A number of minor bodies in the Solar system (asteroids and comets) exist whose orbits intersect that of the Earth (Near Earth Objects or NEOs). The possibility therefore exists that some of these bodies may eventually impact on Earth, as has happened a number of times in geological history. The existence of such a risk has recently attracted considerable attention from the public and the media, including the film industry.
The scientific fact is that the number, orbits, and sizes of NEOs are poorly known at this time. Although estimated time scales for catastrophic impacts range from hundreds of thousands to millions of years, there are good reasons, scientific as well as social, for conducting vigorous research programmes to improve our knowledge of these bodies. Such research has, in fact, already a long history of international cooperation, coordinated within the IAU by the Working Group on NEOs of Division III and through the Minor Planet Center.
In order to clarify the policy of the IAU as regards research on and public information about NEOs, the IAU Executive Committee has issued the Policy Statement reproduced below. The IAU will continue to play a coordinating role in the scientific investigation of NEOs. Possible mitigation or preventive actions are, however, outside the Union's mandate.
The Solar system contains a large number of bodies ranging in size from the major planets to tiny meteorites. Research over the last several decades has revealed that all major bodies of the Solar system have suffered larger or smaller impacts of bodies ranging in size from millimetres to kilometres, the best-known example of which is the abundance of craters on the Moon. Geological features on Earth show that impacts of significant size have occurred also on our own planet. The realization that such impacts occur at long, but presently poorly-known intervals has recently caused growing concern in the public, and in the press.
Research on the minor constituents of the Solar system - the minor planets or asteroids - has formed part of astronomical research for the last two centuries. The International Astronomical Union (IAU) has acted as the international focal point for this research since the foundation of the Union in 1919, in particular through its Commission on the Positions and Motions of Minor Planets, Planets, and Satellites. As part of this function, the IAU has for over 50 years operated a Minor Planet Center (MPC), currently at the Smithsonian Astrophysical Observatory (SAO; Cambridge, Mass., USA), for the collection of data and the dissemination of information concerning minor planets and, lately, comets. When continued research showed that the orbits of several minor planets crossed that of the Earth, the IAU in 1991 appointed a Working Group (WG) on Near Earth Objects (NEO) to coordinate international studies of NEOs and develop suitable strategies for detection, follow-up, and orbit prediction. As one result of this work , the international Spaceguard Foundation was formed, and a number of observational programs for the detection of NEO's have been started. The WGNEO is also active in the development of proven algorithms for long-term NEO orbit prediction and thus for assessing the distance to which NEOs may approach Earth within the next few centuries.
Currently, the number, size distribution, and orbits of individual NEOs are incompletely known from observation. Thus, the most urgent task is the detection and observation of NEO's to determine their orbits. This is an international responsibility that requires the efforts of and support for astronomers around the world. As the international organization of professional astronomers, the IAU coordinates this activity through the NEO Working Group and offers the services of the MPC for the collection and collation of new observations and computation of predictions from which follow-up observations can be made to improve our knowledge of the orbits and sizes of these objects.
It is possible that, sometime in the future, these studies may lead to the prediction of an actual impact on Earth. In such a case, this information must be promptly conveyed to the governments of the world, who may be in a position to organise countermeasures (a subject outside the mandate of the IAU). On the other hand, public announcements of potential impacts without proper verification are clearly undesirable. The IAU has therefore charged the WGNEO, in consultation with astronomers worldwide, to draft a set of recommended procedures to be followed in case minor planets and comets are discovered that lead to predictions by the MPC of potential impacts. These procedures will conform to the following general principles:
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