Hazards: impacts in our future?
Thousands of asteroids and comets cross paths with earth. How dangerous are they?
The great majority of asteroids orbit the Sun in well-ordered bands between Mars and Jupiter. But occasionally, a collision between two asteroids followed by a gravitational nudge from Jupiter shifts an asteroid into a new orbit that crosses paths with Earth.
Fortunately, the largest and potentially most destructive asteroids-measuring several miles across-are extremely rare. Astronomers have already spotted most of them, and so far none poses a serious threat. But many thousands of asteroids, each as wide as a sports stadium, remain undiscovered. Although the odds of one striking any particular place are exceedingly small, such an impact could ruin a large metropolitan area.
Subtopic: Milky Way Galaxy
Keywords: Asteroid belt, Asteroids--Collisions with Earth, Astrogeology, Astrophysics, Collisions (Astrophysics), Natural disasters, Near-Earth asteroids
Asteroids large enough to cause widespread extinctions collide with Earth very rarely.
An asteroid with a diameter of one kilometer (0.6 mile) could completely devastate a land area the size of Europe and blanket Earth with dust.
Less damaging but more numerous are the asteroids with Earth-crossing orbits that are roughly 200 meters (660 feet) across, the size of a large sports stadium.
Asteroids the size of a 10-story building, 30 meters (100 feet) across, are about the smallest that can cause significant damage.
Every year U.S. military satellites detect about a dozen small asteroid explosions in the atmosphere.
In the unlikely event that astronomers discovered a civilization-ending asteroid or comet destined to impact Earth in a month, we wouldn't have enough time to stop it.
Comets—clumps of ice and rock—come near Earth much less frequently than asteroids, but they travel much faster—one hundred times the speed of sound on Earth.