|
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.
-
Red
Nova News -
|
