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Notes on some planetary problems.

1948; Institute of Physics; Volume: 54; Linguagem: Inglês

10.1086/106185

1538-3881

C. O. Lampland,

Space Exploration and Technology

The memorable event of the joint meeting of the American Astronomical Society and the Astronomical Society of the Pacific at the Palomar Observatory could be appropriately called the astronomers' dedication of the giant ~oo-inch Hale Telescope. The world's most powerful instrumental equipment assembled here with its research staff of eminent scientists, working under the favorable observing conditions, can be expected to make advances in many difficult fields, perhaps more in anticipation for the outer reaches of the observable universe; but there is also the promise that some difficult and outstanding problems in our own solar system still await assistance towards more complete solutions. It was with these thoughts in mind that the writer at this time ventured a few comments on planetary problems. Planetary investigations during the first half of this century have made steady progress if one pauses to count what has been accomplished. Visual observations have continued in the traditional systematic way to add to our knowledge, but new methods of research have also been introduced, as one may enumerate briefly, in the way of planetary photography, spectrographic investigations of planetary spectra for rotation and atmospheres, radiation researches in the measurements of planetary radiation with the information this work brought on planetary conditions and temperatures, the developments of quantum mechanics, band spectroscopy and laboratory experiments in the further interpretation of planetary spectra, leading to the identification of methane, ammonia and carbon dioxide in the planetary atmosphere, and lastly the application of recent war time developments of highly sensitive energy detectors, bringing still further additions to our knowledge in such discoveries as carbon dioxide in the Martian atmosphere. In this brief outline it is not possible to give deserving mention and credit to the work of the many eminent investigators who have contributed in essential ways to these important advances. But this progress in our knowledge has not cleared away confusing views concerning conditions prevailing on some of the planets. One might mention that views are still held that the polar caps on Mars may be carbon dioxide deposits, an impossible state of affairs, as recognized by investigators with some knowledge of physics. One also finds quite often remarks that on the planet Mars the temperatures everywhere must be below freezing. That viewpoint was made untenable by the radiometric measurements which showed clearly that the temperature under noonday sun may be as high as 300C, and further that the radiation from the planet followed closely the insolation, rising to maximum values in the higher latitudes at summer solstice of the southern hemisphere. There is, of course, the difficult question to answer as to the temperature of the nightside of the planet, the prevailing opinion being that the temperature falls very low due to the escape of the radiation through the clear and thin Martian atmosphere. The amount of carbon dioxide recently detected in the Martian atmosphere should exercise considerable effect on the heat economy and cli matology of the planet (but one must admit there is apparently a fairly clear window for the escape of planetary radiation). Naturally there would be great interest in efforts to obtain measurements of radiation from the planet's surface after sunset and before sunrise. In this extremely difficult undertaking, one might hold a slight hope that something may be accomplished with the powerful equipment and good observing conditions on Palomar Mountain. Some weeks before and following opposition, areas of the planet's surface are accessible for observations but are not illuminated by the sun. These are the regions of "defect of illumination" which are in the dark some hours before sunrise and after sunset, and which can be explored by receivers sensitive to long wave radiation. However efforts to measure radiation from such areas would seem to meet with almost insuperable difficulties. The energy would be feeble; the problem of contamination by the much more powerful radiation of shorter wave length overflowing from the illuminated parts of the disk by scattering and disturbed seeing, would be difficult to overcome. But modern efficient filters or screens, such as selenium, cutting off radiation of shorter wave length and transmitting efficiently long wave planetary radiation would be helpful observing means. A large image for resolution and analysis would be desirable and the finest definition would be necessary. One must expect valuable planetary contributions through this powerful equipment in several ways, and to mention only one-the spectroradiometer-should bring highly desirable data. Filter separation of the spectral components of the long wave energy of planetary radiation has given important information on planetary conditions and temperatures. Radiation from Mars has been found to follow insolation, as mentioned. In the case of Jupiter, the surprisingly low temperatures were observed where it was formerly supposed by some that the surface was near the glowing point. And there is the task of determining the temperatures of the fainter outer planets. And lastly, will this great instrument help to bring peace to the contending parties of the canals of Mars? Such delicate planetary details have been observed visually and photographed so frequently at Flagstaff and by the expeditions to South America and South Africa that the astronomers at the Lowell Observatory have every conviction of the reality of such details. But it must be admitted that visually the fainter details are of extreme difficulty even under excellent good seeing, and it is not unreasonable to expect divergent views in such matters. One realizes the vigilance it will be necessary to maintain to catch the fleeting moments of unusually favorable conditions when the giant instrument can be efficiently used for planetary photography of the finest details, a view based on long experience with instruments of much smaller apertures. Lowell Observatory, Flagstaff, A ris.