[meteorite-list] Mars Meteorite Reveals 1st Look at Ancient Martian Crust (NWA 7533)

[Ron Baalke]

http://www.space.com/23670-mars-meteorite-ancient-martian-crust.html

Mars Meteorite Reveals 1st Look at Ancient Martian Crust
by Mike Wall
space.com
November 20, 2013
 
A meteorite found last year in the Sahara Desert is likely the first recognized 
piece of ancient Martian crust, a new study reports.

The Mars meteorite NWA 7533 is 4.4 billion years old and contains evidence 
of long-ago asteroid strikes, suggesting that the rock came from the Red 
Planet's ancient and cratered southern highlands, researchers said.

"We finally have a sample of the Martian highlands, that portion of Mars 
that holds all the secrets to Mars' birth and early development," lead 
author Munir Humayun of Florida State University told SPACE.com via email. 

"It's the part of Mars' history where the oceans and atmosphere developed, 
and where life would have developed if it ever did on Mars," Humayun added. 
"I will liken this to opening a treasure chest - it may take a while before 
we find the best treasures, but treasures aplenty lurk in this meteorite."

Humayun and his colleagues subjected NWA (short for northwest Africa, 
where the rock was found) 7533 to a series of analyses. The researchers 
determined the meteorite's age, for example, by determining that crystals 
within it called zircons formed about 4.4 billion years ago.

"This date is about 100 million years after the first dust condensed in 
the solar system," Humayun said in a statement. "We now know that Mars 
had a crust within the first 100 million years of the start of planet-building, 
and that Mars' crust formed concurrently with the oldest crusts on Earth 
and the moon."

The team also found high concentrations of normally rare elements such 
as nickel, osmium and iridium in NWA 7533, indicating that the rock formed 
in a region that was pummeled by chondritic meteors, which are relatively 
enriched in these materials.

Further, after measuring the abundances of certain elements within the 
meteorite, Humayun and his team were able to calculate a thickness for 
the Red Planet's crust.

"The amount of melting on Mars was low, sufficient to accumulate a 
50-kilometer-thickness [31 miles] crust, but Mars evidently escaped the 
giant impact-style melting that affected the Earth and moon," Humayun 
told SPACE.com. (Most scientists think the moon formed from material 
blasted into space when a planet-size body crashed into Earth more than 
4 billion years ago.)

"This is the first reliable geochemical estimate of the thickness of Mars' 
crust, and it agrees with geophysical estimates from gravity and topography," 
he added.

Though researchers believe ancient Mars was relatively warm and wet, the 
team found no hydrous silicate minerals - which form in the presence of 
liquid water - within NWA 7533. Scientists will likely unearth more such 
puzzling details as they study the meteorite further, Humayun said.

"I expect more surprises as we dig deeper into our Martian treasure chest 
- some we will understand, and others may continue to befuddle us for 
a while to come," he said.