New! (2001 10 11):   Most Recent Scientific Analyses







 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Introduction
The meteorite which fell producing the Tagish Lake fireball occurred on January 18, 2000 at approximately 16:43 UT (08:43 PST local).  This exceptionally long and bright fireball was seen throughout the Yukon, Northern British Columbia, parts of Alaska, and the Northwest Territories.  Thousands of residents of the area witnessed the event and many were able to secure photos and video of the resulting dust cloud.  Some produced drawings of what they saw.  Scientists from the University of Calgary and the University of Western Ontario began collecting data related to the fireball and meteorite fall in February 2000 in close cooperation with the original finder of meteorites associated with this event, Mr. Jim Brook.  Expeditions to the area in mid February secured sufficient instrumental records to derive an atmospheric path, with further refinements from additional data gathered in early April during a second expedition.

This second expedition (which ran from April 6 to May 12, 2000) included significant ground recovery operations which began on April 20, 2000 when the first additional meteorite fragments were recovered from the lake ice.  Continuous recovery operations carried out by UWO, U of C, and Jim Brook from April 20 to May 8, 2000 until the lake ice became too unstable resulted in the location of ~500 additional meteorites, documentation of 410 of these and recovery of ~200.  The photo gallery shows the methods of retrieval on the ice and the general condition of the meteorites recovered.
 

Satellite Detection
The impacting meteoroid was detected by both infrared and optical sensors on board US Department Of Defense satellites, which timed the terminal flares to 16:43:42 with a two second duration at 1 micron radiation.  Optical measurements showed the flash energy to be 1.1 X 10¹²J (1.1 terajoules). Bolides of H-chondrite composition have been found to have light energy conversions of order 10%.  Given the low iron content, a more realistic value for the present case is probably in the order of 5% (Nemtchinov, pers. commun.) yielding a total energy release of ~2 X 10¹³ J or ~5 kilotonnes equivalent.  This could possibly be the largest meteor impact ever recorded by satellite sensors over land.

The Satellites also provided information suggesting an entry velocity of ~16 km/s. This velocity and the total estimated energy released imply this object had an entry mass somewhat in excess of 150 tonnes and an entry diameter of 5 metres.
 

Eye Witness Accounts
Approximately 70 eyewitnesses of the fireball and resulting dust cloud were interviewed.  The Fireball was generally described as a multicoloured object with a tail; the only artist rendition looks much like other photographed fireballs.  The fireball produced a spectacular dust trail which was visible for ~2 hours in the local area as it drifted towards the southeast, pushed by high altitude winds.  These same clouds are believed to be responsible for a spectacular display of noctilucent clouds seen from Edmonton Alberta during evening twilight later that day (seen here).

Eye witnesses placed the duration of the fireball at ~15 seconds, which is consistent with repeat-of-actions and other indications of a slow fireball.  The brightest of the two terminal flares was described as lighting up the landscape to ten times brighter than daylight with a bluish to greenish light.  As is typical, approximately one in ten witnesses described sounds simultaneous to the fireball, which is presumed to represent an electrophonic effect.  Witnesses also often described smells associated with the fireball including both prompt and delayed effects.  Smells were frequently described as sulphurous, although hot metal and rock were also mentioned.  Prompt occurrences of smells came from distances as large as 100 km from the ground projection of the fireball.

Ground shaking detonations were widely recorded by seismographs and followed the fireball by several minutes, but were generally of short duration.
 

Dust Cloud / Orbit (photos here)
The singular size of this event resulted in most residents in the area being aware of it.  Many of these saw the fireball illuminated only indirectly but were soon outside to take photographs of the dust clouds that were being lit up by morning twilight (the sun was 6° below the local horizon at the time).  Photos of the dust cloud are available here.

An orbit was found with the following characteristics:
 

a (semimajor axis)	2.1 ± 0.2 AU
e (eccentricity)	0.57 ± 0.05
q (perihelion distance)	0.891 ± 0.009 AU
(argument of perihelion)	222° ± 2°
(longitude of ascending node)	297.900° ± 0.003°
i (inclination)	1.4° ± 0.9°
T (orbital period)	3.0 ± 0.4 years
DT (time since perihelion)	1072 ± 164 days
Q (aphelion distance)	3.3 ± 0.4 AU
Vinf (entry velocity)	15.8 ± 0.6 km/s

Meteorite recovery
On January 25 near dusk, a local resident, Jim Brook (below), found meteorites on the snow covered ice of Taku Arm of Tagish Lake while driving home.  He returned the next day to collect several dozen meteorites in total.  The meteorites represent a particularly fragile variety of carbonaceous chondrites (1, 2). The meteorites were collected without skin contact and have been kept subsequently frozen.  During the spring melt, ~500 additional meteorites were recovered from a strew field ~16 km long and ~5 km wide oriented at ~150°.  For a detailed map of the recovery area click here.

Information from the Meteoritical bulletin
Tagish Lake            59º42'15.7"N 134º12'4.9"W
  British Columbia, Canada
  Fell 2000 January 18, 08:43:42 PST (16:43:42 UT)
  Carbonaceous chondrite (C2, ungrouped)

A brilliant fireball followed by loud detonations was widely observed over the Yukon Territory and northern British Columbia.  The fireball was also detected by satellites in Earth orbit.  Dust clouds from terminal fragmentation events were widely observed.  Mr. Jim Brook recovered several dozen meteorites totaling ~1 kg on the ice of Taku Arm, Tagish Lake, on January 25 and 26 (coordinates of first find given above).  Between April 20 and May 8, ~500 additional specimens were located on the ice of Taku Arm and a small, unnamed lake 1.5 km to the east.  Only ~200 were retrieved however, as many had melted down into the ice making their collection time consuming; recovery was prioritized based on meteorite mass and degree of disaggregation.  The total mass collected was between 5 and 10 kg. The strewn field is at least 16 km by 3 km, oriented ~S30°E. Classification and mineralogy (M. Zolensky, JSC; M. Grady, NMH):  possibly CI2 group; a matrix dominated chondrite, with a few small chondrules, CAIs, and isolated grains; matrix mainly phyllosilicates, Fe-Ni sulfides and magnetite, with abundant Ca-Mg-Fe carbonates; olivine, Fa0-29, PMD = 2%, with a peak at Fa1;  pyroxene, Fs1-7, PMD = 2%, with a peak at Fs2;  bulk C content 5.4 wt%, with d13C = +24.3 ?; shock stage, S1.  Oxygen isotopes (R. Clayton, UChi): d18O = +18.0-19.0 ?, d17O = 8.3-9.2 ?. Specimens:  majority held by UCalg (contact A. Hildebrand) and UWO (contact P. Brown).

Contact information

Alan Hildebrand
University of Calgary
hildebra@geo.ucalgary.ca

Peter Brown
University of Western Ontario
pbrown@uwo.ca

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Last updated 2001 10 11
by Rob Weryk