The mysterious orb you find in your backyard that wasn’t there just the day before has to be a meteorite, right?
Wrong. Overwhelmingly, the chances are it’s a “meteorwrong,” according to Randy Korotev, Ph.D., research associate professor of earth and planetary sciences in Arts & Sciences.
He says that of 1,000 meteorites, 998 are from asteroids, one is from the moon and the other one is from Mars. Of the hundreds of meteorites that have been found in the United States, none has been a lunar meteorite, and only one has been a Mars meteorite.
Korotev is a geochemist whose specialty is analyzing the chemistry of moon rocks, whether they have been gathered from the Apollo missions or collected as meteorites from Antarctica, north Africa or other areas of the world. In recent years, he’s become the go-to guy for anybody — researcher, amateur or professional meteorite collector — who thinks he or she might have discovered a lunar meteorite.
This is largely because of a Web site (epsc.wustl.edu/admin/resources/moon_meteorites) Korotev started about 10 years ago, intending for it to serve his colleagues and the interested public. The site deals in great detail with lunar meteorites, and it is as good an educational resource on the topic to be found anywhere.
Due to very intelligent search engines and an aggressive (though little-known) profession of meteorite dealers and hobbyists — a lunar meteorite retails from $1,000-$40,000 a gram — Korotev’s site began drawing questions from the public about the veracity of their findings.
Some people make appointments to see him and his WUSTL geologist colleagues, but the vast majority e-mailed pictures of their findings to get their answers. While he didn’t keep count of all the contacts he received in the early years, last year alone he received 900 meteorite queries.
“I felt obliged to answer people’s questions and in the process of doing so, found that I was saying the same thing over and over again,” Korotev explained. “Now, I like to build Web sites and I like photography, so I came up with the idea of a Web site that could explain both verbally and visually that ‘your sample is not a meteorite because … .’
“There are scores of reasons.”
“A Photo Gallery of Meteorwrongs” (epsc.wustl.edu/admin/resources/meteorites/meteorwrongs/meteorwrongs) showcases more than 100 objects misidentified as meteorites. Each photo has a caption that explains why the rock is probably not a meteorite and suggests what it most likely is.
The site provides criteria for recognizing space objects. For instance, freshly fallen meteorites will have a fusion crust, a glassy coating that forms on the object during descent. And meteorites are usually not angular, because protuberances tend to be ablated away as the object comes through the atmosphere.
Korotev said there is a growing body of meteorite collectors who, like stamp or baseball card collectors, are seeking samples of every known lunar or Martian meteorite documented — that’s only 35-40 lunar meteorites. Also, people seek meteorite samples for novelties.
“I’ve had two young men tell me they want some grams of a lunar meteorite for their fiancée’s engagement ring,” he said. “My reaction is: ‘Lunar meteorites are not that attractive; get her a diamond.’
“Besides, meteorites were formed at a place that doesn’t have water, which means that they’re unstable in water. And that’s not the sort of thing you want to put in a ring if your fiancée ever wants to wash her hands.”
Korotev said lunar rocks are depleted in volatile elements, and compared with Earth rocks they are low in sodium, potassium and rubidium, though high in chromium. There are about 12 different chemical signatures that indicate a lunar source.
Martian meteorites share some of the same features as lunar ones, except that Martian meteorites are never rich in feldspar, like most lunar meteorites.
Often, Korotev and his colleagues can do simple, quick tests to determine if a rock has meteorite potential. If a rock has layers, forget it — to have layers, gravity is needed. If the rock has low density, it can’t be a meteorite, and they can determine this with a quick lab test.
Still, people want Korotev to confirm that what they have is a meteorite.
“I’ve heard this over and over again,” he said. “‘I heard a thump and went outside and found this rock that wasn’t here yesterday.’
“I can’t help noticing that every single rock that people show me or send me a picture of that ‘wasn’t here yesterday’ is just about the size of a hardball. More than likely, it was chucked into the yard by some mischief-maker.”
Korotev said the public can purchase very small samples of legitimate lunar or Martian meteorites on ebay. Big samples of “regular” — asteroidal — meteorites also can be purchased, and there are museums and dealers who can confirm or deny meteorite designation.
There’s a laboratory in northern Arizona that, for a fee, will do a complete petrographic — analysis of thin sections of the sample under a microscope — to determine if it’s a meteorite.
Korotev has his Web site up to help people and to engage them in science. He gets a wide range of responses.
“I had a fellow ask: ‘Do two meteorwrongs make a meteorite?'” he said. “I’ve had wonderful conversations with schoolchildren in the Philippines and housewives in Scotland, but there are some people who are so convinced that they have a meteorite that they end up not liking me.
“I have a place on the site that suggests that before sending to me, read some of the responses I’ve gotten from people who don’t accept our conclusions. There are some pretty outspoken people who think that I’m an idiot.
“The truth is, it appears human nature just doesn’t like to accept the easy explanation.”