PLEASE NOTE:
*
CCNet DIGEST, 2 February 1999
------------------------------
QUOTE OF THE DAY
(from Larry Klaes <lklaes@BBN.COM>)
Doubt thou the stars are fire;
Doubt that the sun doth move;
Doubt truth to be a liar;
But never doubt I love.
William Shakespeare, Hamlet II.ii
(1) THE CCNet SURVEY: A REMINDER
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(2) ATEN-TYPE ASTEROID 1991 VE AND MERCURY
Piero Sicoli and Manca Franscesco <sormano@tin.it>
(3) WHERE'S ZE MONEY?
Michael Paine <mpaine@tpgi.com.au>
(4) DECIPHERING PHOLUS
Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
(5) NEAR - THE CONNECTION WITH METEORITES
Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
wrote:
(6) TIDAL DISRUPTION OF STRENGTHLESS RUBBLE PILES
J.M. Hahn*) & T.W. Rettig, LUNAR &
PLANETARY INST
(7) MODELLING THE EVOLUTION OF THE SPACE DEBRIS POPULATION
A. Rossi et al., CNR, PISA,ITALY
(8) THE EFFECTS OF METEOROID STREAM ENHANCED ACIVITY ON HUMAN
SPACE
FLIGHT
G. Cevolani*) & L. Foschini,
CNR,BOLOGNA,ITALY
(9) STARDUST SCHEDULED FOR LAUNCH TO RENDEZVOUS WITH COMET
Andrew Yee <ayee@nova.astro.utoronto.ca>
(10) ICE CORES REVEAL LONG-RANGE GREENLAND CLIMATE VARIABILITY
Geophysical Research Letters <jupiter@agu.org>
=====================
(1) THE CCNet SURVEY: A REMINDER
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
A big thank you to all of those 155 list members who have
returned
completed questionnaires, some of which with extensive comments
and suggestions. I intend to post the results of the survey
together with a wide selection of comments early next week.
I won't spill the beans, but I can tell list members already that
there
will be some changes to the CCNet format (not to its features)
which
should satisfy the wishes and requests of the vast majority of
subscribers. In particular, it is planned that subscribers will
be able
to choose between various options in order to deselect those
services
they no longer wish to receive.
For subcribers who still intend to return completed
questionnaires or
who failed to notice it last Friday, I will post the form once
again
today (please ignore the questionnaire if you have already
completed
it).
Benny J Peiser
=================
(2) ATEN-TYPE ASTEROID 1991 VE AND MERCURY
From Piero Sicoli and Manca Franscesco <sormano@tin.it>
A numerical integration of the orbit of asteroid 1991 VE has
shown that
it has repeated close approaches to Mercury, and therefore has
stirred
our interest about this object. During the recent favourable
opposition
(January 1999) the asteroid was included in the observing
schedules of
several observatories (including our own); a new computation,
based on
the improved orbit, confirms that 1991 VE has at least 9
encounters to
Mercury (within 0.021 AU) during the next 200 years. Next
approach
(0.006 AU) will happen on October 23, 2006, but a closer one
seems to
have occurred at the beginning of this century (0.004 AU, on
April 7,
1909).
Our list of close encounters between asteroids and planets
(recently
updated) is available at:
http://www.brera.mi.astro.it/sormano/pcel.html
Piero Sicoli and Francesco Manca
Sormano Astronomical Observatory
E-Mail: Sormano@tin.it
WWW : http://www.brera.mi.astro.it/sormano/
===================
(3) WHERE'S ZE MONEY?
From Michael Paine <mpaine@tpgi..com.au>
Dear Benny,
[You will probably get swamped with email about this!] NASA has
posted
a summary of its FY2000 budget on the internet
http://www.nasa.gov/budget/budget_index.html
I couldn't find a mention of the funding for NEO research
anywhere in
the $13.5 Billion of expenditure!
Michael Paine
========================
(4) DECIPHERING PHOLUS
From Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
From Sky & Telescope, March 1999, p. 29):
A team led by Dale P. Cruikshank (NASA/Ames Research Center)
believes
the large, distant "asteroid" 5145 Pholus fits the
composition of "a
giant comet nucleus that is not, and may never have been, active.
" In
the October 1998 issue of lcarus, Cruikshank's group shows that
Pholus
is a close spectral match to an object covered in most places by
amorphous carbon and elsewhere by a mixture of tiny silicate
grains,
water ice, frozen methanol (CH3OH), and complex organic matter.
