PLEASE NOTE:
*
CCNet DIGEST, 6 May 1999
------------------------
(1) ASTEROIDS CLOSE TO THE EARTH?
NATURE News Service
(2) POSSIBLE LONG-LIVED ASTEROID BELTS IN THE SOLAR SYSTEM
NATURE, 6 May 1999
(3) DO UNSEEN ASTEROID BELTS STILL LURK?
MSNBC Space News
(4) A LINEAR MODEL FOR THE YARKOVSKY EFFECT
D. Vokrouhlicky, CHARLES UNIVERSITY
(5) SPACEGUARD TALK DOWN UNDER
Michael Paine <mpaine@tpgi.com.au>
(6) COLLISIONS BETWEEN GALAXIES MORE COMMON THAN THOUGHT
UniSci, 5 May 1999
(7) TURN LEFT AT CALLISTO
NASA Science News <expressnews@sslab.msfc.nasa.gov>
(8) US SPACE ROCKETS GROUNDED
BBC Online Network, 6 May 1999
=================
(1) ASTEROIDS CLOSE TO THE EARTH?
From NATURE News Service
[http://helix.nature.com/nsu/990506/990506-2.html]
By HENRY GEE
When astronauts set off for Mars, they might have to navigate
through a
hitherto undiscovered belt of asteroids. A computer study by two
UK-based researchers suggests that there could be a narrow ring
of
around 1,000 asteroids, left over from the birth of the Solar
System
4.5 billion years ago, in stable, circular orbits around the Sun,
just
beyond the Earth's own orbit. These remnant asteroids could since
have
been joined by bodies ejected from the 'main belt' of asteroids
between
Mars and Jupiter.
The researchers, N. Wyn Evans and Serge Tabachnik of Oxford
University,
present their study in the 6 May issue of the science magazine
Nature.
They were following up a slew of recent discoveries of asteroids
or
'minor planets' throughout the Solar System.
Ceres, the first known member of the main belt of asteroids
between
Mars and Jupiter, was discovered in 1801: thousands have been
added to
the tally since then, though many asteroids range widely
throughout the
Solar System, from beyond Saturn to well within the orbit of the
Earth.
Some of these latter 'near-Earth objects' or NEOs may be cause
for
concern, as they would cause enormous devastation if they hit the
Earth.
However, astronomers have long realized that many asteroids
outside the
main belt could represent distinct populations of bodies -- in
other
words, there could be more than one distinct asteroid belt. Over
the
past decade, for example, an increasing number of small, icy
bodies has
been found orbiting in the 'Kuiper belt', a broad swath in the
frigid
wastes beyond the orbit of Neptune. More recently, computer
simulations
have predicted that asteroids could be oribiting between Neptune
and
Uranus.
Computer simulations are heavy-duty games of planetary billiards,
in
which astronomers seek to find regions of the Solar System in
which
small bodies could orbit stably for hundreds of millions of
years,
without being deflected by the gravitational fields of the larger
planets, in particular the giant planet Jupiter. The Kuiper belt
beyond
Neptune is one such zone, as is the zone between Uranus and
Neptune
and, of course, the main belt itself between Mars and Jupiter.
Evans
and Tabachnik wondered if there might be zones of stability
closer to
home, in the inner Solar System.
Using a series of 20 personal computers working full-time for
more than
four months, the researchers showed that there could be asteroids
between all the inner planets in orbits stable for periods of
around
100 million years. But this represents only two per cent of the
entire
history of the Solar System. Running their simulation to
represent the
entire history of the Solar System would take almost 16 years of
computer time, so the researchers had to extrapolate as best they
could. Once this was done, they identified two zones of
extraordinary
stability. One was just outside the Earth's orbit. No known
asteroid
has been definitely shown to occupy a circular,
non-Earth-crossing
orbit in this region, although current catalogues hold three
candidates, all discovered since 1996.
The other zone of stability lies in the super-hot zone between
Mercury
and the Sun, where asteroids -- presumably fried to cinders --
could
have lain undetected since the birth of the Solar System.
Detecting
these so-called 'Vulcanoids' would be very hard, though they
might be
revealed through their copious emission of infra-red radiation --
heat.
Searches for Vulcanoids have so far found nothing, but they have
hitherto been rather limited in scope.
© Macmillan Magazines Ltd 1999 - NATURE NEWS SERVICE
==================
(2) POSSIBLE LONG-LIVED ASTEROID BELTS IN THE SOLAR SYSTEM
From NATURE, 6 May 1999
[http://www.nature.com/server-java/Propub/nature/399041A0.abs_frameset]
N. WYN EVANS AND SERGE TABACHNIK
Recent years have seen the discovery of several objects in stable
orbits in the outer Solar System; these bodies include objects in
the
Kuiper belt (also known as the Kuiper-Edgeworth belt) as well as
the
Centaurs. Moreover, another region of orbital stability has been
identified between the orbits of Uranus and Neptune. Here we
report
evidence from numerical simulations of zones of orbital stability
in
the inner Solar System. We find that there are two possible
long-lived
belts of asteroids. The first region lies between the Sun and
Mercury,
in the range 0.09-0.21 astronomical units, where remnant
planetesimals
may survive for the age of the Solar System provided that their
radii
are greater than ~0.1 kilometres. The second region of stability
is
between Earth and Mars (range 1.08-1.28 astronomical units),
where a
population of bodies that are on circular orbits may survive. A
search
through the catalogues of near-Earth objects reveals an excess of
asteroids with low eccentricities and inclinations occupying this
latter region: several examples are the recently discovered
objects
1996 XB27, 1998 HG49 and 1998 KG3.
Copyright 1999, NATURE
===============
(3) DO UNSEEN ASTEROID BELTS STILL LURK?
