Exactly as NASA does to ensure mission success, deep space navigation mandates as accurate as early as possible details, whilst similarly requiring constant monitoring and comparison with desired destination(s).

Small changes made early enough, propagate over long periods of time to huge effective distances. Because fuel is so scarce, every wisp is used as effectively as possible.

When the outcome otherwise is likely mission failure, huge resources are applied and invested to ensure success.

When millions ( or more ) lives on Earth are in the balance, from 5 mile/s collisions of indeterminable megatons of explosive devastation -- one would expect and hope that very careful observations and categorizations of such risks -- are perennially made and updated, worldwide and as a shared global responsibility.

Perhaps the corporations are more inclined to wait for more optimum
"profit centers" to form, in the ashes of a major city near you ?

That we know of some of these near misses is actually great news, as that proves that many of the risks are being monitored and correlated with the vast numbers of negative possibilities.

The absolute worse case, is those huge iron-loaded rocks that literally 'come from directly behind the sun,' where most of our instrumentation is insensitive and woefully likely to be too late to make much of a difference.

Orbital perturbations occur continuously, as unknown ( or poorly characterized ) objects revolve about the sun amongst thousands of other ( mostly ) known massive objects. The tracking of Extinction Level Impactors ( ELI ) is not so easy, nor would be sending out the space marines to intercept and attempt to modify it's orbit.

In the larger context of corporate profits, many millions dying from Chernobyl / Fukushima ( etc ) radioactivity or Near Earth Objects colliding -- is just collateral damage.

We either invest ( better ) in having our future, or risk having ( much ) less of one.

CHOSE LIFE

As I pointed out for a friend over on Facebook, a land impact of a stony object as small as 20 feet would produce energies comparable to the Tunguska blast of 1908, which itself was more powerful than the largest nuclear explosion ever detonated. Such a blast in a densely populated area today would completely destroy a large city, and kill millions. Objects that size are extremely numerous, and small enough to be undetectable with today’s technologies. So we'd never even see it comming. But since it would only destroy a single city sized area, and the targets are widely separated, that’s not the scariest scenario.

Near Earth Objects as wide the one mentioned in this article are also very numerous. And like this one, they too are almost completely undetectable until they are too close to do anything about them. Most of this planet is covered by oceans. And most of human civilization is in low lying areas surrounded those oceans. So the most frightening cosmic impact scenario we face isn’t a land impact at all. It's an ocean impact of a hard stony, or iron, object of that size.

An ocean impact equal to 1000 megatons of TNT would produce a tsunami wave that’s about 4.5 meters high at 1000 kilometers from the point of impact. But that’s just the wave height in deep water. When you factor in a run-up height of about 35 to 1 when it makes landfall on a continental shelf, you get waves coming ashore of as much as 157.5 meters in height. That’s more than 500 feet tall; tall enough to swamp a large skyscraper. And since most of our largest cities are close to sea level, the potential loss of life is in the hundreds of millions.

There probably would be no crater from a deep ocean impact of that size, and very little dust. So aside from torrential rains fro a while, it’s anybody’s guess what the long term climate effects would be. But crop failures due to sudden temporary climate change and resulting famines, especially in third world countries have the potential to kill billions over the next couple of years after the impact.

Bottom line: The next major impact event will most likely be in an ocean somewhere. And there is an awful lot of ocean target area that’s surrounded by large coastal cities. As a result, human civilization is more vulnerable than ever before to an ocean impact. And there isn’t a damn thing we can do about it.

You are forgetting a little detail concerning the conservation of the downwards momentum. Your formula above may work for a point-source detonation, but not for a falling hypervelocity bolide. Supercomputer simulations of airbursts at Sandia Labs have shown that the airburst of a falling hypervelocity object retains almost all of its downwards momentum. The speed of expansion of the fireball is roughly equal to, or slightly less than the speed of the falling object. So you can think of it as a kind of downwards moving explosion like something between a giant supersonic blowtorch hotter than the surface of the sun that's directed downwards at the ground, and an an upside-down nuclear mushroom cloud. [Link] So you get a hell of a lot more energy delivered to the surface than you might expect from the high altitude point-source detonation of a nuclear device of the same yield.

See: The Naure of Airbursts and Their Contribution to the Impact Threat by Mark Boslough https://dl.dropbox.com/u/2268163/boslough_April_16_2009.pdf

So a land impact would be no less violent than somewhere in an ocean. It's just that the resulting impact Mega-Tsunami from an ocean impact would greatly increase the death toll.

Reflected energy, means exactly what it sounds like, and regardless of what you believe is called "the conservation of the downwards momentum," the absolute truth is that the initial kinetic energy ( of motion ) all goes someplace. The real conservation of energy, means that everything has to add up, as energy can neither be created nor destroyed, only transformed.

The usually efficient heat of vaporization of ocean water insures that most of the radiated energy is absorbed and not just re-radiated as heat and light through the atmosphere and ultimately back into space.

For you to imagine that a land and deep sea impact ( of equal mass ) carry the exact same quantity of energy absorbed into the Earth system, denies the obvious amount of electromagnetically radiated wavelengths ( broadband, including both IR heat and light ) that clearly does leave the Earth system.

You describe the relative explosive energies as "no less violent," while ignoring the energy lost to re-radiation into space, which clearly leaves less impact related effects of a violent nature on Earth.

