Asteroid Accident
Asteroids typically top the list of extraterrestrial objects that could hit Earth. A 9-mile wide asteroid that crashed into what is now Mexico’s Yucatan Peninsula was partly responsible for the dinosaurs' extinction about 65 million years ago.
The 2004 announcement that 900-foot long Apophis had more than a 2 percent chance of colliding with Earth in 2029 revved up research on asteroid detection and defense, when scientists recalculated the odds down to 1 in 250,000.
Luckily, nothing of that size is in Earth’s path currently, so “we may be safe for at least a few million years,” said planetary scientist Jay Melosh of Purdue University.
But smaller threats may be looming.
NASA expects that roughly every 100 years, an asteroid larger than 55 yards wide will strike. The impact could cause local catastrophes like massive floods, destruction of entire cities and agricultural collapse. Around once every few 100,000 years, chunks of rock more than three-fifths of a mile wide — the equivalent of about 12 New York City blocks — could come tumbling through the atmosphere causing much more serious problems, on a global scale. Acid rain would kill crops, debris would shield Earth from sunlight, and firestorms would ensue, according to NASA’s Near Earth Object Program.
To understand our cosmic risks, scientists are inspecting the solar system to find asteroids that may be heading our way, said UCSC planetary scientist Erik Asphaug. They’ve discovered about 900 of an estimated 1,000 asteroids wider than three-fifths of a mile thought to have an Earth-crossing orbit. None appears to have Earth as its target.
“The plain vanilla odds are very low” that anything already discovered of that size will strike in the near future, Asphaug said. But that doesn’t mean Earth is 100 percent safe.
It’s close to impossible to find every asteroid that could be a threat to Earth.
“There’s always some uncertainty that we’re going to have to live with,” he said. “Or die with.”
Image courtesy of Don Davis / NASA