To assess whether a given NEO can impact the Earth, we must do more than compute an orbit and predict how close that orbit comes to Earth. Because orbit computations are based on imperfect data, each asteroid will have a range possible orbits that match the observed sky positions. CNEOS designed the Sentry impact monitoring system to analyze the full range of possible orbits for each NEO, searching for potential Earth close approaches over the next 100 years and calculating the probability of impact for each. The results are tabulated on the Sentry Risk Page.
The Scout impact hazard assessment system operates on a different set of objects, the unconfirmed potential new NEO discoveries listed on the Minor Planet Center’s NEO Confirmation Page (NEOCP). Many of these objects are already close to the Earth, making them bright enough to be detected. Scout continually monitors each of the candidate NEOs on the NEOCP, and analyzes the range of possible trajectories over just the next few days and weeks, providing an early and preliminary assessment of the impact risk from these candidate NEOs. Once an object is confirmed, it is removed from the NEOCP and the monitoring of its Earth impact risk switches over to Sentry.
|Sentry||Long-term impact monitoring for confirmed NEOs|
|Scout||Short-term monitoring for newly-detected, unconfirmed NEOs|