IN 1877 Prof. Todd, from a graphic investigation of the still outstanding differences between the computed and the observed places of Uranus, after allowing for the action of Neptune, considered that an unknown planet existed lying beyond the latter. He accordingly made search for it with the great Washington telescope, but was unable to find any such body. Prof. George Forbes has recently revived some earlier calculations indicating the possible existence of a trans-Neptunian planet, and he considers his former speculations have been greatly strengthened by additional facts unknown to him at the earlier period. He thinks that three comets which appeared in 1843, 1880, and 1882 are in reality parts of the comet of 1556 (sometimes known as the comet of Charles Y, from its appearing at the time of that monarch's Abdication), which has been broken up by the action of an unknown planet lying beyond Nep- tune. It is well known that the planets Jupiter, Sat- urn, Uranus, and Neptune are associated in an especial way with particular comets. For instance, the short period comets known by the name of Faye, De Vico, Brorsen, and Encke, which revolve in elliptic orbits having periods of devolution round the sun of from three to eight year's, all of them approach atcertain parts of their orbits very close to that of the planet Jupiter. Similarly, Halley's comet, whose re-turn is hourly expected, Olber's's comet of 1812, and Pons's comet of 1812, rediscovered by Mr. Brooks in1883, approach very near to the orbit of Neptune, their greatest distance from the sun (aphelion) lying a little beyond that planet. Tempel'g comet ajicl two others are similarly associated with Uranus. These various comets are frequently called the “planets' families” of comets, and they are supposed to have become so in the following way: A comet coming from outer space into our system toward the sun will have its rectilinear motion converted into a parabolic one, will approach the sun with increasing speed till it arrives at its nearest point (perihelion), and then once more recede from it. If, however, it comes near a planet in its motion its speed will be either accelerated or retarded. If accelerated, the parabola ecomes a hyperbola and the comet moves off even more quickly from the sun after perihelion. If, however, it is retarded, the parabolic orbit is changed into an ellipse, which is a closed curve, and the comet will now become a permanent member of the system, moving in a path which will pass through the region where the disturbance originally took place. The successive diminutions of velocity may greatly transform the comet's original orbit. The converse instance of an increase of speed seems to have happened in the case of Lexell's comet of 1770, which, it is thought has had its elliptic orbit made hyperbolic by the action of Jupiter. Clover After 54 Days' Growth. Top Box Inoculated; the Bottom Non-inoculated. Inoculated Seed Sufficient for from Twelve to Fifteen Acres of Land Costs Only $1.25. Another theory as to the origin of comet families, suggested by the late Mr. Proctor, supposes these bodies to have been thrown off by some kind of erupr tions from the sun and planets—e. g., that the comets of Jupiter's family once formed part of his mass, but were rejected with sufficient speed to set them free in space, though still under the sun's influence. Bean Boots, Showing Nodules in Which Nitrogen- Fixing Bacteria Work. Peas. Left Inoculated, Giving Greater Boot Growth and Vitality. Right Not Inoculated. INCREASING THE SOIL'S NITROGEN CONTENT. On either theory we see that there must be some connection between the comets and the planets to whose families they respectively belong. As we have seen above, Prof. Forbes considers the three comets 1843, 1880, and 1882 were originally parts of one and the same body. Their aphelion (greatest) distance from the sun is about the same, 88 times tbe earth's distance? an4 the common position of all three is in longitude 101 deg. and latitude 35 deg. S.\ Seven comets have been found having their greatest distance at about 100 times the earth's distance from the sun, and four of these have their orbits lying nearly in a plane passing through the sun. He, therefore, suggests that this is in all probability the true plane of the orbit of an unknown planet revolving at about that distance from the sun, and consequently having a period of revolution of about 1,000 years, in accordance with Kepler's third law. [The squares of the periodic times of revolution are as the cubes of the mean distances from the sun. Expressed in terms of the earth's distance and period as units (100)3= 1,000,000= (1,000)2.] The dates at which the comets were in aphelion were found to agree fairly well with the dates on which a planet of the periodic time of 1,000 years would be found in or near those four positions; so that the position of the unknown planet may be considered approximately