Last Night an asteroid buzzed earth

All the telescopes, observatories, large arrays, etc in the world and we didn't see it until the last minute!?!?

It was tiny, building-sized.

Now comes the speculation about what it would have done to earth if it had hit?

I read about it a couple of days ago.

Tunguska type damage was referenced. I have no idea how accurately:

http://en.wikipedia.org/wiki/Tunguska_event

Hey, I read about this Tunguska thing a few weeks ago. Nuts.

What happens if a bugger like that hits ocean (which is most likely outcome)?

Water fall from sky?


Fish fly?

So, like a big clam bake. Kewl.

Sure. As long as you are not the clam.

Something that small is more then likely to be passing by earth fairly often without us knowing about it.

Not an earth killer but I would not wish to be within a hundred miles of the inpact site.

Far too lazy to do the E=1/2mv^2 and one megtonof tnt=4x10^15 joules math to see how big of a bang it would had been.

Second a water hit would be far worst then a ground inpact, except for the people directly under it, as the energy that would escape back into space as heat in a ground inpact would instead be turn into tide waves and stream/vaper by the 100 of meg ton. Water can tranfer energy with little loss by way of tide waves half way around the planet.

Analog magazine once did an article comparing a ground to water inpact with all the math included. It was contained in the March 1966 issue.

Tunguska was bad enough, thank you very much. As for spotting it sooner, it ain't like governments provide generous salaries ands lots of job opening for people to watch for such things.



Tunguska, then (1908) and a century later.

Boy the place sure looks different!

For what you deem it worth 1:


Why didn’t we see it sooner?

Detecting near Earth objects is very difficult. Think of a matt white wall. Have someone put a half inch dot of white paint on it somewhere. Stand 25 feet away and find the dot. That is about what you are talking about.

If a new object is discovered it can easily be lost in the background stars as it moves (in this case relatively very fast). It usually takes several good observations over a few nights to even be able to calculate an approximate path. So that if the next night is cloudy at my site (where I made the discovery of the object) and others else ware are trying to find it, they may have little to go on and so not find it or even pick the wrong object. New objects are often lost before an orbit can be determined.

Until some politician woke up and found our “window of cosmic vulnerability” open, there was little will and little money for such programs. They are currently little more than a way to hide “stars Wars” money using NASA funding

For what you deem it worth 2:


It is tough to compare anything to Tunguska as there is still far too much that is unknown about that object.

Given an object 30-50 meters in diameter…

This does not provide near enough information to do any calculations as there are a good number of quantities that must be known, or estimated: density, angle of entry, velocity at entry into the atmosphere, etc, etc, etc.

Further there are any number of models for the loss of energy (ground blast, air blast) to name only one, so one has to choose the best model relative to circumstances and the quantities you want to find.

Saying all that, I actually broke down and did some calculations to show low and high-end possibilities.

LOW but not LOWEST
I assumed a porous object (to obtain density). I assumed a low entry velocity, and 45 degree entry angle. The target material as you will see that is moot. The other assumptions are more technical so I’ll omit them.

Its maximum energy at entry would be about 3.4 megatons, 1.4x 10^16 joules.

This type of object would break up around 50 miles up. By about 8 miles from the ground it is completely broken up. Relatively large pieces may hit the ground but the entire object was only 50 meters to start.

The energy of the airburst would be about 3 megatons. No atmospheric effects (pressure change) would be felt at even 10 miles from the explosion. You can see about a ten percent loss of energy from the maximum at this point already.

The damage done on land would be that of about a 3 megaton weapon. The height could significantly mitigate this relative to a weapon detonation because of the extreme height at detonation of this object. Conclusion: you don’t want to be there.

High:
I assumed an iron object (to obtain density). I assumed a maximum entry velocity, and 45 degree entry angle, and the target material as 1000m deep ocean. Again, the other assumptions are more technical so I’ll omit them.

Its maximum energy at entry would be about 35 megatons, 1.5x 10^17 joules.

This type of object would be broken but survive to form an impact crater on the seabed soccer stadium in size. At 15 miles the event would be less than 3 on the Richter scale. In 5000 meter ocean there is no crater >> 1 ft crater.

A friend continued some calculations in more detail for me and found that only about 100 cubic meters of material would be vaporized. Not my field but these seem to be rather small for generating tsunamis. I think amount of material subsidence is more important that amount total energy, again geology is not my field.



I am not sure what this is supposed to mean:



There is no multiplication effect, starting with an energy of 3.4 megatons or 34 it cannot produce “100 of meg ton” effect just because it hits water.

The energy even in water only 1000m deep doesn’t seem to me sufficient to possibly cause tsunamis. Although I know that was reported in the press. The numbers say otherwise. There can be some significant local effects.

Rather than get into a long review of the physics of this I’ll just point out some history. During the bomb tests in the Pacific after WWII they detonated devices of this order; a 13.2 megaton device (for example) at Enewetak Atoll (on a barge sitting in the ocean). No regional, let alone global oceanic effects at all. A few low-lying nearby islands were affected.

There is no multiplication effect, starting with an energy of 3.4 megatons or 34 it cannot produce “100 of meg ton” effect just because it hits water.

The energy even in water only 1000m deep doesn’t seem to me sufficient to possibly cause tsunamis. Although I know that was reported in the press. The numbers say otherwise. There can be some significant local effects.

Rather than get into a long review of the physics of this I’ll just point out some history. During the bomb tests in the Pacific after WWII they detonated devices of this order; a 13.2 megaton device (for example) at Enewetak Atoll (on a barge sitting in the ocean). No regional, let alone global oceanic effects at all. A few low-lying nearby islands were affected.
Quote:
_______________________________________________
Who claimed megtons of added TNT effect?

My statement was megton of stream not the same thing at all.

And my statement that the energy coupling from a any blast effect would be greater with a water impact then a similar land inpact.

I was too lazy to claculate this object inpact energy and the misstatements of my position seem to be my punshment for not so doing.

Oh assuming an iron object a great deal more energy would be couple into the water then a blast of a bomb on the surface with the same energy

I don't know what this horseshit is, it bears absolutely no relationship to my post, which you have referenced. If you want to argue with someone, i suggest you argue with the person who actually posted the material you ineptly quoted.

It's all Farmerman's fault that he didn't see it coming and failed to tell us to hide under our beds.

BBB

Two thoughts.
1. If the impact causes underwater volcanic eruptions, then it could definitely magnify the effect.
2. Perhaps they're discussing something akin to "windchill". As in, a 34 megaton ocean impact = 100 megaton land impact.

I haven't read the entire thread, though, so perhaps I'm mistaken.

I can remember when they had us kids hide under desks at school as practive for nuclear attack!

I know, right? Who needs missile shields; send 'em our vintage desks!