaller speed values upon entry in the atmosphere.

Our DMS database adds another 100 with initial speed < 30 km/s, of which 80
are below 27 km/s, 21 are below 20 km/s, and 16 are below 15 km/s.


> I would begin by adding that the Space Shuttle reentry is
> another interesting case in that the energy management system
> gets switched on at 25 kilometers altitude and 2,750 kilometers
> per hour.  At that speed, I understand zig zags (S-turns) are
> induced by ailerons/rudder to disipate excess momentum, by taking
> advantage of changing the surface area/angle of entry.  That is
> normal operation, and luckily the Shuttle doesn't disintegrate when
>  it changes direction at these speeds, and you might probably believe
>  a factor to the tune of threefold to cover safety = 8,250 km/hr.

This is comparing apples with pears. First, unlike meteorites, space
shuttles are build in order not to disintegrate (and even then, we sadly
have seen that it can happen after all). But more important, we are talking
about a completely different speed regime here, and altitudes at which most
fireballs no longer exists, while even the meteorite droppers go into
dark-flight (i.e., ceasing to produce a meteor) at these altitudes of 25 km
and below. The speed of 2750 km/h you quote is a speed of  0.8 km/s, or
about Mach 2. In the case of meteors during their visible meteor phase, you
are talking of speeds at least tenfold that, and often (quite a lot) more.
Even the slowest meteor has an initial speed of at least 11.2 km/s, and, in
the case of surviving meteorites, extinguishes with speeds between 3 to 7
km/s, and the latter speed values are reached only in the latest part of
their visible trajectory, during the last second or so when deceleration
starts to build up very quickly.

- Marco

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Marco Langbroek
Dutch Meteor Society (DMS)
Leiden, the Netherlands
52.15896 N, 4.48884 E (WGS 84)

e-mail: meteorites at dmsweb.org
DMS website: http://www.dmsweb.org
priv. website: http://home.wanadoo.nl/marco.langbroek
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