HUNTSVILLE, Alabama - Experts say there could be hundreds of meteorites on the ground in northwest Alabama after last week's big meteor fall, but so far only two small ones have been found. That shows how hard it is to find a rock on forest floors deep in fallen leaves.
This week's developments in a rare space story included the word that a second meteorite was found Wednesday in or near the Bankhead National Forest near Addison, Al. Also Thursday, Arizona scientist and meteorite expert Dr. Mark Fries showed Huntsville scientists and meteorite hunters from as far away as Maryland how his small company, Galactic Analytics, Inc., finds meteorite showers using Doppler weather radar. Fries also showed a map of the likely debris field near Addison, but it isn't available publicly yet. It costs a lot of money to develop these models, Fries shrugged, so you have to subscribe to his website. One time access is available.
Meteorites are pieces of meteors that make it to the ground. They are most often found when a meteoroid, a larger meteor fragment, strikes the atmosphere with an explosive noise and shatters into fragments. That is what happened Oct. 30 over northwest Alabama. Eyewitnesses from as far away as Florida and Arkansas saw the fireball in daylight at about 5:30 p.m.
Before explaining how he tracked it to the ground, Fries took a moment at Marshall to explain why meteorites are so important. "They are physical samples of the processes that created our planet and the other planets and the solar system," Fries said. "They are a chunk of something you can take to the lab that is leftover pieces of these processes. " Going into space to collect all the meteorites already found on Earth would be impossibly expensive, Fries said, "but they do us the favor of coming to us."
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"And as far as public outreach goes," Fries told the scientists, "there is nothing like showing a meteorite and saying, there, this predates the Earth. Your average meteorite is 4.5 billion years old. If you hold your arms out at arms' length and say the distance between this finger and this finger is 4.5 billion years, you could take a nail file and with one swipe remove all of recorded human history. But the meteorite has been there the entire time."
Most meteorites found do come from falls that people see, Fries said, but most falls aren't visually tracked all the way to the ground because it's impossible to see the last part - the so-called "dark flight" when the fragments drop without the heat and speed needed to create a visual trail. It was Fries' insight to think of using Doppler weather radars, which are always sweeping the ground from 1 degree above the horizon to 19 degrees. What if you could compare sightings to Doppler data? Fries wondered, and his company was born from the fact that you can.
Doppler radars - like the Hightop radar near the Alabama-Tennessee level that tracked this fall - sweep the ground at intervals ranging from very slow on clear days to very fast on stormy days. Fries said searchers were lucky last week. There were just enough clouds to speed up the radar.
The 3-D composite radar image Fries showed Thursday - a visual map of the Addison-area debris fall - was amazing. Watchers could see in the pixel patterns dark returns that showed debris and light returns that showed none. This meteor clearly dropped meteorites on Alabama - possibly hundreds of them.But what about going after them? Shouldn't we all be in the field on our next day off? It's a tricky question with lots to consider, according to the experts.
1. The area is forested, sparsely populated and leaf-strewn this time of year. Bankhead National Forest is in the target zone. Most American meteorites are found in the wide-open spaces of the West by hunters, and there is a reason for that. Meteorite hunting "stinks" in the forested East, one expert said.
2. Most of the low-hanging fruit is gone. Professionals and NASA teams came to the area within days and raced up and down logging roads, scoured parking lots and checked other locations for meteorites in plain sight. Experienced hunters don't bother with metal detectors, at least at first, because the scanning would slow their progress. An expert will almost run over open ground up to 15 miles a day in the first days of a hunt.
3. Hassling local residents is bad for finding meteorites. If hordes descend on farmers' fields, leave gates open, or otherwise act like fools, locals might close their fields to scientists and those who want meteorites for serious study. If you do go, mind your manners, ask permission, tread lightly.
4. It's illegal to take a meteorite from private property or from the national forest without permission.
And yet. The fragments recovered so far are small, but scientists believe there is at least one - maybe two - meteorites the size of oranges on the ground. There are dozens more of other sizes. It's a significant event that's happened only about a dozen times in recorded Alabama history. But you'll probably be disappointed if you make a special trip to hunt for these space visitors. Scientists and others with special hunting skills have already spent more than a week on the ground and have found only two meteorites.
And yet, they are out there. So, if you're in a forest or walking a logging road or trail near Addison, Alabama, anytime from now on, keep an eye out for dark, heavy rocks that don't belong. You might just find a piece of creation.
And if you do, NASA wants to know about it. The space agency will do its research and return the meteorite to you.
(Follow me on Twitter @leeroop)