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(meteorobs) Official report on Greenland Meteorite (LONG)
The following is excerpted from the Cambridge Conference Digest - January 22,
1998, as quoted on the ASTRO mailing list...
-Lew
From: Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>
CAMBRIDGE CONFERENCE DIGEST, 22 JANUARY 1998
--------------------------------------------
. . . . .
(4) REPORTS ABOUT 1KM IMPACT CRATER CAUSED BY GREENLAND EVENT NOT
SUBSTANTIATED
From: Robert Matthews <rajm@compuserve.com>
Dear dr. Matthews
The report on a 1 km crater on the Greenland Ice Sheet has not been
substantiated. The position has been overflown Jan 4 by the SAR mission
and nothing particular was seen. The "crater" was an observations from
a SAS plane from 27000 feet. A more likely explanation is a melt water
lake on the ice that has been unplugged, emtied and leaving a
depression behind. We dont put any significance this observation.
There are no seismic observations from the event. There are reports on
tremors and violent sound effects from Fiskenaesset, followed by
violent wind effects.( see below)
Yours Sincerely
Torben Risbo
Coordinator of the Greenland Meteorite Search
Niels Bohr Institute AFG, Geophysical Department,
Juliane Maries Vej 30, DK 2100 Copenhagen O, Denmark
tr@gfy.ku.dk +45 35320585, +45 35320602 (sekr.)
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The Greenland meteorite event:
Update Jan 9 1998.
- ----------------------------------------------------------------
The event occurred on Dec 9 1997 08.11 UTC (+-2 min) 05.11 local time.
Observations are visual sightings from the SW coast of Greenland from
the Disco Bay area to the Julianehaabs District, trawlers in the waters
off the coast SE of Greenland, the Bay of Julianehaab and W of
Greenland off Fiskenaesset, a video recording in Nuuk and sounds,
tremors and wind effects observed in Fiskenaesset.
The target area is obtained by a shallow angle intersection between the
video camera view and two visual sightings from trawlers in the waters
off the SE coast of Greenland. Accordingly some uncertainty is
connected with the positioning of the endpoint epicenter of the track.
We are fairly sure that the track ended on a position over land.
The best position of the impact/explosion site is now at the Greenland
ice sheet near the Frederikshaab Isblink at the West Coast between
Fiskenaesset and Frederikshaab (Pamiut).
There has been a discussion and an evaluation of seismic signals
observed by NORSAR, Kjeller, Norway on the array stations in Finmarka
and Svalbard. (ARCES & SPITS). The signals were at about the expected
arrival times for a seismic event in Southern Greenland. The times were
not consistent with the arrival of signals from an explosive event in
Greenland, but they were apparently arriving from about that direction.
NORSAR cannot identify seismic phases in the signals. Also the
frequency (10 Hz) is high for a teleseismic event.
We and NORSAR do not relate the seismic signals at ARCES and SPITS to
the meteorite event in Greenland.
Erik Hjortenberg, Kort og Matrikel Styrelsen (KMS) reports that the SFJ
(Soendre Stroemfjord) seismic station was not in operation on the time
of the event. This is most regrettable since this station is near (300
km) the target area and records seismic signals to high frequency.
Seismic signals were not seen at the seismic station Danmarkshavn (DAG)
in NE Greenland.
Violent sounds and shakings of houses have been reported in
Fiskenaesset 110 km south of Nuuk. This was followed some minutes
later by wind effects of short duration in an otherwise quiet weather.
The meteorite event was recorded by a video surveillance camera placed
in a private house in Nuuk. For about 1 second the meteorite track was
in the field of view of the camera, the camera was saturated for a
moment in a near white out in an explosive flash of light while the
track was in the field of view. Daylight conditions reigned during a
fraction of a second. A terminal light flash was clearly seen on the
video but the origin was below the horizon of the camera, the field of
view was restricted by the nearby mountain Store Malene SE of Nuuk. The
flash gave a diffuse light from the sky (cirrus clouds) as seen from
the camera site. The afterglow on the sky from the track indicates an
angle of the track of 50 dgr. with the horizon as seen from Nuuk.
Analysis of the video sequence is in progress.
We are fairly sure that the track ended on a position over land.
The best position of the impact/explosion site is now at the Greenland
ice sheet near the Frederikshaab Isblink at the West Coast between
Fiskenaesset and Frederikshaab (Pamiut).
A joint SAR mission by the Royal Danish Air Force and the Danish Center
for Remote Sensing (DCRS) at the Technical University of Denmark is
completed on Jan 4 over the target area. An area of 10000 km**2 were
covered in 6 flight tracks extending from the ice border zone and
inland. Two additional tracks were covering the Frederikshaab Isblink.
Since the the surface topography is rough the detection of an impact
feature may be difficult. Data processing in progress at DCRS and is
expected to go on for 3-4 weeks.
The target area is obtained by a shallow angle intersection between the
camera view and two visual sightings from trawlers in the waters off
the SE coast of Greenland. Accordingly it has moved about on the ice
sheet now to end in the coastal region following a critical evaluation
and dismissal of some conflicting trawler observations.
No microbarograph detections are seen by an array in Los Alamos.
A log of aircraft positions in the airspace of Greenland (> 19000 feet)
has been obtained from the control in Gander, Canada. Only 3 aircraft
were in the area and none were judged to be in a position and on a
course at the moment to give useful information.
Some 30 reports of visual observations have been obtained by telephone
interviews with authorities, people in Greenland and trawlers operating
in the waters off Greenland. Most visual observations do not allow
useful bearing determination, but support the picture. Two trawler
observations have delivered accurate and reliable information.
The magnitude of the light flash is cautiously estimated to be m--21 as
seen from the trawlers off the SE coast 400 km away. This certainly
indicate a light effect comparable to a nuclear discharge in the
atmosphere. The owner of the Nuuk camera claims that the light was
comparable to full sunlight conditions as seen in Nuuk (m--26) at a
distance of 150 km. By comparison with published data from satellite
observations of light flashes from meteorite events in the atmosphere
(ref) it is estimated that the flash equals the light emission from a
10 ktons nuclear discharge.
Running updates on the Greenland meteorite event can be obtained at
http://www.astro.ku.dk/~holger/ and http://www.dcrs.dtu.dk
Ref.
J. Kelly Beatty, Sky and Telescope Feb 1994, 26-27 "Impacts Revealed".
Torben Risbo
Coordinator of the Greenland Meteorite Search
Niels Bohr Institute AFG, Geophysical Department,
Juliane Maries Vej 30, DK 2100 Copenhagen O, Denmark
tr@gfy.ku.dk +45 35320585, +45 35320602 (sekr.)