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CCNet DIGEST, 1 July 1998
-------------------------

          Always look on the bright side of life,
          baram - baram - baram, baram, baram .....

          * and thank you for your sympathy.


(1) PLANETARY SOCIETY SEEKS TO AVERT ARMAGEDDON
    Planetary Society
  http://planetary.org/articlearchive/headlines/1998/headln-070198.html

(2) THE ORBITAL EVOLUTION OF ASTEROID 3753 AND ITS UNPREDICTABILITY
    P.A. Wiegert et al., YORK UNIVERSITY, CANADA

(3) ASTRONOMICAL IMAGE RESTRAINABLE COMBINATION METHOD
    Z.Y. Zheng et al., CHINESE ACADEMY OF SCIENCE

(4) THE HIPPARCOS SOLAR SYSTEM OBJECTS CATALOGUES
    D. Hestroffer et al., ASTRONOMICAL OBSERVATORY TORINO

(5) THERMAL OBSERVATIONS OF CENTAUR 1997 CU26
    D. Jewitt & P. Kalas, UNIVERSITY OF HAWAII

(6) WHAT'S IN A COMET?
    N. Bouziani & F.P. Fanale, UNIVERSITY OF HAWAII MANOA

(7) FEBRUARY LAUNCH PLANNED FOR MISSION TO COLLECT SAMPLES OF
    COMET DUST
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

===================
(1) PLANETARY SOCIETY SEEKS TO AVERT ARMAGEDDON

From the Planetary Society
http://planetary.org/articlearchive/headlines/1998/headln-070198.html

Society Helps Fund Astronomers Who Detect Comets and Asteroids

The Planetary Society seeks to avert a future "Armageddon" of an
asteroid obliterating civilization by funding astronomers engaged in
the search for near-earth objects. The Society is currently accepting
applications for the Gene Shoemaker Near-Earth Object Grants, a program
now in its second year.

"Increasing the number of observers is currently the most important
need in studying near-Earth objects," said Louis Friedman, Executive
Director of the Planetary Society. "At the current rate of discovery,
it would take decades to find a majority of even the large NEOs."

The purpose of the grant program is to increase the rate of discovery
and follow-up studies of asteroids and comets in the vicinity of 
Earth's orbit.

The Gene Shoemaker NEO Grants are awarded to amateur observers,
observers in developing countries, and professional astronomers who,
with seed funding, could greatly increase their programs' contributions
to this critical research. In 1997, more than $35,000 was awarded by
the Planetary Society.

A Swarm of Near-Earth Objects

Earth travels through a swarm of near-Earth objects of different sizes
and orbits. Scientists have only recently begun to understand the
significant contribution NEOs have made to the evolution of Earth --
and life on Earth -- as impacts from comets and asteroids have shaped
the evolution of all planets throughout the solar system.

Fewer than 300 NEOs have been discovered thus far. Scientists estimate
that there are a few thousand NEOs larger than one kilometer, and there
may be 150,000 to 100 million objects larger than 100 meters in size.

Popular awareness of the threat of NEO impacts has increased
dramatically in recent months with the report of a future close
approach to Earth by the asteroid 1997 XF11 in October 2028 and with
the summer movies Deep Impact and Armageddon.

"We spend far more on entertainment about dangerous near-Earth objects
than we spend on actually locating them," says Friedman. "A single
Hollywood disaster movie, such as Armageddon which cost over 100
million, has a budget more than 50 times larger than the annual funding
for all NEO searches worldwide."

NEOs have crashed into the Earth in the past with devastating results.
The Chicxulub crater off the coast of the Yucatan was excavated by a
meteor colliding with Earth 65 million years ago. That impact probably
led to the extinction of the dinosaurs. Even relatively small objects
can wreak widespread havoc.

