INCOMING!, Detection and observation of Earth-approaching asteroids. |
INCOMING!, Detection and observation of Earth-approaching asteroids. |
Oct 19 2008, 11:04 AM
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#106
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
I hear ya; I have a couple myself (a Silkhote-Alin & a small Allende piece.)
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Oct 19 2008, 03:58 PM
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#107
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
... a 1 MegaTon event once every MONTH... Um, are you sure about this? Can you give some references? That doesn't jibe with estimates I've found on the web, I could buy a kiloton event every month or a few months, but a megaton event is a major fraction of a Tunguska-type event - those are said to happen once every few decades at most. -------------------- |
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Oct 19 2008, 09:57 PM
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#108
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Member Group: Members Posts: 293 Joined: 22-September 08 From: Spain Member No.: 4350 |
In a 2002 interview for the BBC, a retired member of the US Department of Defense recalled a 100 kT explosion detected over Greenland in 1996. That seems to imply that 1 MT bolids aren't very common.
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Oct 20 2008, 02:48 AM
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#109
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Member Group: Members Posts: 599 Joined: 26-August 05 Member No.: 476 |
Agree with ugordan on the dubious megaton class events. I recall the Sky and Telescope article (c. late 1980's) which discussed the stats when data on atmospheric detonation detections from the US Defense Support Program (early warning satellites) were sanitized and released. The largest events going back decades were in the ten to low tens of kiloton range. A megaton class event would likely make the television news even if it happened over in the middle of the Pacific Ocean.
The sensor that detects these detonations are intended to detect nuclear explosions -- Bhangmeter The etymology of the word is an interesting bit of trivia. In the Cold War days of long nuclear war scenarios, the US had some pretty Strangelovian plans for capabilities that were at least partially implemented. This was the Integrated Operational NUDET Detection System (IONDS) which put bhangmeters on GPS satellites so the location of detonations can be plotted to tens of meters. One use would be for nuclear attack damage assessment, i.e., did the target get blown up or are additional attacks needed? Atmospheric detonations of meteors would similarly be well pinpointed. |
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Oct 20 2008, 04:01 AM
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#110
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Member Group: Members Posts: 356 Joined: 12-March 05 Member No.: 190 |
I was the one who initially created the Bhangmeter article a few years ago.
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Guest_PhilCo126_* |
Oct 20 2008, 10:34 AM
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#111
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Guests |
It looks like nobody noticed the question mark in blue circle at top left of my reply
Indeed the 1 MegaTon event rate seemed over-estimated, I'll check this evening in which book/article I've found that number. I have been using it in lectures during the last few years so for IYA 2009 a recheck might be necessary... BTW superb reply on the etymology of the word "Bhangmeter" US Department of Defense and Department of Energy satellites scanning the Earth for evidence of nuclear explosions over the last eight years detected nearly 300 optical flashes caused by small asteroids (one to 10 metres in size) exploding in the upper atmosphere. This provided research teams with a new estimate of the flux of near-Earth objects colliding with the Earth. The revised estimate suggests Earth's upper atmosphere is hit about once a year by asteroids that release energy equivalent to five kilotons of TNT. The object that exploded above Tunguska, Siberia in 1908 was considered 'small' (30 to 50 metres across), yet its energy was big enough to flatten 2,000 square kilometres of forest. It would have completely destroyed a city the size of New York. Prior estimates suggested that Tunguska-like events (10-15 MegaTon) happened every 1,000 years or so. New estimates put that closer to the 250-300 year range. Although estimates are based on a lot of uncertainty, every couple of centuries there could be a significant event… So I guess that brings numbers down to a 10 KiloTon event every year |
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Guest_PhilCo126_* |
Oct 20 2008, 05:53 PM
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#112
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Guests |
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Guest_PhilCo126_* |
Oct 20 2008, 07:25 PM
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#113
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Guests |
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Nov 6 2008, 10:28 AM
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#114
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Member Group: Members Posts: 877 Joined: 7-March 05 From: Switzerland Member No.: 186 |
Summary of the fall on http://neo.jpl.nasa.gov/news/2008tc3.html
It also mentions the Egyptian webcam as a possible capture of the flash http://home.pages.at/thie/asteroid_2008_tc3/ Btw. the search for fragments in Sudan seems to be under way. -------------------- |
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Nov 8 2008, 10:43 AM
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#115
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Member Group: Members Posts: 877 Joined: 7-March 05 From: Switzerland Member No.: 186 |
Wow, eventually someone managed to capture the persistent train after the impact http://asima.seti.org/
http://antwrp.gsfc.nasa.gov/apod/ap081108.html -------------------- |
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Guest_PhilCo126_* |
Nov 22 2008, 09:21 AM
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#116
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Guests |
Another Fireball this month: Canada 20th November 2008
YouTube video: http://www.youtube.com/watch?v=e_2aX-784sw More info: http://www.ctvbc.ctv.ca/servlet/an/local/C...ishColumbiaHome |
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Guest_PhilCo126_* |
Nov 28 2008, 11:06 AM
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#117
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Guests |
The search continues: http://www.sciencedaily.com/releases/2008/...81125141602.htm
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Nov 28 2008, 11:48 AM
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#118
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Member Group: Members Posts: 401 Joined: 5-January 07 From: Manchester England Member No.: 1563 |
Another Fireball this month: Canada 20th November 2008 YouTube video: http://www.youtube.com/watch?v=e_2aX-784sw ! Thats beautifull, but quite scary... -------------------- |
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Nov 29 2008, 05:19 PM
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#119
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Member Group: Members Posts: 877 Joined: 7-March 05 From: Switzerland Member No.: 186 |
First piece has been located (looks nice... the meteorite) http://www.youtube.com/watch?v=UjU8boyXwqc
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Guest_PhilCo126_* |
Nov 29 2008, 09:36 PM
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#120
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Guests |
Indeed a very nice piece:
http://www.foxnews.com/story/0,2933,458984,00.html http://skyriver.ca/astro/bruce/meteorite.htm |
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