Russian Meteorite Probably Collided with Space Bodies Before Entering Earth's Atmosphere

Chelyabinsk meteorite either missed colliding with another object in the solar system or grazed past the sun before landing on earth, according to a new research.

A large chunk of the meteorite fell in the Chebarkul Lake near Chelyabinsk on  Feb. 15, this year. A team from the Institute of Geology and Mineralogy (IGM) in Novosibirsk has now analyzed fragments of this meteorite.

The study found that the meteorite had undergone intensive melting before it fell on 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," said Dr Victor Sharygin from IGM, according to a news release. "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."

Researchers divided fragments of the meteorite in three categories based on their color and structure; light, intermediate and dark.

The dark fragments are rarer than the light and intermediate type  and researchers found clear signs of intensive melting in them.

According to researchers, this type of melting is possible if the meteorite collided with another object or was near the sun before it entered Earth's atmosphere.

Meteorites have a thin layer called the fusion crust, which forms when the meteoroid enters the Earth's atmosphere. As the air around the falling meteorite is compressed severely, the temperature on its surface increases and begins to melt the stony exterior of the meteoroid. Once the temperature lowers, the material on the meteorite forms a thin, glassy coating.

Researchers in the present study said that the type of structures they saw in the dark fragments were different from the fusion crust.

 "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 dark fragments also have small bubbles that either are metal with sulfide or crystals of oxides, silicates and metals.

 The team also found traces of metals belonging to the platinum group in the fusion crust of the meteorite. The finding is unique because the fusion crust is formed very fast to allow accumulation of these elements.

"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 research is being presented at the Goldschmidt conference in Florence.