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KRONOS Vol VI, No. 2
For the Record . . .
VENUS'S INTERNAL HEAT
LEWIS M. GREENBERG AND C. LEROY ELLENBERGER
One of the most important advance claims made by Velikovsky dealt with the heat of Venus. In Worlds in Collision ["The Thermal Balance of Venus"], he wrote:
"Radiometric observations . . . have shown that 'a considerable amount of heat' is emitted by the dark part of the disc of the planet Venus . . . and it was found that there is 'a nearly uniform temperature over the planet's surface both on the illuminated and dark hemispheres'....
"What explanation can be given for the phenomenon of the nearly uniform temperature of the day and night hemispheres of Venus? . . . The night side of Venus radiates heat because Venus is hot. The reflecting, absorbing, insulating, and conducting properties of the cloud layer of Venus modify the heating effect of the sun upon the body of the planet; but at the bottom of the problem lies this fact: Venus gives off heat.... [And because of its violent history] between the third and first millennia before the present era, the core of the planet Venus must still be hot" [emphasis added] . However, the discovery that Venus's atmosphere is 90 times more massive than Earth's complicated the picture. As it turns out, the atmosphere is so massive that during the long night on Venus the atmosphere would barely be expected to cool 1°K [ Velikovsky Reconsidered, p. 177; Indus. Res./Dev. June 1979, p. 114] .
Velikovsky's detractors have been most vociferous in denying the correctness of his thermal prognostication. For example, in Scientists Confront Velikovsky, Carl Sagan countered with these remarks:
"What I think Velikovsky is trying to say here is that . . . Venus . . . is giving off more heat than it receives from the sun, and that the observed temperatures on both the night and day sides are due more to the 'candescence' of Venus than to the radiation it now receives from the sun. But this is a serious error. The bolometric albedo of Venus is about 0.73, entirely consistent with the observed infrared temperature of the clouds of Venus of about 240°K; that is to say, the clouds of Venus are precisely at the temperature expected on the basis of the amount of sunlight which is absorbed there.
"Velikovsky proposed that both Venus and Mars give off more heat than they receive from the sun. He is wrong for both planets" [pp. 79-80 ] .
And, in the same book, David Morrison offered the following:
"That Venus has a 'hot' surface and large internal heat source is perhaps the most widely quoted prediction made by Velikovsky....
"Velikovsky argued that Venus was hot, in part on the basis of observations published before 1950, which showed that the cloud top temperature did not vary from day to night; he inferred that such a state would be a natural consequence of an internal heat source that dominates the energy balance of the planet . . . the fact that the observed cloud temperature is equal to the equilibrium value is inconsistent with the explanation given by Velikovsky; rather, it is clear that a massive atmosphere must play a vital role in the thermal affairs of Venus....
"Nature sometimes finds ways to accomplish feats that mystify the theoretician. It is much more satisfying to learn that direct, model-independent information exists to demonstrate that internal heat cannot contribute significantly to the surface temperature of Venus.... Thus, independent of the past history of Venus or its present internal temperature, it can be asserted with confidence that sunlight, rather than internal heat, is the dominant source of energy to the Venerian surface and lower atmosphere. It follows, therefore, that the high surface temperature must result from atmospheric trapping of this heat (the greenhouse effect) and cannot be due to a massive heat flux from the interior as Velikovsky continues to claim" [pp. 158-166] .
Morrison reaffirmed his position in the very pages of this journal [KRONOS V:2, p. 67]:
"Note that if internal heat sources supplied much more energy than sunlight, then Venus would have a significant energy imbalance, which is not observed.... observations of total heat balance preclude any internal source as large as the solar radiation absorbed (by both surface and atmosphere) of 1017 watts. The original Velikovsky hypothesis that internal heat swamps solar heat is untenable in view of the direct measurements of the total energy radiated by Venus.... the main conclusion is that Venus today has a high surface temperature as the result primarily of atmospheric trapping of sunlight, not because of a massive outpouring of heat from the interior. Whatever its past history, the temperature of Venus is not an argument in favor of Velikovsky."
Earlier in Icarus, Morrison stated the issue more succinctly in a twelve word title/abstract: "Can Internal Heat Contribute to the High Surface Temperature of Venus?"/"No" [Icarus 28, 423-424 (1976)] . The conclusion, however, hinted that all was not well with the greenhouse: "In the absence of any other plausible heat source, the [heat] provided . . . by the Sun is all there is to maintain a 750 K surface temperature. Thus, we can assert with confidence that a very efficient atmospheric trapping mechanism (greenhouse effect) is operating, whether or not the details of this mechanism are fully understood." At that time, greenhouse models could only account for about 87% of Venus's surface temperature, or 650°K [Space Science Reviews 20, 4, 398-399 (1977)] . Thus, Pioneer Venus concentrated on identifying additional infrared absorbers in Venus's atmosphere to increase the efficiency of the greenhouse effect.
