Incoming!

Illustration by John MacNeill MEET 1950DA
This 1-kilometer-wide rock is the only known big asteroid on a possible collision course with Earth. But until the asteroid search is done, we won't know if others are out there, closer to Earth and headed our way.
Laser pulses could move the asteroid off course, averting a collision. But like many schemes, this would require decades or even centuries of advance notice to work. Illustration by John MacNeill

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Its name is 1950DA, it's the size of a small mountain, and it's headed for Earth. According to one grim scenario, 1950DA will hit its target-most likely water, since there is more water than land on our planet-and plunge to the seabed in a fraction of a second. When the asteroid meets the ocean floor, it will explode, excavating a crater 11 miles wide.
A column of water and debris will shoot a few miles into the sky-to the height of a low-flying jetliner. Then skyscraper-high walls of water will head for shore, eventually breaking in the shallows
and flooding the coast. The rest you know, if you saw the weepy 1998 asteroid movie Deep Impact.



Worse things may already have happened: One theory credits an 11-kilometer-wide asteroid with roasting dinosaurs alive 65 million years ago.
The enormous impact sent debris flying back into space—some of it halfway to the Moon. When the asteroid bits reentered the atmosphere, the heat that was generated flash-baked plant and animal life. (Had that not happened, mind you, we probably wouldn't be here today.) 1950DA is minuscule by comparison, though even a still smaller asteroid could take out an entire city with a direct hit. And make no mistake, there are plenty of space rocks out there; one missed Earth by only 75,000 miles in June 2002—and wasn't spotted until after it had whizzed by.



Now for the good news. First, 1950DA is 877 years away and a 300-to-1 long shot for actually striking the planet and doing the damage in the scenario above, which is part of a simulation recently created by planetary scientists Steven Ward and Erik Asphaug of the University of California, Santa Cruz. And although there are more 1950DAs out there—maybe bigger, maybe due to arrive much sooner—the search for potential killer asteroids is at least under way, though sorely underfunded. Furthermore, a small band of scientists, many of them fueled more by passion than by actual government grants, is working on novel methods to deal with asteroids before they get too close to be diverted or destroyed. (The time spans involved give a new definition to advance thinking:
As the foldout on the previous pages shows, some diversion operations would require centuries to work.)



NASA is more than halfway through a search for asteroids and comets that come within striking distance of Earth—called "near Earth objects," or NEOs—and are wider than a kilometer. Experts calculate that the chance of an object that size hitting Earth in the next century is only one in several thousand, but the result would be global havoc.



After astronomers spot an asteroid in their telescopes, they use radar tracking to get a more precise picture of where it's headed, how fast it's moving, and whether its orbit around the Sun will intersect with Earth's orbit. Before 1950DA's predicted encounter with Earth in 2880, the asteroid will swing around the Sun almost 400 times, while Earth will complete 876 orbits.