The
silicate mineral forsterite (Mg2SiO4) was the key to a good fit;
this
form of olivine is commonly observed in the dust clouds around
other
stars. Traveling in a highly elongated orbit with a mean
heliocentric
distance of 20.2 astronomical units (3.02 billion kilometers),
Pholus
is a 190 km-wide member of the Centaurs objects considered
escapees
from the distant Kuiper Belt. It was discovered in 1992 and
shortly
thereafter found to be one of the solar system's reddest objects
(S&T:
January 1993, page 15).
Copyright 1999, Sky & Telescope
=========================
(5) NEAR - THE CONNECTION WITH METEORITES
From Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
wrote:
From Astronomy, February 1999, p. 59:
Scientists hope NEAR’s close look at Mathilde and Eros will
solve one
of the biggest mysteries of asteroid and meteorite study: To what
asteroid class do meteorites belong? Scientists think that nearly
all
meteorites were once parts of asteroids, and collisions broke off
pieces and changed their orbits to ones intercepting Earth.
Although
the S and C classifications make up almost 75 percent of all
known
asteroids, the spectrum of neither type corresponds very closely
to
most meteorites found on Earth. ln fact, only a handful of
asteroids
fit precisely the spectral class of 90 percent of all known
meteorites.
Even more puzzling, the closer you get to Earth, the worse the
match. C
asteroids, orbiting from the middle of the asteroid belt outward,
match
only poorly. S asteroids, orbiting from the middle of the
asteroid belt
inward, match not at all. While almost all near-Earth asteroids
belong
to the S class, only 10 percent of meteorites found on Earth
resemble
these asteroids even vaguely. In many ways the study of asteroids
today
is comparable to the study of the major planets in 1968. Before
the
first orbital missions to Mars and Venus, most of our knowledge
of the
planets was based on their telescopic appearance and spectra. Our
only
good views had been limited to a few quick flybys, mere glimpses
by a
handful of spacecraft. Overall we knew little and understood
less.
Similarly, other than the tantalizing glimpses provided by the
NEAR and
Galileo spacecraft, we have not yet seen an asteroid in detail.
Astronomers have approximated the make-up and shape of these
mysterious
objects, but without actually looking at them close up, we can't
really
know what they are. This should all change in 1999, as NEAR slips
into
orbit around Eros and begins to pick at its mysteries. (Robert
Zimmermann)
Copyright 1999, Astronomy Magazine
=========================
(6) TIDAL DISRUPTION OF STRENGTHLESS RUBBLE PILES
J.M. Hahn*) & T.W. Rettig: Tidal disruption of strengthless
rubble
piles - a dimensional analysis. PLANETARY AND SPACE SCIENCE,
1998,
Vol.46, No.11-12, pp.1677-1682
*) LUNAR & PLANETARY INST,3600 BAY AREA BLVD,HOUSTON,TX,77058
A relatively simple prescription for estimating the number of
debris
clumps n that form after a catastrophic tidal disruption event is
presented. Following the breakup event, it is assumed that the
individual debris particles follow keplerian orbits about the
planet
until the debris' gravitational contraction timescale t(c)
becomes
shorter than its orbital spreading timescale t(s). When the two
timescales become comparable, self-gravity breaks up the debris
train into n similar to L/D clumps, which is the debris
length/diameter
ratio at that instant. The clumps subsequently orbit the planet
independent of each other. The predicted number of clumps n is in
good
agreement with more sophisticated N-body treatments of tidal
breakup
for parabolic encounters, and the dependence of n upon the
progenitor's
density as well as its orbit is also mapped out for hyperbolic
encounters. These findings may be used to further constrain both
the
orbits and densities of the tidally disrupted bodies that struck
Callisto and Ganymede. A cursory analysis shows that the Gomul
and
Gipul crater chains on Callisto, which have the greatest number
of
craters among the known chains, were formed by projectiles having
comet-like densities estimated at rho(0) less than or similar to
1
gm/cm(3). (C) 1998 Elsevier Science Ltd. All rights reserved.
====================
(7) MODELLING THE EVOLUTION OF THE SPACE DEBRIS POPULATION
A. Rossi*), L. Anselmo, A. Cordelli, P. Farinella, C. Pardini:
Modelling
the evolution of the space debris population. PLANETARY AND SPACE
SCIENCE, 1998, Vol.46, No.11-12, pp.1583-1596
*) CNR,CNUCE,I-56126 PISA,ITALY
The current space activities are already disturbed and
jeopardized by
the growing number of orbiting debris. Those planned for the near
future, such as the launch of large satellite constellations and
the
construction of the international space station, are even more
sensitive to the evolution of the space environment. Therefore, a
clear
picture of the present situation in Earth orbit and its future
evolution is needed. In this paper we describe in some details
the work we have carried out on this problem in the last several
years.
