Caption: OXYGEN ISOTOPES Mars, the asteroid Vesta, and angrite
meteorites all have notably different ratios of oxygen's three isotopes than terrestrial samples do.
Because the angrite rock formed close to the beginning of the solar system, their content speaks to what that young system was like.
Researchers analyzed some of a rare type of meteorite called angrites, measuring the volume of volatile elements like hydrogen and carbon.
These meteoritic bits that have occasionally fallen to Earth are called angrites, and they formed about four million years after the start of the solar system.
"If angrites have the same hydrogen isotopes as Vesta and Earth, it means water was accreting into these planetary bodies throughout the time they were forming, almost from time zero," he said.
But by looking at some of the oldest meteorites on Earth, known as angrites
, Huapei Wang (MIT) and colleagues put the solar nebula's lifetime at 3 to 4 million years.
All previous candidates for pieces of Mercury (called angrites and aubrites; S&T: April 2012, page 31) are close but imperfect matches to the surface composition found by NASA's Messenger spacecraft.
"NWA 7325 is tantalizing, and certainly more consistent with the Messenger results than either angrites or aubrites," he explains, "but we need a [spacecraftreturned sample] for 'ground truth'."