The Gene Shoemaker NEO Grants

Gene Shoemaker, for whom the Society's grant program is named, was the
first scientist to demonstrate that the mile-wide crater in Arizona,
now known as Meteor Crater, was caused by a catastrophic impact of an
asteroid with Earth 50,000 years ago. Before his work, it was believed
to be the remnant of an extinct volcano.

Even though various astronomical groups and NASA advisory committees
have strongly recommended that discovery of these objects be
accelerated, government support for NEO searches and follow-up programs
is very modest.

Funds for the Gene Shoemaker NEO Grants program come from the Planetary
Society's 100,000 worldwide members, whose voluntary dues and donations
permit targeted support to research and development programs.

The Society's Gene Shoemaker NEO Grants program is coordinated by
Daniel D. Durda, an asteroid researcher at the University of Arizona's
Lunar and Planetary Laboratory. An international advisory group will
advise the Planetary Society grant awards. The advisory group includes
noted near-Earth object scientists Richard Binzel of the Massachusetts
Institute of Technology, Clark Chapman of the Southwest Research
Institute, Andrea Carusi of the Spaceguard Foundation, and Brian
Marsden of the Smithsonian Astrophysical Observatory.

Linking to Near-Earth Objects

For more information on the Society's Gene Shoemaker NEO Grants
program, send e-mail to Susan Lendroth at tps.sl@mars.planetary.org.

For more links and information on near-Earth objects, visit the
Planetary Society's NEO Page.

======================
(2) THE ORBITAL EVOLUTION OF ASTEROID 3753 AND ITS UNPREDICTABILITY

P.A. Wiegert*), K.A. Innanen, S. Mikkola: The orbital evolution of
near-Earth asteroid 3753. ASTRONOMICAL JOURNAL, 1998, Vol.115, No.6,
pp.2604-2613

*) YORK UNIVERSITY, DEPT PHYS & ASTRON, 4700 KEELE ST, N YORK,
   ON M3J 1P3, CANADA

Asteroid 3753 (1986 TO) is in a 1:1 mean motion resonance with Earth,
on a complex horseshoe-type orbit. Numerical experiments are performed
to determine its medium-term stability and the means by which it may
have entered its current orbit. Though 3753 moves primarily under the
influence of the Sun and Earth, the giant planets (and Jupiter
especially) play an important role by influencing, through
torque-induced precession, the position of the asteroid's nodes.
Variations in the nodal distance strongly affect the interaction of
3753 with Earth and may change or destroy the horseshoe-like behavior
currently seen. This precession of the nodes provides a mechanism for
placing minor planets into, or removing them from, a variety of
horseshoe-type orbits. The chaotic nature of this asteroid's orbit
makes predictions difficult on timescales longer than its Lyapunov time
(similar to 150 yr); therefore, ensembles of particles on orbits near
that of 3753 are considered. The asteroid has a high probability of
passing close to Venus and/or Mars on 10(4) yr timescales, pointing to
a dynamical age much shorter than that of the solar system. Copyright
1998, Institute for Scientific Information Inc.

======================
(3) ASTRONOMICAL IMAGE RESTRAINABLE COMBINATION METHOD

Z.Y. Zheng*), J. Zhu, J.S. Chen, H. Wu, Z.J. Jiang, S.J. Xue:
Astronomical image restrainable combination method and its
application. PROGRESS IN NATURAL SCIENCE, 1998, Vol.8, No.3, pp.316-320

*) CHINESE ACADEMY OF SCIENCE, BEIJING ASTRON OBSERV, BEIJING
   100080, CHINA

A new method of finding moving objects from charge-coupled device (CCD)
observation data has been presented based on the experiences oi
observation and data reduction, which is called the image restrainable
combination method (IRC method). Using the computation programs based
on this method, more than 4000 asteroids have been detected from the
observations of Beijing Astronomical Observatory (BAO) Schmidt CCD
Asteroid Program. Among them 770 asteroids obtained provisional
designations from the Minor Planet Center, while 3 asteroids were
permanently numbered. Copyright 1998, Institute for Scientific
Information Inc.

