The meteor that blazed across the East Coast sky Friday night and lit up the Twittersphere was the size of a washing machine and not at all unusual, scientists said. It's just that they generally don't make their appearances over densely populated areas and in front of so many witnesses.
People from Florida to Maine — including many in the Washington metro area — reported seeing a streak of light around the size and brightness of a full moon, just before 8 p.m. They said it shot from west to east and then appeared to break up.
"Something that size hits the Earth at least monthly, if not every few weeks," said Richard Binzel, a professor of planetary science at the Massachusetts Institute of Technology, adding that it was probably traveling around 15 miles per second, or about 50,000 mph, and probably disintegrated without sending debris to Earth.
"Most meteor streaks are over the ocean or remote uninhabited parts of the planet," he said. "It's rare that they happen over widely populated regions where a lot of reports come in."
Those reporting the event may have been more aware of meteors in the wake of a larger one that exploded over Chelyabinsk, Russia, and whose pressure wave injured more than a thousand people and caused millions of dollars in property damage. And in February, an asteroid narrowly missed hitting Earth.
Despite the closeness of the two events to Friday night's, scientists said there is no evidence that more meteors are entering the atmosphere than in the past.
"These things are very common," Timothy Spahr, director of the Minor Planet Center at the Smithsonian Astrophysical Observatory, said in an e-mail. "The Earth accumulates tons and tons of material every day through collisions. Most of it is small dust particles, but we get a few 'large' things like baseball-sized chunks every day or few days."
A meteor like the one in Russia occurs every 30 to 50 years, Binzel said.
On Tuesday, in the wake of the Russia meteor, the House Science, Space and Technology Committee held a hearing on what the United States is doing to track and monitor "near-Earth objects" that pose a threat to the planet. The meteor in Russia was estimated to be 50 to 60 feet across, and scientists generally don't track objects that size.
"We look for bigger ones, ones that could really screw up our planet," said David Morrison, senior scientist at the NASA Ames Research Center in California.
If a meteor half a mile to a mile wide were to hit land, it could form a crater and blow enough dust into the stratosphere to block out the sun and affect crops worldwide for a year, he said.
Should such an object be detected by telescopes, all hope would not be lost. "If we had enough warning, then we could build a spacecraft that would go out and change its course," he said.
But if scientists learned only a few weeks in advance that a large object was heading toward a particular spot on Earth, he said, "all we could do is evacuate."