known. Estimates formed by roughly calculating the probable disturbances produced by this planet upon Neptune give such small quantities for the perturbations that no certain evidence of its existence is likely to be obtained by this method at present, unless its mass be enormously greater than that of Neptune, though sooner or later its presence may be thus revealed- Prof. Forbes has estimated that the unknown > planet has a mean distance from the sun 105 times that of the earth (more than three times Neptune's distance), that the inclination of the plane of its orbit to the ecliptic is about 52 deg., and that its elliptic orbit has an eccentricity of about 0.16. The fact- of the inclination of its path to the ecliptic causing it to be for a large part of its revolution outside the region of the Zodiac, in which the search for new planets has been mainly carried on, may perhaps be the reason that it has hitherto escaped detection. Prof. Forbes concludes that its present longitude in its orbit is about 202 deg. (Or 216 deg. with regard to the ecliptic), and its south latitude (distance from the ecliptic) is 34 deg. It is consequently at present only to be looked for in the southern hemisphere or from observatories nearer to the equator than we ar e. Prqf. W. H. Pickering has just given the place of a supposed trans-Neptunian planet. Its present position is in R. A. 7 h. 47 min., north declination 2i deg.; or in the southeastern part of the constellation Gemini (the Twins). This cannot be the same object as that referred to by Prof. Forbes, but nothing seems to prevent there being two or morfc. bodies moving in plane: tary jorbits outside the orbit of - Neptune. It is- quite certain that there are many comets revolving in elliptic orbits and, thus returning from time to” time to perihelion, which recede to far greater distances from the sun. For instance, the famous comet of 1680, which approached so very close to the sun at perihelion that it must have passed through the outer regions of the solar atmosphere, its distance being only about 55,000 miles from the sun's center at that time, recedes in its aphelion to a distance 850 times the earth's distance, or 28 times that of Neptune from the sun. The amount of light and heat received by an equal area of the comet these respective times must accordingly be 19,000 million times more in perihelion than in aphelion, and its velocity also subject to enormous variations. The apparent diameter of the sun would only be 2 sec. when seen from the comet at aphelion, while in perihelion, according to Newton, the comet would be subject to a heat “2,000 times that of red-hot iron,” the sun subtending an angular diameter of 85 deg. Owing to the rapidity of its motion, however, the comet would only be subjected to this intense heat for a very short time. At the other end of our system we have the question of an intra-Mercurial planet. Leverrier, the great French astronomer and one of the discoverers of Neptune, found in 1859 that the motion of Mercury is such that the perihelion (or point of least distance from the sun) changes its position in a manner which cannot be altogether accounted for by the action of the other known planets. It might be explained by the attraction of a planet or a number of small planetoids revolving inside Mercury'3 orbit and lying nearly in the same plane. Dr. Lescarbault, a French country physician, announced that lie had seen a planet crossing the sun on March 29th, 1859. He was visited by Leverrier who, after severe cross-questioning, apparently satisfied himself that Lescarbault's observation was a genuine one, and calculated an orbit therefrom, the name of Vulcan being given to the supposed planet. However, it has never been certainly seen again, though, if real, it ought several times to have been visible in transit across the sun. Very careful observations at the times of solar eclipses should certainly reveal the presence of such... a body; but so far no one else has yet found the, planet, though both Prof. Watson and Mr. Swift, during the eclipse of 1878, thought they saw two bright objects which could not very well be identified with any known stars. Later investigations made by Dr. Peters have shown that Prof. Watson's stars may very possibly have been the stars $ and C Cancri; but, so far, Mr. Swift's observations remain unexplained. However, up to the present, no planet lying nearer to the sun than Mercury has been certainly found. Prof. Young considers it “extremely probable that there are a number—perhaps a very great number—of intra-Mercurial asteroids,” perhaps each of them not having a diameter exceeding 50 miles or so. So small objects, lying very near to the sun, would be nearly certain to escape detection either in transit or during an eclipse.—Knowledge and Scientific News.
This article was originally published with the title "Is There a Trans-Neptunian Planet?" in s , , 297-298 (January 2012)