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
Estimating the risks
There are two schemes for classification of impact hazards:
As of 2003, the following NEOs had a Torino scale value greater than zero:
Currently, the only known NEO with a Palermo scale value greater than zero is
1950 DA, which is predicted to pass very close to or collide with the Earth (p≤0.003) in the year
2880. If this collision were to happen, the energy released by a collision with 1950 DA would cause an
Extinction event which would destroy most life on the planet. However, humanity has over 800 years to refine its estimates of the orbit of 1950 DA, and to deflect it if necessary.
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