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KRONOS Vol V, No. 1
On Some Problems Of Venus
V. A. FIRSOFF
[* Reprinted from the J. Brit. astron. Assoc. by permission of the author and the journal. The reprinting of this article is not to be construed as an endorsement by Mr. Firsoff of Velikovsky's theories. On the contrary, Mr. Firsoff, while an exponent of the interdisciplinary approach and recognizing that there are difficult cosmogonical problems regarding the planet Venus, subscribes neither to the time scale nor the dynamical scenario of Worlds in Collision...]
The media and science popularizers tend, perhaps inevitably, to impress a stamp of finality on findings and interpretations that are at best tentative and sometimes misleading. There is hardly any subject of study to which this applies more than to Venus. In what follows I do not propose to lay down the law, but merely to indicate some inadequacies and contradictions in the "state of the art", as well as set forth some – certainly tentative – suggestions of my own. The matter is made topical by the launching in May  of NASA's very comprehensive mission to study the planet.
We have come to accept more or less unquestioningly that Venus has a retrograde axial period of 243 days, but its atmosphere turns round in 4.1 days at the equator and in something like 2 days nearer the poles.(1) Yet not only is this situation intrinsically incredible, but it still lacks any satisfactory explanation.
It is clear that the equatorial air masses flowing towards the poles will be subject to the Coriolis force by virtue of preserving their initial velocity, and so, moving over a decreasing circle, will complete a revolution in a shorter time, to be exact, in proportion to the cosine of latitude ø. For 60°, cos ø = 0.5, and so the period will be halved, as observed. The effect cannot be more than approximate owing to the intervention of turbulence and local convection cells.(1)
So far so good, but this leaves two questions unanswered.(1) Why does the equatorial air flow towards the poles?(2) How does the 4-day equatorial period originate in the first place?
The air flow away from the equator requires a sufficiently steep temperature gradient between it and the poles. But their is no evidence of such a gradient. Murray and Wildey's temperature chart reproduced here (figure 1)(2) may be somewhat dated, but it is in good agreement with other observations, including those by Veneras 9 and 10.(3) The chart shows a total temperature drop of 25-35°K, with the warmest region about the equator in the dark hemisphere, but the effect is spurious, because of the high thermal opacity of the atmosphere(3, 4) and the fact that in this region we are simply looking into the deeper atmospheric layers at a higher temperature. Microwave emission is substantially uniform all over the globe, which is taken to indicate isothermal conditions at the surface.
[*!* Image] Figure 1. Radiometric temperature chart of crescent Venus after Murray and Wildey. The dashed line marks the terminator. Isotherms at 5°K intervals.
The cloud patterns portrayed in the UV pictures of Venus do, nevertheless, clearly show that the relatively warm (one can hardly describe it as "hot") air is flowing from the equator to the poles, and this must inevitably be paralleled by a counter-flow of colder atmospheric masses from the poles towards the equator at lower levels, about which nothing is known as yet. Presumably, since chilling favours condensation, this counter-flow will be located within the main cloud blanket of Venus. Once again a thermal "engine" in the form of a steep temperature gradient is implied.
To say that the vigorous circulation smoothes out the temperature differences will not do, for, firstly, if these differences were smoothed out the flow would stop and, secondly, an effect cannot be its own cause. We are thus left with an unresolved contradiction.
The second question is even more difficult.
The solar day of Venus is 117 of our days – say, 120 for even count. The Sun does not shine at night, and will take 60 days to traverse the day arc of 180°. This makes 3° per day. The Sun's diameter as seen from Venus is about 45', so that the Sun will creep through four of its own diameters in 24 hours. It is obvious that this must lead to a powerful build-up of heat at the subsolar point, the air streaming away from it in all directions, in a star or radial pattern, towards the terminator. Indeed, such a circulation pattern is apparent, but far from dominant, in the so-called Y-effect, or a kind of "eye" formed by the prising apart of the weather belts. But why does not the star pattern prevail, as it should on a planet in slow rotation?
Obviously, the equatorial air moves about the "geographical" axis in four days, and the period is still shorter in high latitudes. Thus the Sun travels all round the equatorial atmosphere in four days only. Yet, for one thing, a four-day period and the concomitant Coriolis effects do not seem to be quite enough to produce a belted cloud structure. The Earth rotates faster than that, but this is insufficient to yield weather belts comparable to those of Venus. It may be argued that the input of solar energy is greater in the atmosphere of the latter. But is it? The Russian investigators(3) put the radiometric albedo of Venus at 0.79, which means that only 21% of the theoretical allowance of solar energy is available to heat the atmosphere, and this is a good deal less than on Earth.
Even, however, if we brush this objection aside – which we have no right to do – we cannot explain the four-day atmospheric period by the differential heating of the equatorial air due to the four-day period. The subsolar point travels around Venus in 117 days and it cannot generate a "toroidal" wind of 400 km/h. Such a wind needs an "engine" to drive it, but there exists no thermal gradient along the equator to provide the necessary driving force.
