There’s no doubt that *something* happened in the stony Tunguska river basin in the early morning hours of June 30, 1908, and based on the areal phenomena observed by Evenks witnesses in the area it was most likely some non-terrestrial object impacting the Earth, but the brutal truth is that after 104 years we have yet to discover any “nail in the coffin” evidence that conclusively identifies what that object was.

I submit that the primary factor affecting a different location for the impact, assuming a gravitational perturbation delaying Tunguska’s arrival, would have been determined by the Earth’s revolution in its orbit around the Sun, not its axial rotation. The practical upshot of this is that preventing a dangerous impact would be a matter of altering the impactor’s motion in its orbit just enough that it would not intersect the Earth moving in its own orbit.

Seen in this light, the problem is more like managing air-traffic control (albeit from one of the aircraft). Once methods are determined for deflecting objects (and it seems several will be necessary, owing to the differing natures of asteroid and comet types), then the only difficult task will be to monitor the inner Solar System closely enough to catch rogues. Of course this argues for better asteroid study, as well as more mathematicians.

We often hear, in relation to Tunguska, that if it were delayed by x number of hours, it would have struck more densely populated regions, of course more disastrously.

Well, I did some mental calculations. To be sure, an hour’s rotation of the Earth (about 1000 mph at the equator [7900mi x pi / 24h]) would have brought western Siberia to a point parallel with the Tunguska object’s original trajectory (2 hrs., Moscow; 3 hrs., Berlin; 4hrs., London [this is where my math breaks down--is it still ~1000mph at that latitude, or does it matter? Or should I rather calculate speed of longitudinal displacement?]), but then I considered the speed of Earth’s REVOLUTION.

I was a little freaked out when I first realized, some years ago, that we are all constantly travelling faster than any astronaut has travelled relative to the Earth, our orbital speed around the Sun being about 65,000 mph (93,000,000mi x 2 x pi / 365.25d / 24h). And then reading ASTRONOMY magazine just today I learned that our solar system’s speed around the galactic center is about ten times that!

(Now there’s a cute subplot for a time-travel story. Too often has the intrepid time-traveller pushed “the button,” and miraculously re-appeared at exactly the same relative physical location in a different time, rather than empty space hundreds of billions of miles away! [Well, admittedly, the very acronym T.A.R.D.I.S. accounts for this, but there don't seem many other examples. Oh, well. Nothing in the universe is faster than the Speed of Plot, by definition.])

Anyway, the Earth itself would have moved tens of thousands of miles in the intervening time, assuming the Tunguska meteor was somehow delayed. Indeed, by the time Earth’s rotation would have brought western Europe around, the meteor’s original trajectory would have been at the distance of the Moon’s orbit!

Even as little difference as fifteen minutes means the meteor would have missed by as much as 99942 Apophis is scheduled to miss on 13/4/2029, and no one would ever have known (and so the unanswerable follow-up question is: how many times have we been missed in the past by so little?).

But what if it had struck fifteen SECONDS later (I have a student who was born in Novosibirsk; we talked about this very subject this spring.), or a minute, two, three, or four? Then the impact zone would have shifted to the west by the speed of the Earth’s revolution, rather than its rotation (although by 4min., there seems a possiblity it may have struck the atmosphere at such a shallow angle that it would have skipped).

These differences seem more in line with what gravitational perturbations might reasonably be expected to produce, and seen in this light, the narrowness of humanity’s escape seems all the more troubling. What do you think?

That’s presuming that we CAN do something about it. But what if we cannot? As we explore how we might monitor and even affect an approaching NEO, we should give equal effort to developing a comprehensive Impact Event Contingency Plan; and we should do it right now rather than later. As you note, we may not have the luxury of time.

I’ve thought about it often. WHAT exactly will we do, when we determine that an asteroid has our name on it and that there is nothing we can do to change its course? For example, what if Apophis does make the keyhole on that first pass in 2029? Will we evacuate vast regions of populations? Will we even know exactly whom to evacuate? How and to where will all of those people be evacuated? We will have seven years to react – will we use that time wisely, or will we wait until the last minute and then panic? Are we now waiting until that 2029 pass to even begin to consider how we should react?

There are many questions that could actually be answered now; yet, as seems to be typical of those whom we enlist to address such issues, the response is slow and inadequate.

I read and hear arguments for the need to more agressively address the issue of impact. Let’s hope that those putting forth the arguments are taken more seriously and with more expediency than what we have thus far seen.