Heavenly Bodies

: LAST OF EARTH

The following day, while in their observatory, they saw something

not many miles ahead. They watched it for hours, and in fact all

day, but notwithstanding their tremendous speed they came but

little nearer.



"They say a stern chase is a long one," said Bearwarden; but that

beats anything I have ever seen."



After a while, however, they found they WERE nearer, the time

tak
n having been in part due to the deceptive distance, which

was greater than they supposed.



"A comet!" exclaimed Cortlandt excitedly. "We shall really be

able to examine it near."



"It's going in our direction," said Ayrault, "and at almost

exactly our speed."



While the sun shone full upon it they brought their camera into

play, and again succeeded in photographing a heavenly body at

close range. The nucleus or head was of course turned towards

the sun; while the tail, which they could see faintly, preceded

it, as the comet was receding towards the cold and dark depths of

space. The head was only a few miles in diameter, for it was a

small comet, and was composed of grains and masses of stone and

meteoric iron. Many of the grains were no larger than peas or

mustard-seeds; no mass was more than four feet in diameter, and

all of them had very irregular shapes. The space between the

particles was never less than one hundred times their masses.



"We can move about within it," said Ayrault, as the Callisto

entered the aggregation of particles, and moved slowly forward

among them.



The windows in the dome, being made of toughened glass, set

somewhat slantingly so as to deflect anything touching them, and

having, moreover, the pressure of the inside air to sustain them,

were fairly safe, while the windows in the sides and base were

but little exposed. Whenever a large mass seemed dangerously

near the glass, they applied an apergetic shock to it and sent it

kiting among its fellows. At these times the Callisto recoiled

slightly also, the resulting motion in either being in inverse

ratio to its weight. There was constant and incessant movement

among the individual fragments, but it was not rotary. Nothing

seemed to be revolving about anything else; all were moving,

apparently swinging back and forth, but no collisions took place.

When the separate particles got more than a certain distance

apart they reapproached one another, but when seemingly within

about one hundred diameters of each other they swung off in some

other direction. The motion was like that of innumerable

harp-strings, which may approach but never strike one another.

After a time the Callisto seemed to become endowed with the same

property that the fragments possessed; for it and they repelled

one another, on a near approach, after which nothing came very

near.



Much of the material was like slag from a furnace, having

evidently been partly fused. Whether this heat was the result of

collision or of its near approach to the sun at perihelion, they

could not tell, though the latter explanation seemed most simple

and probable. When at about the centre of the nucleus they were

in semi-darkness--not twilight, for any ray that succeeded in

penetrating was dazzlingly brilliant, and the shadows, their own

included, were inky black. As they approached the farther side

and the sunlight decreased, they found that a diffused luminosity

pervaded everything. It was sufficiently bright to enable them

to see the dark side of the meteoric masses, and, on emerging

from the nucleus in total darkness, they found the shadow

stretching thousands of miles before them into space.



"I now understand," said Bearwarden, "why stars of the sixth and

seventh magnitude can be seen through thousands of miles of a

comet's tail. It is simply because there is nothing in it. The

reason ANY stars are obscured is because the light in the tail,

however faint, is brighter than they, and that light is all that

the caudal appendage consists of, though what produces it I

confess I am unable to explain. I also see why the tail always

stretches away from the sun, because near by it is overwhelmed by

the more powerful light; in fact, I suspect it is principally in

the comet's shadow that the tail is visible. It is strange that

no one ever thought of that before, or that any one feared the

earth's passing through the tail of a comet. It is obvious to me

now that if there were any material substance, any gas, however

rarefied, in this hairlike[1] accompaniment, it would immediately

fall to the comparatively heavy head,

and surround that as a centre."



[1] Comet means literally a hair.





"How, then," asked Cortlandt, "do you account for the spaces

between those stones? However slight gravitation might be

between some of the grains, if it existed at all, or was

unopposed by some other force, with sufficient time--and they

have eternity--every comet would come together like a planet into

one solid mass. Perhaps some similar force maintains gases in

the distended tail, though I know of no such, or even any

analogous manifestation on earth. If the law on which we have

been brought up, that 'every atom in the universe attracts every

other atom,' were without exceptions or modifications, that comet

could not continue to exist in its present form. Until we get

some additional illustration, however, we shall be short of data

with which to formulate any iconoclastic hypothesis. The source

of the light, I must admit, also puzzles me greatly. There is

certainly no heat to which we can attribute it."



Having gone beyond the fragments, they applied a strong repulsion

charge to the comet, creating thereby a perfect whirlpool among

its particles, and quickly left it. Half an hour later they

again shut off the current, as the Callisto's speed was

sufficient.



For some time they had been in the belt of asteroids, but as yet

they had seen none near. The morning following their experience

with the comet, however, they went to their observatory after

breakfast as usual, and, on pointing their glasses forward,

espied a comparatively large body before them, a little to their

right.



