Comments on: David Morrison comments on Tunguska http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/ I am an astronomer, writer, and skeptic. I likes reality the way it is, and I aims to keep it that way. My real name is Phil Plait, and I run the Bad Astronomy blog. Sun, 05 Jul 2009 20:39:53 +0000 http://wordpress.org/?v=2.3.1 By: DTdNav http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60258 DTdNav Thu, 20 Dec 2007 21:01:54 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60258 IMO: No more than token funding will ever be directed towards a defense against extra-terrestrial threats of any sort until AFTER an event has already occured that directly impacts one of the G-8 countries. Political will in republics is reactionary. Pro-active thinking only applies to oligarchies, and is rarely for the benefit of the many. (How's that for cynicism?) IMO: No more than token funding will ever be directed towards a defense against extra-terrestrial threats of any sort until AFTER an event has already occured that directly impacts one of the G-8 countries. Political will in republics is reactionary. Pro-active thinking only applies to oligarchies, and is rarely for the benefit of the many. (How’s that for cynicism?)

]]> By: Michael Lonergan http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60257 Michael Lonergan Thu, 20 Dec 2007 20:20:12 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60257 Crux: New Zealand is out. They just got hit with a big quake. Maybe it's a sign? linusrp: Ahhh, Denmark! A thoroughly liberal country with awesome chocolate. That I could handle! :) Crux: New Zealand is out. They just got hit with a big quake. Maybe it’s a sign?

linusrp: Ahhh, Denmark! A thoroughly liberal country with awesome chocolate. That I could handle! :)

]]> By: Rob http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60256 Rob Thu, 20 Dec 2007 19:21:51 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60256 Radar isn't used to find objects - that's best done in the optical. Where it is useful is getting their orbits nailed accurately and quickly, which is something Arecibo does. One small note: it's the NSF that cut Arecibo's funding, not Congress. Congress may well reinstate it (possibly via NASA, who have a congressional mandate to characterize asteroids). Radar isn’t used to find objects - that’s best done in the optical. Where it is useful is getting their orbits nailed accurately and quickly, which is something Arecibo does.

One small note: it’s the NSF that cut Arecibo’s funding, not Congress. Congress may well reinstate it (possibly via NASA, who have a congressional mandate to characterize asteroids).

]]> By: Michael Lonergan http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60255 Michael Lonergan Thu, 20 Dec 2007 17:01:55 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60255 I really do not think a radar the size of Arecibo would detect objects the size we are talking about here. Also, isn't Arecibo limited by the amount of sky it can scan? I'm no expert but it seems as that if Arecibo was adequate for the task, dozens of them would need to be placed around the world. I really do not think a radar the size of Arecibo would detect objects the size we are talking about here. Also, isn’t Arecibo limited by the amount of sky it can scan? I’m no expert but it seems as that if Arecibo was adequate for the task, dozens of them would need to be placed around the world.

]]> By: Ken S http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60254 Ken S Thu, 20 Dec 2007 16:32:02 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60254 How many blasts like this are in our known history? While I agree it's something that needs to be thought about and looked into, if you're thinking about cost effective ways to save people and make their lives better you might want to be careful of how much you spend worrying about a blast the size of Tunguska. I think it's the bigger objects we should worry about more. How many blasts like this are in our known history? While I agree it’s something that needs to be thought about and looked into, if you’re thinking about cost effective ways to save people and make their lives better you might want to be careful of how much you spend worrying about a blast the size of Tunguska. I think it’s the bigger objects we should worry about more.

]]> By: Irishman http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60253 Irishman Thu, 20 Dec 2007 15:33:34 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60253 Pat said: > why cant they hunt for asteroids with radar? Money. It boils down to money. Money for facilities, money for people to operate the facilities, money to cover 24 hrs a day and 360 deg by 360 deg looking at the sky. Impium Orexis said: > Well, how many incoming rocks end up detonating above the ground, as opposed to slamming into it? Would actually impacting the Earth significantly change or reduce the effect? I'm not a specialist, but my understanding is that you have a certain amount of energy from the meteor - that is determined by the size of the object. Impacting the surface would place most of that energy in the local zone of impact. Airbursts were thought to spread spherically, spreading the energy over a much larger area. Causing more widespread damage, vs. more intense localized damage, and dissipating energy to the sky rather than to the ground. What this appears to be saying is that the airburst energy was directed to a more localized area, intensifying the amount reaching the ground overall. That means a smaller rock can have a more devestating localized strike, but the surrounding zones might get off more luckily. I think this puts airbursts closer to a ground strike rather than further away from a ground strike. Sprocket said: > We might also wonder where all these small strikes are- shouldn’t they be proportinately more frequent, say once every 2 years rather than every 200? Smaller meteor strikes <i>are</i> more frequent than the 50 m diameter objects, but the effects aren't proportionate. Below a certain size, the meteors tend to burn up on entry rather than airburst, and so that energy is spread over a larger segment of the sky much further up. Thus, no devestating fireballs, impacts, flame blasts, pressure bursts, etc. Pat said:
> why cant they hunt for asteroids with radar?

Money. It boils down to money. Money for facilities, money for people to operate the facilities, money to cover 24 hrs a day and 360 deg by 360 deg looking at the sky.

Impium Orexis said:
> Well, how many incoming rocks end up detonating above the ground, as opposed to slamming into it? Would actually impacting the Earth significantly change or reduce the effect?

I’m not a specialist, but my understanding is that you have a certain amount of energy from the meteor - that is determined by the size of the object. Impacting the surface would place most of that energy in the local zone of impact. Airbursts were thought to spread spherically, spreading the energy over a much larger area. Causing more widespread damage, vs. more intense localized damage, and dissipating energy to the sky rather than to the ground. What this appears to be saying is that the airburst energy was directed to a more localized area, intensifying the amount reaching the ground overall. That means a smaller rock can have a more devestating localized strike, but the surrounding zones might get off more luckily. I think this puts airbursts closer to a ground strike rather than further away from a ground strike.

Sprocket said:
> We might also wonder where all these small strikes are- shouldn’t they be proportinately more frequent, say once every 2 years rather than every 200?

Smaller meteor strikes are more frequent than the 50 m diameter objects, but the effects aren’t proportionate. Below a certain size, the meteors tend to burn up on entry rather than airburst, and so that energy is spread over a larger segment of the sky much further up. Thus, no devestating fireballs, impacts, flame blasts, pressure bursts, etc.

]]> By: Briony http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60252 Briony Thu, 20 Dec 2007 11:33:54 +0000 http://blogs.discovermagazine.com/badastronomy/2007/12/19/david-morrison-comments-on-tunguska/#comment-60252 So, we need to be able to detect small NEO's. To do that, we need a good planetary radar system. Hey, what about Arecibo?! Oh yeah, Congress cuts its funding to save a measly 1 million dollars. Oh well, maybe we'll get lucky and the meteors will miss population centers. Let's give a B-2 a week's worth of fuel instead. So, we need to be able to detect small NEO’s. To do that, we need a good planetary radar system. Hey, what about Arecibo?!

Oh yeah, Congress cuts its funding to save a measly 1 million dollars.

Oh well, maybe we’ll get lucky and the meteors will miss population centers. Let’s give a B-2 a week’s worth of fuel instead.

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