THE STARS--HAVE THEY PLANETARY SYSTEMS? ARE THEY BENEFICIAL TO US?
Most of the writers on the Plurality of Worlds, from Fontenelle to Proctor,
taking into consideration the enormous number of the stars and their
apparent uselessness to our world, have assumed that many of them _must_
have systems of planets circling round them, and that some of these
planets, at all events, _must_ possess inhabitants, some, perhaps, lower,
but others no doubt higher than ourselves. One of our well-known modern
astronomers, writing only ten years ago, adopts the same view. He says:
'The suns which we call stars were clearly not created for our benefit.
They are of very little practical use to the earth's inhabitants. They give
us very little light; an additional small satellite--one considerably
smaller than the moon--would have been much more useful in this respect
than the millions of stars revealed by the telescope. They must therefore
have been formed for some other purpose.... We may therefore conclude, with
a high degree of probability, that the stars--at least those with spectra
of the solar type--form centres of planetary systems somewhat similar to
our own.'[21] The author then discusses the conditions necessary for life
analogous to that of our earth, as regards temperature, rotation, mass,
atmosphere, water, etc., and he is the only writer I have met with who has
considered these conditions; but he touches on them very briefly, and he
arrives at the conclusion that, in the case of the stars of solar type, it
is probable that _one_ planet, situated at a proper distance, would be
fitted to support life. He estimates roughly that there are about ten
million stars of this type, that is, closely resembling our sun, and that
if only one in ten of these has a planet at the proper distance and
properly constituted in other respects, there will be one million worlds
fitted for the support of animal life. He therefore concludes that there
are probably many stars having life-bearing planets revolving round them.
There are, however, many considerations not taken account of by this writer
which tend to reduce very considerably the above estimate. It is now known
that immense numbers of the stars of smaller magnitudes are nearer to us
than are the majority of the stars of the first and second magnitudes, so
that it is probable that these, as well as a considerable proportion of the
very faint telescopic stars, are really of small dimensions. We have
evidence that many of the brightest stars are much larger than our sun, but
there are probably ten times as many that are much smaller. We have seen
that the whole of the past light and heat-giving duration of our sun has,
according to the best authorities, been only just sufficient for the
development of life upon the earth. But the duration of a sun's heat-giving
power will depend mainly upon its mass, together with its constituent
elements. Suns which are much smaller than ours are, therefore, from that
cause alone, unsuited to give adequate light and heat for a sufficient
time, and with sufficient uniformity, for life-development on planets, even
if they possess any at the right distance, and with the extensive series of
nicely adjusted conditions which I have shown to be necessary.
Again, we must, probably, rule out as unfitted for life-development the
whole region of the Milky Way, on account of the excessive forces there in
action, as shown by the immense size of many of the stars, their enormous
heat-giving power, the crowding of stars and nebulous matter, the great
number of star-clusters, and, especially, because it is the region of 'new
stars,' which imply collisions of masses of matter sufficiently large to
become visible from the immense distance we are from them, but yet
excessively small as compared with suns the duration of whose light is to
be measured by millions of years. Hence the Milky Way is the theatre of
extreme activity and motion; it is comparatively crowded with matter
undergoing continual change, and is therefore not sufficiently stable for
long periods to be at all likely to possess habitable worlds.
We must, therefore, limit our possible planetary systems suitable for
life-development, to stars situated inside the circle of the Milky Way and
far removed from it--that is, to those composing the solar cluster. These
have been variously estimated to consist of a few hundred or many thousand
stars--at all events to a very small number as compared with the 'hundreds
of millions' in the whole stellar universe. But even here we find that
only a portion are probably suitable. Professor Newcomb arrives at the
conclusion--as have some other astronomers--that the stars in general have
a much smaller mass in proportion to the light they give than our sun has;
and, after an elaborate discussion, he finally concludes that the brighter
stars are, on the average, much less dense than our sun. In all
probability, therefore, they cannot give light and heat for so long a
period, and as this period in the case of our sun has only been just
sufficient, the number of suns of the solar type and of a sufficient mass
may be very limited. Yet further, even among stars having a similar
physical constitution to our sun and of an equal or greater mass, only a
portion of their period of luminosity would be suitable for the support of
planetary life. While they are in process of formation by accretions of
solid or gaseous masses, they would be subject to such fluctuations of
temperature, and to such catastrophic outbursts when any larger mass than
usual was drawn towards them, that the whole of this period--perhaps by far
the longest portion of their existence--must be left out of the account of
planet-producing suns. Yet all these are to us stars of various degrees of
brilliancy. It is almost certain that it is only when the growth of a sun
is nearly completed, and its heat has attained a maximum, that the epoch of
life-development is likely to begin upon any planets it may possess at the
most suitable distance, and upon which all the requisite conditions should
be present.
