[meteorite-list] Chelyabinsk Meteorite May Have Collided with Another Body in Solar System

[Ron Baalke]

http://www.sci-news.com/space/science-chelyabinsk-meteorite-another-body-solar-system-01338.html

Chelyabinsk Meteorite May Have Collided with Another Body in Solar System
Sci-News.com
Aug 27, 2013 

According to a team of Russian scientists reporting today at the Goldschmidt 
conference in Italy, the Chelyabinsk meteorite either collided with another 
body or came too close to the Sun before it fell to our planet.

The researchers from the Institute of Geology and Mineralogy in Novosibirsk 
have analyzed fragments of the meteorite, the main body of which fell 
to the bottom of the Chebarkul Lake near Chelyabinsk on February 15, 2013. 
Although all of the fragments are composed of the same minerals, the structure 
and texture of some fragments show that the meteorite had undergone an 
intensive melting process before it was subjected to extremely high temperatures 
on entering the Earth's atmosphere.

"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, who is a 
first author of the study (an abstract has been published in the Mineralogical 
Magazine).

"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 their color and structure, the researchers have divided the meteorite 
fragments into three types: light, dark and intermediate.

The lighter fragments are the most commonly found, but the dark fragments 
are found in increasing numbers along the meteorite's trajectory, with 
the greatest number found close to where it hit the Earth. The dark fragments 
include a large proportion of fine-grained material, and their structure, 
texture and mineral composition shows they were formed by a very intensive 
melting process, likely to have been either a collision with another body 
or proximity to the Sun. This material is distinct from the "fusion crust" 
- the thin layer of material on the surface of the meteorite that melts, 
then solidifies, as it travels through the Earth's atmosphere.

The fine-grained material of the dark fragments also differs from the 
other samples as it commonly contains spherical "bubbles" which are either 
encrusted with perfect crystals of oxides, silicates and metal or filled 
with metal and sulfide.

Surprisingly, the scientists also found small quantities of platinum group 
elements in the meteorite's fusion crust. They identify these elements 
as an alloy of osmium, iridium and platinum, but its presence is unusual 
as the fusion crust is formed over too short a time period for these elements 
to easily accumulate.

"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," Dr Sharygin said.

"We think the appearance 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."

______

Bibliographic information: Sharygin V et al. 2013. Mineralogy of the Chelyabinsk 
meteorite, Russia. Mineralogical Magazine, 77 (5), p. 2189; doi: 10.1180/minmag.2013.077.5.19