PLEASE NOTE:
*
CCNet DIGEST, 14 October 1998
-----------------------------
(1) BNSC STATEMENT SERIOUSLY UNDERESTIMATES IMPACT HAZARD
Michael Paine <mpaine@tpgi.com.au>
(2) A NEW THEORY OF GRAVITY?
Bill Napier <wmn@star.arm.ac.uk>
(3) CLOSE TO RENDEZVOUS: SATELLITE NEARING ASTEROID ORBIT
ABCNews Online
http://www.abcnews.com/sections/science/DailyNews/asteroid981012.html
(4) CONTROVERSY--CATASTROPHISM AND EVOLUTION
Jo Lawrence <Jo@plenum.co.uk>
(5) COLORADO RESEARCHERS DISCOVER MISSING LINK IN PLANET
FORMATION
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) CHAOTIC ORBIT OF 4179 TOUTATIS MAKES IMPACT PREDICTION
IMPOSSIBLE
G. Sitarski, UNIVERSITY OF BIALYSTOK
(7) NONGRAVITATIONAL MOTION OF COMET 32P/COMAS SOLA
M. Krolikowska et al., POLISH ACADEMY OF
SCIENCE
(8) SEARCHING FOR BRIGHT KUIPER BELT OBJECTS
M.J.I. Brown & R.L. Webster, UNIVERSITY OF
MELBOURNE
(9) SATELLITE ORBITS AROUND A COMETARY NUCLEUS
D.J. Scheeres et al., UNIVERSITY OF PADUA
(10) LUNAR ICE: COMETARY ORIGIN?
A.A. Berezhnoi & B.A. Klumov,
SHTERNBERG STATER ASTRON INST
(11) THE EFFECTS OF GLACTIC DISC TIDAL ACTION ON OORT CLOUD
COMETS
A.J. Maciejewski & H. Pretka, ADAM
MICKIEWICZ UNIV POZNAN
(12) NEW IMAGES OF IMPACT CRATERS ON CALLISTO & EUROPA
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
====================
(1) BNSC STATEMENT SERIOUSLY UNDERESTIMATES IMPACT HAZARD
From Michael Paine <mpaine@tpgi.com.au>
The statement is very disappointing. It gives the impression that
"the
next big impact" is 100,000 years away. It would have helped
if the
statement had at least referred to the risk calculated by
Morrison and
Chapman - US citizens have a 1 in 20,000 chance of dying from an
asteroid/comet impact - the same risk as dying in a commercial
airliner
crash and comsiderably greater than the risk from floods and
hurricanes. In my efforts to get government support for
Spaceguard
Australia I have looked more closely at the risk from tsunami -
since
most Australians live on the coast. Subject to uncertainty about
the
dynamics, I have estimate that people living in low-lying coastal
areas
on the edge of the Pacific or Altantic Oceans have a high risk of
dying
from impacted-generated tsunami - about the same risk as
dying in a
car crash. This calculation is only for NEOs between 50 and 100
metres
diameter - with an average interval between impacts ranging from
100 to
1000 years. For larger NEOs Prof Yabushita from Kyoto University
has
estimated there is a 1 in 100 chance of all the cities around the
Pacific Rim being inundated by a large tsunami in the next
century.
Consideration of "big asteroids" hitting "about
once every 100,000
years" seriously underestimates the hazard. See
http://www1.tpgi.com.au/users/tps-seti/spacegd7.html
for more on
tsunami from asteroid impacts.
Michael Paine
New South Wales Co-ordinator
The Planetary Society Australian Volunteers
======================
(2) A NEW THEORY OF GRAVITY?
From Bill Napier <wmn@star.arm.ac.uk>
Dear Jay,
Inertia usually prevents me from reacting to items on Benny's
excellent
bulletin board, but I must say the BNSC material has done the
trick.
I am particularly intrigued by the statement that `Knowing more
about
the structure of comets and asteroids will help us to predict
their
path in space...' Clearly, BNSC has access to aspects of
gravitation
theory unknown to Newton, Einstein and the modern celestial
mechanicians.
