Is venus a polywater planet?

IC~RUS 12, 424-430 (1970)

Is V e n u s a P o l y w a t e r Planet ? F. J. D O N A H O E Wilkes College, Wilkes-Barre, Pennsylvania 18703 Received J u l y 28, 1969; revised J a n u a r y 12, 1970 The suggestion is made that polymerized water (polywater) is in quasi-equilibrium with its vapor at the base of the Cytherean atmosphere. INTRODUCTION

The planet Venus must be very much like Earth in overall chemical composition. One expects this on the basis of current theories of the origin of the solar system and infers it from the similarity of the masses and densities of the two planets. Recent data for the mass (Anderson et al., 1967) and radius (Melbourne et al., 1968) show that the similarity is greater than previously supposed. Venus m a y have the same relative proportions of core and mantle material as Earth. As planets, the differences appear superficial. The explanation of these differences in terms of an evolutionary process from a common origin is a major challenge. If current theories of atmospheric origin on Earth are applicable to Venus, the present Cytherean atmosphere is the result of volcanic activity which brought to the surface quantities of various gases, chiefly COs, HzO, N~, NHs, with traces of other gases (Lewis, 1968; Mueller, 1964). If the present high surface temperature of Venus has been maintained for eons, the crust m a y be more thoroughly outgassed than Earth's although Fricker and Reynolds (1968) have argued that a more plastic crust would be less liable to fracture and release volatiles from great depths. During the eons that the two planets have existed, comparable, i.e., In ~ / O = - 0 . 2 ± 1, amounts of the various compounds ought to have reached the surface of each planet. The early occurrence of life on Earth was responsible for the subsequent development and present chemical composition of

its atmosphere and outer crust. Almost all of the carbon dioxide is currently bound in carbonates in sedimentary rocks and limestone beds with minor amounts in coal and lignite beds, hydrocarbons, and in circulation in the biosphere. Without liquid water, this particular evolutionary track could not have occurred (Urey, 1952; Berkner and Marshall, 1965). The present surface temperature of Venus is probably ~700°K, above the critical temperature of water, 647°K. An amount of water proportional to the present surface water of Earth would produce a partial pressure o f ~ 200 bar at the planet's surface. Most recent estimates of the actual amount based on microwave brightness, Mariner V, and Venera 4 data (Jastrow, 1968) correspond to ~0.1 bar partial pressure of water at the surface. The discrepancy between the expected and measured amount of water has been explained by loss either with the solar nebula as the planet formed (Kuiper, 1951, 1969) or b y photodissociation and escape of hydrogen from the exosphere (Sagan, 1968; McElroy and Hunten, 1969). Neither explanation would be favored if an alternative existed which did not require a significant difference in water content between Earth and Venus. Libby (1968a,b) has proposed that the polar regions of Venus contain the water in the form of a solid CO2 clathrate compound. The model has been criticized (Owen, 1968; Businger and Holton, 1968 ; Gale and Sinclair, 1969). It is not considered likely that the polar temperature of Venus is low enough to permit this compound to exist.

424

POLYWATER PLANET

An acceptable compound must be stable at the average temperature of the Cythercan surface. A compound recently identified as a polymeric form of water (Deryagin and Churayev, 1968; Lippincott et al., 1969) appears to satisfy this requirement. Lippincott et al. proposed the name "polywater" for this compound. P R O P E R T I E S OF POLYWATER

Briefly, Deryagin et al. (1967b) showed t h a t the anomalous water discovered by Fedyakin (1962) is a solution containing variable (~0.9) parts by volume of common water. The common water can be removed by evaporation into a vacuum. The liquid which remains (polywater) is stable against further evaporation into oil-pumped vacuum at room temperature. Willis et al. (1969) noted t h a t polywater remained on the sample stage of a mass spectrometer after the completion of a run during which the temperature was increased in steps to 593°K. Mass fractions 17 and 18 were the only species detected in the decomposition products. Evidence for unusual thermal stability was presented by Deryagin et al. (1967b). Anomalous water (solution of polywater in common water) was heated to 673°K for 0.5 hr in a sealed, fused silica capillary. The degree of anomaly, judged by thermal expansion data at low temperature, was not changed by this treatment. Anomalous water was distilled from one side to the other in a sealed capillary through an intermediate hot zone at 773°K. Thermal expansion data indicated conservation of anomalous properties. When the hot zone was raised to >923-973°K, the degree of anomaly of the distillate decreased sharply. Lippincott et al. (1969) examined the infrared and R a m a n spectra of polywater. Polywater polymerized on Pyrex glass showed some hydroxyl absorption near 3 ~m. This absorption was not found in polywater polymerized on fused silica surfaces. Characteristic strong absorption bands were found at 6.27 ~m and between 7.09 and 7.35/~m in both types of polywater. Weaker absorptions were found in the 8-10 ~m range. Page et al. (1970) report