================
(4) THE HIPPARCOS SOLAR SYSTEM OBJECTS CATALOGUES

D. Hestroffer*), B. Morando, E. Hog, J. Kovalevsky, L. Lindegren,
F. Mignard: The Hipparcos solar system objects catalogues. ASTRONOMY
AND ASTROPHYSICS, 1998, Vol.334, No.1, pp.325-336

*) ASTRONOMICAL OBSERVATORY TORINO, STR OSSERVATORIO 20, I-10025 PINO
   TORINESE,ITALY

Astrometric and photometric measurements of a number of solar system
objects were performed by the Hipparcos satellite in both the Hipparcos
main mission and the Tycho experiment. The results concern mainly
asteroids but also the planetary satellites Europa, Ganymede, Callisto,
Titan and Iapetus, and the major planets Uranus and Neptune. The
specific aspects of the Tycho/Hipparcos observations and reduction
process implemented for the solar system objects are presented. Special
attention is paid to the error budget of the reduction which is
accurate to the mas (milliarcsecond) level for the Hipparcos main
mission. The contents of the Hipparcos and Tycho Solar System Objects
Catalogues are briefly described. Comparison between the results
derived from the two Consortia FAST and NDAC, as well as comparisons
with ground-based observations, are given. Copyright 1998, Institute
for Scientific Information Inc.

================
(5) THERMAL OBSERVATIONS OF CENTAUR 1997 CU26

D. Jewitt & P. Kalas: Thermal observations of Centaur 1997 CU26.
ASTROPHYSICAL JOURNAL, 1998, Vol.499, No.1 Pt2, pp.L103-L106

*) UNIVERSITY OF HAWAII, INST ASTRON, 2680 WOODLAWN DR, HONOLULU,
   HI, 96822

We combine new measurements of the thermal emission from the Centaur
1997 CU26 with published optical photometry to determine the geometric
albedo (0.045 +/- 0.010) and effective diameter (302 +/- 30 km). While
these values are model dependent, they clearly show that 1997 CU26 is
the largest of the known Centaurs and that its surface is very dark.
Copyright 1998, Institute for Scientific Information Inc.

=================
(6) WHAT'S IN A COMET?

N. Bouziani* & F.P. Fanale: Physical chemistry of a heterogeneous
medium: Transport processes in comet nuclei. ASTROPHYSICAL JOURNAL,
1998, Vol.499, No.1 Pt1, pp.463-474

*) UNIVERSITY OF HAWAII MANOA, SCH OCEAN & EARTH SCI & TECHNOL, HAWAII
INST GEOPHYS & PLANETOL,HONOLULU,HI,96822

We present a time-dependent transport model of a binary gas mixture
through a porous comet nucleus. We critically discuss the modeling of
this process in previous cometary models. We give the relationship
between the time t(c) required to reach steady state and the
permeability of the porous nucleus. It is shown that t(c) is very short
(about a few seconds to a very few hours) compared to the rotation time
(t(R) similar to a few hours to 1 day). We show qualitatively what the
effect of the structure of the nucleus on the H2O-to-CO ratio could be
for a comet approaching the Sun. We find that H2O/CO = f(P) (where P
represents the total pressure) passes through a maximum. We use this to
propose an indirect method to study the internal physical heterogeneity
of comet nuclei by using the H2O-to-CO ratio. It is shown that our
approach considerably improves the modeling of mass transport in porous
comet nuclei. Copyright 1998, Institute for Scientific Information Inc.

=====================
(7) FEBRUARY LAUNCH PLANNED FOR MISSION TO COLLECT SAMPLES OF
    COMET DUST

From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

FROM: Vince Stricherz
University of Washington
206-543-2580
vinces@u.washington.edu
DATE: June 29, 1998

February launch planned for UW mission to collect samples of comet dust

It might sound like something from a popular science fiction movie, but
a University of Washington astronomy professor's nearly two-decade
dream of launching an unmanned spacecraft to collect interstellar dust
from a comet is close to coming true.                      

