The Planet Venus Author(s): Carl Sagan Source: Science, New Series, Vol. 133, No. 3456 (Mar. 24, 1961), pp. 849-858 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/1706530 . Accessed: 24/02/2015 13:54 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve and extend access to Science. http://www.jstor.org This content downloaded from 128.103.149.52 on Tue, 24 Feb 2015 13:54:17 PM All use subject to JSTOR Terms and Conditions 24 March 1961, Volume 133, Number 345-6 CURRENT PROBLEMS IN RESEARCH eventual manned expeditions to Venus must be exceedingly perplexed over whether to send along a paleobotanist, a mineralogist, a petroleum geologist, or a deep-sea diver. But new informa? tion has recently become available The Planet Venus which probably eliminates three of the four proposed surface environments; taken together with some of the earlier Recent observations shed light on the atmosphere, data, it points the way to a consistent surface, and possible biology of the nearest planet. picture of the atmosphere and surface of Venus. Carl Sagan Composition of the Atmosphere Only the portions of the Cytherean The launching of the Soviet inter? thetical Carboniferous swamp was gen? atmosphere which are above the cloud planetary vehicle toward Venus on 12 erally abandoned, to be replaced by an layer are accessible to spectroscopic in? February 1961 opens a new era in arid planetary desert, overlain by vestigation. Since the cloud layer may planetary studies. This article is an clouds of dust from the wind-swept be situated tens of kilometers above the assessment of current knowletlge of surface (3) (Fig. 1). The arid surface surface (see the discussion below), the Venus at the dawn of this era. also explained the great abundance of spectroscopic data are not necessarily The planet Venus is enshrouded by carbon dioxide [which was accidentally directly applicable to the lower atmos? clouds which prevent telescopic exami? discovered (4) in a search for water phere. It is possible that gases present nation of its surface. In the absence of vapor]; for, in the absence of water, the above the cloud layer in undetectable direct observations, reasons have been Urey equilibrium pressure of carbon amounts are abundant in the lower at? adduced for proposing a variety of dioxide will not be established (5). mosphere. By laboratory intensity- differing and mutually iaconsistent sur? Hoyle (6) explained the lack of water matching of the Cytherean carbon di? face conditions. Since onty water clouds by assuming a great excess of hydro- oxide intercombination bands near were familiar to terrestrial observers, carbons over water on primitive Venus, 8000 angstroms, the abundance of the apparent thickness of the Cytherean and subsequent oxidation of the hydro- carbon dioxide (above the atrnospheric (i) cloud layer seemed to argue for a carbons to carbon dioxide, until all the level at which an 8000-angstrom great abundance of water. From there water was depleted. He suggested that photon is efTectively reflected) is esti? it was only a step to the assertion (2) the surface is now covered with the re? mated to be 1 kilometer-atmosphere that "everything on Venus is dripping mainder of the hydrocarbons, and that (km-atm) (8). The only other pos? wet. A very great part of the sur? the cloud layer is composed of smog. sibly identified atrnospheric constituent face of Venus is no doubt covered with Menzel and Whipple (7) replaced is water vapor, marginally detected on swamps. , . The constantly uniform the wind-swept desert and the planetary Venus recently by high-altitude balloon climatic conditions which exist every- oil field with a global Seltzer ocean; spectroscopy. The abundance of water where result in an entire absence of they argued that if Venus were com? vapor (above the atrnospheric level at adaptation to changing exterior condi? pletely covered by water (because of which a 1.13-micron photon is effective- tions. low Only forms of life are there? the high atrnospheric content of carbon ly reflected) is estimated by Strong to be fore represented, mostly no doubt, be- dioxide, the water would, of course, be about 2 X 10-8 gm/cm2 (9). Kozyrev longing to the vegetable kingdom; and carbonated), the access of carbon di? reports observing several features in the the organisms are nearly of the same oxide to silicates would be impaired, aurora and night sky of Venus corre? kind all over the planet." and for this reason the Urey equilib? sponding in wavelength to known emis? After many unsuccessful spectro? rium would not be established. The sion bands of N2, N2+, and CO+ (10). scopic attempts to discover water vapor state of our knowledge of Venus is From considerations of