John Gribbin, Sagan's British sycophant, also believes that Velikovsky's conclusion that Venus would be found to radiate more heat than it receives from the Sun has "fallen flat on its face" [New Scientist, 4/10/80, p. 103] . In fact, Gribbin has so deliberately gone out of his way to vilify Velikovsky that he reminds one of the proverbial "lady who doth protest too much".
In this country, Sagan's and Morrison's parrot - James Oberg has been especially busy of late filling the pages of Astronomy and The Skeptical Inquirer with invective against Velikovsky's predictions. Writing in the July 1980 issue of Astronomy, Oberg had this to say:
"One of the cornerstones in the edifice of the 'successful' Velikovskian predictions is the heat of Venus. When he wrote Worlds in Collision, the scientific world supposed Venus' surface temperature only slightly hotter than Earth's. Yet space probes later found that the temperatures exceeded 800°F, a figure which seemed to bear out Velikovsky's claim that the newborn planet had at one time been 'candescent,' or glowing, with excess heat....
"But the heart of Velikovsky's prediction was not so much the temperature, but that Venus would be giving off more heat than it received from the Sun, and therefore still be cooling off. The greenhouse effect postulates a planet in thermal equilibrium at high temperature .... Velikovsky's key claim is wrong" [p. 26] .
Oberg continued in the same vein in the Fall 1980 issue of The Skeptical Inquirer:
"Take Venus, for example: Velikovsky predicted it would be giving off heat because of its short, violent history. Although it turned out to be hotter than scientists had guessed . . ., it is not giving off more heat than it gets from the sun, nor is it cooling off (as Velikovsky also predicted). On both counts, Velikovsky's predictions were in error" [p. 25, emphasis in original].
Thus we have Sagan, Morrison, Oberg, et al. clearly on record against Velikovsky's thermal prediction for the planet Venus. Their position has been adamant and unyielding. It is, therefore, gratifying to discover that there is now tentative evidence indicating that Venus does indeed radiate some 15 per cent more energy than it receives from the Sun. This most recent finding was reported in New Scientist 13th November 1980, under the title "The mystery of Venus's internal heat" [p. 437]. It is reprinted here with the permission of New Scientist, London, the weekly review of science and technology, where it first appeared.:
Taylor's reluctant conclusion confirms what had been suspected for some time. Based on preliminary Pioneer Venus data, rudimentary calculations indicated the possibility of this thermal imbalance which was mentioned in an earlier Forum exchange in KRONOS IV: 3, p. 85: ". . . the clouds radiate 15% more energy than they absorb." Later, in a survey article on the Pioneer Venus mission [Science 207, 289-293 (18 January 1980)], Richard A. Kerr reported: "When Pioneer Venus's probes looked at the amount of radiant energy passing through the atmosphere, each one found more energy being radiated up from the lower atmosphere than enters it as sunlight.... To further complicate the situation, the size of the apparent upward flow of energy varies from place to place by a factor of 2, which was a disturbing discovery about a planet thought to be relatively uniform" [p. 292].
In an accompanying boxed article, "Venus and Science's Fringe", Kerr cautioned: ". . . observations from the Pioneer orbiter suggest that the planet as a whole is not acting like a radiator.... Although the precision of the measurement (± 15 percent) is not yet as great as it will be, Frederic [W. ] Taylor of the Jet Propulsion Laboratory in Pasadena believes there is little room left, if any, for a source of heat on Venus" [p. 293] . But there was enough room left. It seems as though K. l. Kellermann's article in the September 1966 Icarus, pp. 478-490, suggesting "that the heat of the ground surface of Venus comes, not from the atmosphere above, but from the sub-surface" [KRONOS IV:3, p. 67], has been long forgotten.
