Part III: Location, Location, Location
Most asteroids and comets orbit the Sun far from Earth.
However, some space rocks travel along orbits that are just a little farther away from the Sun than is the Earth.
In fact, some of these orbital paths actually approach Earth, coming just a little farther or a little closer than the Moons distance.
It is these objects, especially the larger ones, that we closely observe and track.
Over time, gravity from nearby planets may change their orbital paths, thus allowing for a potential future collision.
By immediately tracking potentially hazardous near-Earth objects and learning more about their orbital paths, we have
more time to study potentially threatening situations.
Comet Hits Jupiter
|Infrared image shows fragments of Shoemaker-Levy hitting Jupiter.||
From July 16 through July 22, 1994, pieces of an object designated as comet Shoemaker-Levy 9 collided with Jupiter at 60 kilometers per second (37 miles per second). This was the first collision of two solar system bodies ever to be observed. The impacts resulted in plumes rising many thousands of kilometers above Jupiters surface, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere, which lasted for weeks. The comet was destroyed by the impacts.
Craters Beyond Earth
The surfaces of Mercury and the Moon are like historical records, showing evidence of thousands of asteroid and comet impacts. These bodies dont experience erosion or subsurface movements, like volcanic or tectonic activity, that would cause the craters to be slowly erased.