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, 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 much less ΔV; (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. According to the most widely accepted estimates, only about half of these large NEOs have been found. Approximately 500 of these NEOs are estimated to await detection. 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 ~30% of the sky that is not currently surveyed.

Classification of near-Earth objects by kind and size

• Meteoroids < 50 m diameter
• Asteroids > 50 m diameter. See Near-Earth asteroid.
• Comets

Table of contents

1 Number of near-earth objects 2 Estimating the risks 3 NEO near misses 4 See also 5 External links

Number of near-earth objects

To April 18, 2004, 2808 NEOs had been discovered. These were 49 near-earth comets, 217 Aten asteroids, 1114 Amor asteroids and 1427 Apollo asteroids. 708 of them had diameters over 1 km.

Estimating the risks

There are two schemes for classification of impact hazards:

• the simple Torino scale
• and the more complex Palermo Technical Impact Hazard Scale

As of April 2004, the only NEO with a Torino scale value greater than zero is 1997 XR2; it is ranked a one (the scale is 0–10).

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.

NEO near misses

Flyby of Asteroid 2004 FH''

March 18, 2004 saw the closest recorded approach of a near-Earth object. Asteroid 2004 FH, about 30 meters (100 feet) in diameter, passed approximately 43,000 kilometers (26,500 miles) above the earth's surface. Astronomers had detected it three days before. While the time from detection to nearest approach may seem short, Asteroid 2004 FH is extremely small. A NEO with globally cataclysmic potential would presumably be sighted much earlier.

See also

• Space debris
• Bolide

External links

• The JPL Near Earth Object Program:
  • The Jet Propulsion Laboratory's NEO website
  • Update on number of NEOs
  • Top risk estimates for known NEOs over the next 100 years
  • A special case: asteroid 1950 DA
• The UK NEO Information Centre
• The Italian NEODyS system