----- Doorgestuurd bericht van Pavel Spurny <[EMAIL PROTECTED]> -----
Datum:Thu, 18 Apr 2002 00:46:43 +0200
Van:Pavel Spurny <[EMAIL PROTECTED]>
Antwoord aan:Pavel Spurny <[EMAIL PROTECTED]>
Onderwerp[IMO-News] EN060402 bolide
Aan:IMO-NEWS <[EMAIL PROTECTED]>
Dear all,
I am sending you the information about the results on the EN060402
bolide
which was observed by many people over a large teritorry of Central
Europe.
As you can read below, it was a really exceptional case.
The April 6, 2002 fireball
A very bright fireball illuminated large territory of Western
Austria
and Southern Bavaria on Saturday evening, April 6 at 22:20:18 local time
(UT+2h). The fireball was observed by many casual witnesses over the
territory
of almost whole Central Europe, but most observations were reported from
Bavaria
and Western Austria. Except of numerous visual observations, the
fireball was
recorded by several kinds of scientific instruments. The most important
records
were obtained by the systematic long-term observational photographic
program -
the European Fireball Network (EN). The records were taken at 5 German,
one
Czech and one Austrian station of the EN. Each of these stations is
equipped
with one all-sky camera, which is open whole night and whole sky is
photographed
on one image. The German and Austrian stations are equipped with mirror
all-sky
cameras and are operated by the German Aerospace Center DLR, Berlin. The
Czech
stations of the EN are equipped with very precise Zeiss Distagon
fish-eye
objectives and are operated by the Astronomical Institute of the Academy
of
Sciences of the Czech Republic, Ondrejov. Most Czech stations had cloudy
skies
on April 6, however. The photographic records are most important for
exact
determination of the fireball atmospheric trajectory, including
prediction of
meteorite impact area and derivation of heliocentric orbit. In addition
to these
photographic data, the fireball was recorded by three radiometric
systems placed
in the Czech Republic at Ondrejov Observatory and Kunzak station, which
gives us
basic information about light curve and maximum brightness of the
fireball and about exact time of the event. Furthermore the fireball was
recorded by at least at two infrasound stations, one located at Freyung,
Germany
(see http://www.seismologie.bgr.de) and second at Deelen, The
Netherlands (see
http://www.knmi.nl/~evers/infrasound/events/020406/bavaria-bolide.html)
and also
at several seismic stations from Austria, Southern Germany and
Switzerland.
All data presented below are based only on above-mentioned
photographic
and radiometric data recorded within the EN observing program and are
very close
to final values. All records were measured, reduced and all computations
were
performed at the Ondrejov Observatory, the headquarters of the European
Fireball
Network.
The fireball started its almost 92 km long luminous trajectory
at an
altitude of 85.6 km about 15 km NE from Innsbruck, Austria (longitude
11.564 deg
E, latitude 47.304 deg N). Maximum brightness of about -18 absolute
magnitude
was reached in a bright flare at a height of 21 km near
Garmisch-Partenkirchen,
Germany (longitude 10.91 deg E, latitude 47.51 deg N). The fireball
terminated
at an altitude of only 15.8 km about 20 km W from Ga-Pa (longitude 10.85
deg E,
latitude 47.53 deg N). Such deep penetration of a fireball is very
scarce and
this fireball belongs to the deepest ever-photographed fireballs in the
history.
It also implicates, that some part of the initial mass survived the
ablation
processes in the atmosphere and landed on the ground as meteorites. The
slope of
the atmospheric trajectory to the Earth's surface was 49.5 degrees. The
fireball
entered the atmosphere with the velocity of 20.9 km/s and during its
flight
substantially decelerated to the final value of only 4 km/s, when
ablation
process was stopped. According to the dynamic behavior in the atmosphere
this
fireball belongs to the fireball type I, which is usually identified
with stony
material, mostly ordinary chondrites. The initial dynamic mass of the
entering
meteoroid was about 500 kg and most of this mass was ablated and only
about 30
kg of total mass could land on the ground in several fragments. The
impact area
is relatively large, it is at least several kilometers long and about
1km wide.
The main fragments will lie eastwards from Schwangau, Germany. Smaller
fragments
could be found also around the Austria-Germany border westwards from
Ga-Pa. The
whole area is located in high mountains (the Alps), which is
unfortunately very
unfavorable for any systematic search.
>From the exact time of the fireball occurrence, its initial velocity,
and the
position of the radiant, we computed the heliocentric orbit. We found
that the
body, before its collision with Earth, orbited the Sun on an elliptic
orbit
defined by the following orbital elements: semimajor axis 2.4 AU,
eccentricity
0.67, perihelion distance 0.79 AU, argument of perihelion 241.4 degrees,
longitude of ascending node 16.8 degrees and inclination 11.4 degrees.
Such kind
of heliocentric orbit is quite usual for fireballs which penetrate very
deep
into the Earth's atmosphere and which can produce meteorites. The
aphelion of
these orbits lies in the main belt of Asteroids and therefore the
asteroidal
origin of these bodies is inferred. However, the heliocentric orbit of
this
fireball has one very significant exceptionality: we found that this
orbit is
the same as the orbit of the first photographed meteorite fall in the
history -
the Pribram meteorite fall on April 7, 1959. Both orbits are so close
that there
is no doubt that both bodies have the same origin. It is very important
evidence
for the existence of asteroidal streams and meteorite streams as
suggested
earlier by Halliday and others. From observations of both bolides we
know that
both bodies were far from each other in the orbit (probably about half
of the
period) when the Pribram collided with the Earth. It implies that many
such
bodies have to be on this orbit, because it is fantastic chance to
photograph
two meteorite falls from the same orbit on practically the same
territory within
only 43 years! It also substantiates why it is important to operate such
long
term observing program as the European Fireball Network is.
Finally, from the perfect similarity of both heliocentric orbits we can
predicate, that both bodies had also the same composition and therefore
we can
expect that meteorites produced by the April 6 fireball are H5 ordinary
chondrites.
Pavel Spurny
Astronomical Institute of the Academy of Sciences
Ondrejov Observatory
The Czech Republic
e-mail: [EMAIL PROTECTED]
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