Our Window on Nature

Watching the night sky can be fascinating any time of year, but during meteor showers it takes on the characteristics of a fireworks show. But just what is the object that causes all the excitement?

Let’s start with the name, because it changes depending on where you find it. While they are still out in space they are called meteoroids. As they flash though the sky on their way to the earth they are called meteors. And if they don’t burn up in the atmosphere, when they reach the ground their name changes to meteorites.

Some meteors are made up of a stony substance, mostly silicate materials. Others may be an iron-nickel combination. Or perhaps it is a blend of the two. But this is material from outer space that intersects our path as the earth travels around the sun.

A few people collect meteorites as a hobby while others do it for the sake of science. The problem with meteorites, unless you just buy them on EBay, is to find them. To be successful you either need a lot of luck or must understand why certain locations are better than others.

Meteorites deteriorate just like other rocks and minerals on earth, but in very dry areas this process can take millennia. So when scientists want to search for these space visitors, they usually head toward the South Pole.

At first thought this might seem a strange place to look for a dry climate, but the pictures of ice that come to mind ignore the fact that the Antarctic is classified as a desert because of the lack of moisture – an almost complete lack of liquid water. This means that rocks, or in this case the meteorites, will resist deterioration for a very long time.

The average age of a meteorite found in Antarctica is about 4.5 billion years, and scientist say that most of these discoveries have been on the earth for between 25,000 and 65,000 years.

Since 1976 the Antarctic Search for Meteorites (ANSMET) has sent 20 search teams to Antarctica, collecting over 10,000 meteorites. A combination of wind conditions and shrinking ice packs provide concentrations of these space fragments found nowhere else.

There is a real advantage to looking for meteorites on an ice pack. In most areas of the world these hunks of rock can easily disappear – buried in the ground, behind a bush, or hidden deep in a forest. But on an ice pack, there is almost no place to hide. Add to this the contrast between a black piece of rock and a white background, and an ice field becomes the perfect area to search.

Most meteorites come from debris caused by collisions of larger bodies in the asteroid belt, but some are actually from the moon or from Mars, blasted into space by a grazing blow from another space visitor. Those from the moon were identified by comparing them with rocks collected by astronauts, while fragments from Mars were determined when the gasses held inside their bodies matched those collected by robotic travelers to the red planet.

If you can’t afford the time for a quick trip to McMurdo Station in Antarctica, you can join them vicariously on the ANSMET website at http://geology.cwru.edu/~ansmet/index.html. Lots of pictures and a great explanation of what they do.