Please dig deeper: in an open society we should all have access
to this
new knowledge.
I also liked the `Therefore' linking the statements that (i)
debris from a blown-up asteroid may be dangerous, and (ii) BNSC
are
funding instruments for the comet Rosetta mission. Was this
really
the motivation for the funding? BNSC can only do itself good by
making available the documentary evidence revealing that the
celestial
hazard was indeed the issue which drove it to fund this
instrumentation.
Best regards
Bill
======================
(3) CLOSE TO RENDEZVOUS: SATELLITE NEARING ASTEROID ORBIT
From ABCNews Online
http://www.abcnews.com/sections/science/DailyNews/asteroid981012.html
By Paul Recer
The Associated Press
M A D I S O N, Wis., Oct. 12 — A
small satellite launched more than
two years ago is just weeks from becoming the first manmade
object to
be placed into an orbit of a distant asteroid.
The Near Earth Asteroid Rendezvous, or NEAR, spacecrafts will
fire
rockets on Dec. 20 to settle into an orbit of an asteroid called
Eros
that is streaking across space some 163 million miles from Earth.
Andy Cheng, a Johns Hopkins University researcher and the project
scientist for NEAR, said today that all instruments on the
spacecraft
are working well and that the small satellite is on target for
its deep
space meeting with Eros.
The rocket firing comes while NEAR is still distant from Eros,
and the
satellite will not start orbiting the asteroid until Jan. 10,
1999.
Up-Close With an Asteroid
During months of circling the asteroid, the craft will be slowly
lowered until its orbit is just 21 miles above the space rock,
said
Cheng. The craft will give the first prolonged, up-close look at
an
asteroid, which are minor planets, in space.
Six instruments aboard NEAR will analyze the composition,
magnetic
field and mass of the asteroid, sending the data back to Earth by
radio.
Eros is something of a mystery. The rock is about the size of a
mountain, 24 miles by 8 miles. It is a near-Earth asteroid, one
whose
orbit routinely carries it close to the orbit of Earth.
Scientists don’t know if the rock is solid or if it is a
highly porous
body with empty cavities or chunks of ice.
But it similar to the asteroids that pounded Earth early in the
planet’s history. One such asteroid smashed into Earth 65
million years
ago and is thought to have caused the extinction of the
dinosaurs.
Eros’ Mysterious Origin
Like most asteroids, said Cheng, Eros probably formed early in
the
history of the solar system. What isn’t known is whether
Eros was once
part of a bigger planet or if it formed independently.
“There were many collisions in the early solar system,”
said Cheng.
Sometimes huge chunks of a planet are knocked into space by such
celestial smashups and became independent bodies. The Earth’s
moon is
thought to come such a collision.
Asteroids could also form from the leftover debris of
planet-building.
Bits of stray rock and dust slowly clump together until they form
one
object.
Concern Over Space Rocks
The process may not be finished, said Cheng. He said there is
some
concern that wandering space rocks or gravel that imperil the
NEAR.
As NEAR approaches Eros, researchers will use cameras and
instruments
on board to search for any stray bits of rock or gravel that are
still
orbiting the asteroid.
After months in orbit of Eros, researchers may attempt to put the
craft
onto the surface of the asteroid. Cheng said the spacecraft was
not
designed to land, but that is one option the researchers are
considering. The density of Eros is unknown, but the asteroid is
so
small that its gravity force will be only a fraction of Earth’s,
making
landing there less violent.
But it would still be tricky steering the craft to a touchdown
because
Eros is so far away that there is a long delay between sending a
signal
and getting a response. Cheng said it takes about 45 minutes for
a
radio signal to make a round trip between Earth and NEAR.
Copyright 1998 Associated Press
====================
(4) CONTROVERSY--CATASTROPHISM AND EVOLUTION
From Jo Lawrence <Jo@plenum.co.uk>
Dear Benny
Re: CONTROVERSY--CATASTROPHISM AND EVOLUTION: The Ongoing Debate
by Trevor Palmer
Please find attached the catalogue page from our web site for
this
particular volume. You may add a link to this page very
easily using
the address given here:
http://www.plenum.com/title.cgi?0306457512
Controversy -- Catastrophism and Evolution: The Ongoing Debate
By Trevor Palmer, Nottingham Trent University, Nottingham, United
Kingdom.
