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TheNEW PLANET!
Is There Another ?
Although it is perhaps too early to
feel absolute certainty, there would
seem to be no reason for doubting the
news just received from America that
another major member of the Solar
System has been discovered. The dis-
covery is hardly more interesting than
the manner by which it was achieved
(writes Sir James Jeans, in the London
"Observer," of March 16).
Five planets-Mercury, Venus, Mars,
Jupiter, and Saturn-form such con-
spicuous objects in the sky that they
have been known from the earliest
times. These and our Earth were the
only planets known until Sir William
Herschel discovered Uranus, almost by
accident, in 1781. What appeared at
first glance to be an ordinary star, a
mere bright point of light, was seen
on closer examination to have a visible
disc of sensible size, which was mov-
ing at a comparatively rapid rate
across the face of the sky. Its size
and the rapidity of its motion both
suggested that it must be a near
neighbor in the sky, and further study
showed that it was an ordinary planet,
the farthest from the sun so far known.
The Vagaries of Uranus.
If this had been the only planet ac-
companying the sun on its voyage
through space, its orbit round the sun
would have been a perfect ellipse, in
accordance with Newton's law of gra-
vitation. Careful observation showed
that the orbit was not a perfect ellipse.
Indeed, it could not have been, for
each time the new planet's motion
took it near to either Jupiter or Saturn
the gravitation pulls of their huge
weights would necessarily draw it a
bit out of a strictly elliptical orbit.
But it was soon found that the pulls
of the known planets did not account
for the whole of the observed aberra-
tions of Uranus, and suspicions were
aroused that part of them must be
attributed to a still unknown planet
even further away from the sun.
By following this scent, Neptune was
discovered in 1846. The Cambridge
astronomer, Adams, then only twenty
seven years old, and the French as-
tronomer Leverrier, aged thirty-five,
had set to work almost simultaneously
to calculate where the suspected outer
planet would have to be, in order to
account for the observed vagaries in
the motion of Uranus. The rest of
this chapter of astronomical history is
only too well known. Adams finished
his calculation first-easily first-yet,
owing to the dilatoriness of the, English
observers, the new planet was first
identified at a German observatory in
the place assigned to it by the French
astronomer.
"Mistaken for an Asteroid."
The story was not yet complete, for
further study showed that even the
added gravitational pull of Neptune
could not account for all the observed
vagaries in the motion of Uranus.
Once again various astronomers, in
particular Dr. Percival Lowell, the
founder and late director of the Flag-
staff Observatory in Arizona, began to
suspect that yet another planet must
be moving round the sun, even farther
out in the depths of space than Nep-
tune. And now we are told that the
suspected planet has been discovered
at Dr. Lowell's own observatory, mov-
ing in almost exactly the orbit which
Dr. Lowell's own mathematical calcu-
lations had predicted.
It is a tremendous event in the his-
tory of astronomy, although it is
hardly likely to make such a stir as
the discovery of Neptune, which was
hailed as the greatest triumph of the
human intellect since the time of New-
ton. For one thing, the intervening
eighty-four years has seen the main
interest of astronomy passing out be-
yond the confines of the Solar System
to the remotest of stars and nebulae.
Perhaps, too, the matter for won-
der is not so much that the discovery
has now been made, as that it was
not made sooner, for, in spite of its
smallness and remoteness, the new
planet is bright enough to be very
easily visible in a modern telescope of
even moderate power. One may even
hazard the conjecture that it may often
have been seen in the past and mis-
taken for an asteroid, one of the
thousands of tiny planets which move
round the sun in the vacant belt be-
tween the orbits of Mars and Jupiter.
Is there another?
300-Year Journey Round the Sun.
It will be interesting to see whether
the existence of the new planet ac-
counts adequately for all the outstand-
ing vagaries in the motions of Uranus,
as well as for those which are begin-
ning, to appear in the motions of Nep-
tune, or whether history will yet again
repeat itself, and astronomers will once
more find evidence, through its dis-
turbing influence; of yet another un-
known planet still farther out in the
depths of space.
Neptune, which now yields up its
distinction of being the outermost
planet, is thirty times as remote from
the sun as the earth is, but the new
planet is about forty-five times as re-
mote. Neptune's year is nearly 165 of
our years; but the new planet's jour-
ney round the sun must take over 300
of our years.
To an inhabitant of the new planet
the sun would appear about as large as
Jupiter appears to us. Without tele-
scopic aid, eyes like our own would see
the sun merely as a point of light; in-
deed they would see it for what it
really is-just one star among innum-
erable similar stars in the sky. But
the new planet can have no inhabit-
ants; its great distance from the sun
must make it far too cold. Its surface
will probably be found to have a tem-
perature in the neighborhood of -230
degrees Centigrade, which represents
over 400 degrees of frost on our or-
dinary English scale. If the earth
were put in its place not only we, but
even the atmosphere surrounding us
would be frozen solid.
The Genesis of the Planets.
In time the new planet may provide
valuable information bearing on the
question of how the Solar System
came into being.
Most astronomers now suppose that
the planets were pulled out of the sun
by the intense tidal action of a pas-
sing star. The very close passage of
a second star would raise huge tides on
the sun's surface. These would differ
in quality as well as in degree from
the feeble tides which the moon raises
in our oceans. A huge mountain of
matter would be raised which, in the
case of a very close approach indeed,
would become detached as a cigar-
shaped filament of gas. This would
ultimately break up and condense into
detached masses, somewhat as a cloud
of steam condenses into detached drops
of water.
In some such way, it is supposed,
the present planets came into being.
We can still see traces of the cigar-
shaped configuration of the original
filament in the fact that the largest
planet, Jupiter, occurs in the middle
of the sequence, while, generally speak-
ing, the planets tail off, both in size
and in weight, as we recede from
Jupiter in either direction.
Unless still more planets remain to
be discovered, the new planet must
represent the extreme tip-end of this
cigar: its substance must be the spray
thrown off by the very crest of the
huge tidal wave which a passing star
raised on our sun's surface some two
thousand million years ago. Thus it
ought to be smaller than Neptune, its
next neighbor in the sequence of plan-
ets, as-satisfactorily for theory-it is
said to be. It ought also to have been
the first of all the planets to cool down
and solidify. As a consequence of
this it will probably prove to be unat-
tended by satellites, being in this re-
spect like Mercury and Venus at the
other end of the cigar. Or (although
much less probably) it may prove to
have a single relatively large, satel-
lite like Neptune or the Earth.
But it is rash to prophesy; the new
planet may not only falsify our pre-
dictions, but may even compel us to
abandon our present views as to the
origin of the sun's family of planets.
This is part of the value inherent in
its discovery.
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