PLEASE NOTE:
*
LETTERS TO THE MODERATOR, 12 May 1999
-------------------------------------
(1) ARE LOCAL ETs SHORT-SIGHTED?
Alan Fitzsimmons <A.Fitzsimmons@Queens-Belfast.AC.UK>
(2) RESPONSE TO ALAN FITZSIMMONS
Gregory Matloff <gm21@is3.nyu.edu>
(3) THE CAPTURE THEORY OF THE ORIGIN OF THE SOLAR SYSTEM
John McCue <mccue@johnast.demon.co.uk>
(4) AND FINALLY....
Robert Matthews <rajm@compuserve.com>
=============
(1) ARE LOCAL ETs SHORT-SIGHTED?
From Alan Fitzsimmons <A.Fitzsimmons@Queens-Belfast.AC.UK>
Dear Benny,
Just a comment on Gregory Lee Matloff's suggestion of looking at
KBOs
for sign of ET presence. I am a big fan of SETI, and believe that
looking at alternatives to 21-cm searches is a good thing. So
considering different methods of SETI, what Gregory has done,
should
be applauded. However, having looked at the web site mentioned, I
find
the reasoning behind this particular strategy to be unconvincing.
The statement is made that the colour of some KBOs are very red,
and
that the reason for that is unknown. In fact, it is entirely
unsurprising. Many small bodies in the outer Solar system share
this
property, from the Trojans at 5.2 AU outwards. It is generally
believed to be due to the irradiation of organic-bearing ices on
the
surfaces of these bodies.
What was surprising was finding in the paper quoted on the web
site
(Tegler and Romanishin 1998) that there may exist two distinct
spectral classes in the Kuiper belt. This point is still debated,
and
it is fair to say that no consensus has yet emerged between the
people working in this area. That there is a wide variation in
optical and near-IR colour is undisputed, but work by Jane Luu
and
others implicates the past collisional and resurfacing histories
of
these bodies as the cause, rather than any artificial culprit.
Finally, the existence of the belt itself is well explained by
current formation theories (hence its name!), and there is no
reason
to suspect it is full of ET spacecraft.
In summary, there is no observational reason to look at the
Kuiper
belt for ETs rather than the asteroid belt, or I guess any other
place in the Solar system that can handle stable orbits. I will
let
someone else comment on the prospect of finding ETs on NEOs,
although
placing yourself on a body that will one day hit a planet or the
Sun
is a bit short-sighted in my opinion!
Best Wishes
Alan
============
(2) RESPONSE TO ALAN FITZSIMMONS
From Gregory Matloff <gm21@is3.nyu.edu>
Thanks for the opportunity to respond to Dr. Fitzsimmon's
comments
regarding the possibility of ET habitats among the Kuiper Belt.
First, the anomolous red excess of some Kuiper objects had been
discovered but not explained while the NIDS essay was under
preparation. One paper a few months ago in Icarus, I believe,
explains this red-excess as caused by Tholin, a natural organic
compound.
We need a true infrared excess to really point
towards the
possibility of an ET habitat.
I think that the Kuiper or Oort Belt objects
are better habitat
sites than most main-belt asteroids because of the larger
concentration of water-ice in these objects. Of course, some
main-belt objects are almost certainly hydrated as well.
The main argument of my essay, and one that is
very hard to
argue with, is that the solar-system may have been colonized. As
I
will present in a co-authored paper during the Amsterdam IAF
Congress
in October 1999, this is probable if one in 10,000 stars or so
has
evolved a long-lived technological civilization. This is the
basic
unknown--how many ET techies are there???---GREG MATLOFF
================
(3) THE CAPTURE THEORY OF THE ORIGIN OF THE SOLAR SYSTEM
From John McCue <mccue@johnast.demon.co.uk>
Dear Benny,
May I make this contribution, my first?
The latest BBC TV production "The Planets" prompted me
to contact my
former supervisor, Dr. John Dormand at Teesside University, UK,
for
his views. The first programme in the BBC series discussed the
formation of the planets exclusively, and at length, in terms of
the
accretion theory, though it admitted that the formation of Uranus
and
Neptune by accretion cannot yet be established by computer
modelling.
John Dormand is well aware of this, being a collaborator on the
alternative Capture Theory with Prof. Michael Woolfson, of York
University, also in the UK.
The Capture Theory proposes that the planets formed in the same
way
as stars, i.e. by the gravitational collapse of material. In
particular, this cool material is captured by the sun from a
protostar.. John has given me permission to reproduce extracts
from
his joint book on the subject "The Origin of the Solar
System" (Ellis
Horwood, UK, 1989), as follows.
"The early capture theories of Schmidt (1947), and Lyttleton
(1961)
rely on random processes occurring in a dispersed medium for the
actual production of planets. A satisfactory description of such
processes is still to be found despite the close attentions of
many
nebula cosmogonists (e.g. Safronov, 1972). The only undisputed
mechanism permitting the condensation of tenuous material to form
relatively dense bodies is gravitational instability, and all
theories of star formation rely on this process. It seems
reasonable
to suppose that planets are formed in a similar way. Of course, a
cloud of planetary mass will not condense if it is too hot. It is
logical to propose two major requirements of a theory of the
origin
of planetary systems:
1. planetary material must be captured (to solve the angular
momentum
problem);
2. primitive planetary material must be sufficiently cool and
dense
to be gravitationally unstable.
The Capture Theory, proposed originally by Woolfson, satisfies
both
of these requirements. In this theory, it is proposed that an
encounter took place between the sun and a cool protostar, both
bodies having originated in the same stellar cluster. The density
of
stars in a young cluster would be sufficiently large to make
close
encounters fairly common. During a close approach, the protostar
would be greatly affected by solar tidal forces. Material would
be
removed from the protostar, captured by the sun, and eventually
form
the planetary bodies by gravitational collapse. The Capture
Theory
proposes that the protostar is a very extended body, and
therefore
not well-described by a single point mass. Fortunately, the power
of
computer modelling is able to test this theory in a comprehensive
manner. The results indicate the plausibility of the Capture
Theory
for the formation of the planets beyond any reasonable
doubt."
The discoveries in recent years of protoplanetary disks does not
necessarily lend weight against the Capture Theory. In a recent
correspondence with me, John Dormand wrote "I can't see why
a capture
mechanism is at odds with 'protoplanetary disks'. Perhaps these
are
also the products of tidal events."
After ten years of modesty, perhaps the time is right for the
Capture
Theory to be considered by the wider astronomical community, and
accepted as a work that can explain the observed features of the
solar
system.
Dr. John McCue, FRAS,
40, Bradbury Rd.,
Norton,
Stockton-on-Tees,
UK,
TS20 1LE
============
(4) AND FINALLY....
From Robert Matthews <rajm@compuserve.com>
Hi Benny
> >(9) STILL NO CLUES AS TO WHY AGRICULTURE WAS INITIATED
> >
> >A.M. Mannion: Domestication and the origins of
agriculture: an
> >appraisal. PROGRESS IN PHYSICAL GEOGRAPHY, 1999, Vol.23,
No.1,
> >pp.37-56
Shouldn't the reference read: LACK OF PROGRESS IN PHYSICAL
GEOGRAPHY ?
best wishes
Robert
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