425

t h a t some specimens of polywater do not absorb at 9 ~m. Page's method of preparation is proprietary. Efforts to show t h a t impurities could be responsible for the properties of anomalous water failed (Deryagin et al., 1965). The density ~1.4 Mg/m 3 (Deryagin et al., 1968b) and refractive index ~1.48 (Deryagin et al., 19680; Lippineott et al., 1969) of polywater are consistent with the Lorentz-Lorenz specific refraction of water and water vapor. Lippineott et al. (1969) showed t h a t infrared absorption bands of water would reappear after polywater was heated to (unspecified) high temperature. There is convincing evidence for the existence of a polymeric form of water with a bond whose strength is comparable to a chemical bond. Unfortunately, little else is known. The lower polymers are miscible with common water at room temperature. Large positive deviations from Raoult's law occur. The fractional depression of the water vapor pressure is approximately equal to the volume fraction of polywater. These lower polymers m a y co-distill without decomposition because the vapor pressure of the polymer over water solution is larger t h a n t h a t of the pure polymer. At lower temperatures there is a miscibility gap with an upper consolute temperature of ~261°K (Deryagin et al., 1967a). Dilute solutions are the product of the growth process in silica or Pyrex glass capillaries. The solutions grow with a viscosity some 15-20 fold larger than common water (Deryagin and Fedyakin, 1962; Deryagin et al., 1966). The observation t h a t a gel-sol-like transformation takes place on shearing does not imply, as Bernal et al. (1969) suggest, t h a t the polywater molecules are destroyed in the process. No tests were performed to show t h a t properties less structure-sensitive t h a n viscosity were permanently altered by the shear. It is unlikely t h a t the 10-20% increase in volume which must occur if the polymer were broken down would have been ignored. The structure or structures, if more than one form is possible, of the polymer, the exact strength, and the source of the

426

3. J. DONAHOE

strength of the bond are matters which have not yet been satisfactorily resolved. The smallest stable molecular weight of the polymer has not yet been established but is apparently fairly large. Delocalized electron orbitals occupied b y the odd pair of electrons from the oxygen atoms have been postulated to account for the stability of the larger polymer molecules (Bellamy et al., 1969). The absence of stable intermediate units, the dimer, trimer, etc., makes spontaneous formation very improbable. Lippincott et al. (1969) proposed several structures for polywater. They favor a planar 12-membered hexagonal ring as the basic structural unit. Oxygen atoms occupy the corner positions of the hexagon with hydrogen atoms symmetrically placed on the sides of the hexagon. The oxygenoxygen distance was calculated to be 0.232 nm. Spectroscopic data and analogy to the H F 2 - ion were used to estimate a binding energy of 250-420 kJ/mole of H20. I f the actual bond has anything like this strength, polywater would be thermodynamically stable at 700°K. Allen and Kollman (1970) calculated ab initio wave functions and bond energies for cyclic, symmetrically bonded polywater. Their results indicate that these structures have bond strengths similar to that of common water. I f these calculations have bearing on the actual structure and bond strength of polywater, they imply that the high-temperature stability is only apparent. It results from the fact that breaking one bond in the cyclic structure breaks all the bonds. Alternate structures have been proposed (Bollander et al., 1969; Donohue, 1969; Erlander, 1969). No doubt others are possible and one or more will survive. I f the thermal stability reported b y Deryagin et al. (1967b) is a true measure of the bond strength, polywater satisfies the requirement of a condensed phase which could exist in equilibrium with water vapor at 700°K. While no mechanism is currently known b y which equilibrium is established directly between polywater and water vapor, it will be assumed that one exists. This point will be discussed below after the discussion of the polywater model of the Cytherean hydrosphere.