From MSNBC Space News
http://www.msnbc.com/news/265993.asp
Two extra rings are theoretically possible, researchers say
By Alan Boyle, MSNBC
May 5 Researchers say our solar system could accommodate
two
as-yet-undetected rings of space rocks: one between Earth and
Mars, the
other between Mercury and the sun. If such asteroid belts really
exist
and harbor large objects, they could represent a new worry
but
asteroid-watchers say theyve seen no sign of the belts.
FULL STORY at http://www.msnbc.com/news/265993.asp
===================
(4) A LINEAR MODEL FOR THE YARKOVSKY EFFECT
D. Vokrouhlicky: A complete linear model for the Yarkovsky
thermal
force on spherical asteroid fragments. ASTRONOMY AND
ASTROPHYSICS,
1999, Vol.344, No.1, pp.362-366
CHARLES UNIVERSITY, ASTRON INST,CZ-18000 PRAGUE 8,CZECH REPUBLIC
A linear theory for heat conduction in a spherical, solid and
rotating
body illuminated by solar radiation is developed. The recoil
force due
to the thermally re-emitted radiation by the surface of the body
is
computed, including all the terms depending both on the body's
rotation
frequency and the mean motion of its revolution about the Sun.
The
present solution thus overcomes a drawback of the previous
approaches,
which have been tailored separately either to the diurnal or to
the
seasonal variant of the so-called Yarkovsky effect, corresponding
to
different Limiting cases of the current theory. We pay a special
attention to compute the secular effects on the semimajor axis of
the
body's orbit about the Sun. The results from the general model
coincide
with those of the previous approaches to a high level of
accuracy, as
the relative size of the additional ''mixed'' terms is smaller
than
10(-3) for plausible parameter choices. This confirms that the
use of
the simplified formulae is warranted in the relevant Solar System
applications. Copyright 1999, Institute for Scientific
Information Inc.
===================
(5) SPACEGUARD TALK DOWN UNDER
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
I have just returned from Canberra where I helped AAO astronomer
Ken
Russell deliver a talk on the asteroid threat as part of the
Australian
Science Festival. It was very well attended and has helped to
generate
more interest in the nation's capital. I also stood in for Ken
during a
TV news interview which was broadcast nationally (probably got a
whole
ten seconds of air time!).
Following this attention we are about the lobby the Australian
politicians once again so any contribution by CCNet subscribers
would
be appreciated (approaches from the governments/departments of
other
countries make a good impression!).
We are thinking of a new motto for the Australian asteroid search
"Cover your ass" with reference to:
* the lack of major NEO search program "down under",
* a preoccupation of politicians
* the (unfortunate) acronym of Australian Spaceguard Survey
(which
is an unofficial title) :)
By an extraordinary coincidence, Ken's talk was on the same day
as
Duncan Steel's talk in Cardiff UK (CCNET Digest 5 May 1999). Ken
and
Duncan worked on NEO detection in Australia until the program was
cut in
1996.
Michael Paine
The Planetary Society Australian Volunteers
=====================
(6) COLLISIONS BETWEEN GALAXIES MORE COMMON THAN THOUGHT
From UniSci, 5 May 1999
http://unisci.com/stories/19992/0505991.htm
Astronomers compiling a catalog of spiral galaxies have
discovered that
collisions between such galaxies, as well as near-collisions, are
more
common than had been thought.
FULL STORY at http://unisci.com/stories/19992/0505991.htm
================
(7) TURN LEFT AT CALLISTO
From NASA Science News <expressnews@sslab.msfc.nasa.gov>
NASA Space Science News for May 5, 1999
Turn Left at Callisto: This morning NASA's Galileo spacecraft
zoomed
past Jupiter's moon Callisto. The maneuver was designed to bring
Galileo closer to Jupiter in preparation for a daring encounter
with a
volcano on Io.
FULL STORY at http://science.nasa.gov/newhome/headlines/ast05may99_1.htm
=======================
(8) US SPACE ROCKETS GROUNDED
From the BBC Online Network, 6 May 1999
http://news.bbc.co.uk/hi/english/sci/tech/newsid_336000/336592.stm
All United States rockets capable of launching large satellites
are
grounded as an investigation begins into a series of launch
failures.
The latest launch to misfire was a Delta III carrying a
communications
satellite. It was an unprecedented sixth failure in nine months.
FULL STORY at
http://news.bbc.co.uk/hi/english/sci/tech/newsid_336000/336592.stm
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