They are generally known among planetary scientists as Near-Earth Objects (NEOs). Their total population is unknown, but the number of Earth-Crossing Asteroids with sizes larger than about 1 km is estimated to be about 2,000. These objects are the most dangerous and only a tiny fraction of them have been detected to date.
Considering that the explosion close to the Earth's surface of even an object with a diameter of 50 m can have the effect of a 10 megaton nuclear weapon, the consequences of larger impacts would be disastrous on a global scale. The best known, recent examples are the Tunguska explosion of an NEO about 60 metres in size (over Siberia in 1908, resulting in the destruction of over 2,000 square km of largely-unpopulated forest), and the violent impacts into Jupiter of the fragments of comet Shoemaker-Levy 9 (in July 1994); those fragments were only about 0.5 km in size, but caused devastation over a larger area than that of the Earth. Traces of other smaller impacts on our planet are frequently being discovered, as well as fossil records of cataclysmic impact events in the past.
The significant amount of information gathered over the last few years on asteroid and comet collisions indicates how they can trigger large-scale and large-standing ecological catastrophes, sometimes leading to mass extinctions of species; thus such impacts represent a significant threat to human civilisations.
Although, statistically speaking, the risk of major impacts in the near future is low, the possible consequences are so vast that every reasonable effort should be encouraged in order to minimise them.
The Assembly therefore welcomes various initiatives -- i.e. the "Spaceguard Survey" report published by NASA, the creation of the "Working Group on Near-Earth Objects" by the International Astronomical Union, and the recent decision of the NEO community to set up a "Spaceguard Foundation" to coordinate the efforts at an international level -- as important steps paving the way towards the development of a world-wide surveillance programme aimed at discovering all potentially-hazardous NEOs and tracking their orbits forward by computer so that any impact could be foreseen some years in advance, allowing preventive actions to be taken as necessary.
The Assembly invites governments of member states and the European Space Agency (ESA) to urge the setting-up and development of the above-mentioned "Spaceguard Foundation" and to give the necessary support to an international programme which would:
Strasbourg, March 20 1996
- establish an inventory of NEOs as complete as possible with an emphasis on objects larger than 0.5 km in size;
- further our understanding of the physical nature of NEOs, as well as the assessment of the phenomena associated with a possible impact, at various levels of impactor kinetic energy and composition;
- regularly monitor detected objects over a period of time long enough to enable a sufficiently-accurate computation of their orbits, so that any collision could be predicted well in advance;
- assure the coordination of national initiatives, data collection and dissemination, and the equitable distribution of observatories between northern and southern hemispheres;
- participate in designing small, low-cost satellites for observing NEOs which cannot be detected from the ground, and for investigations which can most effectively be conducted from space;
- contribute to a long-term global strategy for remedies against possible impacts.