Starting from the current population and simulating a reasonable
scenario for the space activities in the next decades, we have
obtained
plausible quantitative models of the possible future space
environment.
We summarize some results concerning the effectiveness of
possible
mitigation measures and assess the robustness of these results,
by
checking how sensitively they depend upon the initial conditions
and
the choice of some model parameters. We also analyze the effect
of the
launch of a number of satellite constellations, showing the
importance
of the adoption of some debris prevention measures in their
launch
policies. Finally, we study the possible problems arising from
the
recent discovery of a new family of debris composed by drops of
NaK
coolant, that leaked outside the nuclear reactors of the Soviet
RORSAT-class satellites. Our preliminary results indicate that
these
drops are going to cause an increasing number of small-scale,
possible
satellite-damaging impacts but, due to their small size, no
additional
catastrophic collisions; therefore their influence on the
long-term
evolution of the overall debris population is limited. (C) 1998
Elsevier Science Ltd. All rights reserved.
================
(8) THE EFFECTS OF METEOROID STREAM ENHANCED ACIVITY ON HUMAN
SPACE FLIGHT
G. Cevolani*) & L. Foschini: The effects of meteoroid stream
enhanced
activity on human space flight: an overview. PLANETARY AND SPACE
SCIENCE, 1998, Vol.46, No.11-12, pp.1597-1604
*) CNR,IST FISBAT,VIA GOBETTI 101,I-40129 BOLOGNA,ITALY
The origin, dispersion mechanisms and evolution of particle
streams
producing enhanced activity (outburst or storm) of meteoroids are
discussed in relation to their effects on artificial satellites
and
space platforms. A review of the active meteoroids suggests that
at
least five streams may undergo outburst or storm activity in the
next
few years. Modern radio techniques not affected by illumination
conditions and cloud coverage, improve significantly the
detectability
of meteor streams. The impact probabilities of storm meteoroids
on
space platforms in Earth orbit can increase by factors in excess
of
10(2)-10(4) over the sporadic background. (C) 1998 Elsevier
Science
Ltd. All rights reserved.
======================
(9) STARDUST SCHEDULED FOR LAUNCH TO RENDEZVOUS WITH COMET
From Andrew Yee <ayee@nova.astro.utoronto.ca>
University of Washington
FROM: Vince Stricherz
206-543-2580
vinces@u.washington.edu
FOR IMMEDIATE RELEASE: Feb. 1, 1999
UW astronomy professor's Stardust quest set for launch Saturday
It's a moment University of Washington astronomy professor Donald
Brownlee has been awaiting for nearly two decades. If all goes as
planned, that moment will arrive Saturday afternoon when a Boeing
Delta
II rocket, with "University of Washington" emblazoned
on the side,
sends a desk-sized spacecraft on a seven-year journey to
rendezvous
with a comet.
Stardust is scheduled to launch from Cape Canaveral, Fla., at
1:07 p.m.
PST, and UWTV will provide live coverage. The mission, selected
in 1995
by NASA as part of its Discovery series, aims to capture
particles from
comet Wild 2 (pronounced Vilt 2) and return them to Earth for
analysis
in laboratories at the UW, NASA and around the world. There's
much to
be learned, Brownlee said.
"People have long suspected that comets played a role in the
origin of
life. No one really knows this because no one knows how life
began. But
we do know that comets are the most carbon-rich materials in the
solar
system, and we know they're full of organic compounds and they
fall on
the Earth all the time. Even now we have tens of thousands of
tons of
comet particles landing on the Earth every year," he said.
Even though microscopic comet particles blanket open spaces such
as
parks and football stadiums every year, those particles don't
tell the
same story as ones collected from a comet such as Wild 2,
Brownlee
said. That's because Wild 2 only recently started orbiting close
enough
to the sun to make the mission feasible, so there hasn't been
time
enough for the sun's heat to destroy the characteristics of
particles
that have been preserved in a cryogenic deep freeze of space for
billions of year.
