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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 to their size and proximity, NEOs 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 a much smaller change in velocity than the Moon.

In the United States, NASA has a congressional mandate to catalogue all NEOs 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.

Approximately 800 of these NEOs have been detected.

According to the most widely accepted estimates, there are still 200 more that have not been found yet.

The United States, European Union and other nations are currently scanning for NEOs in an effort called Spaceguard.

Currently efforts are under way to use an existing telescope in Australia to cover the approximately 30 percent of the sky that is not currently surveyed.

Note:   The above text is excerpted from the Wikipedia article "Near-Earth object", which has been released under the GNU Free Documentation License.
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August 29, 2015

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updated 12:56 pm ET