Asteroid Threat : Defending Our Planet from Deadly Near-earth Objects (9781616149147) (7 page)

Earth's oceans and shifting terrain hide, obscure, or erase many impact sites. Yet more than 160 remain on all seven continents, many of them chillingly massive. The Sudbury crater in Ontario, Canada, is slightly more 130 kilometers across, and the Vredefort ring in South Africa is 190 kilometers in diameter and looks like an immense flat canyon when observed from high in the air or from space. The Acraman crater in Lake Acraman, South Australia, is a scar that was made about 580 million years ago and measures 90 kilometers across, while the Woodleigh crater in Western Australia was made roughly 364 million years ago. The Manicouagan crater in Quebec, which is 100 kilometers wide, resulted from an impact made 215 million years ago. And a crater was discovered in Chesapeake Bay, 201 kilometers from the nation's capital, in the early 1980s. Its estimated age is 35 million years, so it cannot be blamed on an incompetent administration, Republican or Democrat.
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There are innumerable examples all over Target Earth. The Hoba meteorite is a sixty-ton slab of iron that slammed into what is now Namibia about eighty thousand years ago, and since no one in that country seems to have the inclination or resources to move it, it has become a national monument to be appreciated and studied. The Willamette meteorite, which is a ten-foot-tall mass of pitted iron that weighs around fifteen tons, is thought to be the worldly remains of the iron core of a planet that crashed into what is now this one billions of years ago. It was discovered on Native American land in 1902, the local indigene's pleas to leave it alone because they believed it had healing power were ignored, and it was unceremoniously taken away and wound up on display at the American Museum
of Natural History in New York. Another one, ALH 84001, is one of the most intriguing artifacts from out of this world. Its dull name notwithstanding, it comes from Mars, was discovered in Antarctica in 1984, and, after scientists saw on close examination, contains the fossilized remains of what may have been very small bacteria. If they really were living microscopic organisms, it would be further proof that Martians, however tiny, have indeed lived on the Red Planet.

Bombardment by near-Earth objects (NEOs) is widely associated by the public with the demise of the dinosaurs and, therefore, with prehistoric and ancient “history.” But Tunguska and Chelyabinsk were dramatic demonstrations that the attacks are still underway, and those “events” were in fact only two among thousands that have occurred since records of the rain of rocks and ice started being kept in the eighteenth century.

Like every other body in the Solar System, Earth is under constant bombardment from objects ranging in size from tiny grains of sand to enormously large rocks, many of which are laced with iron. Most of them come from the Asteroid Belt between Mars and Jupiter and are the remnants of a planet that failed to form because of Jupiter's and Saturn's gravitational pulls (and with a little help from Mars). The asteroids in the belt collide with each other constantly and break into fragments that head in all directions, including this one, at velocities that can reach fifty thousand miles an hour. The small rocks range from the size of a beer can to a Winnebago. Those in the medium category start at the size of a two-car garage and can be as large as a small building in the average town. The big ones would sit in a professional football stadium the way a hard-boiled egg would sit in a porcelain cup. And the really big ones start at a kilometer across and go upward to perhaps six to twelve kilometers. The good news is that the size of the asteroids is inversely proportional to their number, meaning that there are relatively few of the really big ones in the kilometer-or-larger
class—also known as the Doomsday rocks. That means the neighborhood is fairly infested with thousands that could demolish downtown Peoria, Rangoon, or Nairobi, but the ones that are large enough to end civilization show up only about once every one hundred years. Some are round, some look like dog bones, and some like Idaho potatoes. Their composition varies, as well. The overwhelming majority of Gene Shoemaker's bullets are solid rocks, but there are also relatively soft ones that are of a substance like sand held together with glue, while still others are made mostly of iron.

