Exoplanet

“ The planets are divided into “primary” and “secondary.” By a “primary” planet we mean one which directly circulates round the Sun; by 8 a “secondary” planet we mean one which in the first instance circulates round a primary planet, and therefore only in a secondary sense circulates round the Sun. The planets are also “major” or “minor”; this, however, is only a distinction of size.
The secondary planets are usually termed “satellites,” or, very often, in popular language, “moons,” because they own allegiance to their respective primaries just as our Moon—the Moon—does to the Earth. ”

“ The temperature readings would, therefore, be correspondingly higher at the limbs.
The other theory, held by most scientists, visualized a hot surface on Venus, with no heavy concentration of electrons in the atmosphere, but with cooler clouds at higher altitudes. Thus, the spacecraft would look at a very hot planet from space, covered by colder, thick clouds. Straight down, the microwave radiometer would see the hot surface through the clouds. When approaching the limb, the radiations would encounter a thicker concentration of atmosphere and might not see any of the hot surface. ”

“ After ten more years the Sun would be unable to support its family. The planets they now inhabited—Earth, Venus and Mercury—were supported artificially. The atmospheres of all the planets had long since slowly dissipated into space, and with them had gone the water. These vital things were being replaced constantly by transmutation of the elements of the rocks of the planets. Long ages ago Earth had had a large satellite, which had been used through the ages to supply energy for the factories of man, and to supply the necessary atmosphere. ”

“ Thirteen major planets they counted as they searched the system with their powerful telectroscope, the outermost more than ten billion miles from the parent sun, while planet six, the one indicated by the world number, was at a distance of five hundred million miles, nearly as far from the sun as Jupiter is from ours, yet the giant sun, giving more than twenty-five times as much heat and light in the blue-white range, heated the planet to approximately the same temperature Earth enjoys. ”

“ Several of these have one or more attendants, or satellites, which revolve around them as they revolve around the sun. The Earth has one satellite, namely, the Moon; Jupiter has four; Saturn, seven; and Uranus, six. These bodies are also planets, but, in distinction from the others, they are called secondary planets. Hence, the whole number of planets are twenty-nine, namely, eleven primary, and eighteen secondary, planets.
You need never look for a planet either very far in the north or very far in the south, since they are always near the ecliptic. ”

“ In addition to the five or six large planets in each group, which, however, are many millions of miles apart, there is in some clusters a small planet that swings backward and forward across the common centre, like a pendulum, but in nearly a straight line; and while this multiplicity of motion goes on, the whole aggregation sweeps majestically around Sirius, its mighty sun. Our little solar system contains, as we know, about one thousand planets, satellites, and asteroids large enough to be dignified by the name of heavenly bodies. ”

“ Actually, most of the planets have been found by this technique, either from telescopes on Earth or space ones.
The Kepler space telescope, which is currently on the TESS mission and, in the near future the PLATO mission, have been and will be responsible for discovering new planets, such as the Earth, orbiting other stars, and bringing humanity one step closer to the search for another possible Earth where life may exist because, despite the progress achieved, the most crucial question remains unanswered: Is there life beyond our planet? ”

“ The number and size of the satellites a planet has depends upon the size, and hence the controlling force, of the nucleus which is its foundation, and also upon the number of spots of condensation that chanced to be formed in its neighborhood sufficiently near to come under the gravitational control of the planet. If by any chance the nucleus which was to form the largest satellite of Jupiter had been in the situation of Mercury, for instance, it might well have given its allegiance to the sun, instead of to Jupiter, and thus have become a planet. ”

“ A secondary planet two or three thousand miles in diameter, even if solid, would become unstable before coming in contact with its primary, and would undergo a sudden dilapidation; so that a numberless host of its fragments, scattering into smaller orbits and plunging as meteors into the atmosphere of the great central orb, would send forth a flood of brilliancy sufficient to rival solar light, and to proclaim the great work of destruction to the most distant parts of the universe. ”

“ Few people without a training in science can realise the huge isolation of the solar system. The sun with its specks of planets, its dust of planetoids, and its impalpable comets, swims in a vacant immensity that almost defeats the imagination. Beyond the orbit of Neptune there is space, vacant so far as human observation has penetrated, without warmth or light or sound, blank emptiness, for twenty million times a million miles. ”

“ Now proceeding to reason back from the past to the present, it has been shown that the abandonment of successive equatorial belts by the contracting solar mass must have ensued in accordance with known mechanical laws; and in similar wise, under ordinary circumstances each belt must have parted into fragments, and the fragments chasing each other around the same orbit, must have at last coalesced into a spheroidal planet. Not only this, but it has also been shown that as the result of such a process the relative sizes of the planets would be likely to take the order which they now follow ”

“ Indeed, we may say at once that this little object was not a star at all; it was a planet. That such was its true nature was confirmed, after a little further observation, by perceiving that the body was shifting its place on the heavens relatively to the stars. The organist at the Octagon Chapel at Bath had, therefore, discovered a new planet with his home-made telescope.
I can imagine some one will say, "Oh, there was nothing so wonderful in that; are not planets always being discovered? ”

“ If we assume that there are a hundred million stars within the ken of our telescopes, we may well believe that not more than one in a hundred of these would fulfil the condition of being a single and stable sun, such as ours. Of the planets revolving round these million suns—stable and efficient suns—can we expect that in more cases than one in a hundred there will be a planet in the habitable zone fulfilling all the other conditions of habitability, of size, mass, inclination of axis, circular orbit, and rotation? ”