Plenum Press, 1998, 470 pp.
ISBN: 0-306-45751-2
Price: $85.00 (US and Canada) / $102.00 (elsewhere)
Text adoption price on orders of six or more copies: $49.50 each.
Description
In Controversy, Trevor Palmer fully documents how traditional
gradualistic views of biological and geographic evolution are
giving
way to a catastrophism that credits cataclysmic events, such as
meteorite impacts, for the rapid bursts and abrupt transitions
observed
in the fossil record. According to the catastrophists, new
species do
not evolve gradually; they proliferate following sudden mass
extinctions. Placing this major change of perspective within the
context of a range of ancient debates, Palmer discusses such
topics as
the history of the solar system, present-day extraterrestrial
threats
to earth, hominid evolution, and the fossil record.
Contents
The Context of Evolution: The Earth and Its Surroundings. The
Establishment of Gradualism. Gradualism under Challenge. Nemesis
for
Evolutionary Gradualism? The Erratic Descent of Man. Towards a
New
Evolutionary Synthesis. Index.
==================
(5) COLORADO RESEARCHERS DISCOVER MISSING LINK IN PLANET
FORMATION
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Office of Public Relations
University of Colorado-Boulder
354 Willard Administrative Center
Campus Box 9
Boulder, Colorado 80309-0009
(303) 492-6431
Contact:
Henry Throop, 303-492-1628
Larry Esposito, 303-492-7325
Jim Scott, 303-492-3114
Oct. 12, 1998
COLORADO RESEARCHERS DISCOVER MISSING LINK IN PLANET FORMATION
Three University of Colorado at Boulder researchers have observed
the
growth of dust particles in discs around three nearby stars, a
phenomenon that appears to be a missing link between space dust
and
planet formation.
Doctoral candidate Henry Throop of the department of atmospheric
and
planetary sciences said some of the dust particles surrounding
one
"birthing star" some 1,500 light years away in the
Orion Nebula are
about 100 times larger than particles generally found in the
interstellar medium. The particles apparently are growing by
accreting
together, somewhat like a snowball that picks up flakes and grows
as it
is rolled along the ground.
"This is the first time scientists have been directly able
to see the
accretion process in the formation of planets," said Throop,
who is
affiliated with CU-Boulder's Laboratory for Atmospheric and Space
Physics. "These particles are much, much bigger than they
started out
to be."
Images of one of the discs were taken by John Bally, director of
CU-Boulder's Center for Astrophysics and Space Astronomy, with
the
Hubble Space Telescope in 1995.
The researchers used Hubble to look at the discs by using
different
wavelengths of light, which bounce off the dust particles in
different
ways, said Throop. The way the light scatters allows the
researchers to
estimate the particle sizes.
"It's simlar to how a rainbow works," sad Throop.
"The rain drops
themselves aren't dazzling colors, but we can tell some things
about
the drops based on what the rainbow looks like. Likewise, by
looking at
the colors scattered off these discs, we can tell something about
the
dust orbiting there."
A paper on the subject primarily authored by Throop was presented
at
the 30th annual Division for Planetary Sciences meeting in
Madison,
Wis., Oct. 11 to Oct 16. Co-authors include Bally, CU-Boulder
Professor
Larry Esposito of LASP and Mark McCaughrean of the Astrophysical
Institute in Potsdam, Germany.
When a star forms, swarms of gas and dust contract into a titanic
ball,
causing the star to "turn on," said Throop. The dust
ring left circling
the birthing star resembles a large doughnut.
The interstellar dust particles drawn into the ring surrounding
the
newborn star initially are only about one-tenth of a micron
across,
Throop said. The Hubble images showed some of the particles had
grown
100 times larger -- to 10 microns, or about one-tenth the width
of a
human hair -- as the accretion process occurred.
