This story was updated at 4:50 p.m. EDT.
GOLDEN,
Colo. – A space rock explosion earlier this
month over an island region of Indonesia is now being viewed as perhaps the
biggest object to tangle with the Earth in more than a decade.
On Oct. 8,
reports from Indonesia told of a loud air blast around 11 a.m. local time. One
report indicated a bright fireball, accompanied by an explosion and lingering
dust cloud, as the origin of the air blast.
According
to experts at the NASA/JPL Near-Earth Object Program Office in Pasadena,
Calif. – Don Yeomans, Paul Chodas, Steve Chesley – the blast is thought to
be due to the atmospheric entry
of an asteroid more than 30 feet (10 meters) in diameter. Due to
atmospheric pressure, the object is thought to have detonated in the
atmosphere, yielding an energy release of about 50 kilotons (the equivalent of
110,000,000 pounds of TNT explosives).
"My
understanding is that this may have been the largest object to strike the Earth
since the fireball near the Marshall Islands in the South Pacific on February
1, 1994," said Clark Chapman, a noted specialist in asteroids and a planetary
scientist at the Southwest Research Institute (SwRI) in Boulder,
Colo.
"Although the
Indonesian object was large and the resulting atmospheric
explosion may have been the equivalent of several Hiroshima bombs, it is
not unexpected for our planet to be hit every decade or so by such an object,"
Chapman told SPACE.com.
Preliminary
investigation
A
preliminary look at the incident has been performed by Canadian researchers Peter
Brown and graduate student Elizabeth Silber, of the Meteor Infrasound group in
the department of Physics and Astronomy at the University of Western Ontario in
London, Ontario.
The researchers made a detailed
examination of all International Monitoring System infrasound stations
of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). An initial
look found that a total of 11 stations showed probable signals from a large
explosion.
Based on
their scrutiny of the infrasound records, the Canadian research team reported that
a large (40-50 kilotons of TNT) bolide detonation occurred near the coastal
city of Bone in South Sulawesi, Indonesia. The infrasonic geolocation is not
precise enough to determine if the bolide was over water or land, but it was
relatively near the coast, the team reported.
Follow-on
observations from other instruments or ground recovery efforts, the Canadian
team added, would be very valuable in further refining this unique event. Their
analysis corresponds to an object some 16-33 feet (5-10 meters) in diameter.
Based on the earlier work by Brown, such objects are expected to impact the
Earth on average every two to 12 years.
"We are
trying to coordinate with some local scientists to secure more local data, but
that will likely take several weeks," Brown told SPACE.com.
Brown said
a YouTube
video that was aired a few days after the
event convinced them it was a bolide.
"Had this
happened over the ocean we would only have known that there had been a big
explosion...we would presume it was a fireball, but it could be anything
producing a large impulsive shock in the atmosphere," Brown said.
More data
is expected from U.S. military space assets that likely detected the event.
From their vantage point in space, multiple sensor systems would have seen the
huge explosion and there surely is a rich dataset of measurements to be plumbed
relating to the detonation.
Wall of
secrecy
Why wasn't
this asteroid observed before it hit?
SwRI's
Chapman said he was not aware that the object was seen before it plowed into
Earth's atmosphere.
"The body
was large enough that some of the current Spaceguard Survey telescopes might
have detected it a couple of days before it hit, were it coming from the night
sky. But it struck during daytime and probably could not have been seen by
those telescopes," Chapman explained.
A second question is whether it was detected by military satellites that monitor
bright flashes in the Earth's atmosphere for defense and security purposes.
"Almost
certainly it was detected and presumably immediately identified as an explosion
of a large meteoroid rather than, say, an explosion of a human-made device in
the atmosphere," Chapman figures. "But these satellites are secret and, in
the past, the establishments controlling them have delayed releasing the data,
for weeks or months."
Earlier
this year, Chapman added, a change in previous policy led the U.S. military to withhold
the data from the public.
"Scientists
hope that they will reverse that policy. This event will demonstrate
whether the wall of secrecy is coming down again, or not," Chapman noted. "Evidently,
because of the passage of weeks since the event, there has been no decision to
release the data promptly."
Leonard
David has been reporting on the space industry for more than four decades. He
is past editor-in-chief of the National Space Society's Ad Astra and Space
World magazines and has written for SPACE.com since 1999.
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