"That must be Pallas," said Cortlandt, scrutinizing it closely.

"It was discovered by Olbers, in 1802, and was the second

asteroid found, Ceres having been the first, in 1801. It has a

diameter of about three hundred miles, being one of the largest

of these small planets. The most wonderful thing about it is the

inclination of its orbit--thirty-five degrees--to the plane of

the ecliptic; which means that at each revolution in its orbit,

it swings that much above and below the imaginary plane cutting

the sun at its equator, from which the earth and other larger

planets vary but little. This no doubt is due to the near

approach and disturbing attraction of some large comet, or else

it was flung above or below the ordinary plane in the catastrophe

that we think befell the large planet that doubtless formerly

existed where we now find this swarm. You can see that its path

makes a considerable angle to the plane of the ecliptic, and that

it is now about crossing the line."



It soon presented the phase of a half moon, but the waviness of

the straight line, as in the case of Venus and Mercury, showed

that the size of the mountains must be tremendous compared with

the mass of the body, some of them being obviously fifteen miles

high. The intense blackness of the shadows, as on the moon,

convinced them there was no trace of atmosphere.



"There being no air," said Cortlandt, "it is safe to assume there

is no water, which helps to account for the great inequalities on

the body's surface, since the mountains will seem higher when

surrounded by dry ocean- bottom than they would if water came

halfway up their sides. Undoubtedly, however, the main cause of

their height is the slight effect of gravitation on an asteroid,

and the fact that the shrinking of the interior, and consequent

folding of the crust in ridges, may have continued for a time

after there was no longer water on the surface to cut them down.



"The temperature and condition of a body," continued Cortlandt,

"seem to depend entirely on its size. In the sun we have an

incandescent, gaseous star, though its spots and the colour of

its rays show that it is becoming aged, or, to be more accurate,

advanced in its evolutionary development. Then comes a great

jump, for Jupiter has but about one fourteen-hundredth of the

mass of the sun, and we expect to find on it a firm crust, and

that the planet itself is at about the fourth or fifth period of

development, described by Moses as days. Saturn is doubtless

somewhat more advanced. The earth we know has been habitable

many hundreds of thousands or millions of years, though three

fourths of its surface is still covered by water. In Mars we see

a further step, three fourths of its surface being land. In

Mercury, could we study it better, or in the larger satellites of

Jupiter or Saturn, we might find a stepping-stone from Mars to

the moon, perhaps with no water, but still having air, and being

habitable in all other respects. In our own satellite we see a

world that has died, though its death from an astronomical point

of view is comparatively recent, while this little Pallas has

been dead longer, being probably chilled through and through.

From this I conclude that all bodies in the solar system had one

genesis, and were part of the same nebulous mass. But this does

not include the other systems and nebulae; for, compared with

them, our sun, as we have seen, is itself advanced and small

beside such stars as Sirius having diameters of twelve million

miles."



As they left Pallas between themselves and the sun, it became a

crescent and finally disappeared.



Two days later they sighted another asteroid exactly ahead. They

examined it closely, and concluded it must be Hilda, put down in

the astronomies as No. 153, and having almost the greatest mean

distance of any of these small bodies from the sun.



When they were so near that the disk was plainly visible to the

unaided eye, Hilda passed between them and Jupiter, eclipsing it.

To their surprise, the light was not instantly shut off, as when

the moon occults a star, but there was evident refraction.



"By George!" said Bearwarden, "here is an asteroid that HAS an

atmosphere."



There was no mistaking it. They soon discovered a small ice-cap

at one pole, and then made out oceans and continents, with

mountains, forests, rivers, and green fields. The sight lasted

but a few moments before they swept by, but they secured several

photographs, and carried a vivid impression in their minds.

Hilda appeared to be about two hundred miles in diameter.



"How do you account for that living world," Bearwarden asked

Cortlandt, "on your theory of size and longevity?"



"There are two explanations," replied Cortlandt, "if the theory,

as I still believe, is correct. Hilda has either been brought to

this system from some other less matured, in the train of a

comet, and been captured by the immense power of "Jupiter, which

might account for the eccentricity of its orbit, or some accident

has happened to rejuvenate it here. A collision with another

minor planet moving in an orbit that crossed its own, or with the

head of a large comet, would have reconverted it into a star,

perhaps after it had long been cold. A comet may first have so

changed the course of one of two small bodies as to make them

collide. This seems to me the most plausible theory. Over a

hundred years ago the English astronomer, Chambers, wrote of

having found traces of atmosphere in some of these minor planets,

but it was generally thought he was mistaken. One reason we know

so little about this great swarm of minor planets is, that till

recently none of them showed a disk to the telescope. Inasmuch

as only their light was visible, they were indistinguishable from

stars, except by their slow motion. A hundred years ago only

three hundred and fifty had been discovered; our photographic

star-charts have since then shown the number recorded to exceed

one thousand."



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