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Geology and radiophysical properties of the Venera and Vega landing sites
| Content Provider | Semantic Scholar |
|---|---|
| Author | Weitz, Catherine M. Basilevsky, Alexander T. |
| Copyright Year | 1993 |
| Abstract | Introduction; We have produced geologic maps for all seven Venera and Vega landing sites. Because the radius of error for each landing site is 150 km, we have mapped the entire landing circle centered about the estimated landing point. We found correlations between the Magellan imagery and the lander TV panoramas and geochemical measurements made at the landing site. Radiophysical properties, including backscatter crosssections, altimetry, emissivity, and rms slopes, were determined for each landing circle. After mapping the geology of the landing circles, we mapped the regional geology of the seven sites and determined the geologic history of these large regions. Geol~pv of the Landinv Sites; Geologic mapping of the seven Venera/Vega landing sites has shown that the dominant type of terrain at these sites is plains. The Venera 8 site contains ridged and fractured plains and a younger plains-forming volcanic complex [I]. A 23-km-diameter pancake dome and several smaller steep-sided domes were also identified within the landing circle. Geologic mapping of the Venera 9 site, which is located on the eastern slope of Beta Regio, has shown the geology of this area to be dominated by fractured plains with complex ridge terrain (CRT) units located both inside and outside the landing circle. A large trough oriented transverse to Devana Chasma cuts through the plains and a lava channel in the plains. The Venera 10 site contains an elder and a younger plains unit and the same CRT mapped at the Venera 9 site. The younger plain unit consists of lava flows from a gentle-sloped 60-km-diameter dome. Concentric fractures in the plains to the northeast indicate uplift of some of the CRT and adjacent plains to the west of the fractures. The Venera 13 site is dominated by plains that are radar-dark in the SAR imagery because of a mantling of fine debris. At least four steep-sided domes surround the landing circle. A 230-km coronalike feature and its associated flows are located in the southeast of the landing circle. A lineament belt trending NW-SE from a large CRT unit to the west cuts through the plains and domes in the site and lava flows from volcanism to the west both embay and are disrupted by the lineament belt. This lineament belt continues to the southeast where it disrupts the Venera 14 site. The Venera 14 geology shows a site dominated by radar-bright and -dark lava flows from a 75-km-diameter gentlesloped volcano. Heavily fractured terrain, possibly representing CRT, has been embayed and infilled by the plains. Concentric fracture systems can be identified to the west and south of the volcano. Geologic mapping of the Vega 1 site has shown that the site consists of ridged radar-bright and -dark plains covered by debris and wind streaks. The Vega 2 site contains similar (and probably the same) radar-bright and -dark plains. The plains here, however, do not have the debris visible at the Vega 1 site but the Vega 2 site is disrupted by numerous lineations resulting from activity associated with Dali Chasma to the south. w e l l a n and Lander correlation^; Based upon Magellan data and the lander geochemical [2] and TV panoramas [3], we have been able to suggest the most likely material in the Magellan imagery sampled by the landers. Lamprophyrelike lavas, silicic ash beds, or the pancake dome are the most likely material sampled at the Venera 8 site [I]. At the Venera 9 site, the sampled tholeiitic material most likely represents fractured plains. Plains from either the gentle-sloped dome or from earlier volcqic activity are the most probable tholeiitic material sampled at the Venera 10 site. Lavas from a steep-sided dome or a coronalike feature at the Venera 13 site might match the nontholeiitic composition measured by the lander. Basalts erupted from a gentle-sloped volcano represent the most likely tholeiitic material sampled by the lander at the Venera 14 site. At both the Vega 1 and 2 sites, the landers measured the tholeiitic composition of the radar-bright or -dark plains at these sites. At the Venera 8 and 13 sites, where a non-tholeiitic composition was measured for the surface material, the Magellan imagery revealed that both these sites have unusual volcanic features associated with them, such as steep-sided domes and coronalike features with flows. Unusual volcanic activity was not o b s e ~ e d inside the landing circle at the other five sites and at these sites the landers measured geochemical signatures of tholeiitic basalts. This correlation indicates that the geochemistry measured by the landers correlates well with the morphology seen in the Magellan imagery. A strong correlation also exists between the SAR imagery and the TV panoramas taken by the Venera 9,10, 13, and 14 landers. The Venera 9 panorama showed cobbles on a sloped landing surface. The SAR imagery shows a fractured plain for the Venera 9 landing site. Both Venera 10 and 13 TV panoramas showed soil on the plains and the SAR imagery shows radar-dark debris on the plains. The Venera 14 TV panorama showed a plain with almost no debris and the SAR imagery of the site shows mottled lava flows with no debris covering the flows. Radiophysical Properties; Backscatter cross-sections, altimetry, emissivity, and rms slopes were calculated for each VeneraNega landing circle. The minimum, mean, and maximum values for each radiophysical parameter are shown in Table 1. Most of the variations in backscatter, emissivity, and rms slopes reflect variations in roughness at each site. The Venera 8 and Vega 1 and 2 sites consist predominantly of plains so the radiophysical |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.lpi.usra.edu/meetings/lpsc1993/pdf/1753.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
