Zoom: From Atoms and Galaxies to Blizzards and Bees: How Everything Moves (29 page)

Meteor watching is always fun, especially between midnight and dawn, when six shooting stars reliably tear across the sky every hour. If this isn’t enough for you, Earth intercepts a thick swarm of comet debris several times a year, and then it’s an all-you-can-eat affair. We then see sixty or more meteors an hour if we observe away from city lights. One a minute. These meteor showers—on August 11, December 13, and sometimes on November 18—offer vivid motion demos, and here’s why:

The speed at which a meteor rips through our atmosphere depends, oddly enough, on its direction. This is very different from our experience on earth, where the crosstown bus doesn’t race more furiously than the downtown one. But meteoroids’ space speeds are all rather similar to ours.

Notice the new term meteoroids. Space rocks always seem to change their names. Here’s how it works: when a hurtling rock flies through space, it’s called a meteoroid. That’s what can and does occasionally strike our satellites and even the International Space Station. A stone in space even a foot across, zooming at sixty thousand miles an hour and not giving off any light, is utterly invisible. But if it enters the atmosphere and burns up, it’s then called a meteor. We rarely see the metallic chunk itself, since it’s typically the size of a raisin or even an apple seed. Rather, we view the glowing, ionized, heated air that surrounds the invisibly tiny white-hot stone. The phenomenon is commonly called a shooting star. Finally, if the meteor does make it to the ground and gets discovered, it undergoes another name change. Now it’s a meteorite.

In any case, a meteoroid’s speed is less crucial than its direction. What matters is whether it’s barely catching up to Earth from behind or instead hitting us head-on. That’s what’s all-important. The August 11 meteors, those famous Perseids, smash into us head-on. So we witness the violence of their orbital speed added to our own for a combined impact velocity of thirty-eight miles per second. The November Leonid meteors do the same thing. These screaming shooting stars streak across the sky in a mere second or two. No time to say, “Hey, look at that!” Glance down and you miss them.

But the December 13 Geminid meteors arrive here at a 90-degree angle relative to our orbital direction. There is no head-on collision. They’re like a car backing out of a driveway and crunching softly into ours from the side. The impact speed is just half that of the others. They only streak at twenty miles a second, and it shows as they lope lazily across the heavens. In the vast majority of cases, they are even too slow to create glowing trains behind them, unlike fully one-third of the Perseids and Leonids. What’s wild and satisfying is how easy it is, with no telescope or any other equipment, to witness these disparate cosmic velocities.

That 1908 Tunguska meteor was moving from the east toward the north. At that early hour of the morning, this corresponded to a sideways entry into our atmosphere. Similarly, the Siberian bolide (exploding meteor) of 2013 came in at about eleven miles a second from the sunward direction, sideways to us. Had either come from an overhead direction it would have had far more speed and thus released far more energy. Our thin, dirt-covered 1908 witness, Semen Semenov, whose wife led him back into his house, the windows of which were now broken, may not have fared as well if that had been the case.

Obviously, celestial movement isn’t necessarily a textbook sort of thing. It parades overhead right in our faces when we take a few minutes to look.

But if celestial speeds do seem too cerebral, we can bring the whole thing home, quite literally. Remember that our planet is not an isolated island. Comets and asteroids continue to pay us close encounters of the clobbering kind.

The public has many misconceptions about meteorites—the name for meteors that land. People imagine they’re hot when in truth they’re barely warm, after being flash-frozen by passage through our cold atmosphere. On August 31, 1991, two boys standing on a front lawn in Noblesville, Indiana, saw a meteorite thud into the grass a few feet away and picked it up immediately without harm.

People also imagine they’re deadly, when the only person ever directly hit, Ann Hodges of Sylacauga, Alabama, was merely bruised when one tore through her roof, struck a console radio, then bounced onto her hip on November 30, 1954.

To merely state that Ann Hodges was the only person in history to be hit and injured by a meteorite is to simplify an amazing story. It started that afternoon when Ann, not feeling well, fell asleep on her living room sofa—in a rented white house located across the street from the Comet Drive-In Theatre, whose neon logo depicted a zooming, meteorlike object.

