investigation 11 · planetary defense

The Morning the
Sky Split.

June 30, 1908, 7:17 a.m., over the Podkamennaya Tunguska river: the sky split in two, 2,000 km² of forest went down in a radial butterfly, windows broke hundreds of kilometres away — and expeditions found no crater and no fragments. Into that vacuum poured a century of theories: Tesla's death ray, a passing black hole, antimatter, a crashed starship. The event is actually real, the object's identity is genuinely open, and the exotica are overclaims — and the whole case turns on physics you learned in the first week: ½mv².

A 60-metre rock at cosmic speed carries a 9-megaton secret. Let's compute it.

▽ run the numbers
The Computable Centerpiece

Half m v squared,
eight kilometres up.

Fig. 1 — The airburst, computed. Top: damage rings from cube-root yield scaling anchored on the 1908 observation, with a 30 km metro area for scale. Bottom: the energy ladder, log scale, from Hiroshima to the dinosaur-killer — your slider value marked live.

Take the honest core first. Whatever happened at Tunguska was recorded by instruments, not just witnesses: seismographs across Eurasia, barographs as far as London that caught the pressure wave lapping the planet, and — nineteen years later — Leonid Kulik's expeditions, which mapped ~2,150 km² of trees felled radially outward from a centre where the forest still stood, scorched and upright. That last detail is the signature: the blast came from above.

So put a rock in the sky and do the arithmetic. A sphere of diameter $D$ and density $\rho$ arriving at cosmic velocity $v$ carries

$$E \;=\; \tfrac{1}{2}\,m v^{2}\,,\qquad m=\tfrac{\pi}{6}\,\rho\,D^{3}$$

Drop in an ordinary stony asteroid, $D=60$ m, $\rho=3000$ kg/m³, at $v=15$ km/s: $E \approx 3.8\times10^{16}$ J — about 9 megatons of TNT, six hundred Hiroshimas, squarely inside the modern 3–15 Mt estimate for Tunguska. Cube-root blast scaling anchored on the observation puts the tree-fall ring near 26 km — an area of ~2,200 km², matching Kulik's map. And because a stony body this size shatters and vaporizes ~8 km up, the model predicts the two facts that spawned every conspiracy: no crater, no fragments.

This stopped being a thought experiment on February 15, 2013, when a 19-metre sibling detonated over Chelyabinsk on a hundred dashcams — 0.5 Mt, windows down across a city, no crater, same physics, filmed. Press the preset and compare.

The same event, read by parallax — from the barograph record to the crashed starship.

actually real

A ~10-megaton airburst, on the record.

Signal. Seismic waves logged across Eurasia, atmospheric pressure waves recorded circling the globe (yield reconstructed by Ben-Menahem in 1975), ~2,150 km² of radially felled trees mapped by Kulik's expeditions from 1927 on — and in 2013, Chelyabinsk replayed the physics on camera at one-twentieth the energy.

Kill test. Feed an ordinary stony asteroid into ½mv² and blast scaling: it must reproduce the yield, the tree-fall map, and the missing crater at once. It does — the calculator above is the test.

↳ run the calculator above
genuinely open

Asteroid or comet? Nobody has the body.

Signal. A century of expeditions has recovered no unambiguous meteorite. Stony-asteroid airburst models fit well, but a fragile comet fragment fits too — and Lake Cheko, 8 km from ground zero, has been seriously proposed (Longo et al.) as a fragment crater.

Unresolved. Sediment cores and dating cut both ways — some analyses give the lake a pre-1908 age, others don't. The object's identity is a real, live question; the energy is not.

Kill test. Core the lake, date the sediments, find a fragment. Diggable, ongoing, honestly unsettled.

real kernel · overreached

The exotic-physics era: black holes and antimatter.

Signal. The kernel is respectable: with no crater and no fragments, serious physicists published serious exotica in serious journals — antimatter annihilation (Cowan, Atluri & Libby, 1965) and a passing mini black hole (Jackson & Ryan, Nature, 1973). Taking a weird gap seriously was the right instinct.

Noise. Both theories made killable predictions. A black hole transiting the Earth must exit through the North Atlantic with its own shock wave — the barograph record shows none. Antimatter annihilation floods the atmosphere with radiation — the 1909 tree rings show no radiocarbon excess.

Kill test. Run. Both died by their own predictions — the way good hypotheses are supposed to.

no mechanism

"Tesla's death ray. Or a crashed starship."

Signal. The mood is honest: Wardenclyffe was real, Tesla really did boast of transmitting destructive power, and 1908 sat inside his publicity era. And the starship story has a traceable origin — Kazantsev's 1946 tale, written before any expedition data he used was public.

Noise. Wardenclyffe had no megaton mechanism — its entire input power was orders of magnitude short of one second of Tunguska — and it was effectively defunct by 1906. The UFO account began as labeled science fiction and was retconned into testimony. Neither forbids any observation.

Kill test. None possible — which is the tell. A ray with no power budget and a ship with no wreckage predict nothing and survive everything.

Notice the sift: the exotic theories died honorably, by prediction — that's science working, not embarrassment. What survives the arithmetic is scarier than any of them: ordinary rocks at ordinary cosmic speeds, delivering a Tunguska every few centuries, on schedule, for free.