Tegaza 001, a group of eight Martian meteorite fragments found through the Sahara Desert meteorite trade, appears to have formed from magma that cooled slowly within Mars’ crust. Scientists identified the rock using oxygen-isotope measurements and found unusual mineral and chemical features that distinguish it from more common Martian meteorites.
Meteorite hunters searching the Sahara for dark stones collected eight pieces of Tegaza 001, with a combined mass of just under 800 grams. A private collector purchased the stones and sent them to the University of New Mexico for classification. There, planetary scientists Carl Agee and Karen Ziegler measured their oxygen isotopes.
“Each planetary body has very characteristic oxygen isotope values,” Liu says. The values for Tegaza 001 matched those of other Martian meteorites.
The rock was initially classified as a shergottite, the most common and youngest type of Martian meteorite. But Agee noticed several unusual features and contacted Ryu. One of Tegaza 001’s minerals had altered internally while its exterior remained in its original state—opposite to the pattern typically produced by weathering on Earth. The oxygen-isotope measurements were also somewhat unusual, and the meteorite contained a manganese-rich material similar to the material Liu studied in Black Beauty.
“When I got to the sample, I looked around and said, ‘I’m bored,’” Liu said. “Although high-manganese material actually exists on Earth, we quickly realized that our sample was very different and very special.”
Tegaza 001 consists primarily of feldspar, a light-colored mineral commonly found in the crusts of rocky planets. The feldspar is mixed with dark pyroxene crystals. According to Liu, the crystals resemble minerals in rocks exposed in the Moon’s highlands.
The crystals are relatively large, reaching about 1 millimeter in diameter. Scientists interpret their size as evidence that the rock cooled slowly. “Rocks that cool slowly tend to take longer to grow,” Liu said.
Using laboratory experiments and comparisons with terrestrial rocks and crystals, the research team estimated that Tegaza 001 is cooling at a rate of about 0.01 degrees Celsius per year. That slow cooling suggests the meteorite did not form in an eruption, but instead crystallized from magma that solidified within the Martian crust.
Source: arstechnica.com
