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1.
Venus: mapping the surface reflectivity by radar interferometry 总被引：2，自引：0，他引：2
The surface reflectivity of Venus obtained by radar interferometry at a wavelength of 3.8 centimeters has been mapped for a region extending approximately from -80 degrees to 0 degrees in longitude (Carpenter's definition) and from -50 degrees to +40 degrees in latitude. The map is free from the twofold range-Doppler ambiguity because the interferometer fringe pattern makes possible the separation of two points of equal range and Doppler shift. The map presents many new features and clearly delineates features already observed. Most notably, the map shows large circular regions of significantly lower reflectivity than their surroundinigs. 相似文献
2.
The common ranges of pressure and temperature of the atmosphere of Venus measured last October establish the connection between the Soviet Venera 4 altitude scale and the United States Mariner V radial scale. But if the Venera 4 measurements extended to the surface, as claimed, this comparison implies a radius of the planet which is about 25 kilometers greater than the radius deduced from Earth-based radar data. This impasse has been resolved in favor of the smaller value by a new determination of the radius which is more direct than the method used in deriving the radar radius, and which involves concurrent ranging from Earth both to Mariner V near encounter and to the surface of Venus. It is concluded that neither spacecraft reported on atmospheric conditions near the level of the mean surface, but extrapolations of the measurements yield surface values for mid-latitudes of 100 atmospheres pressure (within a factor of 1.5) and 700 degrees K temperature (within 100 degrees ), in distinction to the Soviet values of 19+/-2 atmospheres and 544 degrees +/-10 degrees K. The higher values support radiometric and radar data on temperature and atmospheric absorption. It appears that the Soviet probe was not designed to work through such a thick atmosphere. A particularly simple (times two) ambiguity in the Venera 4 altimeter reading suggests itself, since this would bring all other data into excellent agreement and would explain the reason for the supposition that the probe reached the surface. 相似文献
3.
The radio brightness temperature and radar cross section spectra of Venus are in much better accord with surface boundary conditions deduced from a combination of the Mariner V results and the radar radius than those obtained by the Venera 4 space probe. The average surface temperature and pressure are approximately 750 degrees K and 90 atmospheres. 相似文献
4.
Campbell DB Jurgens RF Dyce RB Harris FS Pettengill GH 《Science (New York, N.Y.)》1970,170(3962):1090-1092
A radar interferometer was used to map unambiguously the surface reflectivity of Venus in the polarized mode at a wavelength of 70 centimeters. The observed region extended from 260 degrees to 30 degrees in longitude and from -60 degrees to 50 degrees in latitude with a surface resolution of approximately 3 degrees by 3 degrees . The result agrees well in most respects with earlier maps made elsewhere at shorter wavelengths and, in addition, discloses a number of new "features." 相似文献
5.
Use of Earth-based microwave data in extrapolating the atmospheric profile of Venus below the region probed by Mariner V and Venera 4 reveals an isothermal layer at 670 degrees +/- 20 degrees K that extends to an altitude of 7 +/- 2 kilometers. This model gives a value of 6054.8 kilometers for the radius of Venus, and agreement with brightness spectrum, radar cross sections, and results of microwave interferometry. 相似文献
6.
A new radar image of Venus covering the latitude range 46 degrees to 75 degrees and the approximate longitude range 290 degrees to 10 degrees is shown. The resolution is approximately 20 kilometers. 相似文献
7.
Arecibo high-resolution radar images of the southern hemisphere of Venus extending to 78 degrees S show that the surface of the Themis-Alpha-Lada region is characterized by linear deformation zones with volcanoes and corona-like features and by regional volcanic deposits (primarily plains, small shields, and large edifices). Large-scale areal deformation is limited to the tessera of Alpha Regio. Lada Terra, in the southern high latitudes, contains several large coronae, in contrast to Ishtar Terra in the northern high latitudes. The density of craters of possible impact origin is somewhat lower than that observed in the Venera 15 and 16 coverage; these data extend to 43 percent of the areas of the surface of Venus with ages of less than about 1 billion years. 相似文献
8.
Ash ME Campbell DB Dyce RB Ingalls RP Jurgens R Pettengill GH Shapiro II Slade MA Thompson TW 《Science (New York, N.Y.)》1968,160(3831):985-987
The Venus radius of 6085 +/- 10 kilometers, deduced from combining observations made with the Venera 4 and Mariner V space probes is incompatible with the value of 6050 +/- kilometers determined from Earth-based radar mesurements. 相似文献
9.
Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas. 相似文献
10.
Hord CW West RA Simmons KE Coffeen DL Sato M Lane AL Bergstralh JT 《Science (New York, N.Y.)》1979,206(4421):956-959
The photopolarimeter instrument on Voyager 2 was used to obtain a map of Jupiter at an effective wavelength of 2400 angstroms. Analysis of a typical north-south swath used to make this map shows strong absorption at high latitudes by a molecular or particulate constituent in the Jovian atmosphere. At 65 degrees north latitude, the absorbing constituent extends to altitudes above the 50-millibar pressure level. 相似文献
11.
Sjogren WL 《Science (New York, N.Y.)》1979,203(4384):1006-1010
Doppler radio-tracking data have provided detailed measurements for a martian gravity map extending from 30 degrees S to 65 degrees N in latitude and through 360 degrees of longitude. The feature resolution is approximately 500 kilometers, revealing a huge anomaly associated with Olympus Mons, a mascon in Isidis Planitia, and other anomalies correlated with volcanic structure. Olympus Mons has been modeled with a 600-kilometer surface disk having a mass of 8.7 x 1021grams. 相似文献
12.
Brace LH Theis RF Niemann HB Mayr HG Hoegy WR Nagy AF 《Science (New York, N.Y.)》1979,205(4401):102-105
Empirical models of the electron temperature and electron density of the late afternoon and nightside Venus ionosphere have been derived from Pioneer Venus measurements acquired between 10 December 1978 and 23 March 1979. The models describe the average ionosphere conditions near 18 degrees N latitude between 150 and 700 kilometers altitude for solar zenith angles of 80 degrees to 180 degrees . The average index of solar flux was 200. A major feature of the density model is the factor of 10 decrease beyond 90 degrees followed by a very gradual decrease between 120 degrees and 180 degrees . The density at 150 degrees is about five times greater than observed by Venera 9 and 10 at solar minimum (solar flux approximately 80), a difference that is probably related to the effects of increased solar activity on the processes that maintain the nightside ionosphere. The nightside electron density profile from the model (above 150 kilometers) can be reproduced theoretically either by transport of 0(+) ions from the dayside or by precipitation of low-energy electrons. The ion transport process would require a horizontal flow velocity of about 300 meters per second, a value that is consistent with other Pioneer Venus observations. Although currently available energetic electron data do not yet permit the role of precipitation to be evaluated quantitatively, this process is clearly involved to some extent in the formation of the nightside ionosphere. Perhaps the most surprising feature of the temperature model is that the electron temperature remains high throughout the nightside ionosphere. These high nocturnal temperatures and the existence of a well-defined nightside ionopause suggest that energetic processes occur across the top of the entire nightside ionosphere, maintaining elevated temperatures. A heat flux of 2 x 10(10) electron volts per square centimeter per second, introduced at the ionopause, is consistent with the average electron temperature profile on the nightside at a solar zenith angle of 140 degrees . 相似文献
13.
McIntyre A 《Science (New York, N.Y.)》1967,158(3806):1314-1317
Selected species of Coccolithophoridae from recent sediments and mid-Wisconsin glacial sediments of the North Atlantic were examined in an attempt to determine cooling effects. All species showed a definite shift southward during the glacial period. The average shift in this planktonic population was 15 degrees of latitude, with the greatest change in the eastern Atlantic. A paleoisotherm map can be drawn on the basis of the temperature boundaries of coccolithophorids. The species boundaries indicate a possible shift in position of the subtropical gyral to a glacial position roughly parallel to the 33-degree line of latitude. 相似文献
14.
On the basis of the physical and chemical measurements made on the surface of Venus and transmitted back to Earth by the Soviet automatic landers Venera 9 and Venera 10, a geomorphically inactive environment should be expected. An analysis of the television photographs reveals, however, that at least two processes of degradation occur. One operates on a scale of decimeters to meters and is responsible for the fracturing of a layered source rock and the subsequent downslope movement of the fragments. Mass-wasting, perhaps activated by venusian quakes or by unknown geological processes, is likely to be the agent. Another geomorphic degradation process occurs on the scale of a centimeter or less and is responsible for the rounding of edges and the pitting of rock surfaces. The agents of this process are not known, but atmospheric action, perhaps in connection with volcanic episodes, may be the cause. From a geomorphic point of view, the landscape of the Venera 9 landing site can be considered young and that of the Venera 10 landing site, mature. 相似文献
15.
