NWA 7325 — Maybe a Messenger from Mercury
I finally procured one of these mysterious green meteorites.
Comparing data from the Messenger spacecraft orbiting Mercury, Professor Anthony Irving of the University of Washington determined that the singular NWA 7325 meteorite has a consistent composition and magnetism with Mercury or a smaller, Mercury-like proto-planet.
The interiors is full of relatively large and obvious crystals (see below for detail), suggesting that the magma from which they solidified had cooled slowly. The stunning emerald-green color comes from a silicate mineral called diopside that's infused with chromium. Irving and his team found lots of magnesium and calcium in the suite of silicate minerals, but even more important is what they didn't find: there's virtually no iron.
Lead isotopes in the rock were tested for the radioactive decay of uranium by the University of Canberra, Australia, and it was determined that the age of the meteorite is approximately 4.563 billion years. This places it very close to the formation of the planet Mercury itself, and in the first 5 million years of our solar system’s formation.
Despite the proximity of Mercury to the Sun's gravitational pull, it has been calculated that detritus thrown up by rocks hitting the planet would be propelled fast enough (faster than 9 km per second) to break free not only of the atmosphere but also of the Sun's gravitational field, and that 2 to 5% of such matter could reach Earth within 30 million years.
"If this rock isn’t from Mercury, it’s still amazing," Irving notes. “It’s from a planet; we just need to figure out which one.”
NASA in 2019: “The parent body of NWA 7325 underwent complex planetary processes, and was large enough to form a core, mantle, and crust. Based on their model, the researchers believe that the parent body of NWA 7325 underwent multiple episodes of low‐pressure, metal‐silicate equilibration, followed by limited late accretion and mantle homogenization. The results help paint a picture of the evolution of the Solar System.”
And a summary of Irving’s work: “Tests on the weird green rock also support the idea that it may have made the trip from Mercury, says Irving, who presented his theory at the 44th Lunar and Planetary Science Conference. It has the lowest magnetic intensity ever measured in any meteorite—a magnetism that matches Mercury’s modern field almost exactly, Irving says. The magnetism, the low iron content and the high magnesium content all suggest that Mercury is the meteorite’s original home.”
There have been scores of studies of this mysterious green stone. One from France in 2015: “It is almost certainly derived from a distinct planetesimal, not previously sampled by other achondrites. The low Na/Al, Ga/Al, Zn/Al ratios as well as the low K, Rb and Cs shown by NWA 7325, suggest a volatile-depleted parent body. Such a melt cannot be the product of the early magmatic activity on a small parent body.”
The mysteries of a messenger, maybe from Mercury.
NWA 7325 — Maybe a Messenger from Mercury
I finally procured one of these mysterious green meteorites.
Comparing data from the Messenger spacecraft orbiting Mercury, Professor Anthony Irving of the University of Washington determined that the singular NWA 7325 meteorite has a consistent composition and magnetism with Mercury or a smaller, Mercury-like proto-planet.
The interiors is full of relatively large and obvious crystals (see below for detail), suggesting that the magma from which they solidified had cooled slowly. The stunning emerald-green color comes from a silicate mineral called diopside that's infused with chromium. Irving and his team found lots of magnesium and calcium in the suite of silicate minerals, but even more important is what they didn't find: there's virtually no iron.
Lead isotopes in the rock were tested for the radioactive decay of uranium by the University of Canberra, Australia, and it was determined that the age of the meteorite is approximately 4.563 billion years. This places it very close to the formation of the planet Mercury itself, and in the first 5 million years of our solar system’s formation.
Despite the proximity of Mercury to the Sun's gravitational pull, it has been calculated that detritus thrown up by rocks hitting the planet would be propelled fast enough (faster than 9 km per second) to break free not only of the atmosphere but also of the Sun's gravitational field, and that 2 to 5% of such matter could reach Earth within 30 million years.
"If this rock isn’t from Mercury, it’s still amazing," Irving notes. “It’s from a planet; we just need to figure out which one.”
NASA in 2019: “The parent body of NWA 7325 underwent complex planetary processes, and was large enough to form a core, mantle, and crust. Based on their model, the researchers believe that the parent body of NWA 7325 underwent multiple episodes of low‐pressure, metal‐silicate equilibration, followed by limited late accretion and mantle homogenization. The results help paint a picture of the evolution of the Solar System.”
And a summary of Irving’s work: “Tests on the weird green rock also support the idea that it may have made the trip from Mercury, says Irving, who presented his theory at the 44th Lunar and Planetary Science Conference. It has the lowest magnetic intensity ever measured in any meteorite—a magnetism that matches Mercury’s modern field almost exactly, Irving says. The magnetism, the low iron content and the high magnesium content all suggest that Mercury is the meteorite’s original home.”
There have been scores of studies of this mysterious green stone. One from France in 2015: “It is almost certainly derived from a distinct planetesimal, not previously sampled by other achondrites. The low Na/Al, Ga/Al, Zn/Al ratios as well as the low K, Rb and Cs shown by NWA 7325, suggest a volatile-depleted parent body. Such a melt cannot be the product of the early magmatic activity on a small parent body.”
The mysteries of a messenger, maybe from Mercury.