Table Of ContentOn the
Origin Planets
of
By Means of Natural Simple Processes
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On the
Origin Planets
of
By Means of Natural Simple Processes
Michael M. Woolfson
University of York, UK
Imperial College Press
ICP
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ON THE ORIGIN OF PLANETS
By Means of Natural Simple Processes
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Preface
I began to write this book in the year 2009, the 200th anniversary
of the birth of Charles Darwin and the sesquicentenary of the pub-
lication of The Origin of Species. The BBC has commemorated this
doubleanniversarywithtwosplendidseriesoftelevisionprogrammes,
one highlighting the experimental side of Darwin’s work and the
other the impact made by his theory of natural selection on both
thescientificandreligiousestablishmentsofhistimeandonpolitical
philosophies until quite recently. Come to think of it, the impact can
be felt even today. There are still many who believe that the world
andallitcontainswasmadesome6,000yearsagobyanactofdivine
creation and that, in particular, mankind was created in its present
form. Such fundamentalist views are quite common in the United
States but perhaps less so in most European countries.
StimulatedbytheBBCprogrammes,Ilookedagainatmycopyof
The Origin of Species, the sixth edition published in 1888. Included
on the title page is the line ‘THIRTY-THIRD THOUSAND’, the total
number of copies printed by John Murray, the publisher, up to that
date. This is quite a modest print run for a work of such importance
andIfinditsurprisingthatsofewcopiesofthebookcouldhavemade
such a great impact. Probably the newspaper cartoons depicting
Darwin’s head on the bodies of apes made more of an impression
on the public than the book itself, a lengthy scholarly presentation
thatfewlaymenwouldhaveregardedasattractivereading.Browsing
through it, I am struck by the detail in the presentation of the
arguments in favour of natural selection. Darwin was worried about
the consequences of presenting his theory, fearing adverse reactions
from both the clergy and scientists. To defend himself against
potential criticism he laid out his ideas in meticulous detail, building
his case step by step in a logical progression. Even so, it took the
v
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vi On the Origin of Planets
interventionofAlfredRusselWallace,ayoungEnglishanthropologist
livingintheEastIndiesatthetime,topushDarwinintopublication.
In 1858 Darwin received from Wallace a draft paper which described
ideas on evolution and natural selection very similar to his own.
To his credit, Darwin helped in the publication of this paper but
covered his own proprietary rights on the theory by arranging for a
presentation of both his and Wallace’s ideas to the Linnean Society
of London, the world’s leading society devoted to natural history, in
July 1858. One is left wondering when, and if, The Origin of Species
would have appeared without Wallace’s influence on events.
A striking aspect of Darwin’s style is that it is written in the
first person, so the reader feels as if the narrative is related to him
personally — at least this is the impression I have. The kinship I
feel with Darwin is a particular one. Much of my scientific work
has been in a field where the word ‘origin’ has relevance; in my
case it is the origin of planets. Darwin took 20 years to develop
his ideas while I have taken 47 years to develop my own. Darwin’s
ideas on evolution were themselves evolving as he uncovered more
and more evidence to support the basic concept of natural selection.
My own ideas have evolved as observational evidence has revealed
more and more facts about the presence of planets in our galaxy and
the locations in which stars, and presumably planets, are formed.
Let it not be thought that I am claiming equal importance for the
topic of planet formation as that of natural selection. The Universe
is full of material and finding out how this is assembled by physical
processes to form planets is mundane and humdrum compared with
how new species of both animate and inanimate life evolved from
simple forms through to creatures as complex as ourselves. However,
there are problems even more fundamental than those addressed by
Darwin; natural selection describes how new types of life develop
from previous forms but does not deal with the origin of life in the
simplest forms of single-celled bacteria and archaea. The origin of
life and the origin of the Universe — these are the really important,
fundamental problems to which, as yet, we have no solutions.
Humdrum or not, the problem of how planets originated is
regarded to be of sufficient importance for space agencies worldwide
to assign considerable resources to support projects that make
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Preface vii
observations that might help to solve this problem. Even if it is not
one of the great fundamental problems of our age, looking for the
mechanisms by which planets may have formed is of interest and has
exercised, and still exercises, the minds of many scientists, especially
during the last 200 years.
Looking at Darwin’s great opus, I am inspired to take it as a
model and, to the best of my ability, to emulate his thoroughness
in describing my own ideas in The Origin of Planets. There must,
of course, be important differences between the general form of
presentation of The Origin of Species and the one I shall be using.
A treatise on natural history can be cast in everyday language and
The Origin of Species deals with the problems of the general reader
by providing a glossary of scientific terms at the end of the book. By
contrast, astronomy, dealt with in a formal way, must be expressed
in terms of physics and mathematics — foreign languages to the
majorityofnon-specialistreaders.Manyofthephysicalrelationships
that describe astrophysical processes are most clearly expressed in
theformofequationsandwouldbeimpossiblydifficulttodescribein
words, except in a most handwaving way. Another difference is that,
whereas Darwin made do with a single simple figure illustrating an
evolutionary tree, modern printing technology allows for the prolific
use of pictures and diagrams to assist the reader. I shall try to walk
the tightrope of giving a proper formal presentation of the science
whilealsoexpressingideasinwordsthatshouldconveytheessenceof
thesciencetoanon-specialist.InplaceofDarwin’sglossaryisaseries
of appendices. Some of these are designed to help the non-specialist
reader to understand the physical concepts and terminology; others
will derive physical relationships and will be of more interest to the
specialist reader.
I shall begin this book in much the style that Darwin did in The
Origin of Species, with an historical review of the important theories
and ideas that have gone before. Thereafter I shall revert to a more
modern format, although I shall try to maintain the detailed and
rigorousreasoningthatDarwinemployed.WillIsucceedinspanning
the divide between the professional scientist and the non-specialist?
We shall see.
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Contents
Preface v
An Historical Sketch of the Progress of Opinion
on the Origin of Planets xix
1. Observations of Stars 1
1.1 Locations of Stars. . . . . . . . . . . . . . . . . 1
1.2 Stellar Material . . . . . . . . . . . . . . . . . . 4
1.3 Determining the Distances of Stars . . . . . . . 5
1.3.1 The distances of nearby stars . . . . . . 5
1.3.2 Distance measurements using
variable stars . . . . . . . . . . . . . . . 7
1.4 The Temperature of Stars . . . . . . . . . . . . 9
1.5 Stellar Radii . . . . . . . . . . . . . . . . . . . . 12
1.6 Estimating Stellar Masses . . . . . . . . . . . . 13
1.7 The Physical Properties of Main-Sequence
Stars . . . . . . . . . . . . . . . . . . . . . . . . 14
1.8 Stellar Spin Rates. . . . . . . . . . . . . . . . . 15
1.9 Summary . . . . . . . . . . . . . . . . . . . . . 15
2. Producing Protostars — Embryonic Stars 19
2.1 Star-Forming Regions . . . . . . . . . . . . . . 19
2.2 The Formation of Dense Cool Clouds . . . . . . 21
2.3 Maser Emission from Star-Forming Regions . . 26
2.4 The Process of Protostar Formation . . . . . . 27
2.5 The Formation of Binary Systems . . . . . . . . 28
ix
