Many thanks to Marilyn Kennedy Wall for graciously writing this Junior Journal based on Scott's original writing. Marilyn teaches at John Wayland Elementary School in Bridgewater, Virginia.
CHASING METEORITES IN ANTARCTICA
Dr. Scott Sandford
What are Meteorites?
Meteorites are pieces of rock that fall onto the surface of the Earth Scientists think that meteorites came from asteroids colliding with each other and these pieces of rock we call meteorites were just thrown into space.
A Place to Study Meteorites:
Most students think that to study meteorites you would have to study space. But, strangely enough, my interest in meteorites has taken me all the way to Antarctica. I am sure it is a great surprise to many students that the world's coldest continent Antarctica is also the world's BEST place to find meteorites. The ice and snow in Antarctica preserve the meteorites for long periods of time, even as long as a million years. When meteorites land on the other continents, the meteorites rarely last more than just a few hundred years. On the other continents, meteorites are plowed under by machines, paved over by roads, eroded or worn away by weather, or just plain lost. So Antarctica is the perfect "safe" place for meteorites.
An Ice Cube Cocoon:
When meteorites fall and land on Antarctica, they are slowly buried in snow. As the snow piles up or accumulates on top of the meteorite, the weight of the snow on the top squeezes the snow below so hard that it turns into ice. Now the meteorites are frozen in ice, something like being in an ice cube. But their ice cube cocoon protects the meteorites from things that could destroy it. The ice makes the meteorites safe!
On the Ocean Floor:
Then this meteorite ice cube slowly flows down hill, until this meteorite ice cube reaches the ocean. At the ocean, the ice breaks off into large icebergs which float out to sea and melt. So, most of the Antarctica meteorites end up in the ocean where they sink to the bottom.
There are areas in Antarctica where meteorites can be collected before they get into the ocean. These areas are called "ablation zones". You can find these collection zones in places where the large meteorite ice cube (as it flows down hill) runs into a barrier or obstacle. Often these barriers are the mountains. When the meteorites hits the mountains, the ice is thrown "upward". Now the meteorite ice cube is exposed to the constant winds that blow in Antarctica. These winds wear away the ice and expose the trapped meteorites. [Ablation is a process where a solid material evaporates without first becoming a liquid. This is the same process that makes your ice cubes shrink in a 'frost-free' freezer!]
Think of the flowing ice as a large conveyor belt that collects meteorites for scientists to study. Some of these special Antarctic "collection" locations contain huge numbers of meteorites. One year I participated in a search expedition that found over 1000 meteorites in six weeks!
Ordinary and Not So Ordinary meteorites:
Did you know that here are many types of meteorites? The most common meteorites are called "ordinary chondrites." Scientists study meteorites because they can tell us a lot about the how our Solar System was formed and about its history, what has happened in its "life." Scientist who study meteorites are also interested in the rarer types of meteorites that are not "ordinary chondrites." These rarer meteorites can help scientists learn new things about our Solar System.
Searching for meteorites:
Here's how we search for meteorites in Antarctica. We do most of our studies during the Antarctic summer when the sun never actually sets. There are almost 24 hours of daylight. Each "morning" 4 to 8 people (men and women) leave their tents and go out on foot or on snowmobiles to search.
In good locations, the ice field being searched is created by a submerged mountain. This type of ice field is a great location for searching for meteorites because there are not Earth (terrestrial) rocks. Scientists call this area "uncontaminated. It is easy to find meteorites on this type of ice field. Anything that isn't snow or ice is probably a meteorite.
But When It's All Mixed Up:
But, many ice fields are not so "pure" and these ice fields are found near exposed mountains. These meteorites are mixed in with a lot of terrestrial "junk" rock. Finding meteorites on these mixed fields requires that every rock be painstakingly examined to see if it's a meteorite. This is hard slow work!
So How Do You Know?
