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.
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.
Collection Zones:
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.
Good Places:
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.
Special Discovery:
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.