Welcome to the web page of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory. This Program Office was established in mid-1998 to help coordinate, and provide a focal point for, the study of those comets and asteroids that can approach the Earth's orbit. The Earth's mean orbital distance from the sun is defined as an astronomical unit (1 AU) or approximately 93 million miles. Near-Earth Objects (NEOs) are generally defined as those objects whose close approaches to the sun are 1.3 AU or less. As a result, Near-Earth Objects are those comets and asteroids that can come within about 28 million miles of the Earth's orbit.

The intent of this web page is to bring together relevant information on all aspects of Near-Earth Object studies and, in particular, to explain why these objects are so important to life on Earth. These objects have struck the Earth in the past and they will do so in the future. It has only been relatively recently that the role of NEOs on the formation of the early Earth and Earth's life forms has been realized. Small Near-Earth Objects collide with the Earth on a daily basis. Fortunately, as the size of a NEO increases, there are fewer of them so that a collision with a truly large NEO is a very unlikely event. Nevertheless, there is a growing scientific consensus that numerous collisions of comets and asteroids with the early Earth first frustrated the development of life and then, as the bombardment lessened, these same collisions delivered to the Earth the veneer of carbon-based materials and water that allowed life to form. Subsequent, intermittent strikes by large comets and asteroid then punctuated the development of life, allowing only the most adaptable species to develop further. For example, a large comet or asteroid collided with the Earth 65 million years ago thus eliminating about 75% of the Earth's life forms including the large reptiles (dinosaurs). With the demise of these dominant creatures, the smaller but more adaptable mammals could develop further. As a result, we humans may owe our very existence to comet and asteroid impacts with the Earth. Although comets and asteroids are among the smallest of the solar systems bodies, in terms of life on Earth, their importance is in no way proportional to their size. Next to the sun itself, theirs is the most important realm.

Don Yeomans
January 1, 1999