Libby WF 《Science (New York, N.Y.)》1968,159(3819):1097-1098
The data on Venus obtained by Mariner V and Venera 4 are interpreted as evidence of giant polar ice caps holding the water that must have come out of the volcanoes with the observed carbon dioxide, on the assumption that Earth and Venus are of similar composition and volcanic history. The measurements by Venera 4 of the equatorial surface temperature indicate that the microwave readings were high, so that the polar ice caps may be allowed to exist in the face of the 10-centimeter readings of polar temperature. Life seems to be distinctly possible at the edges of the ice sheets. 相似文献
16.
Florensky CP Basilevsky AT Kryuchkov VP Kusmin RO Nikolaeva OV Pronin AA Chernaya IM Tyuflin YS Selivanov AS Naraeva MK Ronca LB 《Science (New York, N.Y.)》1983,221(4605):57-59
Venera 13 and Venera 14 transmitted almost complete panoramic views of their landing sites. Analyses of the photographs show the presence of rock formations undergoing geomorphic degradation. The formations display ripple marks, thin layering, differential erosion, and curvilinear fracturings. Some of them are interpreted as lithified clastic sediments. The lithification could have taken place at depth or at the surface, resulting in a type of duricrust. The origin of the sediments is unknown but could be aeolian, volcanic, or related to impacts or to turbidity currents. 相似文献
17.
Pieters CM Head JW Pratt S Patterson W Garvin J Barsukov VL Basilevsky AT Khodakovsky IL Selivanov AS Panfilov AS Gektin YM Narayeva YM 《Science (New York, N.Y.)》1986,234(4782):1379-1383
Multispectral images of the basaltic surface of Venus obtained by Venera 13 were processed to remove the effects of orange-colored incident radiation resulting from interactions with the thick Venusian atmosphere. At visible wavelengths the surface of Venus appears dark and without significant color. High-temperature laboratory reflectance spectra of basaltic materials indicate that these results are consistent with mineral assemblages bearing either ferric or ferrous iron. A high reflectance in the near-infrared region observed at neighboring Venera 9 and 10 sites, however, suggests that the basaltic surface material contains ferric minerals and thus may be relatively oxidized. 相似文献
18.
Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term "aeolian feature" is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37 degrees to latitude -62 degrees . Likely indicators of previous activity (dark surface streaks) occur from latitude -5 degrees to -70 degrees , but are most abundant from -15 degrees to -45 degrees , generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40 degrees and 80 degrees measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59 degrees . Winds at 1- to 3- kilometer altitude are eastward, while those at &8 kilometers blow west. 相似文献
19.
Evans WD Glore JP Klebesadel RW Laros JG Tech ER Spalding RE 《Science (New York, N.Y.)》1979,205(4401):119-121
The Pioneer Venus orbiter gamma burst detector is an astrophysics experiment for monitoring cosmic gamma-ray bursts. It is included in this planetary mission to provide a long baseline for accurately locating the sources ofthese bursts in order to identify them with specific astronomical objects. Responses to 14 gammaray burst events were examined; these events were verified from data acquired by other systems. Preliminary locations are proposed for three events, based on data from the Pioneer Venus orbiter, ISEE C, and Vela spacecraft. These locations will be improved, and additional locations will be determined by including in the analyses data from Helios B and the Russian Venera 11, Venera 12, and Prognoz 7 spacecraft. 相似文献
20.
Observations of the latitude dependence of water vapor made from the Viking 2 orbiter show peak abundances in the latitude band 70 degrees to 80 degrees north in the northern midsummer season (planetocentric longitude approximately 108 degrees ). Total column abundances in the polar regions require near-surface atmospheric temperatures in excess of 200 degrees K, and are incompatible with the survival of a frozen carbon dioxide cap at martian pressures. The remnant (or residual) north polar cap, and the outlying patches of ice at lower latitudes, are thus predominantly water ice, whose thickness can be estimated to be between 1 meter and 1 kilometer. 相似文献