“ Increase man's knowledge of the universe.
Exploration of the solar system and observations beyond the solar system should be important continuing broad objectives of the Nation's space program. Many unanswered scientific questions remain about the planets, the interplanetary medium, the sun - both as a type of star and as a source of the earth's energy - and about a variety of celestial objects, such as pulsars, quasars, X-ray and gamma ray sources. ”

“ But if we admit that the substance of which the solar system consists once existed in a nebulous condition, and was in rotation, all the above peculiarities follow as necessary mechanical consequences. Nay, more, the formation of planets, the formation of satellites and of asteroids, is accounted for. We see why the outer planets and satellites are larger than the interior ones; why the larger planets rotate rapidly, and the small ones slowly; why of the satellites the outer planets have more, the inner fewer. ”

“ While it is tacitly assumed that there are planets revolving around other stars than the sun, it would be impossible for us to see them with any telescope yet invented, and no instrument now in the possession of astronomers could assure us of their existence; so the only planetary system of which we have visual knowledge is our own. Excluding the asteroids, which could not from any point of view be considered as habitable, we have in the solar system eight planets of various sizes and situated at various distances from the sun. Of these eight we know that one, the earth, is inhabited. ”

“ Vast orbs might be conceived of as rotating in eternal darkness without associated satellites, but the incandescent atmosphere of hydrogen must have—not may have, but must have—subordinate planets substantially similar to ours, surrounded by atmospheres substantially similar to our own (for we find free nitrogen in comets, in meteorites, and in the faintest nebulæ) , and these planets are thus fitted, so far as we can know, for the support of organic life and for the same orderly courses of nature as we see manifest around us. ”

“ Yes, necessarily, all inhabited Planets possess oxygenated atmospheric envelopes, but you are not to confound atmosphere with ether, which fills all interstellar space, and is substance, but so refined as to be imperceptible to physical sense.
Upon all the planets of our solar system, our glowing, radiant Sun sheds its life-preserving beams. Its magnetic waves, pouring across space, quicken into activity latent energies, thus making progress in all directions not only possible, but inevitable. ”

“ It would thus appear that many great luminous exhibitions would attend the awful paroxysms with which a large planet passes away from the stage of existence in a solar or in a secondary system. Though a small satellite, if fluid, may meet its final doom in an obscure manner, yet, if solid, it would be likely to maintain a planetary form until it came very close to the primary ”

“ The solution is—there are nine planets in this solar system! Neptune and Uranus are each far vaster than Earth; they are utterly impossible for life as we know it, but a small colony might be established there to refine metals for the distant Earth. We might be able to build domed and sealed cities. But first we could try the nearer planets—Mars, Venus, or some satellites such as our Moon. I certainly hope that this machine will make it possible. ”

“ In the smaller systems the largest outer planet sometimes draws to itself its neighboring worlds, while those planets near the sun begin their terminal plunge. With your solar system, such an end would mean that the four inner planets would be claimed by the sun, while the major planet, Jupiter, would be greatly enlarged by capturing the remaining worlds. ”

“ But most comets come from illimitable space, far, far beyond Neptune’s circle and at all angles to the plane of the planetary orbits; and we have already seen that a disk of space of the diameter of Neptune’s orbit and half as thick (see Proctor’s “Familiar Essays”) would, to contain all the matter of our solar system equally distributed, have a density of only one four-hundred-thousandth that of hydrogen gas at [275] atmospheric pressure,—that is to say, such a volume of the lightest substance we know of would make four hundred thousand solar systems like our own. ”

“ She and Phyllis and Ruby joined the others out on the floor.
"You understand," the routing official was saying, "that you're allowed your choice of planets in the Huffer Solar System. We'll read off occupational and other pertinent information and then you make your choice.
"Sunside: First planet from the system sun. Warm, humid climate. Fishing, flower-growing for export, mining, and natural handicrafts. Population ratio 7 to 1, males all somatypes and admixtures.
"Midplanet: Second planet out. Temperate climate. Farming, fur-trapping, slight manufacturing. ”

“ The defect changes to an excess in the different systems of the satellites, where it is proportionally greater than in the planets, and unequal in the different systems. “From the whole of these comparisons,” says he, “I deduced the following general result:—Supposing the mathematical limit of the solar atmosphere successively extended to the regions where the different planets are now found, the duration of the sun’s rotation was, at each of these epochs, sensibly equal to that of the actual sidereal revolution of the corresponding planet ”

“ It is certainly true of double stars, and probably so of all the others. Of course such enormously massive double suns presuppose enormous planets, rotating around them at enormous distances; but when we compare the distance of our own satellite, the moon, from the earth with the distance of Neptune from the sun, and consider that the light of the sun will reach Neptune in about four hours, and then compare this distance with the inconceivable distances of space requisite to retard and merge all radiant energy into the diffused molecular energy of position, our wonder will cease. ”

“ We will therefore find in such planets all the potentialities of life—we can see and study these planets, though physically invisible, as easily and as thoroughly as we do our own, for having the relationship of constitution between our own planets and our sun, we may thereby learn the essential relationship between any fixed star and its planets by directly studying the constitution of such star alone. Among the planets of our own system Neptune and Mercury, and those which exist adjacent to their boundaries, can be studied with difficulty and uncertainty ”