The conclusion seems inescapable that the four-day period is the cause and not the effect of the observed atmospheric circulation, or, in plain English, that the radar period is not the true axial period of Venus. I have suggested as much previously and proposed a possible explanation.(5, 6)
The external magnetic field of Venus is very weak, which would tally with slow rotation, but it has been suggested(7) that the liquid core of Venus consists of non-magnetic troilite, FeS, and the same explanation has been offered for the low magnetic dipole of Mars. Unfortunately, this will not do. The uncompressed density of troilite is 4.6, and the mean density of Venus is 5.25. Considering that Venus is less massive than the Earth (81.5% of the Earth mass) and probably a little hotter withal, the two planets should have approximately the same internal composition and structure, and if anything the iron core of Venus should be somewhat the larger.
The magnetic field of the Earth is subject to periodic reversals, which should apply to Venus as well. Just before the polarity changes sign, the field drops to zero, and it may be that Venus, even if in fast rotation, is close to such a point in its geological history.
[*!* Image] Figure 2. Radar echo from a limb annulus of Venus obtained at Arecibo Ionospheric Observatory. Doppler shifts in cycles per second.
On the other hand, Venus is closer to the Sun and so exposed to a solar wind about twice as intense as the Earth. This will pinch any magnetic field around the planet and may drive the analogue of our Van Allen belts into its upper atmosphere. Indeed, the Veneras have found(4) that the ionosphere of Venus is so pinched. We may, therefore, expect a belt of ionized gas to develop in the upper atmosphere along the planet's equator. Ionized gas is an electric conductor, and it is well known that a circular conductor surrounding a revolving magnet rotates in the opposite sense. Thus the suggested belt would revolve counter to the body of a magnetic planet, while at the same time being partly entrained in concordant rotation by the atmosphere in which it is immersed. Moreover, a moving electric charge constitutes an electric current, which would generate a dipole of polarity opposite to that of the planet and so mask its magnetic field. This principle has been used during the war to protect ships against magnetic mines.
The radar period is obtained by measuring the Doppler dispersion of the radar echo across the disk along the equator.(8) The reflections from the central portions of the disk arrive first, and those from the limb annulus are delayed, so that they can be separated. The frequencies of the echoes from the approaching part of the annulus will be increased, and correspondingly decreased on the opposite receding side. This yields a diagram that looks like a cup in cross-section (figure 2). Since, though, the peak Doppler effect occurs along the equator, an echo from an electrified equatorial belt would produce precisely the same effect. There would, of course, be a reflection from the solid body of the planet as well, but if the latter rotates 60 times as fast as the belt the scatter of velocities would be correspondingly greater, the peaks on the sides would be lower, and 60 times farther apart (figure 3), so that they would be readily overlooked. Moreover, radar would experience at least partial absorption and scattering in the ionized atmosphere (thunderstorms would produce strong "blips"), and the ionized belt, being aligned with the magnetic equator, need not coincide with the rotational equator.
[*!* Image] Figure 3. Possible explanation of the radar period of Venus. A reflecting annulus is isolated by timing. The ordinates represent power and the abscissae frequency, which is increasing towards the right. The left limb is receding, causing a decrease in frequency of the echo, which is increased at the approaching right limb. At O there is no reflection from the ionized belt B and the echo frequency is the same as that of the original pulse. At B, B the echo from the belt forms two peaks. The reflectivity of the belt is low, but so, too, is the dispersion, and the resulting peaks are high and steep (viz. figure 2). The peaks S, S,due to the ground echo are far out in the wings and relatively low owing to the high spread of velocities. The diagram is not to scale; in reality S, S will be 60 times as far from O as B, B.
G. P. Kuiper obtained an equatorial obliquity of 32° from the study of the inclination of the weather belts.(9) This does not seem to be a very reliable method, and it can probably be done better by observing the position of the "polar caps", in the meaning of the bright areas at the poles of the planet, clearly shown in the Mariner-10 UV pictures. These "caps" are readily visible through a blue filter (figure 4), and I have made a series of such observations, described in the Journal,(10) which may well be worth repeating and extending. My results seem to agree fairly well with Kuiper's polar co-ordinates.
[*!* Image] Figure 4. Telescopic view of Venus in blue light as observed by the author.
The question is, does any such belt of plasma really exist? The indications are that it does. The Mariner-10 pictures unmistakably show an equatorial belt which does not participate in the general atmospheric circulation (see figure 5) and has not escaped the notice of the NASA investigators.(1) It also appears in the radar views of Venus (figure 6), where the equatorial region is blurred, and the distribution of some markings on the two sides of this line is oddly symmetrical and somewhat difficult to accept.