Stardust will blast off from Cape Canaveral, Fla., in February. It will
be the fourth mission in NASA's Discovery series, which captured public
imagination a year ago with Mars Pathfinder. It will be the first
mission since Apollo to return samples of space material to Earth for
analysis.

UW professor Donald Brownlee, the principal investigator for the
project, expects to find clues about the formation of the solar system
and perhaps the universe itself.

"We hope to understand how comets were formed and what they're made
of," he said. "We expect them to be the preserved building blocks of
the outer planets."

Brownlee began considering such a mission in1980. The idea was explored
seriously five years later when Halley's comet approached Earth, but it
was deemed unworkable then.

For Stardust's 7-year, 3.1-billion-mile journey, solar panels will
power the spacecraft to encounter Wild 2, a comet that altered course
in 1974 after a close encounter with Jupiter. Now instead of circling
among the outer planets in our solar system, Wild 2 (pronounced vihlt
2) travels among the inner planets. It was discovered in 1978 during
its first close approach to Earth.

Wild 2's recent arrival to the planetary neighborhood makes the $200
million Stardust mission possible. In 2004, the craft will pass about
75 miles from the main body of the comet. That's close enough to trap
small particles from the comet's coma, the gas-and-dust envelope
surrounding the nucleus. A camera built for NASA's Voyager program will
transmit the first-ever close-up comet pictures back to Earth. Though
the encounter will last about 12 hours, Brownlee says the really
intense activity will be over in a matter of minutes.

The collection system will extend from the spacecraft and trap
particles as they collide with it. To prevent damaging or altering the
particles - each smaller than a grain of sand and traveling as much as
nine times the speed of a bullet fired from a rifle - the collector
uses a unique substance called aerogel. Often called "frozen smoke,"
aerogel is a transparent blue silica-based solid that is as much as
99.9 percent air. It is as smooth as glass, something like plastic foam
without the lumps. A block the size of a person weighs less than a
pound but can support the weight of a small car.

On the trip to Wild 2, the aerogel-equipped collection panel will be
deployed to trap interstellar particles traveling in space. During the
encounter with the comet, some 242 million miles from Earth, the
opposite side of the panel will gather bits of comet dust. Trapped
particles will leave a telltale trail through the aerogel that
scientists will follow to find the grains and extract them. Upon
leaving the comet, the collection panel will retract into its capsule.

Once the Stardust capsule parchutes into Utah's Great Salt Desert in
2006, the particles it collects will go to Johnson Space Center in
Houston and then be parceled out to various research facilities,
including the University of Washington. Because comets are about equal
parts ice and dust, Brownlee believes the particles will be
cryogenically preserved interstellar dust left from the birth of the
solar system some 4.6 billion years ago. Such grains can be found only
in the outer solar system, he believes, because heat has destroyed them
nearer the Sun.

Brownlee's previous work collecting cosmic dust particles led to their
being named Brownlee particles. Cosmic dust was brought back to Earth
on Gemini missions in the 1960s. Later, high-flying U2 planes and
balloons gathered particles from different levels in the atmosphere,
and space dust even has been collected from the ocean floor. "A comet
mission is the logical extension," Brownlee said.

The project is being carried out by a consortium that includes the Jet
Propulsion Laboratory and Lockheed Martin Astronautics. When it came to
picking a name, Brownlee said, it just seemed appropriate to select
"Stardust," the title Hoagy Carmichael put on a popular tune that since
has been recorded by numerous artists, including Willie Nelson and
Ringo Starr.

"I liked it because most spacecraft missions had weird, bizarre names.
They were acronyms for something," he said. "This isn't an acronym for
anything. It's just a name that people know."

For more information, contact Brownlee at
brownlee@bluemoon.astro.washington.edu or (206) 543-8575.

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