It may be said that there are great numbers of stars beyond our solar
cluster and yet within the circle of the Milky Way, as well as others
towards the poles of the Milky Way, which I have not here referred to. But
of these regions very little is known, because it is impossible to tell
whether stars in these directions are situated in the outer portion of the
solar cluster or in the regions beyond it. Some astronomers appear to think
that these regions may be nearly empty of stars, and I have endeavoured to
represent what seems to be the general view on this very difficult subject
in the two diagrams of the stellar universe at pp. 300, 301. The regions
beyond our cluster and above or below the plane of the Milky Way are those
where the small irresolvable nebulæ abound, and these may indicate that
sun-formation is not yet active in those regions. The two charts of Nebulæ
and Clusters at the end of the volume illustrate, and perhaps tend to
support this view.
DOUBLE AND MULTIPLE STAR SYSTEMS
We have already seen, in our sixth chapter, how rapid and extraordinary has
been the discovery of what are termed spectroscopic binaries--pairs of
stars so close together as to appear like a single star in the most
powerful telescopes. The systematic search for such stars has only been
carried on for a few years, yet so many have been already found, and their
numbers are increasing so rapidly, as to quite startle astronomers. One of
the chief workers in this field, Professor Campbell of the Lick
Observatory, has stated his opinion that, as accuracy of measurement
increases, these discoveries will go on till--'the star that is not a
spectroscopic binary will prove to be the rare exception,'--and other
astronomers of eminence have expressed similar views. But these close
revolving star-systems are generally admitted to be out of the category of
life-producing suns. The tidal disturbances mutually produced must be
enormous, and this must be inimical to the development of planets, unless
they were very close to each sun, and thus in the most unfavourable
position for life.
We thus see that the result of the most recent researches among the stars
is entirely opposed to the old idea that the countless myriads of stars
_all_ had planets circulating round them, and that the ultimate purpose of
their existence was, that they should be supporters of life, as our sun is
the supporter of life upon the earth. So far is this from being the case,
that vast numbers of stars have to be put aside as wholly unfitted for such
a purpose; and when by successive eliminations of this nature we have
reduced the numbers which may possibly be available to a few millions, or
even to a few thousands, there comes the last startling discovery, that the
entire host of stars is found to contain binary systems in such rapidly
increasing numbers, as to lead some of the very first astronomers of the
day to the conclusion that single stars may someday be found to be the rare
exception! But this tremendous generalisation would, at one stroke, sweep
away a large proportion of the stars which other successive
disqualifications had spared, and thus leave our sun, which is certainly
single, and perhaps two or three companion orbs, alone among the starry
host as possible supporters of life on some one of the planets which
circulate around them.
But we do not really _know_ that any such suns exist. If they exist we do
not _know_ that they possess planets. If any do possess planets these may
not be at the proper distance, or be of the proper mass, to render life
possible. If these primary conditions should be fulfilled, and if there
should possibly be not only one or two, but a dozen or more that so far
fulfil the first few conditions which are essential, what probability is
there that all the other conditions, all the other nice adaptations, all
the delicate balance of opposing forces that we have found to prevail upon
the earth, and whose combination here is due to exceptional conditions
which exist in the case of no other known planet--should _all_ be again
combined in some of the possible planets of these possibly existing suns?
