high cost of large new facilities; this encourages international collaboration as a means of cost-sharing. Thus, the Hubble Space Telescope was developed and is operated as a partnership of NASA and the European Space Agency (ESA), with access available to astronomers from all over the world. The Gemini project, building two 8-meter telescopes, one in Hawaii and one in Chile, is a partnership of the United States, the United Kingdom, Canada, Chile, Argentina, and Brazil.
Even without explicit or formal collaboration, international sharing of astronomical data generally enhances the field. Recent examples include the impact of Comet Shoemaker-Levy on Jupiter, the International Halley Watch, the observations of Comet Hyakutake, and the observations of Supernova 1987a. Still less organized research projects are enabled daily by accessing archived data for historical and multiwavelength comparisons and by facilitating communication among collaborating astronomers.
Astronomers and space scientists establish research strategies and priorities for data collection in their subdisciplines. In the United States, this is usually done within the National Research Council, for example, under the decadal Astronomy Survey Committees or the Space Studies Board's planetary and space physics science strategy panels, or by NASA or National Science Foundation (NSF) science working groups or ad hoc science community studies. Other nations and international organizations develop similar research strategies, for example, the ESA's Horizon 2000, plans for the European Southern Observatory, and the international Gemini project. Such planning efforts are becoming more international and effectively identify data needs and policies in support of the projects.
In the broadest terms, Earth science data are fundamental to the discovery and creation of knowledge concerning the interactions among matter, energy, and living organisms.7 Development of this knowledge is essential for ensuring the prospect for humanity on our finite planet in the face of rapid demographic and economic growth. Between 1820 and 1992, the world population increased 5 times and the gross domestic product per person grew 8 times, with a resulting global economy growth rate of 40 times. World trade grew more than 500 times. 8
The best estimate at this time is that the increase in population over the next 50 years will be greater in real numbers than the increase over the last 170 years, accompanied by further large increases in economic activity and world trade.9 This situation will bring to the fore new environmental issues and problems that will press us ever more urgently to ameliorate the impact of humankind on the environment.
Within the purview of the physical Earth sciences are natural phenomena at all spatial and temporal scales that present major scientific challenges for understanding and prediction. These phenomena include natural hazards such as hur-