One of the more obscure groups that fit into this class are the Near-IIarih Object Discovery teams. Though they hail from many countries, astronomers who participate in NFO projects have but one purpose: to search the night skies for objects that pose a threat to planet Earth. From observatories around the globe, these teams scan the heavens, using an instrument called a "charged couple device," or CCD. Similar in purpose and function to a camcorder, CCD cameras digitally record several images of the same region of the sky over a period of time, usually an hour. The images are then analyzed by computers to determine if any object captured by the CCD has systematically moved in relationship to known stars, which tend to remain fixed in place. When a suspect image has been identified as something other than a star or planet, it is studied in order to ascertain its precise location, size, and, most important, its projected trajectory.
If, as a result of this closer examination, it is determined that the newly discovered object and its orbit may place it in close proximity to the earth, it is classified as a near-earth object. Given a name, the newly discovered NEO is added to a list of known NEO's and monitored. If a NEO's travel through space will bring it to within what is called an earth "minimum-orbit intersection distance," or MOID, it is classified as a potentially hazardous asteroid, or PHA, PHA's, quite naturally, receive special attention. By the end of the beginning of the third millennium of the Common Era, there were over seven thousand known asteroids, with several times that number yet to be discovered.
Asteroids come in many sizes and shapes. The largest known asteroid is 1 Ceres, measuring some 933 kilometers in diameter, or somewhat greater in width than the distance between Washington, D. C., and New York City. The smallest are measured in inches. The asteroid that is credited with bringing the age of dinosaurs to a close, known as the KT Event, was estimated to be 12 kilometers, or 7.2 miles in diameter. When it plowed into the earth some sixty-five million years ago, it gouged out a primary crater 180 kilometers wide. This single event created so much havoc to Earth's climate and environment that it is estimated that two thirds of all species in existence at the time passed into extinction.
An even more spectacular event, if one can use that word to describe such a catastrophic occurrence, led to the creation of Earth's moon. Today it is generally believed that an object the size of Mars, which measures some 6,800 kilometers in diameter, collided with Earth, which is 12,753 kilometers in diameter. The resulting impact threw tremendous amounts of debris into space. In time, this rubble was drawn together to form the moon. That particular cosmic event and its results are credited with creating Earth as it is known today.
The discovery of this geographic history has given the study of asteroids a greater sense of urgency and importance. While the time span between planet-killing events such as the KT Event is measured in millions of years, the fact that astronomers have been unable to identify all but the smallest number of these unwanted visitors has engendered a degree of paranoia among some of those who specialize in this area. For them, it is not a question of "if." Rather, they endeavor to prepare for the time "when" Earth will be struck by an extinction-level event. Like other professionals, the men and women who are part of various Near-Earth Object Discovery teams are committed to searching the skies, waiting, watching, and hoping that somehow their efforts will provide the time necessary to do something about any potential threat.
This effort is not an easy one, for not all asteroids are alike and their travels are often less than predictable. The pull of gravity by the sun and other planets, the weight and shape of the asteroid, not to mention random collisions with other asteroids, influence the path of an asteroid. All of these calculations include some high-speed guessing. To start with, the exact weight of an asteroid cannot be precisely measured. Unlike planets, asteroids are not round. Some look like peanuts. Others bear a striking resemblance to potatoes. Besides their irregular shapes, the exact composition of an asteroid is difficult to gauge. By far, the most numerous are C-type asteroids. Accounting for seventy-five percent of all known asteroids, they tend to be dark. C-type asteroids have the same chemical composition as the Sun, minus hydrogen, helium, and other volatiles. The next largest class are those of the S-type. S-types are made up of a metallic nickel-iron, mixed with iron and magnesium silicates. These are considerably brighter in appearance.
Most asteroids that come into contact with Earth never make it to the earth's surface. Instead, they fall victim to the atmosphere, much as a dead man-made satellite does when gravity finally reclaims it. This is what happened in 1908 when an asteroid measuring fifty to sixty meters in diameter was pulled off its path and onto a collision course by Earth's gravity. Traveling at a speed of twelve to twenty kilometers a second, this stony asteroid exploded approximately six kilometers, or twenty thousand feet above the Tunguska region of Siberia with an estimated force of at least twenty megatons. Had this event taken place over a populated section of the world, say Western Europe instead of the barren wastelands of Eastern Russia, it would have been listed as the greatest natural disaster in recorded history. Knowing full well that the next visit by such an alien force may not be so obliging, the NEO teams watch, plot, and project the travels of a threat few of their fellow human beings concern themselves with.
One of these tireless guardians was a middle-aged astronomer by the name of Frederick Kellermann. As part of the joint French and German OCA-DLR Asteroid Survey Team, it was his task to review the data at the Institute of Planetary Exploration in Berlin, Germany, that was gathered by the Observatoire de la d'Azur, located in southern France. A sickly child, Kellermann had spent much of his youth in clinics and hospitals. Though the quiet orderliness of those institution^ appealed to him, the suffering he endured while confined in them prevented him from pursuing a medical career.
Instead, he opted to pursue another field of study that was just as orderly, and even more sedate: astronomy. Throughout the years when he had few friends and little freedom to wander about this earth, Frederick Kellermann was drawn to the distant heavens. They were boundless, yet orderly. Always in motion, but quite predictable. And above all else, they were silent. Whether it was in the dimly lit office where he spent many an hour hunched over his computer, picking his way through digitized information forwarded to him, or perched behind a telescope under the cavernous dome of an observatory, the German astronomer cherished the reserved world in which astronomers existed. What thoughts and words filled his head were his, and his alone. He could dwell on them and organize them as he saw fit, just as he sought to establish an orderliness out of the marauding chunks of rock and iron that threatened planet Earth. Perhaps one day, Kellermann dreamed, there would be a way of controlling these menaces just as effectively and efficiently as he did his own thoughts and words.
On this particular night, Kellermann was reviewing data on a number of PHA's, potentially hazardous asteroids, that were coming around for another encounter with Earth. None were expected to be of any great danger. All had been identified, analyzed, categorized, named, and listed. Since their travels were predictable, the computer that maintained the list spit out their names when they were about to reach their projected earth minimum-orbit intersection distance so that NEO teams could turn their attention to them, analyze their current activities, and update the data they provided.