[meteorite-list] Black Glass Holds First Mars Soil Sample on Earth (Tissint Meteorite)

[Ron Baalke]

http://www.newscientist.com/article/dn22372-black-glass-holds-first-mars-soil-sample-on-earth.html

Black glass holds first Mars soil sample on Earth
by Joanna Carver
New Scientist
October 11, 2012

Veins of black glass in a meteorite that recently crashed in 
Morocco contain the first chemical traces of Martian soil brought to Earth. 
The find represents a rare chance to look closely at ancient surface conditions 
on Mars.

Robots sent to Mars, such as NASA's Curiosity rover, only have 
limited capabilities to analyse the soil samples that they take. Until 
the launch of a sample-return mission, the most thorough way to study 
Martian rock is via meteorites that originated on Mars, says Hasnaa 
Chennaoui Aoudjehane of Hassan II University in Casablanca.

In July 2011 people saw a fireball streak across the sky and smash into 
the Moroccan desert. The 7-kilogram meteorite, dubbed Tissint, broke apart 
as it fell, and both scientists and private collectors quickly retrieved the 
fragments.

Initial analysis showed that the rock's chemical composition matches that of a 
type of Martian basalt. The meteorite was most likely thrown up from the 
planet about 700,000 years ago as the result of an asteroid impact.

Pristine sample

Tissint is only the fifth Martian meteorite collected promptly 
after falling to Earth. Most of the 90 or so known Mars rocks that have 
been found on Earth had been lying around for years. By contrast, the 
Tissint fragments should provide an unadulterated look at Mars's geology. 
"It's so fresh, such pristine material," says Aoudjehane.

Her team found that the meteorite is laced with a large amount of bubbly black 
glass. It contains carbon and nitrogen isotopes that are characteristic of those 
found in Mars's atmosphere, something that has been seen in other Martian 
meteorites.

More surprisingly, the glass contains relatively high amounts 
of light rare-earth elements not found in the rest of the meteorite, including 
an unusual ratio of cerium isotopes that indicates some of the cerium 
got oxidised. Conditions that would oxidise cerium are most likely to 
exist close to Mars's surface.

The team says weakly acidic water may have leached rare-earth elements from 
Martian soil and deposited them in fractures in surface rocks. Heat from the 
asteroid impact that ejected Tissint melted the material in the fractures, 
which crystallised as it cooled to form the black glass.

Further analysis of Tissint should reveal more details of such geochemical 
processes on Mars, rounding out our picture of the planet's past.

"The history of Mars is interesting for us because it's related to the history 
of the Earth, and it's important to know how Mars was in the past and how it 
evolved with the times," says Aoudjehane.

Journal reference: Science, DOI: 10.1126/science.1224514