Located in the Milky Way, the Orion Nebula is one of the stellar
nurseries closest to Earth. The three stars under observation are
each
about one million years old, Throop said.
"This is the first direct confirmation that dust particles
surrounding
young stars are beginning to grow into planets," said
Esposito.
"Another nifty thing going on here is that we see discs that
appear to
be similar to the three we are studying around about one-third of
the
stars in the Orion Nebula," said Throop. "If these
similar discs are
forming larger particles, it suggests planet formation -- and
thus
solar systems like ours -- may be relatively common."
The Division for Planetary Science is part of the American
Astronomical
Society. Images of two of the discs are available on the website:
http://bogart.colorado.edu/~throop/images.html
================
(6) CHAOTIC ORBIT OF 4179 TOUTATIS MAKES IMPACT PREDICTION
IMPOSSIBLE
G. Sitarski: Motion of the minor planet 4179 Toutatis: Can we
predict
its collision with the Earth? ACTA ASTRONOMICA, 1998, Vol.48,
No.3,
pp.547-561
UNIVERSITY OF BIALYSTOK,INST PHYS,LIPOWA 41,PL-15424
BIALYSTOK,POLAND
Minor planet 4179 Toutatis is an Apollo type object with a very
small
orbit inclination (i = 0.degrees 47), hence it has a possibility
to
approach closely the Earth tan encounter to within 0.01 a.u. is
expected in 2004) and might be a good candidate for a future
collision
with the Earth. We collected 640 astrometric observations of
Toutatis
from the period 1934-1997 to improve the orbit. We had to include
a
nongravitational term into equations of motion expressed by a
secular
change (a) over dot of the semimajor axis a of the Toutatis orbit
to
obtain a fully satisfactory solution of the orbit determination.
A
value (a) over dot = -0.16 x 10(-10) is two orders smaller than
that
determined in the case of short-period comets with known
nongravitational effects. To investigate the long-term motion of
Toutatis we numerically integrated the equations of motion by
recurrent
power series taking into account perturbations caused by the
eight
planets from Mercury to Neptun, treating the Earth and Moon as
separate
bodies, and also by the four biggest asteroids. We randomly
varied the
orbital elements to examine the Toutatis' motion for a number of
different orbits. We present a new method of the random orbit
selection
which allows us to find a set of different orbits but
representing well
all the observations used for the orbit correction. Our results
confirm
a conclusion found by other authors that Toutatis orbit is
exceptionally chaotic. Therefore, we are not able to predict the
motion
of Toutatis further than for 300 years. However, our integrations
spanning 1500 years showed that the evolution of position of the
descending node of Toutatis' orbit might go also in such a
direction
that the orbits of Toutatis and of the Earth would intersect in
the
future. Hence a possibility of the Toutatis-Earth collision is
not
excluded but it is completely unpredictable. To investigate
conditions
of a hypothetical collision of a minor planet with the Earth we
made
the following numerical simulation. Based on the Toutatis' orbit
we
deduced such orbital elements for a fictitious minor planet
''Fatum''
that a shape of the orbit was very similar to that of Toutatis,
but we
knew in advance that ''Fatum'' would certainly collide with the
Earth
in September 2004 and we calculated values of the impact
parameters. We
created a set of 638 artificial observations of ''Fatum'' in
1988-1997
for the same dates and with the same random observational errors
like
those of Toutatis. Then we corrected the ''Fatum's'' orbit for
different observational intervals to examine the exactness of the
impact prediction in 2004. We found that in 1993 we would be sure
that
the collision is inevitable, and in 1997 we could determine an
impact
area on the Earth's surface in range of a square of 100 x 100 km.
We
show that if we knew the impact date so early we could undertake
an
action to avoid the collision by trying to change the ''Fatum's''
heliocentric velocity only by one cm/sec. Copyright 1998,
Institute for
Scientific Information Inc.
