[meteorite-list] Monster Meteor Leaves Dusty Clues Over Antarctica

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Aug 24 19:20:30 2005
Message-ID: <200508242319.j7ONJRY28034_at_zagami.jpl.nasa.gov>

http://dsc.discovery.com/news/briefs/20050822/meteordust.html

Monster Meteor Leaves Dusty Clues
By Larry O'Hanlon
Discovery News
August 24, 2005

A thousand-ton meteor exploded in the atmosphere a year
ago, releasing the power of a nuclear bomb and leaving behind an unusual
dusty trail that has raised questions about the ways extraterrestrial
material finds its way to Earth's surface and the geological record.

The meteor exploded over Antarctica on Sept. 3, 2004, with the energy of
13,000 to 28,000 tons of TNT, roughly equivalent to the atomic bomb that
destroyed Hiroshima in 1945.

Yet it wasn't eye-witnessed by anyone and never reached the Earth's
surface. Instead, its smoky aftermath was picked up in routine
measurements by atmospheric researchers in Antarctica who use lasers to
probe the polar atmosphere for dust particles, called aerosols.

"We were probably the only ones to know of (the meteoroid)," said Andrew
Klekociuk of the Australian Antarctic Division in Kingston, Tasmania,
Australia.

What clued them in was the discovery of a cloud of dust higher than any
particles should be.

"This was unusual," said Klekociuk of the initial dust observations.

He immediately suspected it was the remains of a meteoroid. And after
checking their equipment to make sure it wasn't an instrument error, he
sent word to other scientists in other countries who had access to data
from satellites and infra-sound stations to see if any other instruments
had picked up the meteoroid.

As it turned out, the house-sized chunk of falling rock had been
detected elsewhere by other instruments, but hadn't been identified as
such until Klekociuk started asking around. A report on the meteoroid by
Klekociuk and his colleagues appears in the Aug. 25 issue of Nature.

Satellites picked up the meteoroid blazing down into the atmosphere from
35 miles to 11 miles (56 to 18 kilometers) high.

Infrasound stations picked up a very low-frequency boom from the
explosion as near as McMurdo Station in Antarctica, and as far away as
Germany, Klekociuk said.

"It's pretty remarkable that it reached all the way to 13,000
kilometers," he said of German infrasound detection.

All the data was used in calculations that helped the researchers
discover the impressive size of the meteoroid.

But more important than the event itself is the dust it left behind,
said Klekociuk.

The meteoroid's dust adds a new wrinkle to an ongoing debate about which
kind of meteoroids leave the most extraterrestrial material in the
geological record and ice core records seen on the ground: Is it the
occasional big fiery bodies or an ongoing rain of zillions of tiny
interplatentary dust particles (IDPs) falling to Earth?

Many researchers had thought that big meteoroids like last year's would
leave telltale small particles of dust, just a few nanometers across and
far smaller than IDPs.

But the meteoroid dust measured by the Australian light detection and
ranging instruments (LIDAR) instruments at Davis in Antarctica was 400
to 1,000 nanometers across: bigger than thought and comparable to IDPs,
explains Klekocuik.

So are IDPs seen in ice cores and sediments really IDPs, or the remnants
of larger bodies that burned up in Earth's atmosphere? The answer is not
yet clear, said NASA researcher Kevin Zahnle.

"The people who study the asteroids and meteors have long thought that
the big bodies were the most important," said Zahnle. "The people who
study IDPs seem to think that the IDPs are more important."

"It's actually pretty hard to tell on ordinary time scales, although if
you think of hundred-million-year intervals and the big bodies include
monsters like the K-T event," said Zahnle, referring to the meteorite
impact that coincided with the extinction of the dinosaurs, "it is
inevitable that the big bodies win."
Received on Wed 24 Aug 2005 07:19:27 PM PDT