Hodges was awakened by the eight-pound metallic object crashing at high speed through the living room ceiling. Before she could react, it bounced off the radio, struck her left hip, and bruised her left hand. The incident quickly drew crowds of TV and print reporters and put the thirty-four-year-old woman in the history books. A footnote was added for area physician Moody Jacobs, the only doctor ever to treat someone struck by an object from outer space.

But Ann Hodges did not gain any benefit from this historic occurrence—unlike, say, eighteen-year-old Michelle Knapp of Peekskill, New York, whose life was changed by a 1992 meteorite encounter with her car. For Ann, the trouble began when her husband, Eugene Hulitt Hodges, and she were upset at the crowds descending on their home, then amazed and angered that police officers and government officials took away the meteorite without the family’s permission.

The Hodgeses worked with a lawyer to eventually secure the meteorite’s return, but their hopes of making a fortune from the stone quickly faded when their landlady, Birdie Guy, claimed the meteorite was rightfully hers and fought for its custody in court. Legal battles over its ownership and multiple costly appeals all went against the Hodgeses, while public sentiment went against the “greedy” landlady, as she was generally depicted in news reports. The Hodgeses finally settled, and Guy accepted five hundred dollars in lieu of the meteorite, but by then the headlines were long over and the meteorite was no longer a hot or valuable item. The couple eventually turned it over, for small compensation, to the Alabama Museum of Natural History at the University of Alabama in Tuscaloosa, where it remains on display.

The only person with a positive experience in the entire celestial encounter was a farmer named Julius Kempis McKinney. On December 1, 1954, the day after the meteorite struck the Hodges house, McKinney was driving a mule-drawn, firewood-laden wagon a few miles away when the animals balked at a black rock in the road. McKinney kicked the odd black stone off the road and continued home. But later, upon hearing news reports of the Hodges incident, McKinney returned to the site. He took the rock home and let his children play with it.

He trusted only his postman with the information. The postman helped McKinney find a lawyer, who negotiated an amazing price for the meteorite’s sale. The purchaser was an attorney from Indianapolis acting on behalf of the Smithsonian Institution.

Mineralogy experts confirmed that the three-pound rock was indeed a fragment of the larger Hodges meteorite; it is actually common for a meteoroid to shatter or explode into multiple pieces in the air before hitting the ground. Although the sale price was never revealed, it was enough for the McKinney family to purchase a car and a new house. This unexpected good fortune was a rare event for an African American in that state in that period of history, when racial inequality was the norm.

Is all this sufficient for a movie plot? Bill Field, who as a five-year-old in Sylacauga saw the meteor streak across the sky, leaving a white trail, and heard a loud sonic boom—a somewhat quieter version of what Siberian townspeople experienced in 2013—grew up to be a filmmaker. He researched the incident and what happened to all the people involved and successfully sold his movie script to 20th Century Fox. But no film was ever made.

As for Ann Hodges, she later said she’d been permanently changed—not by the six-inch bruise on her left hip but by the emotional scars resulting from the legal fights and disappointments. She died of kidney failure at a Sylacauga nursing home in 1972, at the age of fifty-two.

History also records a Franciscan friar who was reportedly killed in Milan in the seventeenth century by a two-inch meteor that severed an artery in his leg. But who can say for sure? For all anyone knows, it could have been a stray musket shot. Confirmation is lacking. And in 2009, a German boy claimed that his finger had been injured by a pea-size meteorite that appeared “after a flash of light” and then “buried itself in the road.” Despite global headlines, however, this story is not credible at all. Ann Hodges’s bruise remains the only authenticated human injury from a hurtling space object.

Meteors provide the only visible physical interchange between Earth and the heavens. It’s the sole visual link between what’s “up there” and our terrestrial lives. A meteor’s fall to earth is sudden, and just to add a little spice, there’s even that hint of danger.

Hint or not, Armageddon lovers never tire of the “peril from space” motif—the fear of a giant Earth-smiting stone from hell, a Tunguska meteor on steroids. New end-of-days predictions sprout like poppies, only to dissipate when the dreaded date passes harmlessly and is as promptly forgotten as an opium dream. To appreciate the peril realistically, you have to know how it works.

