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.
Related links:
* Smoke and Mirrors: the Legacy of a Veteran Cosmic Rock
www.aad.gov.au/default.asp?casid=20568
* Dodging Armageddon [PDF]
www.aad.gov.au/Asset/magazine/2005autumn...nitoring%20space.pdf
* Probing the atmosphere with Lidar
www.aad.gov.au/default.asp?casid=2134
IMAGE CAPTIONS:
[Image 1:
www.aad.gov.au/imglib/small/20050825-met...mpression-110436.jpg
(54KB)]
Artist's impression of the view of the meteoroid fireball near the
explosion site. Photo: A. Klekociuk & D. Ratcliffe
[Image 2:
www.aad.gov.au/imglib/small/20050825-lid...-strength-105258.jpg
(35KB)]
Laser scatter caused by the dust cloud, 28-31 km up, over about one hour.
Photo: A. Klekociuk
  