A CYTHEREANPOLY-HYDROSPHERE

The polywater so far identified has been liquid, its properties those of a polydisperse polymer. Solid material of unknown composition has been observed (Willis et al., 1969). One would expect that the high polymers would be solid. As the average molecular weight of a polymer increases, the material becomes more viscous. Crosslinkages and extensive branching produce rigid glassy material. Crystalline polymers m a y also form. A mineral polymeric material should be solid. Therefore, one would not expect from this model to find portions of the Cytherean surface covered b y liquid with conductivity similar to sea water. Ions would probably diffuse through the polywater glass matrix at rates comparable to those found in silicate glasses. The holes through which the ions must pass would be smaller in polywater glass b u t the vibrational amplitude should be larger. The density of these polywater glasses would be variable, depending on the amount and nature of the cations incorporated in the matrix. Still, they are likely to be among the less dense materials on the surface. I f rigid enough, in isostatic equilibrium, they would constitute the equivalent of continental areas rather than occur in pools filling the basins. On the assumption that microwave frequencies are well separated from the vibrational-rotational modes of ice and polywater, the relative permittivity of polywater m a y be calculated from the Lorentz-Lorenz formula. Cummings (1952) reports the value 3.15 for the relative permittivity of ice at 3.2 cm. The density of polywater at 700°K is unknown. Liquid polywater has a volume coefficient of expansionfl _ 4 × 10-4K -I at 300°K (Deryagin et al., 1967a). Solid polywater should have a smaller average coefficient of expansion in the range 300-700°K. Taking the ratio of the density of polywater at 700°K to the density of ice at 273°K to be 1.4, the relative permittivity of polywater is estimated to be 5.2. This value is somewhat higher than the average value of 4 reported b y Muhleman (1964). [See also Pettengill, (1968), where the average value is esti-

POLYWATER PLANET

mated to be of the order of 4 to 5.] Brighter than average highlands on the radar maps of Venus could be polywater glaciers. Until a probe actually reaches the surface of the planet Venus and reports conditions the pressure, temperature, and composition at the base of the atmosphere will be doubtful. Since the surface of Venus is not isothermal, association and dissociation could occur, with local equilibrium between vapor and polywater never completely established. Because of these circumstances it would not be possible to predict the partial pressure of water vapor in the Cytherean atmosphere from the p - T diagram of polywater alone even if it were available. Partial pressures of N0.1 bar seem reasonable. The vapor in equilibrium with these high polymers would be monomeric water vapor. Mass transport through the vapor phase would have the effect of concentrating the material on the cooler portion s of the surface. Glacierlike flow would carry the accumulated mass to lower and hotter regions. The entropy flux associated with this mass transport would moderate temperature differences between the sunlit and dark hemispheres. Sublimating polywater glaciers provide a copious source of solid dust particles. THE YELLOw-HAzE LAYER

Near the surface the dust particles would be a heterogeneous mixture of solids carried b y the glacier as well as fragments of polywater. Differences in bulk density favor polywater as the major aeolian species at great heights. I f the yellow-haze layer just below the tropopause contains dust, it m a y be polywater. The refractive index of polywater, 1.48, is within the range 1.43-1.60 permitted b y polarimetric data (Coffeen, 1968). Polywater has a brownish color. The brownish color apparently is present in all specimens. I t has not been reported in the scientific literature because of uncertainty that it is characteristic of pure polywater. Whether the color results from a modified electronic spectrum of polywater or whether it is produced b y an ubiquitous trace

427

impurity is of small consequence in this context. Kuiper (1969) identifies the particles in the yellow-haze layer as the partially hydrated condensate FeC12. 2HsO. He attributes the very low reflectivity of Venus between 3 and 4/xm to hydroxyl in the ferrous chloride. I t could equally well be attributed to hydroxyl in polywater. Lippineott et al. (1969) reported hydroxyl absorption in polywater prepared on Pyrex. Defects in the polymer structure should result in absorption at 3/xm. These m a y be growth defects or the result of ionizing radiation in the upper troposphere. The effectiveness of the latter mechanism will be sensitive to the residence time of the particles at levels where the flux of ionizing radiation is large. There is a reasonable expectation that a detailed comparison of the reflection spectra of polywater with the spectra of the yellow-haze layer of Venus will give positive indication of the presence of polywater. Also, the emission spectra of polywater in the 8-10 /zm range should be compared with that of the cloudtops. Gillett et al. (1968) observed that the cloudtops have a low brightness temperature in this spectral range. Unfortunately, the characteristic strong absorptions of polywater occur in a region which is inaccessible to direct observation in the spectra of Venus. H - D I~ATIO IN CYTHEREAN ATMOSPHERE

