Another Asteroid comes close

[ianvr]

I find it almost comical that a 13 meter wide rock could cause no damage! If this rock would burn up before hitting Earth, why has other smaller ones struck Earth? I can still remember when Skylab entered the atmosphere and the panic it caused because there was a risk of hitting populated regions.


http://www.spaceweather.com/


ASTEROID FLYBY: That was close. Yesterday, newly discovered asteroid 2008 CT1 flew past Earth only 72,000 miles (0.3 lunar distances) away. Had it struck our planet, the 13-meter wide space rock (similar in size to a school bus) would have done little damage, probably exploding in the atmosphere and peppering some lonely stretch of ocean with meteorites. Maybe next time...http://neo.jpl.nasa.gov/ca

 

[Laura]

What are the estimates for the Tunguska fragment?

 

[Ben]

From Mike Baillie's 'New Light on the Black Death'

"Tunguska is interesting for many reasons, not least the controversy as to what it was. Most discussion relates to whether it was an asteroid or a fragment of comet. One very good reason for assuming it was a 40m lump of comet relates to its trajectory, and to the date of its arrival"

Unfortunately it's not clear from where he has obtained this information.

According to the American Astronomical society it was about 60m, but it was an asteroid
http//www.spaceref.com/news/viewpr.html?pid=9460

 

[Zadius Sky]

There's an article on Tunguska fragment to which it discussed the possible four comet fragments (of Encke) ranging from 95m to 295m (as shown on the table, I think):
_http://www.aero.org/conferences/planetarydefense/2007papers/P4-1--Zlobin_Paper.pdf

If it was an asteroid that impacted the Tunguska region, would it not leave a crater? From what I've read briefly on the Tunguska event, there was no crater found. Comet rarely leaves crater (at least that's my understanding).

EDIT:

I just brought a book, Target Earth by Duncan Steel at a local used bookstore (several books, actually).

Here's the excerpt from the mentioned book regarding the Tunguska:

pg. 86:

For cometary material - made of a mixture of ice and smaller stony components - theoretical modeling indicates that even a lump 500 feet (150 meters) in dimension will not penetrate deeper than a height of around 10 miles. This does not mean that these projectiles are not dangerous, however. When they explode, they produce blasts whose shock waves propagate rapidly downwards, flattening everything for miles around. But it does imply that impact craters will not be formed.

Here's another excerpt from the book called Asimov's Guide to Halley's Comet by Isaac Asimov:

pg. 100-2:

Everyone would assume that a large meteorite had hit [Tunguska], but no meteorites of any kind were found at the site. There wasn't even a crater. Apparently whatever had exploded had done so in midair.

But what could explode in the air and leave no sign of itself? Suppose the Earth had collided with a small comet. It would pass through the air rapidly and be heated to the point where all its icy substance would vaporize at once in a vast explosion. There would be nothing left behind but vapor, which would mix with the atmosphere.

It must have been a small comet. Astronomers estimated that to do the damage it did, it would have to have been about 200 feet across. Most comets seem to be considerably larger than that, so the Tunguska explosion may have been caused by a mere piece of a comet, a piece that had been broken off a much larger comet because of solar heating at perihelion. The piece broken off would have moved along with the parent body but might slowly have been driven farther off by the rocket effect of evaporation into an unfortunate collision course with Earth. It is possible, by reconstructing its orbit, that the comet fragment had been part of Encke's comet to begin with.

Additionally, according to his Rain of Iron and Ice, John Lewis pointed out that Tunguska-type bodies is at least 25 meter diameter (p. 211).

 

[KC Kelly]

Apparently, Ra in session #17 gave a conflicting account of what happened in Tunguska. See here:

Questioner: In meditation I got the question about the crater in Russia in the, I believe, Tunguska region. Can you tell me what caused the crater?

Ra: I am Ra. The destruction of a fission reactor caused this crater.

Questioner: Whose reactor?

Ra: I am Ra. This was what you may call a “drone��? sent by Confederation which malfunctioned. It was moved to an area where its destruction would not cause infringement upon the will of mind/body/spirit complexes. It was then detonated.

Questioner: What was its purpose in coming here?

Ra: It was a drone designed to listen to the various signals of your peoples. You were, at that time, beginning work in a more technical sphere. We were interested in determining the extent and the rapidity of your advances. This drone was powered by a simple fission motor or engine as you would call it. It was not that type which you now know, but was very small. However, it has the same destructive effect upon third density molecular structures. Thus as it malfunctioned we felt it was best to pick a place for its destruction rather than attempt to retrieve it, for the possibility/probability modes of this maneuver looked very, very minute.

Questioner: Was its danger both blast and radiation?

Ra: I am Ra. There is very little radiation, as you know of it, in this particular type of device. There is radiation which is localized, but the localization is such that it does not drift with the winds as does the emission of your somewhat primitive weapons.

Questioner: I believe that analysis has detected very little radiation in the trees in this area. Is this low level of radiation a result of what you are speaking of?

Ra: I am Ra. this is correct. The amount of radiation is very localized. However, the energy which is released is powerful enough to cause difficulties.

Highly questionable. What a variance!

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Edit: OOps! Forgot to provide link. I'm still a novice at this so I hope this shows up right.

_http://wiki.lawofone.info/index.php/Ra_Session_17