August 27, 2013
Chelyabinsk Meteorite Had Close Encounter In Space Prior To Earth Impact
Lawrence LeBlond for redOrbit.com - Your Universe Online
The Chelyabinsk meteor that exploded over Russia’s Ural Mountains region earlier this year was found to have either collided with another celestial body or had a close encounter with the sun prior to reaching Earth.
"The meteorite which landed near Chelyabinsk is a type known as an LL5 chondrite and it's fairly common for these to have undergone a melting process before they fall to Earth," noted Dr Victor Sharygin from IGM, who is presenting the research at the Goldschmidt 2013 conference in Florence, Italy. "This almost certainly means that there was a collision between the Chelyabinsk meteorite and another body in the solar system or a near miss with the Sun."
Based on the color and structure, the researchers divided the fragments into three types: light, dark and intermediate. While the light components are the most commonly found, the darker fragments are found in increasing numbers along the trajectory, with the greatest number found close to where it hit Earth.
The dark fragments contain a large amount of fine-grained material. The structure and texture of these fragments indicate they were formed by a very intensive melting process, due to collision or close proximity to the sun. The researchers explained this material is very distinct from the ‘fusion crust’ – a thin layer of material on the surface of the meteorite that melts and solidifies as it barrels through our atmosphere.
"Of the many fragments we've been analyzing, only three dark samples show strong evidence of earlier metamorphism and melting," said Dr Sharygin. "However, many fragments of the meteorite were picked up by members of the public, so it's impossible to say how large a portion of the meteorite was affected. We hope to find out more once the main body of the meteorite is raised from Chebarkul Lake."
The IGM team also found small quantities of platinum group elements in the fusion crust of the meteorite. However, the team was only able to identify these elements as an alloy of osmium, iridium and platinum. They note the presence of these elements is unusual as the fusion crust is formed over a very short period of time, making it difficult for such elements to accumulate easily.
"Platinum group elements usually occur as trace elements dispersed in meteorite minerals, but we found them as a nanometer-sized mineral (100-200 nm) in a metal-sulfide globule in the fusion crust of the Chelyabinsk meteorite," explained Dr Sharygin. "We think the appearance (formation) of this platinum group mineral in the fusion crust may be linked to compositional changes in metal-sulfide liquid during remelting and oxidation processes as the meteorite came into contact with atmospheric oxygen."
The analysis of the meteorite fragment is ongoing, as well as other research into the meteorite. The IGM is using a scanning microscope, electron microscope and gas chromatography-mass spectrometry to produce a detailed mineral analysis of the Chelyabinsk meteorite.