IN STARRY SKIES

Evening Post, Volume CXVIII, Issue 35, 10 August 1934, Page 16

IN STARRY SKIES

SOME .OF THE CHARACT.ERJSTIGS OF THE SOLAR FAMILY

[(By "Omega Oentauri.")

; • One-of-tho most, striking :f acts with ■regard to the solar system is that all its members are intimately related to ■:on6 ' another. They ' form, a. definito family, and not a. more assembly'of bodies, that havq, como together by chance. . It is not merely that they aro all' composed of the saino elements. In that1 respect the' universe is one. 'But in spite of-all'.the differences between .the':,^several' plaiic,ls. and their.',:satellites' (and wo shall sco that those differences' airo 'striking and extreme) in'Wjving nearly all their physical char, acteristics such as size, mass, do'risity, temperature, iind physical state), ,w.o Khali find that tho relationship is more fundamental, still. Tho sun , is, .of oourse, supreme, and the mptions of the other bodies aro almost entirely controlled ;by his tremendous gravitational attraction.' Tho forces exertbd by. -the other members of tho system «juse only perturbations of a minor (jharactor. Whpn ye made a model of Iho •system, wo found that/.on a, scale of ;pno , yard to a million miles, ,our miniature': system would be 4-J miles ricroßß, but, except for Pluto' and some

o£v'*tlieV Asteroids, would,- bo' less - than 200Vyards 'deep. A box to .hold tho working' model • would v • therefore bo shaped* like a gigantic gramophone disc. Now .the most significant, characteristic of silie:*sjrstem:f'i^:thafc' allh'tte .'planets revolve about the sim in: the same/sense, vii,j; Clockwise ■:-, if ;vieWectvfronv'[ the sontli,. counfer;blockwiso f rom- the northMost' of tHe; sktollitos 'revolve-around theit - primaries'vih .tha' same : direction. IniiadditiOh;.to this' the;sun. and the planets^:;witlv;«ho; or'twd striking cxcepoSns>;.i6tatc'. about.:thcip axes the sam#cv!rayi::;-^::.'■'■'''; ;'.-'::-''.-■■■'■-' -..,.'.■•. ■

Nowv'ik 'considering,...a ■system.- with suc&tremarkable ■ -characteristics-ono canndt^elp looking -back into tho past anao{&>ovaTd ; into - tlifi'Vfu'turOi What expla|sttori can be given of-these coincidpneejjjSV An ; enormous ■ amount of woffehas been; dpnouri;'-atfom'p'ts. to. un-ra'-v^lj(the;:ta:iiglea::cines to tho past :histofy|j^fjMe-: system.: Prom the great nebjfl^S^liyp'othesis of Laplace to the passi)rtg-.'sta<;-'of-;;Sir James Jeans, 'the sricc^ssibni.qf- theories . forms : a, ino^t intwesiitfg'&udy.. But- it is quite clear that,'ti6.:-fitiality, has yet been, reached. Laplace JiaS.to assume a slow rotation of-tho primeval nebula to account for the revolution of all the -bodies .-in one direction. ; Jlo' di d , not. attempt to account for this,initial"rotation..'.To••believe- ail thY rapid motions of the planets iyi their .orbits,-; and, thcir ; rotations on axes differently inclined, to be'idu.e.tb'the action' of a passing, star, scemS'; 'toi make, ."clemah'ds on; ; 'our;.;c];etl^ulity.d " A -much mbro pro-mißJng;"thcb'ry-is^"''that 'of . tho-whirling coale'sc.enco of;;;a,'pair of suns; Hero- is a gTfsatt field'-for the ; matheninticians ofitfie-futpe to cultivate. First, there is;tlio;f 6vinJ of the tidal;protuberances pro^uco'd'" in" each:" star; by' the': grayitational attraction- of tho, other during their.: mutual approach. ":-. If tho.■ stars1 pass; without impact it will bo ncceasary'tb'calcttlate what is likely to happen to each side, and whether any part can; be separated from onb star with'-i out passing to tho other. In the case! of ;an impact sufficiently direct to form whirling coalescence,' it seems certain thati whilst the. inner tides are swal-. lowed up inv tho rotating mass, portions of the outer ones must bo swung off in£6: srjacc. Some of tkeso may leave tfi^e"system.for ever, wliilst.others may form planets and their satellites, comets, and meteor swarms. • Tho whole area surrounding ' the coalescing suns, iar.the neighbourhood of the piano of, thbrr relative motion, must be strewn with' flying fragments of all sizes from broken atoms upwards, and these provide the planetesimal material required