In 1980, Brownlee and NASA first considered a mission to capture
comet
particles. In that case, the target would have been Halley's
comet, but
the idea proved unworkable. Various technological advances and a
bit of
celestial luck changed that. Before 1974, Wild 2 traveled outside
the orbit
of Jupiter. But a close encounter with Jupiter that year altered
the
comet's trajectory, bringing it close enough to make Stardust
possible.
The spacecraft's encounter with the comet in early 2004 will take
place
just outside the orbit of Mars, 242 million miles from Earth on
the
other side of the sun.
The mission is the first since Apollo 17 in 1972 to return
extraterrestrial samples to Earth, and it is the first to bring
back
samples from beyond the orbit of the moon. Scientists will study
the
returned comet particles in the hope of understanding how life
evolved
on Earth. The planet probably was formed without water and
without
carbon or nitrogen, the building blocks of life. "The
building blocks
of life have long been thought to have come from further out in
the
solar system, out further away from the sun, and these would be
materials from asteroids and comets," Brownlee said.
Stardust will have journeyed 3.1 billion miles before it
parachutes
into the Utah desert in early 2006. During its encounter with
Wild 2, a
tennis-racquet shaped collector, sheathed with a wispy substance
called
aerogel, will be extended to collect comet grains when the
spacecraft
is within 100 miles of the comet's icy core. A high-power antenna
will
transmit close-up pictures, and sensitive equipment will gather
data
about the comet.
The mission is a collaboration of the UW, NASA, NASA's Jet
Propulsion
Laboratory at the California Institute of Technology in Pasadena,
Calif., and Lockheed Martin Astronautics in Denver. Other key
members
of the team are The Boeing Co., Germany's Max-Planck-Institut
fuer
extraterrestrische Physik, the NASA Ames Research Center and the
University of Chicago.
Brownlee expects information gathered by Stardust to shed light
on how
the solar system and the universe evolved. The mission also could
have
implications on astrobiology, the search for life beyond Earth.
The UW
this fall will begin the first doctoral program in astrobiology
to
train people to look for life on other celestial bodies, such as
Mars
and Europa, a moon of Jupiter.
"From the astrobiology standpoint, we're interested in what
kind of
organic materials actually exist and how much there is and
whether this
played a role (in the formation of life)," Brownlee said.
"Now this may
be an impossible problem. We can study astrobiology and we can
investigate how life might have formed, but no one was there
taking
notes when life formed.
"You have things ... before there was life and things after
there was
life but the real records aren't there," he said. "But
by insight on
this, you can at least look at what the starting materials were.
So
that's what Stardust is going to do, look at the starting
materials,
what was around in the solar system before life existed on
Earth."
The name "Stardust" seemed appropriate because of the
nature of the
project and the fact that people can relate to that name,
Brownlee
said. A recent radio interview ended with a few bars of the song
"Woodstock" by Joni Mitchell, which includes the
lyrics: "We are
stardust, we are golden, we are billion-year-old carbon."
That's an
appropriate thought, Brownlee said.
"Comets are a vehicle that brings organic materials to the
Earth. Many
of the carbon atoms in our bodies were in comets early in the
history
of the solar system. So one of the bylines of the Stardust
mission is
that we are stardust. Our bodies are actually made of
stardust."
Science aside, there's a hint of romanticism about this mission.
That's
why, come Saturday, it won't be "Woodstock" but instead
the soft
strains of Hoagy Carmichael's "Stardust" drifting
through the launch
area.
###
Additional information is available at http://stardust.jpl.nasa.gov
or
at http://www.washington.edu/newsroom/stardust/stardust.html
================
(10) ICE CORES REVEAL LONG-RANGE GREENLAND CLIMATE VARIABILITY
From Geophysical Research Letters <jupiter@agu.org>
Ice cores from the Greenland Ice Sheet date as far back to 110
kyr b.p.
and are useful for examining fluctuations in chemical and
physical
characteristics on various time scales. Kahl et. al.
["Decadal-scale
variability in long-range atmospheric transport to the summit of
the
Greenland Ice Sheet"] find an association between long-range
atmospheric transport to the Greenland Ice Sheet and large-scale
climate variability on the annual to decadal time scales. This
demonstrates that climate variations far upstream of Greenland
can
influence the contributions of material from specific remote
areas to
the ice sheet. Using a 44-year set of 10-day modeled air
trajectories
arriving daily at Summit, Greenland, the authors show that many
trajectories with long residence times at the 500 hPa and 700 hPa
levels correlate significantly with the Pacific/North American
pattern,
the Southern Oscillation and the North Atlantic Oscillation.
----------------------------------------
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