=========================
(7) NONGRAVITATIONAL MOTION OF COMET 32P/COMAS SOLA
M. Krolikowska*), G. Sitarski, S. Szutowicz: Model of the
nongravitational motion for comet 32P/Comas Sola. ASTRONOMY AND
ASTROPHYSICS, 1998, Vol.335, No.2, pp.757-764
*) POLISH ACADEMY OF SCIENCE, SPACE RES CTR, BARTYCKA 18A,
PL-00716
WARSAW, POLAND
The nongravitational motion of the periodic comet Comas Sola is
studied
on the basis of positional observations made during nine
consecutive
revolutions around the Sun. Nongravitational effects in the comet
motion have been examined for Sekanina's forced precession model
of the
rotating nucleus. We present three models which successfully link
all
the observed apparitions of the comet during 1926-1996. Two
solutions
(Models II and III) represent oblate spheroids and the third one
(Model
I)- a prolate spheroid (nucleus rotation around its longer axis).
We
have determined values of eight parameters: A, eta , I, phi
connected
with the rotating comet nucleus, f(p) and s describing the
precession
of spin-axis of the nucleus, and two constant time shifts tau(1)
and
tau(2) The last two parameters describe displacements of the
maximum
value of the known function g(r) with respect to the perihelion
time.
The best solution was obtained assuming that between the
apparitions of
1935 and of 1944 the time shift changed its value, thus tau(1)
and
tau(2) refer to apparitions before and after 1940 Jan. 1,
respectively.
Variations of angles I and phi with time, describing the nucleus
spin-axis orientation, are presented. It appears that forced
precession
causes the moderate changes of the position of the rotation axis
in
space. The ratio of rotational period to radius of the nucleus
was
found for each model. The present precession models are in
agreement
with sizes and periods of rotation of other cometary nuclei
deduced
from observations. The obtained models give some strong
constraints on
the physical parameters of the nucleus of comet P/Comas Sola.
Assuming
a prolate spheroid for the nucleus of the comet, the expected
rotational period is 14 +/- 4 hours for an equatorial radius of 2
km.
For the same radius, the oblate Model II gives the much smaller
rotational period of 2.4 +/- 0.4 hours. The polar radii are 2.2
km and
1.3 km for the prolate and oblate model, respectively.
Copyright 1998, Institute for Scientific Information Inc.
===================
(8) SEARCHING FOR BRIGHT KUIPER BELT OBJECTS
M.J.I. Brown & R.L. Webster: A search for bright Kuiper Belt
objects.
PUBLICATIONS ASTRONOMICAL SOCIETY OF AUSTRALIA, 1998, Vol.15,
No.2,
pp.176-178
UNIVERSITY OF MELBOURNE, SCH PHYS, PARKVILLE, VIC 3052, AUSTRALIA
Since 1992, 60 large Kuiper Belt objects have been detected by
ground-based telescopes. Previous surveys which have detected
objects
have searched approximately 60 square degrees and detected
objects with
magnitudes 20.6 < m(R) < 25.0. However, the luminosity
function of
brighter Kuiper Belt objects is not well determined. The
detection of
brighter objects would improve our ability to determine the
Kuiper Belt
objects' surface composition and provide constraints on the
population
statistics of different formation mechanisms. This paper
describes a
survey of 12.0 square degrees of sky near the ecliptic to a
limiting
magnitude of m(R) similar to 21. A slow moving candidate was
detected
near the magnitude limit of the survey. Copyright 1998, Institute
for
Scientific Information Inc.
======================
(9) SATELLITE ORBITS AROUND A COMETARY NUCLEUS
D.J. Scheeres*), F. Marzari, L. Tomasella, V. Vanzani: ROSETTA
mission:
satellite orbits around a cometary nucleus. PLANETARY AND SPACE
SCIENCE, 1998, Vol.46, No.6-7, pp.649-671
*) UNIVERSITY OF PADUA,DIPARTIMENTO FIS,VIA MARZOLO 8,I-35131
PADUA,ITALY
This paper discusses the problem of orbiting a comet
nucleus from a
perspective of orbital stability. The main forces perturbing the
motion
of the spacecraft around the comet : shape and rotation rate of
the
nucleus, comet outgassing, solar radiation pressure; are derived
and
quantified for the nominal case of the ROSETTA spacecraft at the
comet
Wirtanen. Their effects on the stability of the spacecraft orbit
are
analyzed in detail and orbital stability criteria are developed
analytically. These criteria have been tested numerically, for
select
cases of interest, integrating the spacecraft orbit about a
Wirtanen
model constructed from mascons (mass concentrations at a point).
