A meteor fireball lit up the morning sky over Chelyabinsk in central Russia, producing a shock wave that shattered windows and injured an estimated 500 1,000 people.** Although much of the parent object likely burned up in the atmosphere, Russian authorities say that several meteorite fragments have already been recovered, according to the Interfax news agency.

A preliminary analysis posted to the Web site of the Russian Academy of Sciences estimates that the object that struck Earth's atmosphere was a few meters in diameter, "the weight of the order of ten tons [and] the energy of a few kilotons," according to a Google translation.* That would make the Chelyabinsk event a fairly common occurrence, although such strikes usually occur over less-populated regions, not cities of more than a million people. On average, a four-meter asteroid hits Earth every year, delivering five kilotons of energy, Southwest Research Institute senior scientist Clark Chapman found in a 2004 analysis.

The Chelyabinsk impact appears unrelated to the close passage of the 50-meter asteroid 2012 DA14, which is expected to zip past Earth at a distance of less than 30,000 kilometers around 2:30 P.M. Eastern time today—inside the orbit of some satellites. On Twitter, the European Space Agency stated that agency experts have confirmed that there is no link between the two events.

A dashboard camera captured some dramatic footage (below) of this morning's event.

We will update this post as more information becomes available.

*UPDATE (11:33 A.M. EST): Other analyses point to a larger size for the impactor. Margaret Campbell-Brown of the University of Western Ontario told Nature that her calculations show an initial size of 15 meters for the object when it hit the atmosphere. "That would make it the biggest object recorded to hit the Earth since Tunguska," a giant blast over Siberia in 1908, she said.

**UPDATE (4:10 P.M.): The New York Times, citing information from Russia’s Interior Ministry, reports that the number of injured is more than 1,000.