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Near-Earth object

Near-Earth Objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earth's orbit and which may therefore pose a collision danger. Due their size and proximity, NEO's are also more easily accessible for spacecraft from Earth and are important for future scientific investigation and commercial development. In fact, some near-Earth asteroids can be reached with much less ΔV (change in velocity) than the Moon.

In the United States, NASA has a congressional mandate to catalogue all NEO's that are at least 1 kilometer (0.6 miles) wide. At this size and larger, an impacting NEO would cause catastrophic local damage and significant to severe global consequences. According to the most widely accepted estimates, only about half of these large NEOs have been found. Approximately 500 of these NEO's are estimated to await detection. The United States, European Union and other nations are currently scanning for NEO's in an effort called Spaceguard. Currently efforts are under way to use an existing telescope in Australia to cover the ~30% of the sky that is not currently surveyed.

Classification of near-Earth objects by kind and size

There are two schemes for classification of impact hazards:

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