[meteorite-list] Large Meteor Observed Over Antarctica

Thu Aug 25 14:13:51 EDT 2005

Australian Antarctic Division
Department of the Environment and Heritage
Australian Government
Kingston, Tasmania, Austraila

Media contact:
Sally Chambers, (03) 6232 3405 or 0417 562 196

Thursday 25 August 2005

Cosmic hole-in-one captured over Antarctica

What at first looked like an electronic glitch turned out to be a 
significant event in space, in fact, a cosmic hole-in-one.

What a powerful telescope had picked up as it stretched towards the night 
sky over Antarctica was the trail of dust left in the wake of the death of 
an asteroid.

The remarkable story features in the latest edition of the prestigious 
international science journal, Nature.

Lead author, Dr Andrew Klekociuk, from the Australian Antarctic Division 
said that early last September, a physicist at Australia's Davis station 
in Antarctica had prepared his monitoring instrument, known as LIDAR, for 
keeping watch on atmospheric activity during the long night ahead.

"Just as observation of the stratosphere began a strange signal was 
recorded from 30 kms overhead. Our physicist thought his preparation of 
the optics may have been amiss so fitted a filter but the signal persisted 
for another 30 minutes.

"What he didn't know at the time was that seven hours earlier an asteroid 
had crashed to Earth in another part of Antarctica, about 1500 kms west of 
Davis. The closest it got to human habitation was around 900 kms west of 
Japan's Syowa station," Dr Klekociuk said.

Shortly after the LIDAR observations it was revealed that the event had 
also been picked up by the global network of satellites and a range of 
other instruments.

But the most detailed evidence of the trail of dust, carried by strong 
winds around Antarctica, has been captured by the LIDAR at Davis station.

Dr Klekociuk said that it was thought that the asteroid had come from what 
is known as the Aten group somewhere between Venus and Earth, ranging 
anywhere up to 46 million kms from the sun. Measuring roughly 10 metres it 
is the biggest body to enter Earth's atmosphere in the past decade.

Its travel time from entering Earth's atmosphere 75 kms up until it 
landed? Just five seconds.

Scientists believe that the asteroid's original size was close to that of 
a small house weighing a thousand tonnes and that if it had not broken up 
on entry into the atmosphere its effect on impact would have been that of 
the bomb dropped on Hiroshima.

"The size of the dust cloud in the stratosphere was 200 kms by 75 kms. Had 
a cloud that size passed over the sun the light would have dimmed by 
around 20 per cent.

"Inevitably particles contained in the dust cloud have fallen to Earth and 
samples from all three Australian Antarctic continental stations -- Davis, 
Casey and Mawson -- have been retrieved for analysis at the Australian 
Antarctic Division."

Dr Klekociuk said that these analyses will enable scientists to validate 
models of atmospheric circulation. The timing and location of the event 
will also allow for testing theories relating to the impact of large 
meteorites on ozone and climate.

"While there were no obvious short-term associated changes in regional 
climate or ozone levels, the longer term implications are still being 
evaluated," Dr Klekociuk said.

The authors:

The paper, Direction of Meteoric Dust from an Asteroidal Airburst, 
published in Nature is the result of collaboration between a number of 
colleagues:

* Dr Andrew Klekociuk, Australian Antarctic Division, Australia.
* Dr Peter Brown, University of Western Ontario, Canada.
* Dr Dee Pack, The Aerospace Corporation, California, USA.
* Dr Douglas Revelle, Los Alamos National Laboratory, New Mexico, USA.

Background:

Importantly, this event occurred just inside the Antarctic stratospheric 
vortex -- a region of air that forms over the continent each winter and 
which is effectively isolated from air at lower latitudes. This means that 
the dust was confined to the Antarctic region for several weeks, giving 
the particles time to fall to the surface and be incorporated in the ice 
record. These and future samples will be important for confirming the 
meteor's composition and determining other properties.

Lidar:

The Davis LIDAR (Light Detection and Ranging) is a remote sensing 
instrument which profiles atmospheric density, temperature and wind 
velocity as a function of altitude. It operates in a manner akin to radar; 
pulses of laser light are transmitted into the sky, and the weak 'light 
echo' scattered back to the instrument from atmospheric gases and aerosols 
is collected and analysed.

The LIDAR, developed by the Australian Antarctic Division in collaboration 
with the Adelaide University, was installed during the 2000/01 summer.