Velikovsky tried to protect himself from criticism of his proposed celestial mechanics by removing the original Appendix on the subject from "Worlds in Collision", hoping that the merit of his ideas would be evaluated on the basis of his comparative mythology and use of literary sources alone. This strategy did not protect him: the Appendix was an expanded version of the "Cosmos Without Gravitation" monograph, which he had already distributed to Shapley and others in the late 1940s — and they had regarded the physics within it as egregiously in error. In his 1979 science book "", astronomer Carl Sagan wrote that the high surface temperature of Venus was known prior to Velikovsky, and that Velikovsky misunderstood the mechanism for this heat. Velikovsky believed that Venus was heated by its close encounter with the Earth and Mars. He also did not understand the greenhouse effect caused by Venus' atmosphere, which had earlier been elucidated by astronomer Rupert Wildt. Ultimately, Venus is hot due to its proximity to the Sun; it does not emit more heat than it receives from the Sun, and any heat produced by its celestial movements would have long since dissipated. Sagan concludes: "(1) the temperature in question was never specified [by Velikovsky]; (2) the mechanism proposed for providing this temperature is grossly inadequate; (3) the surface of the planet does not cool off with time as advertised; and (4) the idea of a high surface temperature on Venus was published in the dominant astronomical journal of its time and with an essentially correct argument ten years before the publication of "Worlds in Collision"" (p. 118). Sagan also noted that "Velikovsky's idea that the clouds of Venus are composed of hydrocarbons or carbohydrates is neither original nor correct." Sagan notes that the presence of hydrocarbon gases (such as petroleum gases) on Venus was earlier suggested, and abandoned, again by Rupert Wildt, whose work is not credited by Velikovsky. Also, the 1962 Mariner 2 probe was erroneously reported in the popular press to have discovered hydrocarbons on Venus. These errors were subsequently corrected, and Sagan later concluded that "[n]either Mariner 2 nor any subsequent investigation of the Venus atmosphere has found evidence for hydrocarbons or carbohydrates" (p. 113). Regarding Jupiter's radio emissions, Sagan noted that "all objects give off radio waves if they are at temperatures above absolute zero. The essential characteristics of the Jovian radio emission — that it is nonthermal, polarized, intermittent radiation, connected with the vast belts of charged particles which surround Jupiter, trapped by its strong magnetic field — are nowhere predicted by Velikovsky.