A new survey telescope is being proposed that could extend the Spaceguard Survey of NEOs down to objects 300 m in diameter. It would operate roughly ten times faster, and reach roughly ten times fainter, than current NEO searches. However, NEO searches are only one of several justifications for this telescope, called the Large-aperture Synoptic Survey Telescope (LSST). The United States astronomical community, working through the National Research Council of the National Academy of Sciences, provides each decade a prioritized list of desirable new projects to NASA and the NSF. The recommendations of these Astronomy and Astrophysics Survey Committees (as they are called) have established the roadmap for development of astronomical facilities in the United States, both in orbit and on the ground. All of the well-known big observatories, from the Hubble Space Telescope and Chandra X- ray Observatory to the 8-m-class optical-infrared telescopes and the VLA and VLBA for radio astronomy, were among the high-priority recommendations from past Survey Committees. It is therefore with considerable interest that we find a recommendation in the just-published report of the most recent Survey Committee for a telescope to search for NEOs. The goal of cataloging 90 percent NEOs larger than 300 m within one decade is one of the primary objectives of the proposed Large-aperture Synoptic Survey Telescope (LSST). Following are excerpts from the report "Astronomy and Astrophysics in the New Millennium" just published by the National Research Council. I note that the UK's recommended program for dealing with the impact threat also includes extending the current NEO surveys from 1 km down to 300 m. The UK has proposed construction of a 3-m telescope to begin such a search. However, reaching reasonable completeness to 300 m in a timely manner will probably require an international consortium of several such 3 m telescopes. The proposers of the LSST apparently have concluded that a single telescope of greater than 6 m aperture can carry out the NEO survey to 90 percent completeness within a decade, as well as meeting its other astrophysics goals. I have not yet seen a detailed plan for how either the proposed UK 3-m telescope or the proposed US 6-m telescope would be used to accomplish the NEO survey goals. David Morrison
Large-aperture Synoptic Survey Telescope: Selected quotes from the NRC Astronomy & Astrophysics Survey Committee (2001) The Large-aperture Synoptic Survey Telescope (LSST) is a 6.5-meter-class optical telescope designed to survey the visible sky every week down to a much fainter level than that reached by existing surveys. It will catalog 90 percent of the Near-Earth Objects larger than 300 meters and assess the threat they pose to life on Earth. It will find some 10,000 primitive objects in the Kuiper Belt, which contains a fossil record of the formation of the solar system. It will also contribute to the study of the structure of the universe by observing thousands of supernovae, both nearby and at large redshift, and by measuring the distribution of dark matter through gravitational lensing. All the data will be available through the [proposed] National Virtual Observatory, providing access for astronomers and the public to very deep images of the changing night sky. [The estimated cost] of the LSST is $170 million. (p 10-11) By surveying the visible sky every week to a much fainter level than can be achieved with existing optical surveys, LSST will open a new frontier in addressing time-variable phenomena in astronomy. This 6.5-m-class optical telescope will detect 90 percent of the Near-Earth Objects larger than 300 meters within a decade, and will enable assessment of the potential hazard each poses to Earth. . . (p 38-39) The Near-Earth Objects (NEOs) are asteroids with orbits that bring them close to the Earth. The orbits of many NEOs actually cross that of the Earth, making NEOs an impact threat to our planet. Extrapolations from existing data suggest that about 1000 NEOs are larger than 1 km in diameter, and that between 100,000 and 1 million are larger than 100 m. . . . it is estimated that the probability of an NEO larger than 300 m will strike the Earth during this century is [only] about 1 percent. Nonetheless, it behooves us to learn much more about these objects. Over a decade, the LSST will discover 90 percent of the NEOs larger than 300 m, providing information about the origin of these objects in the process. . . (p 58-61) With its huge array of detectors, LSST will collect more than a trillion bits of data per day, and the rapid data reduction, classification, archiving, and distribution of these data will require considerable effort. The resulting database and data-mining tools will likely form the largest non- proprietary data set in the world and could provide a cornerstone for the National Virtual Observatory. (p 108) Study of the history of collisions of asteroids and comets with Earth provide the framework for understanding cataclysmic climate changes over geological time scales. While far rarer now than during the first billion years of the solar system's history, collisions of comets and asteroids with planets still take place. On Earth, such collisions can produce dramatic environmental events, from giant tidal waves to Earth-girdling dust clouds that can alter climate for centuries and in some cases lead to mass extinctions of species. Astronomers now have the tools to detect comets and Earth-crossing asteroids of size sufficient to threaten human civilization and to assess the threat of such a collision. (p 154) |