The bullets speed around the planet in all directions and at all altitudes all the time. That is why there were major impacts on or explosions directly over Brazil, Canada, the United States (Michigan), Italy, Spain, the Indian Ocean, the Eastern Mediterranean, and Indonesia between 1930 and 2009.
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The explosion over Brazil happened above the Amazon in the northwestern part of the country, just after sunrise on August 13, 1930, and left physical and emotional scars that are still there. As women began to wash clothes in the Curuçá River and their men fished or tapped rubber trees, the Sun turned bloodred. Then the region was enveloped in darkness. Suddenly there were three very loud whistling sounds, followed by three loud explosions in rapid succession. The blasts turned the jungle into an inferno that burned for several months, which sent many villagers in the region, fearing imminent death, fleeing with as many belongings as they could carry. But others stayed in their huts in an area of several hundred square kilometers. Terrified children tried to hide in corners while some of their parents listened to what sounded like artillery shells and looked at the sky to see what was happening. The ground trembled as it would in an earthquake. Five days later, an Italian monk named Father Fedele d'Alviano began his annual missionary visit to the area and found people who were still shaken by the event. He tried to reassure them that they had suffered from meteorites coming
from the sky, not from the wrath of God. It was subsequently called a possible “Brazilian twin” to the Tunguska explosion.
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And at least two impacts on the homes of individual Americans were offbeat enough to be reported by the news media as just plain quirky. On November 30, 1954, Mrs. Hodges was severely bruised when a five-kilogram rock came crashing through her roof in Sylacauga, Alabama, and hit her while she was napping in her living room. She got off with a severe bruise. (Mrs. Hodges happened to live across the street from—you can't make it up, as some in the news business say—the Comet Drive-In, a movie theater.) And thousands saw another rock as it sped over Kentucky and headed northeast before making a sonic boom and breaking into more than seventy fragments on October 9, 1992. One football-sized fragment that weighed nearly two pounds landed on Michelle Knapp's Chevrolet Malibu that was parked in her driveway in Peekskill, New York, that day. Its trunk was scrunched, but the $69,000 that a consortium of three dealers paid her for it more than took care of the repairs.
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As the dealers in Chelyabinsk were to learn twenty-one years later, souvenirs from heaven are valuable collector's items.

Although some members of Congress undoubtedly read about what happened to Hodges and Knapp, they didn't need those incidents to conclude that their planet was and still is under continuous attack by large and small rocks coming from space and that the dinosaurs were almost undoubtedly terminated by a really big one. Those isolated events would have gone virtually unnoticed by Congress, and certainly by the international community, since, by their nature, they were of no real consequence to the rest of the world. Except that just about everyone who was paying attention knew that some of the rocks out there were a lot bigger than what came down on Sylacauga and Peekskill. Gene Shoemaker had not yet participated in the film
Asteroids: Deadly Impact
for National Geographic Video, but
it was generally understood that a collision with a large-enough impactor could inflict more damage than a nuclear war and even end their planet's existence. The explosion of a 450-ton meteor twelve miles above Chicora, Pennsylvania, on June 24, 1938, and others over British Columbia in March 1967, Lake Huron in September 1966, and Greenland in December 1997, made the point. As British poet and critic Samuel Johnson said, “Depend upon it, sir, when a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully.”

When the comet Shoemaker-Levy 9 slammed into Jupiter in July 1994, it was extensively covered by the news media and concentrated the legislators' and the rest of the world's collective mind. The images of the successive impacts and the inevitable references to what any one of them would have done to Earth drove home the need to find out what, precisely, the nature of the threat was and then come up with an effective defense, or “mitigation,” as the community calls it. Every other conceivable problem was dwarfed by the prospect of Doomsday: by the possibility, however remote, that Earth would be terminated and that existence would end. Lights out forever.

The primal know-the-enemy impulse took concrete form when the Johns Hopkins University Applied Physics Laboratory (APL) designed a spacecraft for NASA that was packed with instruments and that would be the first to be sent to an asteroid to study it in detail as part of the new Discovery program. As was mentioned in
chapter 2
, the asteroid candidate of choice was 433 Eros, a smooth, pockmarked near-Earth boulder that was thirty-three kilometers long and thirteen kilometers wide—about the size of Manhattan—and that was incongruously named after the Greek god of love (as in
erotic
).

