Rocks That Fly
HAVE you ever seen a shooting star blaze across the sky on a clear night? It may be just a matter of time before you do. According to scientists these fireworks of nature trace their paths across earth’s skies some 200,000,000 times every day!
What are they? They are simply chunks of stony or metallic matter known as meteoroids that light up in white heat as they enter the earth’s atmosphere. The bright streak of light they trace across the sky as observed from earth is known as a meteor.
Most meteoroids burn up completely before they reach the earth, but some survive the intense heat and reach the earth’s surface. These are known as meteorites. Some scientists estimate that each day some 1,000 tons of this flying rock is deposited on earth.a
These crashes are seldom dangerous to humans, mainly because of the relatively small size of these flying rocks. In fact, most meteors are caused by meteorites no larger than a grain of sand. (See box, “Rocks From Outer Space.”) But what about the thousands of larger rocks flying in space? Take, for instance, the one known as Ceres, which is about 600 miles [1,000 km] in diameter! And there are about 30 other known rocks with a diameter greater than 120 miles [190 km]. These larger rocks are actually minor planets. Scientists call them asteroids.
What if one of these asteroids were to crash into the earth? This apparent threat is one important reason why scientists study asteroids. Although most asteroids orbit in a belt between Mars and Jupiter, some tracked by astronomers actually cross the orbit of the earth. The threat of a collision is reinforced by the existence of huge craters such as the Meteor Crater (also known as Barringer Crater) near Flagstaff, Arizona, U.S.A. One of the theories for the extinction of the dinosaurs is that a large impact altered the atmosphere and plunged the earth into an extended period of cold weather through which the dinosaurs could not survive.
Such a catastrophic collision today would likely destroy mankind. However, the Bible indicates that “the righteous themselves will possess the earth, and they will reside forever upon it.”—Psalm 37:29.
a Estimates vary.
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A Fireball on Videotape
Some meteors are unusually bright and large. They are known as fireballs. On October 9, 1992, the fireball shown in the above photograph streaked across the skies over several states in the United States. The fireball was seen first over West Virginia and appeared over a 430-mile [700 km] stretch of land. One fragment, weighing about 26 pounds [12 kg], landed on a parked car in Peekskill, New York.
What is unique about this event is that because of the grazing angle at which the meteoroid entered the atmosphere, a bright fireball was produced that lasted more than 40 seconds. This afforded an unprecedented opportunity to record it on video, and this was done from at least 14 different points of view. According to the magazine Nature, “these are the first motion pictures of a fireball from which a meteorite has been recovered.”
The fireball broke into at least 70 fragments, which appear in some of the videotapes as individual glowing projectiles. Although just one meteorite from this event has been found, scientists believe that one or more other fragments may have pierced the earth’s atmosphere and crashed on land. That is all that may be left of the large meteoroid that previously weighed about 20 tons.
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Rocks From Outer Space
Asteroid: Also known as a planetoid or a minor planet. These extremely small planets travel in an orbit around the sun. Most have irregular shapes that may indicate that they are fragments of once larger objects.
Meteoroid: A relatively small chunk of metallic or stony matter floating in space or falling through the atmosphere. Some scientists think that most meteoroids are fragments from asteroids produced by collisions or by the rocky debris from extinct comets.
Meteor: When a meteoroid penetrates the earth’s atmosphere, the air friction produces intense heat and a bright glow. This trail of hot glowing gases is momentarily visible as a streak of light in the sky. The streak of light is known as a meteor. Many call it a shooting star or a falling star. Most meteors are first sighted when they are about 65 miles [100 km] above the earth’s surface.
Meteorite: Sometimes a meteoroid is so large that it does not burn up completely when entering our atmosphere, and it crashes into the earth. Meteorite is the term for such a meteoroid. Some can be very large and heavy. One meteorite in Namibia, Africa, weighs more than 60 tons. Other large meteorites weighing 15 tons or more have been found in Greenland, Mexico, and the United States.
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Ida and Its Baby Moon
While photographing an asteroid named Ida, the Galileo spacecraft, on its way to Jupiter, made an unexpected discovery—the first documented example of a moon orbiting an asteroid. As reported in Sky and Telescope, scientists estimate that this egg-shaped moon, named Dactyl, measures one mile by three quarters of a mile. [1.6 by 1.2 km] Its orbit is about 60 miles [100 km] from the center of asteroid Ida, which measures 35 miles by 13 miles [56 by 21 km]. Their infrared color properties suggest that both Ida and its tiny moon are part of the Koronis family of asteroids, which are thought to be fragments of one single, large rock that was shattered by a collision in space.
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Meteor Crater, near Flagstaff, Arizona, U.S.A. is 4,000 feet [1,200 m] in diameter and 600 feet [200 m] deep
Photo by D. J. Roddy and K. Zeller, U.S. Geological Survey
[Picture Credit Line on page 23]
Sara Eichmiller Ruck