by Chamberlin and jVloulton in their hypothesis. This line of reasoning provides a ■convenient starting point for an attack on tho problem of planetary distances. It is well known that the relation known as Bodo's law served well in leading to the discovery of the asteroids. But it broko down rather badly in the .case of Neptune and much moro completely in that of Pluto. Recently Mr. I. L. Thomson has pointed out ■' a number of curious approximate relations between' tho planetary distances.'. l't: is. doubtful, however, whether these'have any physical basis. It is indeed extremely improbable that any exact mathematical formula can embrace all the, planetary • distances. Tho spaces between the orbits increase as we pass outwards from tho sun. A diagram suggests that the series bears some approximation to a geometrical progression. But some terms in this sew.es.always.refuse .to bo fitted in. The ratio* of" one menu distance to tho preceding one. varies from 1,31 to 2.01. The whole scries from Mercury to Pluto is 1.87, 1.35, 1.52,. 1.75, 1.80, 1.55, 2.01, 1.56, arid 1.31. If we take tfio mean ratio as 1.67 tho relative . distances should bo: Mercury 3.87, Venus 0.47, Earth- -10.S, Mars 181, Asteroids 30.3, Jupiter 50.(5. Saturn 84.7, Uranus 141.0, Neptune 237, Pluto 390, whilst they actually- are 3.87, 7.2, 10, 15.2, 28, 52, 95, 192, 301, and 390, Saturn, Uranus, and Neptune being most seriously oat of place in tho geometric series. If we take tho earth and Neptune as our standards Pluto will be considerably but of place. But wo ought not to cxr pect any closo approximation to such a symmetrical arrangement. The mean

(distance,of any1 planet from the suni ■ must depend chiefly on. ( the plSco atl 1 which ;ifr broke away from tho tide' audi I the ..speed at''which it started. Let us ; suppose,, for instance, that a 'number iof masses' fly simultaneously from: the i advancing.tide at the moment when- the 'main mass is arrested by the collision. They< have' practic ally the same veloj city, but aro at different distances from tho .centre .of gravity of the whirling i massi Tho; points. from -..which they i start wil bo the perihelia of tho re-spective-orbits. Suppose one mass has ■ exactly .the velocity required for a circular orbit.. Then one that is twico as far ' froriiV the ■centre will move 'in a parabola innd escape for ever from the system; ,:Blasses that start with the same velocity from intermediate points will, have- orbits whose major axes lie between the diameter of tho circular one"'arid ; infinity; : If'; the points' from which they start arc evenly placed,' the distances between the orbits increase rapidly as we 'pass outwards.' 'Masses that start' from- points within tho'circular orbit will move1 in' ellipses with the ' starting "points asaphelia. ; Irregularities in the tidal filament, before it breaks',up, will'bc1 quite-sufficient to prcVenb geometrical ■ accuracy in the spacing of tho orbits. A rough diagram of the', position'of the-stars as tho impact ■' commences will show that the whirling mass is derived on ono side chiefly- from pno star and oil tho other side' 'from ;the'other star. - This- is' 'the cause of thd rotation -of the resulting suii. ; Initially the rotation must be most rapid on■ the surf ace : and negligible near the axis. Tfto escaping masses which form tho. nuclei of tho planets acquire their, rotation as they roll along the whirling mass before breaking-away. These rotations' are modified by any possessed originally by the colliding stars. '

T-heso suggestions are meant only to be used as a working hypothesis to be tested by tho deserved facts discovered with regard to each body. On this hypothesis wo should expect many of the planets to be,accompanied by families of satellites, for each fragment, as it .breaks away from tho main mass) is 'subjected to enormous tidal stresses which may well lead to its disruption. This hypothesis can explain tho origin of an inflnito; variety of stellar systems, for tUe parent stars may be of any size a,nd. any- density. They may be dead and cold or intensely heated. They may- pqss' without ■ impact, may just •graze one another, or may como into direct; collision. Our solar system, shows us but one of an infinite number of.typos.,; ■ . ' •