Researchers have conducted a preliminary analysis of the event. "Here is what we know so far," says Bill Cooke, head of NASA's Meteoroid Environment Office. "The asteroid was about 17 meters in diameter and weighed approximately 10,000 metric tons. It struck Earth's atmosphere at 40,000 mph (18 km/s) and broke apart about 12 to 15 miles (20 to 25 km) above Earth's surface. The energy of the resulting explosion was in the vicinity of 500 kilotons of TNT."