Earth stands a 1-in-3 chance of colliding with a small asteroid that could cause massive damage.
Spotts in 99 (Christian Science Monitor, THREAT OF ASTEROID COLLISION MAY BE JUST A MOVIE, AFTER ALL, 7/29/99, EBSCO, znf)
With improved detection, scientists now believe fewer big asteroids will hit the earth than previously thought If the astronomical fireworks of "Deep Impact" or "Armageddon" kept you up at night, you can rest a bit easier. Our cosmic neighborhood appears to hold far fewer objects capable of snuffing out life on Earth than previously thought. New research announced this week at an international meeting on asteroids and comets at Cornell University in Ithaca, N.Y., does not mean Earthlings can stop scanning the skies for objects that might hit home, however. Earth's geological record alone suggests that during the 21st century the planet stands a 1-in-3 chance of colliding with an object that could cause heavy local damage, such as the event that flattened a Siberian forest in 1908. And the planet faces anywhere from a 1-in-1,000 to a 1-in-10,000 chance of being hit by an object that could cause what Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology in Cambridge, calls "instant global change." These new, lower numbers do suggest that astronomers may be closer than they thought to reaching their goal of finding and tracking in the next 10 years at least 90 percent of potential Earth-crossing objects that measure over a half mile wide. This is the size range for asteroids that researchers say could cause a catastrophic change in global climate if one hits our planet. Older approaches to spotting near-Earth objects (NEOs) led astronomers to estimate that from 1,000 to 2,000 asteroids with these diameters and higher had the potential to threaten Earth, according to David Rabinowitz, a member of CalTech's Jet Propulsion Laboratory in Pasadena, Calif. "As of today, our best estimate is between 500 and 1,000," he says. Improved search techniques that include new imaging detectors and telescopes specifically dedicated to finding asteroids have helped thicken the growing catalog of NEOs. These efforts scan over two-thirds of the sky and can spot objects 25,000 to 30,000 times fainter than objects humans can see with the naked eye. Combined with more-powerful computer programs developed in the past year to improve long-term orbital predictions, they have enabled the asteroid-hazard community to act more quickly to confirm or knock down the notion that a new object has the potential to threaten Earth over a 50- to 100-year period. Yet, though researchers have been increasingly successful at finding NEOs, keeping track of them has often presented problems. "The problem of follow-up is one of the show-stoppers" in efforts to determine asteroid hazards, says Andrea Milani, an astronomer at the University of Pisa in Italy. Roughly 10 percent of the NEOs astronomers find move in ways that mask them as more harmless asteroids that orbit in a belt between Mars and Jupiter. As a result, when astronomers find them, they write them off and fail to make the follow-up observations critical to determining their orbits and the likelihood of a collision with Earth. In other cases, bad observing conditions prevent astronomers from keeping track of newly found asteroids. Last year, astronomers tried to keep their eyes on an object listed at 1998 OX4, estimated to have a 1 in 10 million chance of striking Earth in January 2046. They tracked it on and off for two weeks before losing it. To boost the chances of recovering newly discovered, quickly lost asteroids, astronomers turn to computer simulations. Instead of scanning the skies frantically, they calculate the object's "killer" orbits, then look in those directions. Dr. Milani likens it to looking both ways before crossing a street. "If a car is not there, you cross. You don't need to know where all the cars in the city are."
Small Asteroids = damage
Asteroids that are considered small are large enough to create 300ft craters – even those that don’t impact the earth are a threat to human life.
