A strange green rock discovered in Morocco last year was hailed by the press as the first meteorite from Mercury. But scientists who’ve been puzzling over the stone since then say the accumulating evidence may point in a different direction. Maybe, just maybe, they say, the 4.56-billion-year-old rock fell to Earth from the asteroid belt located between Mars and Jupiter.

If that’s true, the rock is “still extremely interesting,” says Tim McCoy, who curates the Smithsonian Museum of Natural History’s collection of 35,000 meteorites. “[It] tells us something about the birth of the solar system, but not the birth of the innermost planet.”

The olive green meteorite, flecked with bits of white and brown, first came to scientists’ attention last year when a German collector, Stefan Ralew, saw the unusual stone in Morocco and shipped it off for analysis to Tony Irving, a geochemist and meteorite specialist affiliated with the University of Washington in Seattle. Irving routinely receives such packages from all over the world.

“From experience, I knew it was very unlikely to be an Earth rock,” Irving says. “It wasn’t from Mars, and if it was a meteorite, it was highly unusual.” As it turns out, the rock was even weirder than it looked.

“The minerals were very low in iron,” he says, “and most meteorites have more iron in their minerals than this.” Irving’s mind turned to the planet Mercury. New data had been coming in from NASA’s Messenger spacecraft, which is orbiting Mercury. It revealed that Mercury’s surface lacked iron.

“I think it was the Messenger data that I had recently studied and just sort of compared it, on a whim almost,” Irving says. “[I was] quite amazed to find that some of the chemical features were a pretty close match.”

He started to get excited. Every now and then, something big strikes a planet and knocks off a few chunks. Experts predict that some chunks of Mercury may have already made the 57-million-mile trip to Earth, but none have been found. This could be a piece. But Irving needed more evidence, so he packed up samples and sent them to colleagues around the country for further analysis.

One of the most exciting findings came from a colleague who had measured the magnetic field of one of the pieces. It was smaller than almost anything yet seen in the solar system.

“And it’s very close to the present magnetic field of Mercury,” Irving says. “Putting it all together, I could see that there was a possibility of proposing this Mercury idea.”

And that’s just what he did. This March, Irving presented his theory at the Lunar and Planetary Science Conference in Texas. But scientists at the meeting were more skeptical. In the audience was Shoshana Weider, a fellow at the Carnegie Institution of Washington, who works on the Messenger mission. Her first thought, when she heard that the rock might be from Mercury, was, “That would be nice.” But she’s not convinced.

“There was nothing that jumped out and said, ‘No, this can’t be from Mercury,’ ” she says, “but there were a few bits that didn’t quite match with Mercury.” For example, the rock lacks sulfur, while Mercury’s surface is covered in it.

She’s not the only one with doubts about the green rock. The Smithsonian’s Tim McCoy has a problem with the rock’s age.

“The meteorite is very, very old — 4.56 billion years old,” he says. “So it’s essentially formed at the same time as the birth of the planet, whereas Mercury is a huge, hot planet that probably wouldn’t have cooled off enough to have solid rock 4.56 billion years ago.”

McCoy has his own ideas about the meteorite’s origins. He has another shiny metallic rock in his collection that, under the microscope, contains some crystals the same color as the Morocco specimen

That crystal is chromian diopside. It’s the same mineral that gives Irving’s meteorite its distinctive green color. And just like Irving’s rock, this one is 4.56 billion years old. But it’s not from Mercury; it’s known to be from that asteroid belt between Mars and Jupiter. McCoy says that maybe the new green meteorite came from the asteroid belt, too.

Irving says he won’t be too upset if it turns out the meteorite came from somewhere else. “As far as I’m personally concerned, if this rock turns out to be not from there and we can find an alternative,” he says, “that’s just fine with me.”

In the meantime, admirers of the little green rock will soon be able to own a piece. The German collector who sent Irving that first sample has several other fragments that he’s planning to sell.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.
 

Comments are closed.

News

AP
November 20, 2017 | NPR · A six-judge panel unanimously dismissed a pair of petitions challenging the Oct. 26 vote that was boycotted by the opposition led by rival Raila Odinga.
 

Getty Images
November 20, 2017 | NPR · Meetings in the wake of September’s election have left the German chancellor empty-handed. Without a deal, her government could collapse, with Germany potentially forced into new elections.
 

AFP/Getty Images
November 20, 2017 | NPR · The ARA San Juan disappeared last week off the coast of Patagonia. Argentine officials say that they can’t confirm that satellite signals received over the weekend came from the sub.
 

Arts & Life

November 19, 2017 | NPR · A young man shared a ride with someone with whom he felt a spark. But he didn’t ask for a phone number, so he put up a flyer. NPR’s Lulu Garcia-Navarro talks to Steven Mion and Robert Dealy.
 

Getty Images
November 19, 2017 | NPR · In his new book, Dr. Aaron Carroll explains that there might be less evidence against some notoriously bad foods than we think. In fact, maybe we should be eating some of them more often.
 

Arsenal Pulp Press
November 19, 2017 | NPR · French graphic novelist Julie Maroh — author of Blue is the Warmest Color — is back with an earnestly sweet collection of vignettes about love, kept from being saccharine by her skill with faces.
 

Music

Courtesy of the artist
November 19, 2017 | NPR · The rapper discusses speaking out on racism, the changing value of radio play in hip-hop and his latest album’s tribute to Bresha Meadows.
 

NPR
November 19, 2017 | NPR · For Riley Knoxx, emulating the pop star transformed her career and personal life — building confidence in herself as an artist and as a transgender woman.
 

Saturday Night Live
November 19, 2017 | NPR · Mature and introspective, the 20-year vet displayed a rare glimpse of vulnerability as he rapped about his pressure to be perfect and his fall from prominence in the game.
 

Get the KRCC iPhone App

The Writer's Almanac

Radiolab