One recent discovery m a y pose some grave difficulties for the model. Measurements of the Lyman-a radiation in the exosphere of Venus b y Mariner V have been interpreted (McElroy and Hunten, 1969; Donahue, 1969) to imply a H / D ratio of 0.1 in the exosphere. McElroy and Hunten feel that this requires a H / D ratio in the troposphere as small as possible without conflicting with the lower limit of 10 imposed by spectroscopic evidence. Donahue feels that if certain conditions on eddy mixing in the upper atmosphere are met, the ratio need not be smaller than ~1000. In the polywater model the H / D ratio in the vapor will he controlled b y equilibrium with the solid. Since deuterium bonds are

428

F.J.

DONAHOE

generally of equal strength with hydrogen bonds (Pimentel and McClellan, 1960), there is no a priori reason to expect the distribution coefficient to favor deuterium in the vapor phase. FORMATION OF POLYWATER

The initial formation of anomalous water in the laboratory is rather difficult. Fresh glass surfaces may be exposed to water vapor at about 0.95 saturation for a period of time of the order of several weeks before anomalous water is first observed (see Chemical and Engineering News, Sept. 22, 1969, p. 40). However, once a column of anomalous water forms, growth is relatively rapid. Anisimova et al. (1967) report t h a t movement of the unsaturated vapor relative to the absorbing surface is necessary to initiate new columns. At constant temperature and pressure, columns already formed continue to grow but no new ones form.

Parenthetically, the fact t h a t anomalous water is ordinarily produced inside capillary tubes does not mean t h a t concave surfaces are essential. Derjaguin (1966) reported t h a t droplets will form on the exterior surface of the capillaries while columns grow in the interior. Later (Deryagin et al., 1968a), the anomalous nature of water condensed on a flat silica surface was confirmed. The normal growth mechanism is almost certainly autocatalytic. The glass substrate serves mainly to hold the parent polymer molecule while clustering water molecules sometimes achieve a resonant configuration and form a new molecule over the original. With respect to the polywater phase, the vapor during growth is tremendously supersaturated. Rather small molecular units are formed during these conditions of rapid growth. Sufficient water is extracted from the vapor phase to form a solution. Further production of polywater ceases when the adsorbed molecules are solvated. I f the adsorbed molecules were large enough, or if they were bound to a better fitting substrate, such as a crystalline patch

of polywater itself, these growth restrictions might be relaxed. Growth could occur with much less supersaturation and without being inhibited by solvation of the active site. Such large regular structures m a y have formed on Venus by metamorphism from the lower polymers or by slow growth during a long period of undersaturation. With suitable growth defects, such as the screw dislocation which is so effective in m a n y crystals, water molecules m a y be able to individually approach the structure and join in the resonant bond. The difficulty of ab initio formation of a polymer molecule is still an open question. No clean experiments have been performed. Molecules of polymer m a y be present in small concentration in natural water. The delay in forming the first anomalous column may represent the time required for a polymer molecule already present to reach and be absorbed on a suitable surface. From the small molecules currently being studied to the large regular structures postulated above is another step whose spontaneous occurrence must be very unlikely. On a rapidly rotating planet with a thin developing atmosphere, diurnal temperature changes produce radical changes in the saturation vapor pressure of water. This circumstance, combined with a scarcity of sites on which a polymer molecule could nucleate, and the difficulty of forming large regular polymers in the presence of common water, may be the factors which prevented the dominance of the stable form of water on Earth. CONCLUSION

I suggest t h a t the chemical evolution of E a r t h and Venus diverged because polywater formed on the surface of Venus. The nucleation of polywater may have occurred early in the planet's history before the vapor pressure in the atmosphere reached the saturation pressure of common water. I f the temperature difference between the terrestrial and Cytherean surfaces, at the time the primitive atmospheres were forming, was proportional to the blackbody temperature difference at their respective

