PLEASE NOTE:
*
Date sent: Tue, 11 Nov
1997 09:40:57 -0500 (EST)
From:
Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:
Re: CC-DIGEST, 11 November 1997
To:
cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DIGEST, 11 November 1997
(1) IMPLICATIONS OF NEO SEARCH PROGRAMMES
(2) WHERE DO COMETS COME FROM?
(3) ASTEROID (3671) DIONYSUS
(4) PUBLIC INVITED TO SEND NAMES ON ROUNDTRIP MISSION TO COMET
(5) IS ANYBODY OUT THERE?
======================================================================
(1) IMPLICATIONS OF NEO SEARCH PROGRAMMES
D. Steel: Meteoroid orbits: Implications for near-earth object
search
programs. ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 1997,
Vol.822,
pp. 31-51
SPACEGUARD AUSTRALIA PL, POB 3303, ADELAIDE, SA 5000, AUSTRALIA
The available orbital database on macroscopic potential
impactors of
our planet (asteroids and comets, collectively near-Earth objects
or
NEOs) numbers less than one thousand, whereas there have been
some
hundreds of thousands of orbits of Earth-impacting meteoroids
determined in various surveys, mostly using meteor radars. If one
assumes that NEOs have orbital characteristics broadly similar to
meteoroids, then the orbits of the latter can give important
indications concerning the conduct of search programs designed to
discover large NEOs well ahead of any catastrophic impact,
allowing
ameliorative action to be taken. For smaller NEOs that cannot be
telescopically detected until the day or so before impact, the
radiant distribution of observed meteors shows the regions of
the sky from which impactors are most likely to emanate. It is
shown that the vast majority of meteoroids striking the Earth
have geocentric (apparent) radiants within two near-ecliptic
regions a few tens of degrees wide and centered on longitudes
+/- 90 degrees from the apex of the Earth's way (the so-called
helion and anti-helion sources). These are bodies with low
inclinations, large eccentricities (e = 0.7 - 0.9) and quite
small semimajor axes (mostly a = 1.3 - 2.5 AU). After allowing
for the terrestrial motion about the Sun (conversion to the
true radiant), the longitudes are around +/- 120 degrees from
the apex. For a ground-based search on the nightside, the best
search region is that within similar to 20 degrees of the are
joining the geocentric and true radiants (longitudes 90 degrees
and 120 degrees). On the dayside, proximity to the solar
direction
argues for a space-based surveillance program, if small NEOs are
to
be found just prior to impact.
========================================================================
(2) WHERE DO COMETS COME FROM?
L. Nuslusan: On the relatively high concentration of the
directions
of long-period comet perihelion points in the North Pole region.
PLANETARY AND SPACE SCIENCE, 1997, Vol.45, No.7, pp.807-812
SLOVAK ACADADEMY OF SCIENCE, INSTITUTE OF ASTRONOMY, TATRANSKA
LOMNIC
05960, SLOVAKIA
The origin of comets still remains an open question. Progress
would
be achieved if it were clear whether the comets were created in
the
frame of the Solar System, or if they have an interstellar
origin.
The hypotheses of interstellar origin are supported by, among
other
facts, the existence of a statistically significant preferred
direction in the distribution of the direction of long-period
comet
perihelion points, whereby the preferred direction is located
near
the solar apex. However, none of the authors who have determined
the
preferred direction has taken into account (or taken into account
adequately) the observational selection effects in the comet
discoveries biasing the real distribution of comet orbits. An
analysis of the selection effects is necessary if the correct
real
preferred direction to be obtained and its statistical
significance
evaluated. Such analysis is also needed if the structure of the
Oort
cloud is investigated. It is well known that the sphericity of
this
comet reservoir is disturbed by the tidal action of the Galaxy. A
correct verification of an arbitrary model of this action, for
example, is impossible without the correction of a used set of
comet;
orbits taking into account the selection effects. The paper
contributes to a complete analysis of the selection effects. The
existence is demonstrated of a higher number of long-period comet
perihelion points per unit space angle (i.e. the concentration of
these points) in the North Pole region in comparison with the
other
regions of the sky. At the same time, an explanation is given of
the
presented phenomenon as a consequence of the observational
selection
effects.
======================================================================
(3) ASTEROID (3671) DIONYSUS
From: Vladimir Damgov <vdamgov@bgearn.acad.bg
I should be most grateful if you could let me have info about
the
discovery of a satellite around a near-Earth Asteroid - small
satellite (moon) orbiting the asteroid (3671)Dionysus.
Prof Vladimir Damgov
Doctor of Sciences(Sc.D.), Ph.D. in Physics and mathematics
Senior Research Professor
Bulgarian academy of Sciences, Space research Institute
JK"Mladost 1A", Bl.522, Vh.5, Ap.98; 1784 Sofia,
Bulgaria
Fax:(+3592) 981 33 47
=======================================================================
(4) PUBLIC INVITED TO SEND NAMES ON ROUNDTRIP MISSION TO COMET
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary Beth Murrill
November 10, 1997
PUBLIC INVITED TO SEND NAMES ON ROUNDTRIP MISSION TO COMET
Through November, NASA is inviting individuals to submit their
names
to be etched on a microchip and flown aboard Stardust, a daring
roundtrip robotic spacecraft mission to a comet.