Instead of watching meteors in space—few of which survive their trip through the atmosphere but instead disintegrate quietly into dust—we should contemplate the rare dramatic meteors that have made it all the way to the ground. We won’t even talk about the really bad events that altered history, including the dinosaur-ending K-T impact sixty-five million years ago, which crashed into the raptors’ favorite Yucatán beach at Chicxulub. Or the even worse Permian “great dying” 251 million years ago, which destroyed most of the planet’s genera as though they were doodles on a chalkboard and nearly erased the intricate, interconnected biosphere. Such events typically involve asteroids more than a mile wide, the kind that seem to hit us every few hundred million years or so. Much more common are the smaller stones in the three-to twenty-five-pound category, which damage homes almost yearly, usually after an expensive renovation.

Meteoroids that make it to the ground are not the meteor-shower variety, which are usually composed of flimsy ices. The survivors are, instead, hardy stony or metallic pieces of asteroids or even fragments of the moon or Mars. They arrive without warning.

A meteoroid can weigh a ton as it strikes our atmosphere; that was the estimated mass of the intruder that broke into dozens of fragments over a Chicago suburb on March 26, 2003. One small piece penetrated a teenager’s bedroom, hit his printer, and shattered a full-length mirror. Bad luck? It could have been much worse.

A meteoroid traveling through space encounters Earth at a sizzling seven to forty-four miles per second. If it weighs more than one hundred thousand tons our atmosphere won’t slow it down in the slightest: it slams into the ground at full cosmic velocity.

At the other extreme, if the meteoroid is less than eight tons, friction from the air robs it of all its original speed. Then its impact, like that of falling garbage or flying squirrels, is strictly determined by terminal velocity. Happily, these lower-mass objects are the rule.

At a height of about ten miles, or fifty thousand feet, a meteorite slows to two or three miles per second and no longer glows. From that altitude on down it’s an invisibly dark tumbling piece of rock, which can be mostly stone or a half-iron, half-nickel amalgam. Nonetheless its seven-thousand-mile-an-hour velocity, three to six times faster than a bullet, gives a one-pound meteor enough kinetic energy to bring down a jetliner. It hasn’t yet happened, but it could.

Continuing downward, unobservable, the meteoroid’s encounter with increasingly thick air slows it to a terminal velocity of around 250 miles per hour. This is its final speed as it strikes the ground. Or anything else.

Buildings are penetrated every year or so in North America alone. Animals, standing naked outdoors, have also fared poorly:

May 1, 1860: A horse is killed by a meteorite in Concord, Ohio.

March 11, 1897: A rain of many stones in West Virginia kills another horse.

June 28, 1911: A meteor later found to have come from Mars kills a dog on the outskirts of Alexandria, Egypt.

October 15, 1972: A cow is killed by a meteorite in Valera, Venezuela.

Cars seem to attract meteors, too. One was quietly parked in its garage on September 28, 1930, in Benld, Illinois, when a meteor penetrated the garage roof, the car’s roof, and the car’s wooden floorboards before bouncing up off the muffler and coming to rest in the seat material, inaugurating a long love affair between asteroid fragments and automobiles.

In the past quarter century the most spectacular encounter was the parked Chevy in Peekskill, New York, whose trunk was destroyed by a twenty-six-pounder on October 9, 1992. Its eighteen-year-old owner found her life changed by the sixty-nine thousand dollars paid to her by a collector. (He wanted the crumpled car as well as the meteorite, and she said, “Sure.” A beat-up, ten-year-old Malibu whose insurance didn’t even cover the damage? Are you kidding? Take it!)

Just between 2002 and 2010, meteorites entered at least seven homes, including two in the United States. The freshly landed stones are usually “barely warm” and have a black fusion crust.

There is no terminal velocity on airless bodies such as Mercury and the moon, where meteoroids captured by gravity keep gaining speed up to a maximum that equals that planet’s escape velocity. On Earth it’s twenty-five thousand miles per hour. If there were no air, meteorites wouldn’t just penetrate roofs and floors. They’d keep going until they converted the basement playroom and much of the surrounding neighborhood into a huge crater. After all, kinetic energy equals the meteorite’s mass times the square of its speed. A meteor reaching your kitchen table at 250 miles an hour is 1002, or ten thousand, times less damaging than if it had struck at even a low space speed of twenty-five thousand miles per hour.