![]() ![]() The uncertainties in an asteroid's position lead to uncertainties in how well we can determine its speed and direction of travel. Most asteroids are small objects, a few meters to a few tens of meters across, and even the resolving power of a large telescope cannot determine their positions exactly. The predicted orbit is then compared to the orbit and position of Earth to check for any times when they might pass close to each other.Īlthough scientists can calculate a most-likely orbit from these early observations, each single observation of the asteroid's position contains some uncertainty. They take successive images of the asteroid over the course of days after its discovery in order to predict its probable orbital path for the near future. When a new asteroid is discovered, astronomers analyze it to determine whether its orbit around the sun could bring it close to the Earth. For that reason several programs, such as the Lincoln Near-Earth Asteroid Research (LINEAR) project at the Massachusetts Institute of Technology, have been undertaken around the world to discover and monitor potentially Earth-threatening asteroids. At the current rate of impacts, we would expect about one large asteroid to impact Earth every 100 million years or so. Many of these objects are called near-Earth asteroids (or NEAs) because they have orbits that repeatedly bring them close to, or intersect with, Earth's orbit.Īlthough the odds of any one particular asteroid ever impacting Earth are quite low, it is still likely that one day our planet will be hit by another asteroid. There are thousands of small bodies that we call asteroids or meteoroids in orbit around the sun. Because most of the earth is covered by oceans, there may also be many small impacts that go unnoticed. A more recent but less devastating example, called the Tunguska event, occurred in 1908, when a meteor or comet exploded over the wilderness of Siberia, damaging farmland and leveling trees for miles around. We have extensive evidence that Earth has already been hit by asteroids many times throughout history-the most famous (or infamous) example is probably the asteroid or comet that created the Chicxulub crater in the Gulf of Mexico and may have contributed to the extinction of the dinosaurs at the end of the Cretaceous Period 65 million years ago. ![]() Gerakines, an assistant professor in the department of physics at the University of Alabama at Birmingham, explains. ![]()
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