This
numerical model allows very irregular nucleus shapes to be
modelled
accurately if a large number of point masses is used. The
stability
criteria derived in this paper denote stability of the spacecraft
against crashing onto the comet surface or escaping from the
comet on a
hyperbolic orbit. They are developed and applied only over the
relatively short time scales that are of interest to a spacecraft
mission. The stability criteria are expressed in terms of minimum
periapsis radii for stability against the non-spherical
gravitational
field, in terms of maximum semi-major axis for stability against
escape
due to the solar radiation pressure, and in terms of preferred
planes
and orbit elements of a spacecraft orbit for stability against
the
combined non-gravitational forces of comet outgassing and solar
radiation pressure. For orbits dose to an irregular body the
gravity
perturbations are minimized, and orbital stability achieved, if
the
periapsis radius is above five mean comet radii if the
inclination is
close to 0 degrees and above three mean comet radii if
inclinations are
between 90 and 180 degrees with respect to the comet rotation
pole.
When considering the combined solar radiation pressure and comet
outgassing forces, stable or bits can be found which ''freeze''
the
orbit geometry with respect to the rotating reference frame
defined
along the comet-sun line. The dependence of these stability
criteria on
the comet model parameters is discussed. The analysis in this
paper is
general enough to be applicable to a wide range of orbital cases,
including spacecraft orbits about asteroids and natural
satellites
about comets and asteroids. (C) 1998 Published by Elsevier
Science Ltd.
All rights reserved.
===================
(10) LUNAR ICE: COMETARY ORIGIN?
A.A. Berezhnoi*) & B.A. Klumov: Lunar ice: Can its origin be
determined? JETP LETTERS, 1998, Vol.68, No.2, pp.163-167
*) P K SHTERNBERG STATER ASTRON INST,MOSCOW 119890,RUSSIA
The comet hypothesis of the origin of lunar ice, which was
recently
discovered in the polar regions of the moon by Lunar Prospector,
is
examined. It is shown that a comet impact produces a temporary
atmosphere whose volatile component accumulates essentially
completely
in cold traps - the permanently shadowed regions of the Moon. The
condensation of volatile compounds leads to the formation of ice
with a
definite chemical and isotopic composition, which contains
important
information about the composition of the comet. This hypothesis
can be
checked during the next lunar missions, and if confirmed,
definite
progress will have been made in understanding the nature of
comets. (C)
1998 American Institute of Physics.
====================
(11) THE EFFECTS OF GLACTIC DISC TIDAL ACTION ON OORT CLOUD
COMETS
A.J. Maciejewski*) & H. Pretka: Galactic disc tidal action
and
observability of the Oort cloud comets. ASTRONOMY AND
ASTROPHYSICS,
1998, Vol.336, No.3, pp.1065-1071
*)ADAM MICKIEWICZ UNIV POZNAN,ASTRON OBSERV,SLONECZNA 36,PL-60286
POZNAN,POLAND
We study qualitatively the effect of the galactic disk potential
on the
comets from the Oort cloud. The problem is examined in the
Hamiltonian
formalism. A simple pre-selection criterion for calculating the
minimal
heliocentric distance of the Oort cloud comets is found. We can
use
this criterion in a simulation to select a sub-population of
potentially observable comets. The proposed criterion is very
effective-it rejects about 90% of orbits randomly chosen from the
initial population of comets. Copyright 1998, Institute for
Scientific
Information Inc.
=======================
(12) NEW IMAGES OF IMPACT CRATERS ON CALLISTO & EUROPA
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
New images taken by the Galileo spacecraft are now available on
the Galileo website:
http://www.jpl.nasa.gov/galileo
Of particular interest to this group are the impact craters on
the moons Callisto and Europa.
Ron Baalke
----------------------------------------
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