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Meteorit Asteroid Jatuh di Bone

26 Okt

LEDAKAN BONE DIDETEKSI SEBAGAI “SUPERBOLIDE”
(BOLA API BESAR)

Ledakan di perairan Bone yang saya duga sebagai
ledakan meteorit besar ternyata benar. Ini catatan saya sebelumnya http://t-djamaluddin.spaces.live.com/blog/cns!D31797DEA6587FD7!608.entry

Ternyata sistem
pemantau internasional untuk larangan percobaan nuklir  dari
11
stasiun melaporkan mendeteksi adanya ledakan besar yang berpusat di sekitar lintang
4,5 LS, 120 BT, sekitar pukul 11.00 WITA pada 8 Oktober 2009, seperti laporan
media massa.
 Analisis
ledakan menunjukkan bahwa kekuatan ledakan sekitar  50 kiloton TNT diduga akibat meteorit yang
berasal dari asteroid berukuran sekitar 10 meter. Ledakan terjadi karena
tekanan atmosfer yang menyebabkan pelepasan 
energi yang cukup besar.
Ledakan tersebut juga sinyalnya mencapai stratosfer
yang tingginya lebih dari 20 km.
Diperkirakan
meteorit dari asteroid itu berukuran 5 – 10 meter dengan kecepatan jatuh
sekitar  20.3 km/detik (73.080 km/jam).
Berdasarkan perkiraan sebaran meteoroid-asteroid di antariksa dekat bumi objek
seperti itu punya kemungkinan jatuh di bumi setiap  2 – 12 tahun.  

Laporan hasil analisis sistem pemantau internasional
itu bisa dibaca di

http://neo.jpl.nasa.gov/news/news165.html

Asteroid
Impactor Reported over Indonesia

Don
Yeomans, Paul Chodas, Steve Chesley
NASA/JPL Near-Earth Object Program Office
October 23, 2009

On October 8, 2009 about 03:00
Greenwich time, an atmospheric fireball blast was observed and recorded over an
island region of Indonesia. The blast is thought to be due to the atmospheric
entry of a small asteroid about 10 meters in diameter that, due to atmospheric
pressure, detonated in the atmosphere with an energy of about 50 kilotons (the
equivalent of 100,000 pounds of TNT explosives).

The blast was recorded visually and
reported upon by local media representatives. See the YouTube video at:

http://www.youtube.com/watch?v=yeQBzTkJNhs&videos=jkRJgbXY-90

A report from Elizabeth Silber and
Peter Brown at the University of Western Ontario indicates that several
international very-long wavelength infrasound detectors recorded the blast and
fixed the position near the coastal city of Bone in South Sulawesi, island of
Sulewesi. They note that the blast was in the 10 to 50 kT range with the higher
end of this range being more likely.

Assuming an estimated size of about
5-10 meters in diameter, we would expect a fireball event of this magnitude
about once every 2 to 12 years on average. As a rule, the most common types of
stony asteroids would not be expected to cause ground damage unless their
diameters were about 25 meters in diameter or larger.

A more extensive report by Elizabeth
Silber and Peter Brown of the University of Western Ontario is here.


Summary of Preliminary Infrasonic Analysis of the Oct 8,
2009 Indonesian Superbolide

Elizabeth
Silber and Peter Brown
Meteor Infrasound group
Dept. of Physics and Astronomy,
Univ. of Western Ontario
London, ON
N6A 3K7
CANADA

Released: October 19, 2009

On Oct 8, 2009, media reports
appeared in the local press in Indonesia concerning a loud air blast occurring
near 11am local time (0300 UT). Subsequent to these first media reports,
additional English language reports appeared suggesting the event was
meteoritic.

http://thejakartaglobe.com/home/mysterious-explosion-panics-locals-in-south-sulawesi-police-still-investigating/334246

http://www.thejakartapost.com/news/2009/10/08/blast-may-be-result-falling-space-waste-or-meteorite-lapan.html