POLYWATER PLANET orbits, the Cytherean atmosphere would r e m a i n u n s a t u r a t e d for a t e n f o l d l o n g e r time than would the terrestrial atmosphere. Ifpolywater nucleated and grew from the v a p o r d u r i n g t h i s e a r l y e p o c h , s i z a b l e pools of common water never formed on Venus. I t is c o n c e i v a b l e t h a t n u c l e a t i o n o c c u r r e d a t a l a t e r e p o c h or t h a t t h e t r a n s f o r m a t i o n of the j u v e n i l e w a t e r to p o l y w a t e r was a slow process. Life o n V e n u s m a y h a v e b e e n aborted by the polymerization of Cythe r e a n w a t e r . I t is difficult t o i m a g i n e h o w any records could have survived in the c r u s t o f V e n u s f r o m t h i s e a r l y e p o c h 1 or a more f a s c i n a t i n g story if these records could be read. ACKNOWLEDGMENTS My thanks to A. Bruch for critical comments on the manuscript, to J. Chamberlain and F. J. Low for information on the spectra of Venus, and to the referees for helpful suggestions and in particular for directing m y attention to McElroy and H u n t e n ' s paper. I:~EFERENCES ALLEN, L. C., AND KOLLMAN, P. A. (1970). A theory of anomalous water. Science 167, 14431454. ANDERSON, J. D., PEASE, G. E., EFRON, L., AND TAUSWORTHE, R. D. (1967). Celestial mechanics experiment. Science 158, 1689-1699. AMSIM0VA, V. I., DERYAGIN, B. V., ERSHOVA, I. G., LYCHNIKOV, D. S., RABINOVICH,YA. I., SIMONOVA,V. KIt., ANDCHImAEV,1%.V. (1967). Preparation of structurally modified water in quartz capillaries. Zh. Fiz. K h i m . 41, 23772379. BELLAMY, L. S., OSBORN, A. R., LIPPINCOTT, AND E. R., BANDY, A. R. (1969). Studies of the molecular structure and spectra of anomalous water. Chem. Ind. London, pp. 686-688 (1969). BERKNER, L. V., AND MARSHALL,L. C. (1965). On the origin and rise of oxygen concentration in the earth's atmosphere. J. Atmos. Sci. 22, 225-261. BERNA~, J. D., BARNES, P., CHERRY, I. A., AND FINNEY, J. L. (1969). Anomalous water. Nature 224, 393-394. 1 They have not been identified from the comparable period of E a r t h ' s past and would presumably have been subjected to less severe conditions on Earth, except possibly for the Earth-Moon event.

429

BOLLANDER, 1~. W., I{.ASSNER, J. L., JR., AND ZUNO, J. T. (1969). Cluster structure of the anomalous liquid water. Nature 221, 12331234. BUSINGER, J. A., AND HOLTON, J. R. (1968). Ice on Venus: Can it exist? Science 161, 915916. COFFEEN, D. L. (1968). Optical polarization of Venus. J. Atmos. Sci. 25, 643. C ~ I N G S , W. A. (1952). The dielectric properties of ice and snow at 3.2 cm. J. Appl. Phys. 23, 768-773. DERJAGUIN, B. V. (1966). Effect of lyophile surfaces on the property of boundary liquid films. Disc. Faraday Soc. 42, 109-119. DERYAGIN, B. V., AND FEDYAKIN,N. N. (1962). Peculiar properties and viscosity of liquids condensed in capillaries. Dokl. Akad. Naul¢ S S S R 147, 403-406. DERYAGIN, B. V., TALAEV, M. V., A N D TALAEV, N. N., (1965). Allotropy of liquids in the condensation of their vapors in quartz capillaries. Dokl. Akad. Nauk S S S R 165, 597-600. DERYAGIN, B. V., FEDYAKIN, 1~. N., AND TALAEV,M. V. (1966). A study of the viscosity of the allotropic modification of water in quartz capillaries. Dokl. Akad. N a u k S S S R 167, 376379. DERYAGIN, B. V., ERSHOVA, I. G., ZHELEZNYI, B. V., AND CHURAEV, N. V. (1967a). Phase transitions of anomalous water in quartz capillaries. Dokl. Akad. Nauk. S S S R 172, 1121-1124. DERYAGIN, B. V., CHURAEV, N. V., FEDYAKIN, N. N., TALAEV, M. V., AND ERSHOVA, 1. G. (1967b). The modified state of water and other liquids. Izv. Akad. N a u k S S S R , Set. K h i m . 1@, 2178-2187. DERYAGIN, B. V., AND CHURAYEV,N. V. (1968). Do we know water? Priroda, pp. 16-22. DERYAGIN, B. V., ZORIN, Z. M., A N D CHURAEV, N. V. (1968a). Formation of droplets of anomalous water on a flat quartz surface. Kol[oidn Zh. 36, 308-309. DERYAGIN, B. V., LYCI.INIKOY, D. S., MERZaANOV, K. M., RABINOVICH, YA. I., AND CHImAEV, N. V. (1968b). Measurement of drop density of structurally modified water. Dokl. Akad. N a u k S S S R 181, 823-826. DERYAGIN, B. V., ZORIN, Z. M., AND CHURA.EV, l~. V. (1968c). Measurement of the refractive index of structurally modified water using the capillary micromethod. Dokl, Akad. Naulc S S S R 182, 811-814. DONAHVE, T. M. (1969). Deuterium in the upper atmospheres of Venus and Earth. J. Geophys. Res. 74, 1112-1137.