The formula I expressed is for calculating the kinetic energy of a moving mass ( which is derived from Newton's F=ma ), not "for a point-source detonation."

I have argument to contradict this: " Supercomputer simulations of airbursts at Sandia Labs have shown that the airburst of a falling hypervelocity object retains almost all of its downwards momentum. The speed of expansion of the fireball is roughly equal to, or slightly less than the speed of the falling object. So you can think of it as a kind of downwards moving explosion like something between a giant supersonic blowtorch hotter than the surface of the sun that's directed downwards at the ground, and an an upside-down nuclear mushroom cloud."

What you appear to be incapable of adding to this, is that that initial downward momentum, is only continuing to be directed primarily downward, until it impacts a solid or liquid surface. At that moment, the vectors still add together and energy is still conserved, even when it turns around and goes back skyward.

Yes, an object will continue to move in the same direction unless acted upon by another force. From your level of analysis, basketballs would be unable to be dribbled, as all of that downward momentum could only continue into the floor, and not bounce the ball back upwards.

Any kid with a ball knows the truth of expecting a ball to bounce upwards after hitting the floor -- why do you so vehemently disbelieve this ?

Have liked the discussion between you two on this topic, and have always enjoyed your commentary about cometary impacts of the past, Dragon (funny lil juxtaposition there :p) It seems like some confusion took place in the comparison btw land and ocean impacts, while incorporating the the airburst element. In all 4 events, it would seem the blast gets radiated in all directions, but with the greatest amounts being directed along its impact/air explosion path towards the earth. It makes sense that more energy will be absorbed in the water impacts. Both will have climate altering changes. I think the difference is the water impact will create a massive evaporation which will in turn generate storms/hurricanes ect, while the land impact will throw up a huge amount of debris, dust into the atmosphere to reflect sunlight and bring down global temperature. All will expel some debris into the atmosphere, but the direct land impact would cause the most (having more of that basket ball bouncing reflective force). As for the most damaging, i agree with Dragon that the direct water would be the case due to the tsunami wave resulting. I am curious about the result from an airburst over water though. I would expect a huge about of water vaporization like a direct impact, but not sure about tsunami aspect, although i would expect it to be to a lesser degree. any thoughts on this last point?

Unless evacuations combined with some way neutralize the wave with an opposing one were used to minimize the effect, the amount of area affected would be far greater due to coastal impacts. (This last sentence was added due to discussion with my partner. I added it as consideration, although his suggestion was nuclear detonation to create a counter wave, but i am doubtful of its effectiveness due to awareness of the event and application of such a method. I am mainly addressing the different impacts)

inpire,

It saddens me to reaize that after studying, writing, and blogging about impact science, and the geomorphology of impacts, and airburst phenomena full time for five years now, (I've authered a few articles here on SOTT as well) and having identified hundreds of new, and previously unstudied impact structures, and in spite of having numerous well known, world class impact physycists, and scientists as mentors I apparently haven't learned anything useful. It would be nice if you could cite some peer reviewed science to support your hypothetical views; maybe even let the rest of us in on the nature of your own expert qualifications, or field of study. Or at least acknowledge that your personal assumptions regarding the physics, and effects of impact events are only a nebulous, and poorly defined hypothesis. Until you do, it's clear you know all there is to know, and I won't waste anymore time with you.

On the contrary I've actually stated the opposite and I've clearly never judged you so harshly as stating anything like this:

"I apparently haven't learned anything useful"

We all make mistakes and either learn from that, or sometimes when my ego triumphs I have attempted to project and blame others.

Go ahead and ask any or all of your "world class impact physycists, and scientists as mentors" about what I've said.

I never stated that what I said was the definitive and absolute truth, but challenged you to consider it and then go and discover what is true for yourself.

I'm absolutely assured what I think that know is a limited perspective, which certainly contains some errors as it come out of the human condition, but it also is the best that I can provide.

REFERENCES

As far as my expertise -- that hardly matters -- as what is true is so regardless of any piece of paper or authority that condones it. My 3 decades working productively, and my degrees in engineering and physics don't necessarily make anything true, just because I say so.

Here's a discussion that I just found that reinforces what I've said -- and although not a peer-reviewed proof, it certainly lends credence to what I've stated:

[Link]
Where Der Trihs, at 07-13-2009, 06:21 PM, says:

"I agree with those who say land is best. The white hot crater will radiate heat to space, while an ocean landing will turn that heat into steam and keep it in the atmosphere.This. A water landing means more energy stays here on Earth, instead of getting blasted/radiated into space. And as I understand it, that hot spot in theory could generate super-hurricanes, more powerful than anything normal climate can produce."

Another article ([Link]a condensation of an excellent article by Sydney van den Bergh called "Life and Death in the Inner Solar System" in the May 1989 issue of the Publications of the Astronomical Society of the Pacific) states part of what I did :

"If the asteroid hits the ocean, the surrounding water returning over the the hot crater floor is vaporized"

Because a land impact has little water to enable the capturing of instantaneous blast energy, where do you think that the equivalent energy to vaporize the water will go ?

Is there any way of attracting some space rocks? I have a feeling I could use a few good meteorites through the roof. Still burning preferably, how about lightning? Can I attract lightning and space rocks? The basement is only 6feet deep, if that helps with anyone's impact math. Oh and I'd like to be home when it happens. Where do I get the math for that?
Cheers