You can usually tell whether a rock is a meteorite just by looking at it. Most meteorites have a distinctive black coating called a "fusion crust." The fusion crust is created when the surface of the meteorite is vaporized by the intense heat generated when the meteorite enters the Earth's atmosphere.
New Discoveries Or Just Plain Junk:
As scientists study an area, they sometimes find a 'mystery rock', a rock that might be a meteorite... or it might not. Of course, these 'mystery' rocks may be the most exciting discoveries. These 'mystery rocks' might be the 'new', rare, unique meteorites that scientists have not yet discovered. Or they might just be 'junk'rock, not meteorites at all.
So Why Not Just Collect It All?
It sure would be simple to collect everything you're not sure about and simply bring your 'collection' pile back to the scientists at Johnson Space Center. The scientists there are able to examine carefully our collected samples. There in the Space Center it is warm, there is no rush to get it done quickly. Out in the 'field' the expedition meteorites searchers work in cold temperatures and under difficult conditions. Often the expedition searchers are just cold and tired and they have limited time to examine the 'rock' and debate back and forth whether it is a meteorites or not.
Dangers of Being Out in the Field:
When a scientist is outside in the 'field', the scientist has to remove his or her gloves and risk freezing their fingers in order to collect a meteorite, package it properly, and record the data in a field book. The scientists want to be sure that they don't want to make a silly mistake and collect something that could not even be a meteorites. How embarrassing it would be to think you have found a "meteorites and it turned out only to be a frozen penguin dropping!
Team Discussions: "Should we collect it?"
The expedition members gather around the found 'rock' and 'discuss' whether it should be collected or not. This discussion solves the problem, either because some everyone agrees it should be collected or someone in the group finally decides it would be less painful to remove his or her gloves even though it is freezing cold than to stand around and continue to listen to the " Should we collect it?" discussion.
In late January of 1989, I and three other scientists were searching for meteorites near the MacAlpine Hills in Antarctica. The weather was VERY cold and the ice field we were searching had a lot of amount of terrestrial "junk" rock on it. We had already found a few meteorites when I came upon a 'mystery rock'. It did not look like a terrestrial rock of the type local to the area, and yet it didn't look like a normal meteorite either. Most meteorites look black, but this rock was a funny sort of greenish-brown. On the other hand, the surface of the rock had the characteristic smoothness of a fusion crust, as if the rock had entered the Earth's atmosphere at a very high velocity or speed.
Once again, the discussion began about whether to collect this 'rock' or not. No one in our group could come to an agreement about whether the rock was a meteorite or not. But as I looked at this 'rock', I was reluctant to leave it behind. Who knows what this 'rock' might be? It was finally decided that I would put the rock - which weighed about one and a half pounds and was about the size of a fist - in my pocket. If no other rocks of this type were found, I would bag this 'sample' for Houston. If we began to stumble onto many more rocks of the same type, we would conclude that we had drifted into an area with a new kind of terrestrial rock and I would throw the sample rock away.
So of course we found one more such sample rock, a smaller one. Once again everyone in our group began discussing whether we should keep the 'rock' as a sample. After listening to all the discussions, I decided to 'bag' or keep both samples.
Pieces of the Moon:
Boy was I glad I did! Several months later, when I was back at work at NASA's Ames Research Center, I received a phone call. The Ames Research Center wanted me to know that both of the 'mystery rocks' had turned out to be luna meteorites. Yes, pieces of the Moon!
It seems that some time in the last 10 million years or so, a large asteroid or comet hit the Moon and the resulting explosion threw or ejected pieces of the Moon into space. Some of these lunar pieces ended up falling on the Earth as meteorites. And some of these lunar pieces landed in Antarctica and one of them came to the surface of the ice just in time to spend a day in my pocket.
Standing Up for Your Ideas:
So... the next time you're worried about doing something that other people might laugh at or your afraid to say what you think because the others will think that you are "dumb", remember my experience. "How many penguin droppings are worth one lunar meteorite?" If I had let everyone talk me out of collecting that sample "rock", we would have missed discovering a lunar meteorite.