Elizabeth Svoboda 2003 (Discover, Less Danger From Falling Rocks, October 2003, EBSCO, znf)
HAVE SOME PROMINENT SCIENTISTS INADVERTENTLY BEEN PLAYING Chicken Little? Working from computer models, several researchers warned that asteroid impacts could trigger devastating tsunamis with frightening frequency, at least once every 4,000 years. Never fear: Philip Bland, a planetary scientist at Imperial College London, says his improved calculations show that the actual rate is probably much lower. The previous simulations portrayed incoming asteroids as continuous blobs--picture a ball of glue flattening and spreading as it hits a hard surface. Bland developed a more realistic model that allows asteroids to disintegrate on the way in. "We're looking at the forces acting on stone or iron fragments as an object breaks up upon entering the atmosphere," he says. Fragmentation greatly reduces the odds of a major tsunami. To generate a 16-foot-high tidal wave, an object must be about 720 feet wide when it hits the surface. According to Bland's model, few objects that large survive passage through the atmosphere. Asteroid fragments 15 feet wide, capable of forming 300-foot craters, strike Earth every 200 to 400 years, he finds. Chunks large enough to trigger a significant tsunami fall just once every 170,000 years. Bland does not dismiss the danger of asteroids, however. "Even if an asteroid shatters in the atmosphere, it's a substantial threat to human life" he says. The still-mysterious Tunguska Event, an explosion in Siberia in 1908, was most likely caused by a comet or meteorite. Although the object disintegrated in the air, it still managed to flatten 800 square miles of terrain. And scientists still do not really understand how the atmosphere interacts with really large impactors, which will be the next focus of Bland's research. "That would let us see what kind of effect a big comet, for example, might have" he says. PHOTO (COLOR): The Wolf Creek Crater in Western Australia testifies to the destructive power of asteroids on land.
A small asteroid has the capability of causing mass damage – tsunamis, worldwide winter,
Prado 2002 (Mark, “1.7 Earth Impact by an Asteroid: Prospects and Effects”, Asteroids Near Earth—Materials for Utilization, http://permanent.com/a-impact.htm)
If an asteroid of size 200 meters hit the ocean (which covers 70% of the Earth), the tsunami (i.e., giant wave) it would create would inflict catastrophic destruction of coastal cities and substantial worldwide human casualties along coastlines. If an asteroid of size 1 kilometer hit Earth, it would cause a dust cloud which would block out sunlight for at least a year and lead to a deep worldwide winter, exhausting food supplies. The latter is what caused the dinosaur extinction, as well as other major extinctions of smaller creatures in geologic time scales. The 200 meter asteroid hits, which are far more common than the 1 km+ hits, wouldn't show up much in geologic histories on a global scale.
IRWIN I. SHAPIRO et al in 10,( Harvard-Smithsonian Center for Astrophysics, Chair FAITH VILAS, MMT Observatory at Mt. Hopkins, Arizona, Vice Chair MICHAEL A’HEARN, University of Maryland, College Park, Vice Chair ANDREW F. CHENG, Johns Hopkins University Applied Physics Laboratory FRANK CULBERTSON, JR., Orbital Sciences Corporation DAVID C. JEWITT, University of California, Los Angeles STEPHEN MACKWELL, Lunar and Planetary Institute H. JAY MELOSH, Purdue University JOSEPH H. ROTHENBERG, Universal Space Network, Committee to Review Near-Earth Object Surveys and Hazard Mitigation StrategiesSpace Studies BoardAeronautics and Space Engineering BoardDivision on Engineering and Physical Sciences, THE NATIONAL ACADEMIES PRESS, http://www.fas.harvard.edu/~planets/sstewart/reprints/other/4_NEOReportDefending%20Planet%20Earth%20Prepub%202010.pdf)
The committee notes that objects smaller than 140 meters in diameter are also capable of causing significant damage to Earth. The most well-known case from recent history is the 1908 impact of an object at Tunguska in the Siberian wilderness that devastated more than 2,000 square kilometers of forest. Previous estimates of the size of this object were on the order of approximately 70 meters in diameter. Recent research indicates that the object could have been substantially smaller (30 to 50 meters in diameter), with much of the damage it caused due to shock waves from the explosion of the object in Earth’s atmosphere. The committee strongly stresses that this new conclusion is preliminary and must be independently validated. Since smaller objects are more numerous than larger ones, however, this new result, if correct, implies an increase in the frequency of such events to approximately once per 3 centuries.