In 2004, as a massive tsunami roiled through the Indian Ocean killing hundreds of thousands of people, a dozen or so scientists quietly confronted an impending disaster potentially even more lethal. They had inside intelligence that a chunk of rock and metal, roughly 1,300 feet wide, was hurtling toward a possible collision with the most populated swath of Earth—Europe, India, and Southeast Asia. Furiously crunching numbers on their computers, the researchers put the odds of impact in the year 2029 at exactly those of hitting the number in a game of roulette: 1 in 37.
“We usually deal with one chance in a million,” recalls Steven Chesley at NASA’s Jet Propulsion Laboratory in Pasadena, California. “This was absolutely extraordinary—I didn’t expect to see anything like it in my career.” By the end of the day on December 27, 2004, to the relief of the observers, archival data turned up trajectory information that rendered the odds of a collision nil. Nonetheless, in 2029 the asteroid, dubbed Apophis—derived from the Egyptian god Apep, the destroyer who dwells in eternal darkness—will zoom closer to Earth than the world’s communications satellites do. And April 13, 2036, it will return—this time with a 1-in-45,000 chance of hitting somewhere on a line stretching from the Pacific Ocean near California to Central America.
Because Apophis was discovered during one of the world’s greatest natural disasters, the worries about the impact went largely unnoticed. But that tense day, December 26, 2004, stunned the small group of astronomers who dutifully detect and plot trajectories of hundreds of thousands of the millions of chunks of rock whizzing around the solar system. Though too small to end civilization—unlike the asteroid that may have doomed the dinosaurs—Apophis could pack a punch comparable to a large nuclear weapon. Traveling at 28,000 miles per hour, it would heat up as it passed through Earth’s atmosphere, turning the dark rock into a fiery sun as it arced across the sky. Then it would either explode just aboveground—as one most likely did in 1908, leveling a vast forest in the Tunguska region of Siberia—or gouge a crater 20 times its size. “If it hit London, there would be no London,” says Apollo 9 astronaut Rusty Schweickart, who had closely followed the discussion of the potential 2029 impact. Slamming into the ocean, Apophis could create a tsunami dwarfing the one that killed more than 200,000 people around Indonesia.
Apophis is one of millions of asteroids roaming the solar system. None are known to pose an immediate threat, but some are bona fide civilization stompers. A monster rock discovered just this year, with the prosaic name of 2007PA8, is more than two miles across, large enough to wipe out most of humanity. Fortunately, the odds that it will hit are essentially zero. Smaller asteroids are less deadly but much more common. Planetary scientists now estimate that 150-foot-wide space rocks, comparable to the one that hit Tunguska, strike only once every thousand years or so. For a brief time in 2004, just months before the Apophis scare, astronomers feared that a 150-foot-wide asteroid was just days away from racing into the atmosphere. Fast-paced observations allowed them to calculate a more exact orbital path, which took it far from Earth.
