Tough to spot: Chelyabinsk meteor tinted by ancient crashes
October 10, 2013 -- Updated 1318 GMT (2118 HKT)
(File) The trail of a falling object is seen above a residential apartment block in the Urals city of Chelyabinsk.
- The space rock that blew up over Russia had been darkened by ancient crashes
- "Dark asteroids are harder to detect because they reflect less light," scientist says
- The meteor injured about 1,500 people when it crashed to Earth in February
- Scientists have found about 100 pieces, the biggest of which is about 11 pounds
(CNN) -- The meteor that blew up over southwestern Russia in February had survived long-ago collisions that blackened its surface, making it harder to spot, a scientist who studied its pieces said Wednesday.
The roughly 60-foot space rock plunged into Earth's atmosphere and exploded over the Russian city of Chelyabinsk with the force of about 30 early nuclear bombs. Of the roughly 100 fragments found so far, the biggest weighs about 11 pounds (5 kilograms), said Maria Gritsevich, a researcher at the University of Helsinki.
Read more: Saving Earth from asteroids
Gritsevich and others who have studied those fragments have found the small asteroid was mostly made of ordinary rock.
Watch this streaking asteroid
Perseid meteor shower lights up the sky
Russian meteor was like 'a rocket bomb'
But it was marbled with metallic elements such as iron -- and when the asteroid collided with other bodies floating around the solar system, the heat and force of that impact melted the metal, which seeped into fissures in the surface of the stone and blackened its surface.
"Dark asteroids are harder to detect because they reflect less light," Gritsevich, who presented her findings at an American Astronomical Society conference this week, told CNN.
Planet of sound: Meteor blast resonated around Earth
While most ordinary rocky asteroids reflect up to 20% of the sunlight that strikes them, and Earth reflects about 40%, dark asteroids reflect 5% of the light or less, she said.
The meteorites collected from the Chelyabinsk incident show varying signs of darkening, with some completely blackened, others made up entirely of light-colored stone and some with a mixture of coloration, Gritsevich said.
"All Chelyabinsk meteorites look different," she said. "You can clearly distinguish three different groups."
She said scientists are still working to determine the age of the Chelyabinsk meteor, the largest to hit Earth since the 1908 Tunguska incident in Siberia.
NASA estimates 4,700 'potentially hazardous' asteroids
The blast left more than 1,500 injured, mostly by glass from shattered windows, and raised concerns about humanity's vulnerability to stray asteroids.
Two months later, NASA announced a goal of sending a spacecraft out to seize and asteroid and tow it into orbit around the moon, where it could be studied by astronauts -- a project billed in part as a planetary defense mission. But it ran into opposition in Congress, where a House committee voted to block any funding for the mission in July.
Part of complete coverage on
March 7, 2014 -- Updated 1527 GMT (2327 HKT)
The U.S. huffing over Ukraine jars with many after recent U.S.-led interventions, writes Simon Tisdall.
March 8, 2014 -- Updated 0354 GMT (1154 HKT)
Venezuelan President Nicolas Maduro is unapologetic about his government's response to opposition protesters.
March 6, 2014 -- Updated 1653 GMT (0053 HKT)
He's 12 years old and going blind -- so his parents are taking him on a trip to fill his world with beautiful images.
Track star Oscar Pistorius is accused of killing his girlfriend, Reeva Steenkamp. Follow live updates of South Africa's trial of the century.
March 6, 2014 -- Updated 1357 GMT (2157 HKT)
To celebrate International Women's Day, CNN's Leading Women is inviting you to a Tweetchat.
March 6, 2014 -- Updated 2247 GMT (0647 HKT)
Women journalists in the testosterone-fueled world of sports are still the target of abuse.
March 6, 2014 -- Updated 1027 GMT (1827 HKT)
Photographer Zack Seckler's series presents Botswana from between 50 and 500 feet, providing a unique view of the savannah.
March 5, 2014 -- Updated 0218 GMT (1018 HKT)
Concorde is a thing of the past, but a number of companies are racing to release the first supersonic business jet.
March 10, 2014 -- Updated 0029 GMT (0829 HKT)
Browse through images you don't always see on news reports from CNN teams around the world.
March 7, 2014 -- Updated 1852 GMT (0252 HKT)
From U.S. President Obama's phone call to Russian President Putin, to a python swallowing a crocodile, browse photos from last week.
March 7, 2014 -- Updated 0543 GMT (1343 HKT)
Did you know that the idea to mark road surfaces reportedly came from watching a milk truck drip milk on the road?
The undersea cables wiring the Earth: this is what the Internet actually looks like.
Today's five most popular stories