25/08/2005 - 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.
To lead:
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.
