The oldest known Martian meteorite ? a space rock that fellto Earth ? is some 400 million years younger than originally thought. It formedabout 4.091 billion years ago, a time when the red planet was wet and had amagnetic field, a new study suggests.
Studying this chunk of ancient Mars, which reflects thevolcanic processes and bombardment by space debris, could help scientistsbetter understand Mars'early evolution, as well as Earth's.
Many other Martianmeteorites have been found in Antarctica, as well as in remote regions ofAfrica, but ALH84001 is the "oldest by billions of years," said TomLapen of the University of Houston, who conducted the new study of themeteorite. It's about 2.5 billion years older than other Mars meteorites, whichget kicked up from the surface of Mars by space rock impacts, flung into space,and then eventually hit Earth.
Previously, ALH84001 had been given an age of about 4.51billion years, which would make it part of the primordial crust of Mars ? thefirst rock to solidify from the planet's cooling magma ocean. But "therewas some question about the generally accepted age," Lapen told SPACE.com.
The team's analysis, detailed in the April 16 issue of thejournal Science, shows that the age of the meteorite is actually 4.091 billionyears old, about 400 million years younger than the earlier estimate.
The new age rules out the rock being a fragment of Mars'primordial crust. Instead, it likely formed from more recent volcanic activityin very active regions such as the Tharsis and Elysium volcanic regions, whichare home to the largest volcanoes in the solar system. The age also supports thelong-lived volcanic activity of these regions.
"We uncovered evidence that the volcanic system in Marswere likely active more than 4 billion years ago," Lapen said. "Thisconnection allows the possibility that regions with the largest volcanoes inthe solar system perhaps host some of the longest-lived volcanic systems in thesolar system."
The meteorite also shows signs of being shocked by impactsto the Martian surface. Estimates of the periods of bombardment of Mars made byexamining the chronology of craters on the planet's surface suggest that aperiod of heavy bombardment occurred just before this rock formed, or perhapswhile it was still forming.
Having a piece of Mars' early crust is helpful to scientistswho want to better understand the conditions on the planet early in its history.While most Mars meteorites are much younger, with few older rocks, "Ithink we'll eventually find more," Lapen said.
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