There is, however, one more hurdle to be cleared. The radar views of Venus on successive days show little change in the position of the surface markings, which is consistent with a slow axial period. It will, though, be noticed that such observations are made, for obvious reasons, at or near culmination. Indeed, the fixed dish at Arecibo cannot be pointed at Venus at any other time. And Mars would behave in exactly the same way, the reason for which is well known: it turns round in substantially the same time as the Earth. Could Venus do likewise? This sounds like an impossible heresy. Yet the Russian astronomer A. Belopolsky deduced from the spectroscopic observations at visual wavelengths made at Pulkovo between 1903 and 1911 an axial period of 34 hours 10 minutes. More recently, in 1956, J. D. Kraus, of the Ohio State University, found that Venus was a source of an 11-metre radio "static" with a periodicity of 13 days, whence he derived an axial period of 22 hours and 17 minutes.(11) True, he recanted (under pressure). So did Galileo. But Galileo was proved right, and supposing that Kraus were, after all, not too far off the mark, we would have to explain not why the UV period is so short, but why it is so long. I believe this could be done on the basis of the star-type circulation originating at the subsolar point. The heat would tend to linger behind the subsolar point, owing to thermal inertia, and so impede the air flow. NASA's Pioneer mission to Venus ought to be able to solve this problem. But this far from exhausts the list of contradictions.
[*!* Image] Figure 5. Three composite views of Venus in UV light by Marina 10, showing rotation. The feature indicated by arrows is about 1000 km across. The equatorial belt stands out clearly in the last picture on the right. Courtesy NASA.
[*!* Image] Figure 6. Radar views of Venus obtained at the JPL Goldstone Tracking Station. The crateriform structures measuring up to 160 km in diameter (see text for further particulars). Courtesy NASA.
The clouds of Venus are said to be 3040 km thick, and only 2% of the incident sunlight was supposed to reach the surface. Yet the Soviet probes, Venera 9 and 10 have found that, in the words of Arnold Selivanov, "it is as light on Venus at noon as it is on a cloudy day in Moscow in June".(12) Since I have never been to Moscow, the immediacy of this comparison is lost on me, but I am familiar with the situation in Scotland and Sweden, which should be geographically equivalent. Ksanfomaliti et al.(3) also say that the surface is "quite light", and even suggest that the cloud cover may be broken at midday. This may corroborate the view that the high temperatures reported by the Veneras and inferred from the microwave radiation are due to the greenhouse effect, which otherwise rested on some rather dubious reasoning,(13, 14) but does not quite fit the overall picture. Nor is there any sign of the "super-refraction" expected at the atmospheric density of 0.07. Something is wrong here.
The alleged lack of water on Venus is not very credible either. The Mariner-10 observations(15) have shown that there is at least 10 times as much atomic oxygen in the atmosphere of Venus as in that of Mars and ozone is present on the latter.(16) It must, therefore, a fortiori, be present in the atmosphere of Venus. In fact, it has a "thermosphere". To quote Ksanfomaliti et al.,(3)"The temperature in the subsolar point is 470°K at minimum, and 800°K at maximum, solar activity above 160 km. At the same height on the opposite, night point of the planet the temperature is 280 to 300°K. The high temperatures of the thermosphere are explained by the absorption of short-wave solar radiation." It is not expressly stated that this absorption is by ozone, but the temperatures are what could be expected of an ozonosphere, and the darkness of the gaps between the UV clouds is itself a potent testimony to UV absorption at lower levels. If so, however, atmospheric water vapour would be shielded against photo-dissociation and consequent loss to space. Moreover, not only is the upper atmosphere very cold (figure 1), but the exosphere itself at 400°K(15) is much below the 2000°K of our exosphere, so that, on the one hand, Venus has a very effective cold trap for water and, on the other, the rate of molecular evaporation to space is low. It is in any case immediately obvious that the photo-dissociation of either water or carbon dioxide by the short UV radiation will generate oxygen and so ozone, which will prevent the continuation of the reaction at lower atmospheric levels.(14) There is also the unsolved problem of the intense sky-glow.
To sum up, when the Pioneer spacecraft reach Venus our entire picture of Venus may have to be scrapped. Thus, for this once, serious students of the planet will have good reason to count the "shopping days to Christmas".
REFERENCES1. Murray, B. C. et al., Science, 183, 1307 (1974).
2. Sky and Telesc., 25, 320 (1963).
3. Ksanfomaliti, L. V. et al., New Sci., 127 (1977 Jan. 20).
4. Chase, S. C. et al., Science, 183, 1291 (1974).
5. Firsoff, V. A., J. Br. astron Assoc., 80, 303 (1974).
6. Firsoff, V. A., The Solar Planets, 110, Newton Abbot, 1977.
7. Lewis, J. S., Scientific Am., 230, 50 (1974).
8. Thomson, J. H., Planetary Radar, Jodrell Bank Reprint No. 301, 1963.
9. Kuiper, G. P., Private communication, 1955 April 19.
10. Firsoff, V. A., J. Br. astron. Assoc., 67 . 108 (1967).
11. Sky and Telesc., 16, 122 (1957).
12. Novosti bulletin No. 26497 (1957).
13. Rasool, S. I. and de Bergh, C., Nature, London, 226, 1037 (1970).
14. Firsoff, V .A., Astronomy and Space, 2, 217(1972).
15. Broadfoot, A. L., et al., Science, 183, 1315 (1974).
16. Barth, C. A. et al., Mariner Mars 1971 Project Final Report, JPL, Pasadena, Calif., 1973.