Indonesian language reports more
clearly identify a bright fireball, accompanied by an explosion and lingering
dust cloud as the origin of the air blast. Finally, a YouTube video posted on
the same day appears to show a large dust cloud consistent with a bright,
daylight fireball.

http://www.surya.co.id/2009/10/09/ledakan-misterius-guncang-sulsel.html

http://www.youtube.com/watch?v=yeQBzTkJNhs&videos=jkRJgbXY-90

Based on these initial reports, a
detailed examination was made of all International Monitoring System (IMS)
infrasound stations of the Comprehensive Nuclear-Test-Ban Treaty Organization
(CTBTO). From this initial examination, a total of 11 stations showed probable
signals from a large explosion centered near 4.5S, 120E, with an origin time
near 0300 UT on Oct 8, 2009, consistent with the media reports. This signal was
notable for having been (a) detected at many IMS stations, including five at
ranges over 10,000 km (and one at a nearly 18,000 km range) and (b) being
confined to very low frequencies. Both of these observations suggest the
explosion source was of very high total energy. All signal motions were between
0.27 – 0.32 km/s, consistent with stratospheric signal returns.

We have used the Air Force Technical
Application Centre (AFTAC) period-yield relation as described by ReVelle (1997)
as the most robust basic indicator of source energy. To generate measured
periods, the average periods of all phase-aligned stacked waveforms at each
station were measured, according to the technique described in Edwards et al
(2006). These periods were then averaged to produce a single, global average
period of 13.4 sec and the AFTAC yield relation applied; this produced an
average source yield of 31 kT of TNT. Averaging the individual yields from all
stations produces a mean source energy near 50 kT of TNT while using only the
eight stations having the highest signal-to-noise-ratio (SNR) and using the
local observed periods of the waveform at maximum amplitude produces a yield
estimate of 40 kT of TNT, all of which are basically consistent. It is important
to note, however, that the standard deviation of this measurement is nearly 30
kT. That is, the best source energy estimate would be 40 +/- 30 kT TNT. Note
that much of this variation may be due to the signal emanating from different
portions of the fireball trail as observed at different stations; each period
measurement is a "sample" of the size of the cylindrical blast cavity
at that particular segment of the trail detected by any one station. As such,
the out of atmosphere yield for this event is likely higher than these
measurements suggest – very probably in the ~50 kT range.

The yield estimates based on
infrasonic amplitude are very uncertain in this instance as the propagation
distances are much larger than is typical and outside the range limits where
such relations have been developed (e.g. Edwards et al, 2006) and hence the
period relationship (which was generated using a dataset of nuclear explosions
having yields in this range) is more applicable.

Some examples of the detected and
processed waveforms are shown in the appendix.

Based on these infrasound records,
it appears that a large (40-50 kT TNT) bolide detonation occurred near 0300 UT
on Oct 8, 2009 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.

Follow-on observations from other
instruments or ground recovery efforts would be very valuable in further
refining this unique event.

Using an average impact velocity for
NEAs of 20.3 km/s, the energy limits (10 – 70 kT) suggested by this analysis
correspond to an object 5-10 m in diameter. Based on the flux rate from Brown
et al (2002), such objects are expected to impact the Earth on average every 2
- 12 years

References

Brown P., Spalding R.E., ReVelle
D.O., Tagliaferri E. and Worden S.P. 2002. The flux of small near-Earth objects
colliding with the Earth, Nature, 420, 314-316.

Edwards W.N., Brown P.G., ReVelle
D.O., 2006. Estimates of Meteoroid Kinetic Energies from Observations of
Infrasonic Airwaves, Journal of Atmospheric and Solar-Terrestrial Physics, 68:
1136-1160.

ReVelle D.O. 1997. Historical
Detection of Atmospheric Impacts by Large Bolides using Acoustic-Gravity Waves,
Annals of the New York Academy of Sciences, Near-Earth Objects – The United
Nations International Conference, editor J.L. Remo, New York Academy of
Sciences, 822, 284-302.

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Posted by pada Oktober 26, 2009 in Sains Antariksa & Astronomi

 

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