From: Australian Antarctic Division
Posted: Monday, September 5, 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 paper, Direction of Meteoric Dust from an Asteroidal Airburst, published in Nature is the result of collaboration between a number of colleagues:
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.
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.
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