The mission was at first called NEAR, for Near-Earth Asteroid Rendezvous, and then NEAR Shoemaker for the legendary godfather of planetary science. It entailed having the spacecraft land on Eros and stay on it—ride it—for a year,
all the while collecting data on its prodigious bulk, composition, mineral content, internal mass, magnetic field, interaction with the solar wind and the space around it, and more. The spacecraft was launched from Cape Canaveral on February 17, 1996, flew by asteroid 253 Mathilde on June 27, 1997, and then went on to 433 Eros. After the first attempt at orbital insertion (as its handlers called it, which describes the adjustment of a spacecraft's momentum to enter into orbit around a space object) failed, it began flying ever-tighter circles around its quarry and started the first orbital study of an asteroid in February 2000. The visitor from Earth eventually landed on 433 Eros on Valentine's Day, February 12, 2001.

NEAR Shoemaker then began sending home everything it learned from its very close encounter. Not surprisingly, the asteroid's mineral composition was typical of other asteroids, and the tough guy had itself been the target of hits—“successive impacts”—in the shooting gallery. Andrew F. Cheng, who was also at the Johns Hopkins APL and who was a member of the science team, reported that there were many impact craters, most of them relatively large, and that the asteroid was “intact but deeply fractured,” probably because it had broken off of an even larger rock.
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The mission also showed that landing people on this or other large asteroids, either for scientific research or to mine them for rare minerals, was feasible. The spacecraft stopped sending data home on February 28, 2001, and an attempt to communicate with it in December 2002 was unsuccessful. It is still riding its asteroid, however, mute in the bitter cold.

The 433 Eros asteroid was no threat to Earth and never will be. But the mission provided the first detailed look at one of the large rocks in its element as representative of others, larger and smaller, that could be potentially hazardous or worse. The images of a scarred, potato-shaped boulder that was twice the size of Manhattan speeding through space were vivid reminders, yet again, that many dangerous objects prowl the neighborhood,
far from home and near it. So the NEAR Shoemaker encounter, like the attack on Jupiter, remained lodged in the minds of the space-science community and those on Capitol Hill who were responsible for knowing about the potential danger posed by asteroids and comets that get too close.

The idea that asteroid and comet impacts are still a hazard had only just taken hold in 1980, as David Morrison has written, which is when the Alvarez team published what it found at the Chicxulub crater. Morrison adds that asteroids are statistically by far the greater threat than comets are; the threat from comets is comparatively miniscule.
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But the threat from NEOs is potential, not immediate. The Wide-field Infrared Survey Explorer telescope, which was called “WISE” by its handlers at JPL, turned up 911 (that number again) of an estimated 981 NEOs larger than a kilometer, but none were thought to be potentially hazardous asteroids. That gestated in the scientific community and in Washington for a little more than a decade. And so, understandably, did the idea that what had come out of the sky to cause such death and destruction could come again, a point that is made to students in Astronomy 101. Those who are assigned
Contemporary Astronomy
by Jay M. Pasachoff, the standard text for that college-level course, learn that some Apollo asteroids—those that cross Earth's orbit—are potential impactors. “Most Apollo asteroids will probably collide with the Earth eventually,” the author explains, “because their orbits may intersect the Earth's. Luckily there are only a few dozen Apollos greater than 1 km in diameter.”
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The widely used textbook—and justifiably so—might have pointed out that even Earth-crossers a lot smaller than a kilometer can, and have been, devastating.

With the Apollo Moon-landing program, NASA scored a monumental victory over the Soviet Union, followed by that enormously successful Solar System exploration program—the high point of which was unquestionably Voyager 2's twelve-year
grand tour of four of the outer planets and the library of knowledge it sent home—and then the Cold War ended and a highly productive “space race” was over. That left NASA with a conundrum. It became the victim of its own success. All of those accomplishments were by definition spectacularly unique, but repeating them was considered irrelevant and wasteful. The resources were there, but there was no mission. So NASA became a powerful and famously inventive agency without a major long-term goal that was inherently dramatic enough to hold the public's (and congressional appropriations committees') interest. There is such a mission, however. It is planetary defense done in conjunction with the international community.