| 释义 |
planetesimal, a. and n. Astr.|plænɪˈtɛsɪməl|
[f. planet n.1 + infinitesimal n. and a.]
A. adj. Pertaining to, involving, or composed of planetesimals; applied esp. to the hypothesis that the planets were formed by the accretion of a vast number of planetesimals in a cold state.
1904T. C. Chamberlin in Carnegie Inst. Year Bk. II. 263 This led to studies upon alternative hypotheses. Among these is the conception that the earth, instead of descending from a gaseous spheroid, may have been built up by the gradual ingathering of its material from a scattered meteoroidal or planetesimal condition. 1904Amer. Geologist XXXIII. 95 The planetesimal hypothesis..seems much better to explain both the astronomical and geological phenomena. 1906Athenæum 18 Aug. 191/1 For the last ten years Prof. Chamberlin, aided by Dr. Forest R. Moulton, of Chicago, has been developing what is called the Planetesimal Theory of the earth's origin. 1937Wooldridge & Morgan Physical Basis Geogr. i. 5 The earth..grew from small beginnings by the addition of planetesimal matter. 1969Nature 19 July 259/1 When planetologists meet to discuss the surface of the Moon they separate into those favouring the dominance of planetesimal (meteoric) impact and those who advocate volcanic activity.
B. n. A small solid body following a planetary orbit; a miniature planet.
1904Amer. Geologist XXXIII. 95 The new hypothesis holds..that the globular planets were formed by the slow accretion or infalling of cold, discrete bodies or particles (‘planetesimals’). 1906Chamberlin & Salisbury Geol. II. ii. 94 The planetesimals originated, by hypothesis, from gaseous matter shot forth from the ancestral sun. 1952H. C. Urey Planets vii. 219 Planetesimals probably formed simultaneously with the protoplanets and accumulated into larger objects. 1971Sci. Amer. Oct. 52/3 Apollo 14 landed on the Fra Mauro formation, believed to be a blanket of ejecta thrown out by the giant meteorite or planetesimal that excavated the basin of Mare Imbrium. 1973Nature 21/28 Dec. 451/3 Courten believes a planetesimal ‘between 80 and 500 miles in diameter’ moves in an orbit about 0·1 AU from the Sun. 1977Ibid. 8 Dec. 506/1 Accumulation and fragmentation of planetesimals may have competed in the planetary accretion process, and a planetesimal which could survive catastrophic destruction may have become a planet. |