ALBUQUERQUE, N.M.—Imagine that we get word that an asteroid is headed for Albuquerque. Estimated time to impact: 19 hours.
The chances of a city-killer hitting Albuquerque, or any other city on Earth for that matter, are slim. But in a remarkable series of events last October, a team of scientists around the world for the first time spotted a space rock headed toward Earth before it hit and were able to track its path and predict its time and place of impact.
Chalk it up partly to luck, said Sandia National Laboratories scientist Mark Boslough, a member of a loose-knit global team of researchers who tracked the space rock and have been studying its aftermath.
They describe how it was done, and what they have learned, in a paper published in the British science journal Nature.
"It was just pure serendipity that this thing was found," Boslough said.
The discovery was made the night of Oct. 5, 2008, by astronomers at the Catalina Sky Survey on Mount Lemmon, in Arizona. The Sky Survey team regularly scans the skies for asteroids, which show up as slowly moving objects against the still backdrop of stars in the night sky.
Usually Catalina's discoveries follow lazy arcs in distant space. But by the next morning, calculations done by a team at the International Astronomical Union in Massachusetts showed this space rock was different, that it was on a collision course with the sky above Sudan later that night.
Shortly after noon, Boslough forwarded an e-mail from an Italian astronomer with details on the coming impact, adding a note at the top that said, "Asteroid on track to collide over Africa tonight ... 2 meters. should be an airburst!"
Space rocks of that size, about 6 feet across, typically hit Earth a few times each year, usually exploding high in the atmosphere with no advance warning. Never before had Boslough and the other members of the global network of scientists who track what are called "near-Earth objects" seen one coming before it hit.
Rocks that size never make it to the ground, exploding in a flash as they are superheated by friction as they speed through Earth's upper atmosphere.
Satellite images show that in this case, the asteroid began burning 40 miles above Earth's surface. Boslough and Sandia colleague Richard Spalding concluded that it disintegrated in three explosive flashes that Boslough said were equivalent to about a thousand tons of TNT.
Witnesses at the town of Wadi Halfa in Sudan and at a nearby train station, described "a rocket-like fireball with an abrupt ending," the scientists reported in Nature.
From the time it was spotted, it was clear the rock posed no danger, and even if it had been headed toward a populated area, no evacuation would have been needed, Boslough said.
But it does raise the question of what might be involved if a more dangerous asteroid were spotted in time to provide warning, Boslough noted.
Asteroids large enough to be city-killers are far more rare, hitting Earth at a rate of a few times per century. Because most of Earth is lightly populated, the chances of one of them destroying a city are "extraordinarily small," Boslough said.
The last asteroid of that size to hit Earth was in Siberia in 1908.
Information from: Albuquerque Journal