Asteroid impact bigger than thought

HOT STUFF::At its peak the fireball from the Chelyabinsk asteroid was about 30 times brighter than the sun and emitted enough UV radiation to cause instant sunburns

Reuters, CAPE CANAVERAL, Florida

Fri, Nov 08, 2013 - Page 7

The asteroid that tore through the skies over central Russia in February, injuring more than 1,200 people, had a more powerful impact than scientists originally assessed, new studies released on Wednesday showed.

The research also raised the prospect that objects the size of the 19m Chelyabinsk asteroid in orbits near Earth are more common than current estimates, perhaps numbering as high as 20 million.

“Chelyabinsk was an eye-opener, but we shouldn’t give it an excessive amount of importance as to what may come in the future,” said Bill Cooke, head of NASA’s Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Alabama.

“A lot is going to depend on where an event occurs ... The odds are an event will occur over the ocean rather than over a populated area,” Cooke said in a conference call with reporters.

Shock waves from the asteroid’s Feb. 15 explosion about 30km above the heavily populated Russian city of Chelyabinsk were powerful enough to knock people off their feet, the new studies showed.

At its peak, the fireball was about 30 times brighter than the sun and pumped out enough ultraviolet radiation to cause instant sunburns, researchers said in a trio of papers published this week.

The explosion over Chelyabinsk was as powerful as about 500 kilotons of TNT — more than 30 times the force of the Hiroshima nuclear bomb, the studies showed.

Debris from shattered windows and damaged buildings sent more than 1,200 people to hospitals for treatment.

Researchers collected hundreds of cellphone, dashboard and security camera videos of the event to reconstruct the asteroid’s flight path, speed and midair explosion.

Teams also analyzed rocks and fragments recovered from the ground and determined that the asteroid had been flying solo for a relatively short 1.2 million years.

Scientists suspect it was once part of a larger body that was torn apart by Earth’s gravity during a previous flyby.

“Perhaps 1.2 million years ago, we already had a close encounter with the Chelyabinsk meteoroid, at which time the rock split in two and this object went on its course, only to hit us now very recently,” Peter Jenniskens, with NASA’s Ames Research Center in Mountain View, California, said in an interview with Science magazine.

The new analysis, pieced together from hundreds of video clips, shows the asteroid entered Earth’s atmosphere at the blistering speed of about 19km per second, slightly faster than previously reported.

A related analysis shows that current computer models underestimate the amount of energy released by fast-moving Chelyabinsk-type asteroids that break apart in midair.

So far, telescopic surveys have found only about 500 similarly sized objects in orbits that pass close to Earth, but that population may be as high as 20 million, Peter Brown, with the University of Western Ontario, reported in a related study.

A trio of papers on the Chelyabinsk fireball was published in the journals Nature and Science this week.