PLEASE NOTE:
*
CCNet DIGEST, 17 March 1999
---------------------------
QUOTE OF THE DAY
"Analysis of data from NASA's Lunar
Prospector spacecraft has confirmed
that the Moon has a small core,
supporting the theory that the bulk of
the Moon was ripped away from the early
Earth when an object the size
of Mars collided with the Earth"
(NASA, 16 March 1999).
(1) NEW PAPER ON THE CAUSE OF THE UNEXPECTED LEONID OUTBURST IN
1998
D.J. Asher*), M.E. Bailey, V.V. Emel'yanenko,
Armagh Observatory
(2) WHEN WORLDS COLLIDE: LUNAR DATA SUPPORT IDEA THAT COLLISION
SPLIT
EARTH, MOON
NASA News <NASANews@hq.nasa.gov>
(3) STAR WARS BACK ON TRACK: SENATE SET TO OK MISSILE DEFENSE
PLAN
MSNBC Online News
(4) BEST SITE FOR MOONBASE REVEALED
BBC News Online
========================
(1) NEW PAPER ON THE CAUSE OF THE UNEXPECTED LEONID OUTBURST IN
1998
D.J. Asher*), M.E. Bailey, V.V. Emel'yanenko: Resonant meteoroids
from
Comet Tempel-Tuttle in 1333: the cause of the unexpected
Leonid
outburst in 1998. Monthly Notices of the Royal Astronomical
Society,
1 March 1999
*) Armagh Observatory, College Hill, Armagh, BT61 9DG, U.K
dja@star.arm.ac.uk
Recent observations of an unexpectedly high incidence of bright
Leonid
meteors about 16 hours before the predicted maximum of the main
shower
are explained by the ejection of dust grains into the 5/14
mean-motion
resonance with Jupiter, principally during the perihelion passage
of
Comet 55P/Tempel-Tuttle in 1333. The dynamical evolution of
resonant
grains has the following properties: first, they do not spread
uniformly around the orbit, but instead librate about a resonance
centre within the main stream; secondly, these resonant zones
contain a
much higher space density of particles than the background
stream, with
the particle density approaching that of recently ejected
cometary
grains; and thirdly, differential precession between the cometary
orbit
and the orbits of resonant particles may lead to meteor storms at
unexpected times, possibly far removed from that of the normal
shower.
The presence of resonant dust grains leads to a complex structure
within the Leonid meteoroid stream, and is an important general
feature
of meteoroid streams associated with Halley-type comets,
themselves
often trapped for long periods in mean-motion resonances.
Copyright 1999, Mon. Not. R. Astron. Soc
======================
(2) WHEN WORLDS COLLIDE: LUNAR DATA SUPPORT IDEA THAT COLLISION
SPLIT
EARTH, MOON
From NASA News <NASANews@hq.nasa.gov>
Douglas Isbell
Headquarters, Washington,
DC
March 16, 1999
(Phone: 202/358-1547)
David Morse
Ames Research Center, Moffett Field, CA
(Phone: 650/604-4724)
RELEASE: 99-43
LUNAR DATA SUPPORT IDEA THAT COLLISION SPLIT EARTH, MOON
Analysis of data from NASA's Lunar Prospector spacecraft has
confirmed
that the Moon has a small core, supporting the theory that the
bulk of
the Moon was ripped away from the early Earth when an object the
size
of Mars collided with the Earth.
Scientists presented this result and other findings today in a
series
of papers at the 30th Lunar and Planetary Science Conference in
Houston, TX. Their data show that the lunar core contains
less than
four percent of the Moon's total mass, with the probable value
being
two percent or slightly less. This is very small when
compared with
the Earth, whose iron core contains approximately 30 percent of
the
planet's mass.
"This is a critical finding in helping scientists determine
how the
Earth and Moon formed," said Dr. Alan Binder of the Lunar
Research
Institute, Tucson, AZ, principal investigator for Lunar
Prospector.
Similarities in the mineral composition of the Earth and the Moon
indicate that they share a common origin. However, if they had
simply
formed form the same cloud of rocks and dust, the Moon would have
a
core similar in proportion to the Earth's. A third theory
suggests that
the moon was captured fully intact by the Earth's gravity.
Based on information first gathered during the Apollo era,
scientists
suggested that the Moon was formed when a Mars-sized body hit the
Earth
during its earliest history. "This impact occurred after the
Earth's
iron core had formed, ejecting rocky, iron-poor material from the
outer
shell into orbit," Binder explained. "It was this
material that
collected to form the Moon.
"Further analysis of Lunar Prospector data to refine the
exact size of
the lunar core and the amounts of elements like gold, platinum
and
iridium in lunar rocks -- all of which are concentrated with
metallic
iron -- is required," Binder added. "This will do much
to pin down for
good if the 'giant impact' model of the formation of the Moon is
correct, or if the Moon formed in a different manner."
The current data come from gravity measurements conducted by Dr.
Alex
Konopliv of NASA's Jet Propulsion Laboratory, Pasadena, CA.
His
results indicate that the Moon's core radius is between 140 and
280
miles (220 and 450 kilometers). This result is consistent
with
independent magnetic data, evaluated by Dr. Lon Hood of the
University
of Arizona, Tucson, which suggest that the core radius is between
180
and 260 miles (300 and 425 km).