The Stardust project, managed by NASA's Jet Propulsion
Laboratory in
Pasadena, CA, is collecting up to 300,000 names by Nov. 30, 1997.
The
names will be electronically etched onto a fingernail-size
silicon
chip in the Microdevices Lab at JPL, where the Stardust mission
is
managed. The collection of names is being coordinated with the
assistance of The Planetary Society, a non-profit space interest
and
education group based in Pasadena.
Now beginning assembly and scheduled for launch in February
1999, the
Stardust spacecraft will embark on a five-year journey through
the
coma and to approximately 150 kilometers (100 miles) of the
nucleus
of Comet Wild-2 (pronounced "VILT-2"), gather cometary
dust particles
and deliver them back to Earth.
"This is a chance for people to take a vicarious trip to
a comet and
back again," said Gloria Jew, coordinator for the Stardust
mission's
public outreach efforts at JPL.
Names on the chip will be so small that the width of the type
used
measures 10 times smaller than the width of a human hair and can
be read only with the aid of an electron microscope. Names may be
submitted electronically to the Stardust web page at
http://stardust.jpl.nasa.gov/
or in writing, mailed to The Planetary
Society, 65 N. Catalina Ave, Pasadena, CA 91106-2301. Those
submitting their names are granting permission for the Stardust
project and its partners to use the names submitted in possible
future exhibits and/or publications.
Stardust will be the first space mission to gather dust and
other
material from a comet and bring it back to Earth for scientific
analysis. In January 2006, an atmospheric reentry capsule housing
the
comet sample will plunge through the skies over Utah and
parachute
softly to the Earth's surface. A direct sample of a comet has
been
long sought by planetary scientists because comets are thought to
be
nearly pristine examples of the original material from which the
Sun
and planets were born 4.6 billion years ago.
Stardust's scientific bounty from its five-year voyage will
also
include samples of the interstellar dust that passes through our
solar system. Return of this interstellar material will provide
scientists with their first opportunity for laboratory study of
the
composition of the interstellar medium.
"Stardust has 'double-barreled' science objectives to
capture samples
of two deep-space phenomena, comets and interstellar
dust," said Dr.
Kenneth Atkins, Stardust project manager at JPL.
Both the comet and interstellar dust samples will be collected
in a
special material called aerogel, a lightweight transparent silica
gel, the lowest density solid material in the world. (Aerogel was
most recently used as a lightweight insulating material to
protect
the Mars Pathfinder Sojourner's electronics from the harsh, cold
climate of Mars.)
As a Discovery-class mission, Stardust is one of NASA's new
"faster,
better, cheaper" missions. "Stardust also represents a
reversal in
traditional exploration technique," said Atkins.
"Instead of taking
expensively-packaged instruments to the target of interest,
Stardust
will bring samples of the targets to laboratories on Earth where
existing instruments with the latest techniques can be used to
examine them. This saves money and provides opportunities for
more
investigators to participate."
Comet Wild-2 is a 'fresh' comet which was recently (in 1974)
deflected by Jupiter's gravity from an earlier orbit lying much
farther out in the solar system. Having spent most of the last
4.6
billion years in the coldest, most distant reaches of the solar
system, Wild-2 represents a well-preserved example of the
fundamental
building blocks out of which our solar system formed.
Stardust is the fourth NASA Discovery mission to be chosen and
follows the Mars Pathfinder, Near Earth Asteroid Rendezvous
(NEAR),
and Lunar Prospector missions. The goal of NASA's Discovery
Program
is to launch many small missions that perform focused science
with
fast turn-around times, cost less than $150 million (in FY '92
dollars) to build, and are joint efforts with industry, small
business and universities.
The principal investigator for Stardust is Dr. Donald E.
Brownlee of
the University of Washington, well-known for his discovery of
cosmic
particles in Earth's stratosphere. JPL's Dr. Peter Tsou,
innovator in
aerogel technology and maker of aerogel, serves as deputy
investigator.
Stardust is being built by Lockheed Martin Astronautics,
Denver, CO.
JPL will provide the mission science payload that includes the
optical navigation camera and manages the overall mission for
NASA's
Office of Space Science, Washington, DC. JPL is a division of the
California Insititute of Technology.
========================================================================
(5)
IS ANYBODY OUT THERE?
R. MAUERSBERGER, T. L. WILSON, R. T. ROOD, T. M. BANIA, H.
HEIN &
A. LINHART: SETI at the Spin-Flip Line of Positronium. ASTRONOMY
AND
ASTROPHYSICS, 1996, Vol.306, No.1, pp. 141-144
UNIVERSITY OF ARIZONA, STEWARD OBSERVATORY, TUCSON, AZ, 85721, USA
A directed search for extraterrestrial intelligence (SETI) has
been
carried out using the IRAM 30m telescope. Following a suggestion
by
Kardashev (1979), the search was conducted at the spin-flip line
of
the lightest atom, namely positronium, at 203 GHz. Most of the 17
targets are mature stars with excess infrared radiation, which
might
be the waste heat of a power-rich technological civilisation. The
rest frame of the cosmic background radiation was chosen as the
velocity frame. The spectral resolution used was 9.7 kHz. From
the
noise level, which was determined by the limited telescope time
and
weather conditions, the upper limit for the power of artificial
omnidirectional transmitters at the positronium line frequency is
of
order 10(15) W. The relevance of this non-detection is discussed.