WASHINGTON, D.C. -- A Cornell University astronomer told a House of Representatives space subcommittee today that Washington should spend $125 million for a new type of ground-based telescope that could detect hundreds of asteroids and numerous comets that pose a potential threat to the Earth from space over the next century.
Reporting on a government-commissioned review of solar system exploration by some of the nation's leading scientists, he said that the new wide-field telescope is needed to produce a weekly digital map of the visible sky in order to track space rocks called near-Earth objects (NEOs), the great majority of which have yet to be discovered. There is, he said, a 1 percent probability of an impact with Earth by a 300-meter-diameter (350 yards) body in the next 100 years, resulting in many deaths and widespread devastation.
The astronomer, Joseph Burns, the Irving Porter Church Professor of Engineering and professor of astronomy at Cornell, in Ithaca, N.Y., is a member of the Solar System Exploration Decadal Survey's steering group. His comments to the House Science Committee panel came during his presentation of a small portion of the findings of the survey, which had been commissioned by the National Research Council (NRC) at the behest of NASA.
The impact of an object of this size, he said, would deliver a thousand megatons of energy and (assuming an average population density of 10 people per square kilometer) result in a million fatalities. The damage caused by an impact near a city or into coastal water would be "orders of magnitude higher." As of November 2001, he said, 340 objects larger than a kilometer had been cataloged as "potentially hazardous asteroids," and the number of new comets with impact potential "is large and unknown."
Burns quoted a section of the survey report (titled New Frontiers in the Solar System ): "Important scientific goals are associated with the NEO populations, including their origin, fragmentation and dynamical histories, and compositions and differentiation. These and other scientific issues are also vital to the mitigation of the impact hazard, as methods of deflection of objects potentially on course for an impact with Earth are explored. Information especially relevant to hazard mitigation includes knowledge of the internal structures of near-Earth asteroids and comets, their degree of fracture and the presence of large core pieces, the fractal dimensions of their structures, and their degree of cohesion or friction."
However, Burns said, a survey for potentially threatening NEOs "demands an exacting observational strategy," and to locate most of the objects with diameters as small as 300 meters requires a capability a hundred times better than that of existing survey telescopes. Because NEOs spend only a fraction of each orbit in Earth's neighborhood, "repeated observations over 10 years would be required to explore the full volume of space occupied by these objects." Such a survey, said Burns, would discover NEOs at the rate of about 100 per night and obtain astrometric information on the much larger, and growing, number of NEOs that it had already discovered. (Astrometry is the technique used to calculate the orbits of NEOs and assess the hazard that each poses to Earth.) "Astrometry at weekly intervals would ensure against losing track of these fast-moving objects in the months and years after discovery," said Burns.
To do this, he said, requires construction of an entirely new type of telescope, the large-aperture synoptic survey telescope (LSST) "to survey the entire sky relatively quickly, so that periodic maps can be constructed that will reveal not only the positions of target sources, but their time variability as well," the Cornell astronomer said. The LSST would be a 6.5-metre-class, very-wide-field (3 degrees) telescope that would produce a digital map of the visible sky every week, and carry out an optical survey of the sky far deeper than any previous survey.
Such a telescope, he said, "could locate 90 percent of all near-Earth objects down to 300 meters in size, enable computations of their orbits and permit assessment of their threat to Earth. It would discover and track objects in the Kuiper Belt, a largely unexplored, primordial component of our solar system."
A previous NRC astronomy and astrophysics survey also had recommended the building of an LSST. The new survey, however, recommends that NASA and NSF pay equally for the telescope's construction and operations, said Burns. The new survey, he said, projects the costs of the LSST at $83 million for capital construction and $42 million for data processing and distribution over five years of operation, for a total cost of $125 million. Routine operating costs, including a technical and support staff of 20 people, are estimated at approximately $3 million per year, he said.
The construction of the LSST, Burns told the legislators, "would provide a central, federal-sponsored location" for tracking the potentially threatening objects.