As encouraging as this indicated thermal imbalance is for Velikovsky's thesis, it needs to be put into perspective. The imbalance is much less than Velikovsky posited in 1963 when he deduced a cooling rate of 1°C or more every 15 years from the data of Pettit and Nicholson, and Sinton and Strong [KRONOS IV:3, p. 62]. Based on the same data, Velikovsky also mentioned a cooling rate "of circa 1°C per eight years" [ Velikovsky Reconsidered, p. 236] . George R. Talbott's model, which showed that Venus's observed surface temperature is consistent with its having been red-hot 3,500 years ago, indicated a present cooling rate of about 1°K every 15 years [KRONOS IV:2, p. 2]. In comparison, the observed 15% excess implies a heat flux about 700 times smaller than that indicated by Talbott's model. Therefore, volcanism is probably not as extensive now as Talbott's model requires. Once volcanism subsides, the heat flux decreases drastically. Because of the complexities involved relating heat flux to cooling rate, the factor of 700 is a lower bound on cooling rate and Venus's actual cooling rate could conceivably be over 1,000 times slower than Talbott and Velikovsky suggested.
Some other comparisons might be helpful. The 15% excess means that Venus's cloud tops are about 8°K warmer than they would be if Venus were in thermal equilibrium with the Sun. If the internal source were as large as the solar radiation absorbed, to borrow Morrison's words, instead of only 15% as large, then the cloud tops would be about 44°K warmer than an equilibrium value and about 36°K warmer than observed. Further, the indicated internal flux is at least 2.5 times greater than the largest possible flux that could be conducted from the interior according to Morrison in Icarus. This would imply either that volcanism is present, though not observed (although Earl Milton has hinted at another unspecified alternative [KRONOS IV:3, p. 84] ), or that the crust is much thinner than Morrison reckoned.
In conclusion, all commentators such as Sagan and Oberg who unequivocally stated that Venus is not giving off more heat than it receives from the Sun were, it seems, wrong. However, Morrison left himself leeway. While he was wrong in concluding that internal heat cannot contribute to the high surface temperature of Venus, he was correct in stating that the Sun dominates internal sources. Despite the fact that Velikovsky over-anticipated the internal contribution, it should be emphasized that conventional thinking has no means either to predict or to explain any thermal imbalance greater than Earth's (which derives primarily from radioactive decay and is minuscule), whereas Velikovsky had the correct qualitative expectation.
POSTSCRIPT 1981: Taylor's results are reported in "The Thermal Balance of Venus in Light of the Pioneer Venus Mission" by Tomasko et al. [Journal of Geophysical Research, Vol.85, No. A13, pp. 8187-8199, December 30, 1980] . Most inexplicably, the New Scientist article bears only superficial resemblance to the results in the technical paper (completed last May) from which their report originated. The most significant discrepancy is that the technical paper gives no credence to the reality of a thermal imbalance on Venus whereas New Scientist, with scant qualification, leaves the impression that the imbalance is probably real, albeit disbelieved. According to Taylor, responding to an unofficial inquiry by a KRONOS staff member, "the New Scientist report was a little over zealous" because the "error bars still embrace a value of zero for the internal source on Venus". Tomasko et al. report that Venus absorbs 132±13 W/m2 of sunlight while radiating 153±13 W/m2 and "The difference . . . corresponds to a net outflux of 20±20 W/m2...." Each time results are stated they are qualified by a statement such as: "The uncertainties of these preliminary results are too large to interpret them as evidence for an internal energy source." The results do not warrant the sensationalism conveyed by the article. Merely comparing medians, as New Scientist did, simplistically implies a 15.9% excess. Since Taylor's "error bars" are most likely standard deviations, the reported component fluxes should yield a net outflux of 21±18 W/m2, not 20±20 W/m2. The latter evidently arises from rounding error and considerations of numerical aesthetics, respectively. Further, the net flux compared to the solar input is erroneously given as 13% instead of 15%.
Since the authors derived the net flux expression on the basis that the component fluxes may be taken as random variables in a normal distribution with a mean and standard deviation, the "uncertainties" can be quantified. In the absence of systematic error, the null hypothesis that there is no difference between the flux components would be accepted at the 95% level of confidence if the probability of the observed difference arising by chance were greater than 0.05. In this case, a difference of at least 20 W/m2 (without regard to direction) being due to chance has a probability of 0.318 (almost one chance in three), over six times the maximum acceptable. Thus, in accordance with the standard two tail test, the null hypothesis that the observed difference is not statistically significant is accepted. The results of this test would be reversed if the difference were at least 40 W/m2 or if the standard deviation were 10 W/m2 or less. Note, this test is conservative and does not rule out the possibility that the observed difference is real.
However, if systematic error is zero (a big if) and credence is given to the observed difference, the same data can also show that the probability of Venus cooling is 0.841; the probability of the cooling rate exceeding 20 W/m2, 0.159; while the probability of Venus heating is also 0.159. For now, all things considered, the status of Venus's thermal balance is still unresolved. CLE