In other results from Lunar Prospector, Dr. Robert Lin of the
University of California at Berkeley, Dr. Mario Acuna of NASA's
Goddard
Space Flight Center, Greenbelt, MD, and Hood also found that a
broad
section of the southern far-side of the Moon has large localized
magnetic fields in its crust. These fields occur opposite
the large
Crisium, Serenitatis and Imbrium basins -- three of the
"seas" that
cover much of the Moon's near side. This result supports earlier
evidence linking strong magnetized concentrations on one side of
the
Moon with young, large impact basins on the other side.
Results of efforts to map the composition of the lunar crust have
surpassed the expectations of the spectrometer team, led by Dr.
William
Feldman of the Department of Energy's Los Alamos National
Laboratory in
New Mexico. Data obtained are so good that the distribution
of thorium
has been mapped with a resolution of 36 miles (60
kilometers). At this
amount of detail, scientists can detect individual deposits rich
in
thorium and related elements. Their current observations
suggest that
thorium was excavated by impacts of asteroids and comets, and
then
distributed around craters, rather than being deposited by
volcanic
activity.
Lunar Prospector conducted its primary mapping mission at an
altitude
of 63 miles (100 kilometers) for almost one year after its
arrival in
lunar orbit on Jan. 11, 1998. In December and January, the
spacecraft's
altitude was lowered to approximately 15 miles by 23 miles (24
kilometers by 37 kilometers). Analyses of data from the
lower-altitude
observations are expected to further improve scientific
understanding of
the origin, evolution and physical resources of the Moon.
The $63 million mission is managed by NASA's Ames Research
Center,
Moffett Field, CA, and was developed under NASA's Discovery
Program of
lower-cost, highly focused small scientific spacecraft.
Further information about Lunar Prospector, its science data
return,
and relevant charts and graphics can be found on the project
website
at:
http://lunar.arc.nasa.gov
=================
(3) STAR WARS BACK ON TRACK: SENATE SET TO OK MISSILE DEFENSE
PLAN
GOP proposal gains favor after revelations of Chinese spying
From MSNBC Online News
http://www.msnbc.com/news/250653.asp
SENATE SET TO OK MISSILE DEFENSE PLAN: GOP proposal gains favor
after
revelations of Chinese spying
ASSOCIATED PRESS
WASHINGTON, March 16. The Clinton administration and Senate
Democrats
on Tuesday agreed to a popular missile-defense bill, reviving the
prospect of former President Ronald Reagan’s "Star
Wars" plan of the
1980s. Support for the Republican proposal, which until Tuesday
the
White House had threatened to veto, comes following congressional
anger
over the alleged theft of U.S. nuclear secrets by China.
THE 99-0 APPROVAL of the plan by Sens. Mary Landrieu, D-La., and
Olympia Snowe, R-Maine, all but assured Senate passage of a
measure
that declares as U.S. policy deployment of a ballistic-missile
defense
as soon as “technologically possible.” A final vote was
expected
Wednesday.
VETO THREATENED
Democrats had blocked the measure from coming to the floor for
years,
and until Tuesday the Clinton administration had threatened a
veto.
But the legislation was gaining considerable bipartisan support
in the
aftermath of ballistic missile tests by North Korea and Iran, and
the
disclosure that China had obtained technology from a U.S. nuclear
laboratory that could have enabled it to build smaller, more
efficient
nuclear warheads.
“This bill recognizes the threat is real,” Landrieu
told the Senate.
“It is clear to many of us that this threat is more real
than ever
before.”
Tom Collina of the Union of Concerned Scientists, which opposes
the
legislation, called the compromise “sort of vacuous policy”
that he
said will do little except alienate China and Russia.
“The Democrats are running scared on this,” he said.
“The Republicans
have had this issue for years. Now the threat has appeared and
the
Democrats were caught flat-footed.”
The Landrieu-Snowe amendment commits the United States to a
missile-defense system while recognizing the importance to
negotiate
with Moscow on reducing nuclear arsenals.
It was endorsed by both Sens. Thad Cochran, R-Miss., the chief
sponsor
of the overall legislation, and Sen. Carl Levin, D-Mich., who had
been
its chief opponent. “It strengthens the bill,” Cochran
said. “Defenses
and offensive reductions are not incompatible.
FULL STORY at
http://www.msnbc.com/news/250653.asp
Copyright 1999, MSNBC
==================
(4) BEST SITE FOR MOONBASE REVEALED
From the BBC News Online
http://news.bbc.co.uk/hi/english/sci/tech/newsid_297000/297783.stm
By BBC News Online Science Editor Dr David Whitehouse
The most detailed analysis ever of the Moon's mysterious polar
regions
has pinpointed the place best suited for a future human base.
The site is on the rim of a crater called Shackleton and meets
two
essential requirements. There is plenty of sunlight around to
generate
solar energy and it is very close to a permanently-shaded region,
where
ice is likely to be stored in deep freeze.
Ice would not only satisfy the thirst of settlers but could be
used to
generate fuel for spacecraft.
FULL STORY at
http://news.bbc.co.uk/hi/english/sci/tech/newsid_297000/297783.stm
Copyright 1999, BBC
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