January 28, 2012
At our daytime field trips here at Perkins Observatory, our temporary students often ask as if we’ve been to space. We explain that we wish we had, but no.
Recently, a variation on that question practically struck me speechless.
As I showed some second graders the craters on the moon, one curious student asked, “What’s it like to be there?” For once, I was able to answer truthfully, “It’s awesome!”
A few summers ago, my family went on a long-needed vacation. Some may choose the beaches of the Bahamas. Others may choose one of the Disney worlds that make up the Disney universe. My family stood in silent awe at the edge of a big hole in the ground.
The American west has many holes and gouges, but none is stranger and more wondrous than a sweet, sweet indentation that sits in the middle of one of the United States’ most desolate regions. Just outside of Winslow, Arizona, and about an hour’s drive from the Perkins Telescope at Lowell Observatory is Meteor Crater, the best-preserved meteorite impact site on planet Earth.
Standing at the rim of Meteor Crater produces the unexpected feeling that you are standing on the moon. The crater has the same look as any of the giant impact sites we find on our nearest celestial neighbor. We see the same signs of an enormous explosion – the same raised rim and the same magnificent emptiness surrounding the impact location.
The area around the crater is basically desert, and that’s a good thing. Like the moon, Earth was once covered with craters, the results of wallops by giant rocks from space billions of years ago. Sadly, our craters have been eroded away by wind, rain, and plate tectonics. The craters on the moon remain because it has no weather at all, no air or water to scrub the craters away over the billennia.
Meteor crater remains because its location in Arizona is arid and because the impact that caused it happened a scant 50,000 years ago. At that time, a giant hunk of iron and nickel called a meteoroid came crashing into Earth’s atmosphere at about 40,000 miles per hour. What a trail of glory it must have left as it rubbed against the air and produced the tell-tail ball of fire we have come to call a meteor, or “shooting star.” Much of the object must have burned away, but a tiny piece remained when the meteoroid hit our planet and became a meteorite.
Still, the meteorite was perhaps 150 feet across and weighed several hundred thousand tons when it slammed into the ground. Perhaps “ground zero” is a better term. The meteoroid had lost little of its velocity when it hit.
The resulting explosion was the equivalent of a good-sized nuclear bomb with an explosive force of 20 million tons of TNT.
The meteorite itself was shattered into many tiny fragments. The largest piece ever found weighs in at a mere 1,400 pounds. Many the size of your thumb are scattered around the area, but 90 percent of the meteorite simply vaporized and became part of Earth’s atmosphere.
Blocks of Earth rock the size of houses were blown into the rim of the crater. Dust, debris, and pieces of meteorite were thrown for many miles around the surrounding landscape. In the blink of an eye, the meteorite excavated a crater 4/5’s of a mile wide and 680 feet deep.
The most amazing aspect of Meteor Crater is how much it looks like the lunar variety. Humans have gotten up close and personal with craters on the moon for only a few hours when the Apollo missions went to the moon. If we were ever to understand how craters were formed on the moon, it was very helpful to have one to examine on Earth.
So inhospitable is the high desert in Arizona that it wasn’t until 1861 that the first Euro-American happened upon it. At the time, no one knew how craters were formed on the moon.
During the 19th century, some lunar experts believed that the craters were extinct volcanoes. Others championed the impact hypothesis. It didn’t hurt the impact theorists that a perfectly formed “lunar” crater had been found in Arizona, and that it was obviously the result of a giant impact.
So if you have a vacation planned out west this summer and you have a second grader with you, why not work in a side trip to the big hole in the ground? The way we’ve deemphasized manned trips to the moon lately, it might be the closest you’ll ever get to a more spectacular, more distant vacation.
Planets: Saturn is still high in the south just after dark. During predawn twilight, check out the nice line-up of planets very low in the east. Jupiter is highest and farthest to the right. Bright Venus is down and to the left. Much dimmer Mars is farthest right. You’ll need an unobstructed horizon and binoculars to see mercury below Venus.
Tom Burns is the Director of Ohio Wesleyan University’s Perkins Observatory. tlburns@ owu.edu