I submit that the probability is _now_ all the other way. So long as we
could assume that all the stars might be, in all essentials, like our sun,
it seemed almost ludicrous to suppose that our sun alone should be in a
position to support life. But when we find that enormous classes like the
gaseous stars of small density, the solar stars while increasing in size
and temperature, the stars which are much smaller than our sun, the
nebulous stars, probably all the stars of the Milky Way, and lastly that
enormous class of spectroscopic doubles--veritable Aaron's rods which
threaten to swallow up all the rest--that all these are for various reasons
unlikely to have attendant planets adapted to develop life, then the
probabilities seem to be enormously against there being any considerable
number of suns possessing attendant habitable earths. Just as the
habitability of all the planets and larger satellites, once assumed as so
extremely probable as to amount almost to a certainty, is now generally
given up, so that in speculating on life in stellar systems Mr. Gore
assumes that only _one_ planet to each sun can be habitable; in like manner
it may, and I believe will, turn out, that of all the myriad stars, the
more we learn about them, the smaller and smaller will become the scanty
residue which, with any probability, we can suppose to illuminate and
vivify habitable earths. And when with this scanty probability we combine
the still scantier probability that any such planet will possess
simultaneously, and for a sufficiently long period, _all_ the highly
complex and delicately balanced conditions known to be essential for a full
life-development, the conception that on this earth alone has such
development been completed will not seem so wildly improbable a conjecture
as it has hitherto been held to be.
ARE THE STARS BENEFICIAL TO US?
When I suggested in my first publication on this subject that some
emanations from the stars _might_ be beneficial or injurious, and that a
central position _might_ be essential in order to render these emanations
equable, one of my astronomical critics laughed the idea to scorn, and
declared that 'we might wander into outer space without losing anything
more serious than we lose when the night is cloudy and we cannot see the
stars.'[22] How my critic knows that this is so he does not tell us. He
states it positively, with no qualification, as if it were an established
fact. It may be as well to inquire, therefore, if there is any evidence
bearing upon the point at issue.
Astronomers are so fully occupied with the vast number and variety of the
phenomena presented by the stellar universe and the various difficult
problems arising therefrom, that many lesser but still interesting
inquiries have necessarily received little attention. Such a minor problem
is the determination of how much heat or other active radiation we receive
from the stars; yet a few observations have been made with results that are
of considerable interest.
In the years 1900 and 1901 Mr. E.F. Nichols of the Yerkes Observatory made
a series of experiments with a radiometer of special construction, to
determine the heat emitted by certain stars. The result arrived at was,
that Vega gave about 1/200000000 of the heat of a candle at one metre
distance, and Arcturus about 2.2 times as much.
In 1895 and 1896 Mr. G.M. Minchin made a series of experiments on the
_Electrical Measurement of Starlight_, by means of a photo-electric cell of
peculiar construction which is sensitive to the whole of the rays in the
spectrum, and also to some of the ultra-red and ultra-violet rays. Combined
with this was a very delicate electrometer. The telescope employed to
concentrate the light was a reflector of two feet aperture. Mr. Minchin was
assisted in the experiments by the late Professor G.F. Fitzgerald, F.R.S.,
of Trinity College, Dublin, which may be considered guarantee of the
accuracy of the observations. The following are the chief results
obtained:--
-----------------------------------------------------------------------
---------------------------------+-------------+-----------+-----------
| Deflection | Light |
Source of Light. | in | in | E. M. F.
| Millimetres | Candles. | Volts.
---------------------------------+-------------+-----------+-----------
1896 Candle at 10 feet distance | 18.70 | |
Betelgeuse (0.9 mag.) | 12.80 | 0.685 | 0.026
Aldebaran (1.1 mag.) | 5.21 | 0.279 | 0.012
Procyon (0.5 mag) | 4.89 | 0.261 | 0.011
Alpha Cygni (1.3 mag.) | 4.90 | 0.262 | 0.011
Polaris (2.1 mag.) | 3.10 | 0.166 | 0.007
---------------------------------+-------------+-----------+-----------
1 volt. | 432.00 | |
| | |
1895 Arcturus (0.3 mag.) | 8.2 | 1.01 | 0.019
Vega (0.1 mag) | 11.5 | 1.42 | 0.026
Candle at 10 feet | 8.1 | |
---------------------------------+-------------+-----------+-----------
N.B.--The standard candle shone directly on the cell, whereas
the star's light was concentrated by a 2-foot mirror.
