NASA keeps an eye on objects close to the Earth
Near-Earth objects are asteroids and comets with orbits that bring them within 195 million kilometers of the Sun, which means that can circulate close to the Earth. Most near-Earth objects are asteroids ranging in size from about a few meters) to nearly 40 kilometers in diameter.
The orbit of each object is calculated by finding the elliptical path through space that best suits to all available observations, which often span many orbits over many years or decades. As more observations are made, the accuracy of an object's orbit improves dramatically and it becomes possible to predict where an object will be years or even decades later and whether it could approach Earth.
Most objects near the Earth they have orbits that are not too close, and therefore present no risk of impact, but a small fraction of them require more attention. These objects are defined as asteroids that are greater than about 140 meters in size with orbits that bring them as close as possible to within 7.5 million kilometers of Earth's orbit around the Sun. CNEOS continuously monitors all near-Earth objects known to assess any risk of impact they might represent.
The orbital positions of objects close to the Earth come from the databases of the Minor Planet Center, the internationally recognized clearinghouse for measurements of the position of small bodies. This data is collected from observers around the world, including significant contributions from amateur observers.
The vast majority of asteroid tracking data, however, is collected by large NASA-funded observatories (such as Pan-STARRS , Catalina Sky Survey, NASA's NEOWISE mission and, in the future, NEO Surveyor). Planetary radar projects (including JPL's Goldstone Solar System Radar Group) are another key component of NASA's NEO Observations Program.
The Center for Near-Earth Object Studies is home to the NASA's monitoring system. Sentry impact, which continuously performs long-term analyzes of possible future orbits of dangerous asteroids. There is currently no known significant impact threat for the next hundred years or more.
The Center also maintains the Scout system which continuously monitors new potential detections of near-Earth objects, even before they have been confirmed as new discoveries, to see if any of these generally very small asteroids could pose a short-term (possibly imminent) impact threat.
CNEOS also supports NASA's planetary defense efforts by conducting hypothetical impact drills to help educate space agencies also to respond to the national and international disasters they are expected to face in a real asteroid impact scenario. The exercises help scientists and key decision makers to refine the warning systems and impact mitigation strategies that could be employed in the event that a threatening object is identified.
