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181.
James B. Pollack Edwin F. Erickson Fred C. Witteborn Charles Chackerian Audrey L. Summers Warren Van Camp Betty J. Baldwin Gordon C. Augason Lawrence J. Caroff 《Icarus》1974,23(1):8-26
We have obtained measurements of Venus' reflection spectrum in the 1.2 to 4.1-μm spectral region from a NASA-Ames operated Lear jet. This was accomplished by observing both Venus and the sun with a spectrometer that contained a circular, variable interference filter, whose effective spectral resolution was 2%. The aircraft results were compared with computer generated spectra of a number of cloud candidates. The only substance which gave an acceptable match to the profile of Venus' strong 3-μm absorption feature, was a water solution of sulfuric acid, that had a concentration of 75% or more H2SO4 by weight. However, our spectra also show a modest decline in reflectivity from 2.3 μm towards 1.2-μm wavekength, which is inconsistent with the flat spectrum of sulfuric acid in this spectral region. We hypothesize that this decline is due to impurities in the sulfuric acid droplets.We also compared our list of cloud candidates with several other observed properties of the Venus clouds. While this comparison does not provide as unique an answer as did our analysis of the 3-μm band, we find that, in agreement with the results of Young (1973) and Sill (1973), concentrated sulfuric acid solutions are compatible with these additional observed properties of the Venus clouds. We conclude that the visible cloud layer of Venus is composed of sulfuric acid solution droplets, whose concentration is 75% H2SO4, or greater, by weight. 相似文献
182.
S. Fred Singer 《Earth, Moon, and Planets》1972,5(1-2):206-209
Of the many proposed modes of origin of the Moon, some violate physical laws; many are in conflict with observations; all are improbable. Perhaps the least improbable - based on recent tidal theory calculations and on the interpretation of lunar rock data - is capture of the Moon as it passed near the Earth in adirect (prograde) orbit, shortly after the formation of Moon and Earth, about 4.5 billion years ago. (Capture of the Moon from an initiallyretrograde orbit which had been proposed some years ago, leads to physically unacceptable consequences.) The effects of capture on the Earth would have been cataclysmic, leading to intensive heating of its interior, to volcanism, and to the immediate formation of an atmosphere and hydrosphere. Thus capture of a Moon may have given rise to the unique properties of the Earth (in the Solar System) and to the early evolution of life, about 3.5 billion years ago.Presented at the NATO Advanced Study Institute on Lunar Studies in Patras, Greece, September, 1971. 相似文献
183.
The Seoni (India) chondrite is an H6 group ordinary chondrite that contains olivine (Fa, 19.7 mole%), orthopyroxene (Fs, 15.9 mole%), clinopyroxene, plagioclase (An, 10.3; Or, 5.6 mole%), together with chromite, troilite, kamacite, taenite, chlorapatite, and whitlockite. Recrystallization has been quite extensive as indicated by the presence of few remnant chondrules, low abundance of clinopyroxene and relatively high abundance of well formed plagioclase. Treatment of Fe2+ and Mg partitioning between clinopyroxene and orthopyroxene and between olivine and chromite indicates equilibration temperatures of between 875–920 °C. 相似文献
184.
Fifteen Apollo, or Earth-crossing, asteroids are now recognized, and their orbital elements tabulated here. None has been accidentally rediscovered, a circumstance that leads to the 50% probability that the total number equals or does not exceed 100 to absolute magnitude 18, or above a diameter of roughly 1 km. Physical observations, orbital characteristics, and associated meteor streams provide clues as to whether the Apollo asteroids are truly minor planets or moribund cometary nuclei. A definitive answer as to the origin of the Apollo asteroids is yet to be found, but a short discussion of the status of the problem is presented.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973. 相似文献
185.
A computer program to convolve numerically any azimuthally symmetric, solar radial brightness distribution with standard antenna patterns of small half power beamwidths has been used to find a solar brightness distribution which is a good fit to the eclipse curve obtained during the 7 March 1970 partial solar eclipse with the NRAO 36-ft antenna at 3.5 mm. This brightness distribution is compared with the brightness distribution at 3.2 mm determined by the Pennsylvania State University Radio Astronomy Observatory group during the same eclipse but observed from Mexico where totality occurred. The two brightness distributions are very similar in shape, showing a double peak near the limb, but differing slightly in the positions of the peaks. 相似文献
186.
A type III solar burst was observed at seven frequencies between 3.5 MHz and 80 kHz by the Michigan experiment aboard the IMP-6 satellite. From the data we can determine burst direction-of-arrival as well as time-of-arrival. We predict these quantities using simple models whose parameters we vary to obtain a good fit to the observations. We find that between 3.5 MHz and 230 kHz the observed radiation was emitted at the fundamental of the local plasma frequency while below 230 kHz it was emitted at the second harmonic. The exciter particles that produced the burst onset and burst peak have velocities of 0.27 and 0.12, respectively, in units of the velocity of light. 相似文献
187.
Fred Ward 《Solar physics》1973,30(2):527-537
A fundamental distinction can be made between those theories of the solar general circulation which require a mean north-south circulation in the photosphere and those which do not. Regardless of the theoretical merits of either group, they must either explain the data, or a theoretical set of data which falls within the observed limits. A detailed analysis of the Greenwich sunspot data supports a mean meridional circulation in either direction with a velocity less than one meter per second. The sunspot data therefore cannot be used to establish the existence of a mean north-south circulation, but may be used as an argument against any theoretical requirement for such a circulation much in excess of 1 m s–1. 相似文献
188.
Cycles of glaciation with an average period of 100 kyr are mediatedby impacts of cometary bolides. Ice-age conditions are dry and dusty withlow rates of precipitation. Comets in the mass range 1015 -1016 gimpacting the oceans could release enough water vapour into the atmosphereto enhance a depleted greenhouse effect. The energy deposited in the oceanswould also warm the surface layers, thus starting up anevaporation-precipitation cycle which ushers in warmer interglacialinterludes. The latter have neutral stability and are necessarilyshort-lived, eventually drifting back to glacial conditions on timescalesof 10 kyr. 相似文献
189.
190.
Cochran Anita Veverka Joseph Bell James Belton Michael Benkhoff Johannes Benkhoff Andrew Clark Benton Feldman Paul Kissel Jochen Mahaffy Paul Malin Michael Murchie Scott Neimann Hasso Owen Tobias Robinson Mark Schwehm Gerhard Squyres Steve Thomas Peter Whipple Fred Yeomans Donald 《Earth, Moon, and Planets》2000,89(1-4):289-300
In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished. 相似文献