Collisions of objects in space are inevitable. Untold millions of comets, asteroids, and meteoroids orbit the sun in orbits that constantly change as gravitational fields interact. The surface of the moon and the inner planets are clear testimony to uncounted past impacts.
Evidence of Impacts by Asteroids and Comets Is Common
The Earth was struck with a large object in an isolated area of Siberia in 1908 that leveled the dense forest in an area exceeding 2,000 square miles. Now known as the Tunguska Event, the energy released by the explosion is estimated to have exceeded a 10 megaton nuclear weapon. Jupiter was struck by 21 fragments of a shattered comet in 1994 and again by an unknown object in 2009.
The remains of about 120 craters can be seen on the Earth — weathering and geological processes likely have eliminated and erased many more.
Asteroids or Comets Don’t Need to Be Huge to Cause Massive Damage
The Tunguska Event could have destroyed a large city had it impacted a populated area — it is estimated to have been only 180 feet in diameter. The Chicxulub impact — thought to have led to the extinction of the dinosaurs — is estimated to have been about 10 miles in diameter. The nearly one-mile wide Barringer Crater in Arizona required an asteroid of about 150 feet in diameter.
The Minor Planet Center maintains a list of potentially hazardous objects. As of July 15, 2011, the list included 1,237 objects — mostly asteroids. Apophis is about 900 feet in diameter and YU55 is a scary 1,200 feet across.
Near-misses by small objects of 50 feet in diameter are common. One passed with 7,500 miles of Earth in June, 2011. Smaller objects would likely break into fragments upon entering the atmosphere and most would be consumed in flames. A few small pieces might rain down over a large area causing little or no damage. An impact of a mile or more in diameter would likely cause mass extinctions — including humans.
Although most asteroids that fall to Earth land in an ocean — about 75% of the Earth is covered with water — there would still be catastrophic results. Tsunamis hundreds of feet high would race inland for many miles. The ocean floor would be ripped apart and debris would fall back to Earth thousands of miles away. Fire storms would cover much of the globe, and smoke and dust would block out sunlight for months or years, chilling the Earth and killing plants that remained.
NASA is Watching the Skies for Near-Earth Objects
Larger objects have a better chance of causing damage. An impact by an asteroid of 300-400 feet in diameter could be genuinely dangerous and might not be spotted until it is a few days away from Earth, if it is spotted at all. NASA maintains the Near-Earth Object Program to search the skies for dangerous objects. Approximately 8,000 objects have been catalogued during its 30 years of operation.
The next issue is what to do if a large asteroid is spotted on a course to Earth. Scientists have many ideas — most of which center around diverting the asteroid. So far, a plan is not in place.
Uncounted, unseen thousand of asteroids are drifting freely in our solar system. They collide with each other, with planets, and Earth. Over a hundred craters remain on Earth from past impacts, and near-misses are frequent. Will we be ready for a major impact?
Sources:
- "Asteroid 2005 YU55 to Approach Earth on November 8, 2011," NEO.JPL.NASA.gov. (Acessed: July 15, 2011)
- “NASA NEO Program Office” impact.arc.nasa.gov. (Accessed July 15, 2011)
Harvey Craft - I am a retired educator with diverse experience. I read anything science, education, and history. I write to share what I learn.
