Of course, the sky is always falling

Of course, the sky is always falling

Photo by Austin Schmid on Unsplash

Originally published 1 September 1986

Thir­ty-one years ago [in 1954], Ann Hodges was sleep­ing on her liv­ing room couch in Syla­cau­ga, Ala., when a 8‑pound rock crashed through the roof of her house and hit her on the side. Life mag­a­zine pub­lished a full-page pho­to­graph of Hodges dis­play­ing her bruise and her unwant­ed tro­phy from the sky.

Hodges’ bruise has become a per­ma­nent foot­note in the his­to­ry of astron­o­my. Hers is the only well-doc­u­ment­ed case of a per­son being hit by a meteorite.

There is lots of stuff fly­ing around out there. Chunks of rock and iron rain down upon the Earth all the time. It has been esti­mat­ed that every year the Earth gath­ers up 100,000 tons of mete­oric mate­r­i­al from space. Most of this mate­r­i­al burns up in its pas­sage through the atmos­phere, but five or six times each year some­one wit­ness­es the fall to the sur­face of a mete­orite of sub­stan­tial size.

Espe­cial­ly in late sum­mer, when we have sev­er­al of the bright­est mete­or show­ers, one is inclined to look up into the night sky a bit appre­hen­sive­ly. And although one does not gen­er­al­ly think about mete­ors in day­time, they are falling down on us then too, out of the blue. It is nat­ur­al to won­der if Hodges’ cos­mic acci­dent could hap­pen again.

Charting the odds

As report­ed recent­ly in Sky & Tele­scope mag­a­zine, a trio of Cana­di­an astronomers have tried to esti­mate a per­son­’s chance of being struck by some­thing from the sky. Ian Hal­l­i­day, Alan T. Black­well, and Alan A. Grif­fin of the Herzberg Insti­tute of Astro­physics stud­ied pho­tographs of mete­or tracks made over a peri­od of nine years in West­ern Cana­da by 60 auto­mat­ic cam­eras. They com­bined the results of the pho­to­graph­ic sur­vey with data on the size, num­ber, and weight of mete­orite frag­ments recov­ered on the ground.

The Cana­di­an astronomers con­fined their study to North Amer­i­ca. And they made the assump­tion that the typ­i­cal North Amer­i­can spends 95 per­cent of the day indoors, which would pro­tect that per­son from any mete­orite weigh­ing less than about half a pound. Putting it all togeth­er — the pho­tographs, the recov­ered frag­ments, and pop­u­la­tion char­ac­ter­is­tics — the Cana­di­ans cal­cu­late that on an aver­age of once every 180 years, a North Amer­i­can will be struck by some­thing falling from the sky. An extrap­o­la­tion to the world’s 5 bil­lion peo­ple sug­gests a hit rate of once every nine years. Hodges’ acci­dent is rare, but appar­ent­ly not unique.

The his­to­ry of human inter­est in things falling from the sky has had sev­er­al curi­ous twists and turns. Pliny the Elder, the Roman nat­ur­al philoso­pher, described stones that fell from the sky and chunks of iron that resem­bled sponges. In this, he was a per­cep­tive observ­er. But he also record­ed a rain of milk and blood, and a rain of flesh. Once, he tells us, wool fell from the sky, and on anoth­er occa­sion it rained baked bricks.

Denial by decree

The less cred­u­lous con­tem­po­raries of Galileo and New­ton thought sto­ries of rocks from the sky — not to men­tion wool and baked bricks — smacked of super­sti­tion. In the 18th cen­tu­ry, the pres­ti­gious Acad­e­my of Sci­ences at Paris attempt­ed to put an end to the non­sense once and for all by sim­ply decree­ing that objects could not fall from the sky, where­upon Euro­pean muse­ums tossed out valu­able col­lec­tions of authen­tic mete­orites. In Amer­i­ca, when two Yale pro­fes­sors described a mete­orite that fell in Con­necti­cut, Thomas Jef­fer­son is said to have remarked, “It is eas­i­er to believe that Yan­kee pro­fes­sors would lie, than that stones would fall from heaven.”

But the Yan­kee pro­fes­sors did­n’t lie, and even­tu­al­ly their view pre­vailed. Stones do fall from heav­en. The largest metal­lic mete­orite that has been recov­ered weighed 60 tons and fell in South West Africa. The largest recov­ered stony mete­orite fell in the Kirin Province of Chi­na in 1976 and weighed about two tons. Mete­orites show no pref­er­ence for geo­graph­ic loca­tion. About 25,000 years ago a chunk of iron weigh­ing 20,000 tons smashed into Ari­zona and knocked a hole in the ground a half mile wide.

Stones will con­tin­ue to rain down from heav­en, and there is noth­ing we can do to stop them. If an object the size of the Ari­zona mete­orite fell into the Atlantic, it would set up a tidal wave that would dev­as­tate coastal cities. At inter­vals of tens of mil­lions of years some­thing is going to hit the Earth that will wreak hav­oc for entire pop­u­la­tions. There is grow­ing evi­dence that it was some sort of celes­tial bom­bard­ment that wiped out the dinosaurs.

Should we take out insur­ance against the pos­si­bil­i­ty of being struck by a mete­orite? Of course not. But if the Cana­di­an astronomers are right, every decade or so, some­one, some­where is going to get knocked on the head.

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