The sensitive surface on which the light of the stars was concentrated was
1/20 inch in diameter. We must therefore diminish the amount of candle
light in this table in the proportion of the square of the diameter of the
mirror (in 1/20 of an inch) to one, equal to 1/230400. If we make the
necessary reduction in the case of Vega, and also equalise the distance at
which the candle was placed, we find the following result:--
Observer. Star. Candle power at 10 ft.
Minchin. Vega 1/162250
Nichols. " 1/22000000
This enormous difference in the result is no doubt largely due to the fact
that Mr. Nichols's apparatus measured heat alone, whereas Mr. Minchin's
cell measured almost all the rays. And this is further shown by the fact
that, whereas Mr. Nichols found Arcturus a red star, hotter than Vega a
white one, Mr. Minchin, measuring also the light-giving and some of the
chemical rays, found Vega considerably more energetic than Arcturus. These
comparisons also suggest that other modes of measurement might give yet
higher results, but it will no doubt be urged that such minute effects must
necessarily be quite inoperative upon the organic world.
There are, however, some considerations which tend the other way. Mr.
Minchin remarks on the unexpected fact that Betelgeuse produces more than
double the electrical energy of Procyon, a much brighter star. This
indicates that many of the stars of smaller visual magnitudes may give out
a large amount of energy, and it is this energy, which we now know can take
many strange and varied forms, that would be likely to influence organic
life. And as to the quantity being too minute to have any effect, we know
that the excessively minute amount of light from the very smallest
telescopic stars produces such chemical changes on a photographic plate as
to form distinct images, with comparatively small lenses or reflectors and
with an exposure of two or three hours. And if it were not that the
diffused light of the surrounding sky also acts upon the plate and blurs
the faint images, much smaller stars could be photographed.
We know that not all the rays, but a portion only, are capable of producing
these effects; we know also that there are many kinds of radiation from the
stars, and probably some yet undiscovered comparable with the X rays and
other new forms of radiation. We must also remember the endless variety
and the extreme instability of the protoplasmic products in the living
organism, many of which are perhaps as sensitive to special rays as is the
photographic plate.
And we are not here limited to action for a few minutes or a few hours, but
throughout the whole night and day, and continued whenever the sky is clear
for months or years. Thus the cumulative effect of these very weak
radiations may become important. It is probable that their action would be
most influential on plants, and here we find all the conditions requisite
for its accumulation and utilisation in the large amount of leaf-surface
exposed to it. A large tree must present some hundreds of superficial feet
of receptive surface, while even shrubs and herbs often have a leaf-area of
greater superficial extent than the object-glasses of our largest
telescopes. Some of the highly complex chemical processes that go on in
plants may be helped by these radiations, and their action would be
increased by the fact that, coming from every direction over the whole
surface of the heavens, the rays from the stars would be able to reach and
act upon every leaf of the densest masses of foliage. The large amount of
growth that takes place at night may be in part due to this agency.
Of course all this is highly speculative; but I submit, in view of the fact
that the light of the very faintest stars _does_ produce distinct chemical
changes, that even the very minute heat-effects are measureable, as well as
the electro-motive forces caused by them; and further, that when we
consider the millions, perhaps hundreds of millions of stars, all acting
simultaneously on any organism which may be sensitive to them, the
supposition that they do produce some effect, and possibly a very important
effect, is not one to be summarily rejected as altogether absurd and not
worth inquiring into.
It is not, however, these possible direct actions of the stars upon living
organisms to which I attach much weight as regards our central position in
the stellar universe. Further consideration of the subject has convinced me
that the fundamental importance of that position is a physical one, as has
already been suggested by Sir Norman Lockyer and some other astronomers.
Briefly, the central position appears to be the only one where suns can be
sufficiently stable and long-lived to be capable of maintaining the long
process of life-development in any of the planets they may possess. This
point will be further developed in the next (and concluding) chapter.
FOOTNOTES:
[21] _The Worlds of Space_, by J.E. Gore, chapter iii.
[22] _The Fortnightly Review_, April 1903, p. 60.