cosmic abun? in the Cytherean atmosphere, the hypo- amply illustrated by the fact that the dance and from terrestrial analogy, we Carboniferous the would to find N2?which has no The author is Miller research fellow at the swamp, wind-swept expect Institute for Basic Research in Science, the desert, the planetary oil field, and the permitted absorption spectrum in the Space Sciences Laboratory, and the Department Seltzer ocean each have their accessible of Astronomy, University of California at global presently wavelength region Berkeley. serious proponents, and those planning ?on Venus, and we would expect to 24 MARCH 1961 849 This content downloaded from 128.103.149.52 on Tue, 24 Feb 2015 13:54:17 PM All use subject to JSTOR Terms and Conditions find carbon monoxide from the photo- observed; occasionally dark bands are features, the terminator has a serrated dissociation of carbon dioxide. [It is a seen extending perpendicularly from appearance. The bright protruding fea? curious incidental fact that at one time the terminator onto the disk. The dif- tures are prominent near the apparent Kozyrev (II) believed the spectral ficulties encountered in making visual poles, especially near the southern pole; features discovered by him were due to observations of Venus are illustrated by they were also detected visually by microorganisms in the Cytherean at? the fact that the outstanding American such early observers as Schroter and mosphere.] Nevertheless, Newkirk (12) observer at the turn of the century, in Trouvelot, who explained them as found no evidence of many of the over a decade of regular observation enormous mountains, 60 or more kilo? strongest features reported by Kozyrev of Venus, was able to see distinct meters high. Ross proposed the more and found strong emission at a neigh- markings only once. On that occasion likely explanation that the protrusions boring wavelength (4505 A) not re? shading was evident, parallel to the are areas of atmospheric haze sur- ported by Kozyrev and corresponding terminator but not perpendicular to it rounding the planetary poles, such as to no known molecular emission. The (19). Danjon and Dollfus (20) have exist around Mars. This, in turn, im? only features common to both observa? constructed planispheres from their plies an appreciable difference in tem? tions are unidentified emission bands at visual observations which show dark perature between the equator and the 4415 and 4435 angstroms (13). markings with little relative displace? poles. It would be of interest to deter? One might attribute the absence of, ment over periods of weeks. In some mine the composition of the polar for example, the N2+ first negative sys? drawings the markings tend to radiate haze. More recent ultraviolet photo? tem in Newkirk's spectra to low from the subsolar point. Danjon and graphs show three bright and three magnetic activity at the time of his Dollfus interpret these dark markings dark bands, roughly perpendicular to observations, but the absence of the as surface features seen through stable the terminator and extending across the feature at 4505 angstroms in Kozyrev's gaps in the cloud layer. The apparent entire visible hemisphere of Venus. The spectra then remains puzzling. Unsuc- constancy in the position of the mark? inclination of these bands to the plane cessful searches for carbon monoxide ings suggested to the French astrono- of the Cytherean orbit is estimated by absorption place the amount of carbon mers that the period of rotation of Kuiper (22) at 32? and by Richardson monoxide above the relevant reflection Venus is equal to its period of revolu? (23) at 14?. The difference between level at less than 100 cm-atm (14). At tion, 225 days. However, Kuiper (21) these values emphasizes the observa? the present writing, it must be con? has pointed out that on a slowly ro- tional difficulties. cluded that there is no convincing direct tating planet, cloud patterns near the Ross attributed the presence of band evidence for nitrogen or carbon mon? terminator will bear an approximately structure to atmospheric circulation, as oxide on Venus. The present upper constant relation to the terminator, just has been suggested for the Jovian limit on oxygen in the high Cytherean as characteristic cloud patterns appear planets. If the explanation is correct, atmosphere is 100 cm-atm (3, 15); the at a given time of day on the earth. then the speed of rotation at the equa? limit is 100 cm-atm for N2O, 4 cm-atm Photographic detail of Venus is most tor must exceed the speed of random for NHs, 20 cm-atm for CH*, 3 cm-atm evident in the near-ultraviolet region atmospheric winds (17), giving a maxi? for C2H4, and 1 cm-atm for CsHo (14).