Dear Friends & Students of NEOs:

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).

As many of you know, 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: 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)


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