Page 2/2 - Posted September 25, 2009
NASA publishes a biannual newsletter with classification data on the latest rocks returned from Antarctica to alert scientists on what kind of samples are available for research. Righter estimates the active meteorite community probably consists of between 1,000 and 2,000 members.
His lab responds to a couple hundred requests for samples each year, he said. Long-term storage of samples is at the Smithsonian.
What is a meteorite?
Meteorites are stony or metallic bodies that fall to the Earth from space. All meteorites show peculiarities not observed in known rocks of Earth, and it is therefore possible to recognize them even if they have not been seen to fall.
Most meteorites come from asteroids, a rare few come from larger bodies such as Earth’s moon and Mars, and many of the smallest meteorites, “micrometeorites,” are dust from comets.
Many meteorites preserve chemical and physical properties that were established 4.5 billion years ago, during the earliest history of the solar system, and provide the only hard data on the nature of the events that occurred in that remote time.
There are three major classes of meteorites: stony meteorites, iron meteorites and stony-iron meteorites.
— Smithsonian Natural Museum of Natural History
“It’s an interesting system. When they started collecting these samples 30 years ago, nobody had any idea it would continue for 30 years or it would be [17,500] samples,” Righter said. “It’s been great dealing with the Smithsonian and every institution that’s in the meteorite recovery program. It’s a fun project to be associated with.”
McCoy said about once or twice a year his lab will come across a meteorite that they’ve never seen before, like those from Graves Nunatak that took two years to classify.
“Those are really exciting,” he said. “They tell us about a place or a process — something we have even envisioned, thinking this kind of rock should exist but we haven’t seen it — and those rocks can help us fill in those gaps.”
While the asteroids that fall to Earth are from our solar system, some contain what scientists call “pre-solar grains” — bits of stardust that predate our solar system. That means the bits of dust are older than 4.65 billion years, though how much older is a matter of some debate, ranging from 40 million to a billion years.
“We can actually do astrophysics. We can look at the formation of other stars by studying meteorites,” McCoy said. “That’s a pretty remarkable finding over the last decade or so.”
Other areas of planetary study involving meteorites include speculation on whether Earth’s water originated here or was carried on a comet like an interstellar seed. “Water-bearing comets may have been building blocks for the Earth,” Righter said.
And, of course, lunar and Martian meteorites offer insight into those planetary bodies. In fact, while the Apollo astronauts returned from the moon with rocks samples, it turns out those are not very representative of most moon material that’s fallen to Earth, according to Cari Corrigan, a geologist at the Smithsonian involved in classifying the Antarctic meteorite collection.
“The lunar meteorites should be a random sampling of the whole moon. There are places on the far side, the south pole, or places we haven’t sampled by being there that these are giving us,” she said.
Noted Harvey about the utility of the Antarctic meteorite collection, “It’s amazing how many times a specimen 20 years back is still immensely valuable as people try to reconfigure again the catalog of material that are out there in the solar system.”