[meteorite-list] U.S. Satellites See Russian Impact

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:07:01 2004
Message-ID: <200210141626.JAA13042_at_zagami.jpl.nasa.gov>

http://www.nearearthobjects.co.uk/news_display.cfm?code=news_intro&itemID=127

U.S. Satellites See Russian Impact
Near Earth Object Information Centre (United Kingdom)
October 13, 2002

The U.S. Department of Defense have released
information obtained by U.S. satellites on the
fireball event that occurred over Siberia on Sept 24.
Eye-witness accounts of the event reported a
large luminous object falling to Earth near Bodiabo
in Siberia. Hunters in the region have also reported
the existence of a crater surrounded by burnt forest
suggesting that an impact event had occurred. The
event was detected by near-by geophones as a
moderate-earthquake.

U.S. satellites initially detected the fireball at
57.91N and 112.90 E at an altitude of 62 km and it
was tracked to 58.21 N and 113.46 E at an altitude
of 30 km. The satellite measurements indicate that
the total energy radiated from the fireball was
roughly the equivalent of 0.2 kilotonnes of TNT.

Although the amount of energy of a meteoroid that
is converted into heat and light as it falls through
the atmosphere is not simply related to the size of
the meteoroid it can be used to estimate the size of
the event. The fireball seen over Alaska on January
18, 2000, for example, was likewise observed by
U.S. satellites and released an energy of around
0.26 kilotonnes. This event, like the Siberian
fireball, was detected by earthquake geophones
and resulted in the fall of the Tagish lake meteorite.
Only around 1 kg of Tagish lake was recovered
from the frozen surface of a lake, most of this
fragile meteoroid was probably destroyed during
atmospheric entry. If the Siberian meteoroid,
however, consisted of tougher materials such as
iron then more mass may have survived to collide
with the ground. Weak meteoroids also lose more
of their energy during flight through the atmosphere
because of their break-up.

The Sikhote Alin meteorite fell in Russia in 1947
and more than around 70 tons of this meteorite
were recovered, many from steep sided impact pits
in soft soil. Estimates of the energy released by
Sikhote Alin vary, however, it is likely to have
been up to 10-20 kt with most of this energy lost
during fall through the atmosphere. The event in
Siberia on Sept 24 is unlikely to have been as
significant as Tunguska or the event that generated
meteor crater in Arizona since both of these
liberated tens of megatonnes of energy. It may,
however, prove to have resulted in the fall of an
iron meteorite although the fact that the fireball
was tracked to an altitude of 30 km, where most
fireballs associated with meteorites end, suggests
it is perhaps not likely to be as large as the Sikhote
Alin fall. Only once scientists have located and
examined the impact site, however, will the size of
the event be known for certain.
Received on Mon 14 Oct 2002 12:26:16 PM PDT