Blasted into space by a collision with an asteroid, the jagged hunk of Mars rock tumbled silently through the solar system for 7,000 centuries.
Finally, on July 18, 2011, the rock's long journey ended as violently as it had begun: It plunged to Earth as a fireball that illuminated the Moroccan night, awakening soldiers and nomads with a sonic boom. Such was the dramatic arrival of the so-called Tissint meteorite, named for a village where pieces fell. The unusually pristine specimen is one of only five Martian projectiles that have been observed entering Earth's atmosphere and then recovered for study.
It turns out the meteorite has a great deal in common with other rocks that have made the trip from Mars to Earth, said a report published online Thursday by the journal Science. An international team of researchers examined its molecular structure and determined that Tissint was probably ejected from Mars by the same impact that launched another group of meteorites that also landed on Earth, many in Antarctica, after a shorter journey through the solar system. They determined this by calculating the meteorite's exposure to cosmic rays.
About 15 pounds of scorched and shattered rock have been plucked from the desert by meteor hunters. Its relatively swift collection made it largely free of the earthly contamination that's typical of most Martian meteorites.
"Most other samples were collected long after their arrival on Earth and thus have experienced variable degrees of terrestrial weathering," wrote lead author Hasnaa Chennaoui Aoudjehane, a geochemist at Hassan II University of Casablanca. The samples are among the few pieces of alien planet that scientists can hold in their hands and study in the comfort of their laboratories.
The largest samples were covered with a shiny black fusion crust -- the result of its super-heated entry into Earth's atmosphere. Inside, the rocks were pale gray and studded with pale yellow olivine crystals.
Among other conclusions, the study authors wrote that the rock appeared to contain traces of the Red Planet's surface and atmosphere. The elements appeared to be trapped in particles of black glass and melted rock that were formed during the heat and shock of impact on Mars. The authors also suggested that the rock was weathered by acidic fluids before departing Mars.
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