Large near-earth objects that are difficult to discover

Earth continues to be hit by Near-Earth Objects (NEOs), and major mass extinctions are related to impacts by large objects. Impacts by objects 100 meter diameter or larger would likely cause significant loss of life, and impact by an object 1 km in diameter or larger would be catastrophic to life on Earth. For this reason, efforts are being made (primarily funded by NASA) to discover all of the larger NEOs, so that any possible future impacts can be predicted well in advance, thereby allowing efforts to be made to deflect the NEO before impact. Although substantial progress has been made in finding most of the larger NEOs, it is clear that a significant number remain undiscovered. It appears likely that it will take many years to complete the inventory of 1 km or larger NEOs. Factors that contribute to the difficulty in discovering the remaining large NEOs include periods close to multiples of 1.0 years, the difficulty in searching for NEOs close to the Galactic Plane, the geographical asymmetry in NEO search assets, and the difficulty in searching for NEOs at small solar elongation.