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Pieces of Other Planets |
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We've gone to the Moon, Mars, and Venus to study their rocks, but pieces of them are (or might be) on the ground on Earth.
The more advanced our studies of planet Earth get, the more important it becomes to find samples from other planets. We have sent men and machines to the Moon and elsewhere, where our instruments have examined the surface close up. But with flights so expensive and rare, it's easier to look on Earth for rocks from Mars and the Moon.
We didn't know until recently that Moon and Mars rocks occur on Earth; all we knew was that there were a few particularly strange meteorites. Almost all meteorites come from the asteroid belt, a wide region between Mars and Jupiter where thousands of small solid objects orbit the sun. While we still don't know the whole story, we know that the asteroids are ancient bodies, as old as Earth itself. They have been little altered from the time they formed, except when they shattered against other asteroids. The pieces range in size from dust specks to the asteroid Ceres, some 950 kilometers across.
A handful of meteorites are very different from the rest: they show geochemical signs of having been part of an evolving planet. Their isotopes are unbalanced, among other anomalies. Some are similar to basaltic rocks known on Earth. After we went to the Moon and sent sophisticated instruments to Mars, it became clear that these rare stones come from those heavenly bodies.
These are meteorites created by other meteoritesby asteroids themselves. Asteroid impacts onto Mars and the Moon blasted these rocks into space, where they drifted for many years before falling on Earth. Out of many thousands of meteorites, only a few dozen are Moon or Mars rocks. You can own a piece for a few thousand dollars a gram, or find one yourself.
You can look for meteorites in two ways: wait until you see one fall or search for them on the ground. Historically, witnessed falls (like
this one in Yukon in 2000) were the primary means of discovering meteorites, but in recent years people have started looking for them more systematically. Both scientists and amateurs are in the huntit's a lot like fossil hunting that way. One difference is that many meteorite hunters are willing to give or sell pieces of their finds to science, whereas a fossil can't be sold in pieces so it's harder to share.There are two kinds of places on Earth where meteorites are more likely to be found. One is on parts of the Antarctic ice cap where the ice flows together and evaporates in the sun and wind, leaving behind meteorites as a lag deposit. Here scientists have the place to themselves, and the Antarctic Search for Meteorites program (
ANSMET) harvests the blue-ice plains every year.The other prime meteorite hunting grounds are deserts. The dry conditions tend to preserve stones, and the lack of rain means they are less likely to wash away. In windswept areas, just as in Antarctica, fine material does not bury the meteorites either.
Significant finds have come from Australia, Arabia, California, and the Saharan countries, and here's where politics comes in. In June 2001 a scientific institution, the University of Bern in Switzerland,
called in the media to display some 100 meteorites found that year in the desert of Oman. One of them was the Mars rock shown below.
Other Mars rocks have been found in Oman by amateurs; in fact it was the appearance (and sale) of those rocks and lunar meteorites that alerted the Swiss researchers. They enlisted the support of the government of Oman, which saved them a great deal of trouble. A piece of the stone was presented to the Natural History Museum in Muscat, Oman, at the same media event.
The university made a point of boasting that this meteorite is the first Mars rock that is fully available to science, as well as the first meteorite expedition done with permission of the Omani authorities. The Swiss earned this goodwill after 30 years of cooperative research in Oman, training scientists, and similar favors.