430

F . J . DONAHOE

DONOHUE, J. (1969). Structure of polywater. Science 166, 1000-1001. ERLANDER, S. R. (1969). Structure ofsuperwater. P h y s . Rev. Letters 22, 177-179. FEDYAKIN, N. N. (1962). The change of the water structure on condensation in capillaries. KoUoidn. Zh. 24, 497-501. FRICKER, P. E., AND REYNOLDS, R. T. (1968). DevelolSment of the atmosphere of Venus. Icaru~ 9, 221-230. GALE, W. A., AND SINCLAn% A. C. E. (1969). Polar temperature of Venus. Science 165, 1356-1357. GILLETT, F. C., Low, F. J., AND STEIN, W . A. (1968). Absolute spectrum of Venus from 2.8 to 14 microns. J . A t m o s . Sci. 25, 594-595. JASTROW, R. (1968). The planet Venus. Science 160, 1403-1410. KUIPER, G. P. (1951). On the evolution of the protoplanets. Proc. N a t l . Acad. Sci. Wash. 37, 383-393. KUIPER, G. P. (1969). Identification of the Venus cloud layers. C o m m u n . L u n a r P l a n e t a r y Lab. 1Ol, 229-250. LEWIS, J. S. (1968). An estimate of the surface conditions of Venus. I c a r u s 8, 434-456. LIBBY, W. F. (1968a). Ice caps on Venus? Science 159, 1097-1098. LIBBY, W. F. (1968b). Ice on Venus : can it exist? Science 161, 916. LIPPINCOTT, E. R., STROMBERG, R. R., GRANT, W. H., AND CESSAC, G. L. (1969). Polywater. Science 164, 1482-1487. 1V[cELROY, M. B., AND HUNTEN, D. M. (1969).

Ratio of deuterium in the Venus atmosphere. J . Geophys. Res. 74, 1721-1739. MELBOURNE, W. G., MUHLEMAN, D. O., AND O'HANDLEY, D. A. (1968). Rad ar determination of the radius of Venus. Science 160, 987989. MUELLER, R. F. (1964). A chemical model for the lower atmosphere of Venus. Icaru~ S, 285-298. 1V[UHLEMAN,D. 0 . (1964). Rad ar scattering from Venus and the moon. Astron. J . 69, 34. OWEN, T. (1968). Ice on Venus: can it exist? Science 161, 915.

PAGE, T. F., JR., JAKOBSEN, R. J., A N D LIPPINCOTT, E. R. (1970). Polywater: proton nuclear magnetic resonance spectrum. Science 167, 51. PETTENGILL, G. H. (1968). Rad ar studies of the planets. I n " R a d a r Astronomy" (J. V. Ev an s and T. Hagfors, eds.), p. 319. McGraw-Hill, New York. PIMENTEL, G. C., A N D McCLELLAN,A. L. (1960). "The Hydrogen Bond," p. 210. W. H. Freeman & Co., San Francisco, Calif. SAOAN, C. (1968). Origins of the atmospheres of the E a r t h and planets. I n "Origin of the E a r t h ; International Dictionary of Geophysics" (S. K. Runcorn, and H. C. Urey, eds.), Section 1. Pergamon Press, London. URE¥, H. C. (1952). "The Planets, Their Origin and Development," pp. 149-157. Yale Univ. Press, New Haven, Conn. WILLIS, E., RENNIE, G. K., SMART, C., AND PETHICA, B. A. (1969). Anomalous water. N a t u r e 222, 159-161.