Status: completed

contract N.: 12314
contractor(s):Spaceguard Foundation (I)

Study of a global network for research on Near-Earth Objects

Since its formation, the Earth - like all other bodies in the solar system - has been subject to continuing bombardment by cosmic debris ranging in size from a fraction of a millimetre to several tens of kilometres.
The frequency of these impacts depends primarily upon the size of the projectiles and their dynamical status, over time intervals spanning from minutes (objects smaller than 1 mm) to hundreds of million years (objects larger than 10 km).

The phenomena associated with impacts of large objects have been studied in detail in the last 10-20 years.
The results of these studies, although still preliminary, indicate that the probable consequences for the human society of these natural events are comparable to, and sometimes more serious than those produced by other major natural catastrophes, such as earthquakes, floodings, eruptions.

The existence of a possible problem has been recognized by individual scientists directly involved in re-searches dealing with impacts and their consequences (mainly astronomers and geo-paleontologists).
It has also been acknowledged by important international scientific organizations, such as the International Astronomical Union and the European Science Foundation, and by international political bodies, such as the United Nations and the Council of Europe.
All these organizations have taken steps towards a better understanding of the problem and possible measures that could be adopted in order to minimize the risk.

It is a widespread opinion among the experts in the field, that the first action to be taken in approaching this problem consists in monitoring continuously the sky in search for the objects which may encounter the Earth at a very small distance, now or in the next centuries, and in predicting their motion so that a possible collision can be identified decades in advance. These bodies are called Near-Earth Objects (NEO).
Early warning is an essential pre-requisite to plan
counter-measures in order to avoid an impact, whatever their technical nature.

Based on this strategy, the community of planetary astronomers has discussed at length a project, called the Spaceguard Survey, with the goal to discover all of the most dangerous objects within a couple of decades.
The implementation of an observational system able to reach this goal (the Spaceguard System) is currently under way.

It is understood, that such an international system will not be able to achieve the desired results unless it is strongly supported from both a financial and an organizational point of view.
Therefore, the IAU has set up, in 1996, an international organization called The Spaceguard Foundation, whose main purpose is to coordinate the observations worldwide, thus promoting the establishment of the Spaceguard System.

Thanks to the support of the Council of Europe and the European Space Agency, The Spaceguard Foundation has started its coordination activity by building a facility called the Spaceguard Central Node (SCN).
The SCN was developed within the ESA contract
"Study of a Global Network for Research on Near-Earth Objects".

The Study of a Global Network for Research on Near-Earth Objects was intended to design and implement the SCN as a facility to reach three goals:

  • To coordinate the observational activity, especially the number, type and timing of observations necessary to refine the preliminary orbits (follow-up observation);
  • To provide access to, and utilization of, the numerous databases and tools located in various places in the world, such as orbital and observational databases, image archives, software tools;
  • To provide tutorials for people willing to take part in the Spaceguard Survey, for journalists and media, and for the general public.

The SCN is one essential element of the Spaceguard System, to which it will provide assistance and coordination.

The Study began with an extended inquiry on the observational centres involved in NEO research, including an assessment of the instruments and detectors in use, of the weather and visibility conditions, of the planned observational activities and observing strategies and - more general - of all information that can be useful in planning coordinated efforts. The study concentrated mainly on the groups performing
follow-up activity - about half of which are of amateurial nature - because follow-up observations, contrary to discovery observations, require a high degree of efficient mutual coordination which currently does not exist.
Without a sufficient amount of follow-up observations, the newly discovered object will be lost.
Follow-up observations after the discovery are also important in order to lengthen the observed arc and, therefore, to improve the accuracy of the computed orbit.

A substantial fraction of the Study has been devoted to the identification of requirements for the SCN and to the definition of its structure.
The SCN takes advantage of modern network capabilities.
The Node is structured as a set of web pages containing all the services useful for observers, as well as ancillary documentation and information.
The Node does not duplicate facilities already active at other sites around the world.
An important result of the Study was to clarify the respective roles and competences of the various centres providing services to observers.
These include the IAU Minor Planet Center in Cambridge, USA (which collects astrometric measurements, performs object identifications, computes preliminary orbits and provides short-term ephemerides) and the NEODyS system at the University of Pisa, Italy (which performs dynamical analyses of all minor bodies including NEOs, providing support to the planning of observation strategies).

The entire Node is built around an "observatory database", where all information on the participating observatories is stored.
It is also connected to the MPC, to get information on newly discovered objects, and to NEODyS, to obtain dynamical details. This information is used to compile "priority lists" of objects, sorted in order of priority for follow-up observations.
Based on the observatory database, suitable observing stations are attached to each entry in the lists.
These sites are then invited to observe specific objects at specific times, a strategy that will allow to obtain the best results, in terms of orbit refinement, with the minimum of effort and duplication.

The core of the Node is the so-called "Situation Room", where the afore-mentioned lists are located together with the observatory database.
By connecting to that site any observer will know in real-time what are the best targets for his observatory and what are the plans of other observers.
Furthermore, suggestions on possible observing opportunities for each observatory will also be offered in the same place, which will allow a better medium-term planning of observations.

The Study has also included an inquiry on available software tools to acquire and process images, to identify moving objects, and to make first-hand dynamical analyses.
The Node contains a specific sector devoted to software tools, each accompanied by a short description and by links useful for getting more information.
In some cases the original codes are hosted at the Node and can be downloaded.

An important result of the Study is to underline the relevance of past image archives for NEO studies.
This was demonstrated by the case of asteroid 1997 XF11 for which a very close passage to Earth in 2028 was predicted based on a two-month observational arc.
A search in past archives provided "pre-discovery" observations in 1990 and the new orbit, computed on a 8-year arc, ruled out the possibility of a passage even inside the orbit of the Moon. It is evident that in cases of prediction of very close passages for objects whose preliminary orbits cannot provide sufficiently precise indications, it is of great importance to have the possibility to prolong substantially the arc in the past.
The Node will therefore provide a service by identifying the archives that contain images in which specific objects could be present.
To establish such a service is, however, a longer-term goal that requires an extended and thorough knowledge of the location and content of archives.

The work done so far, however, has not taken into account space-based observations, and this aspect of the network needs further study.
It can be anticipated that the best configuration of the Spaceguard System will in the end be based on three major segments:

i) the ground-based observation facilities,
ii) one or more space-based observation facilities,
iii) the collecting and coordinating centres. Each of these components has peculiar characteristics and addresses different aspects of the problem.

An essential character of this network is its distributed nature; not only the ground stations are located in different countries and need to be connected (and this is what the Node will do), but also the possible presence of one or more orbiting satellites would require the support and concurrence of several space agencies, both for building and launching the spacecraft and for their operation.
In addition, the coordination centres must operate on behalf of all observers, and the data that they collect and distribute must be freely available to everybody, without national limitations.
There will certainly be several centres, providing different services.
It is important that all of them are interconnected and their services are integrated.
The current information technology allows to establish such a complex, super-national facility which would permit a substantial reduction of costs, both in manpower and in hardware.
In such a scenario the role of the Spaceguard Central Node could be the communication centre for the observation stations. Furthermore, the SCN could provide information on the best observation strategies; it could also process ground- and
space-based observations.

In this Study a facility was designed and implemented, the Spaceguard Central Node.
This facility provides planetary astronomers with tools and information to maximise the efficiency of NEO observations, especially follow-up observations.

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