These include tesserae, areas of deformed terrain that consist of closely packed sets of grooves and ridges (Fig. Many other unique and unfamiliar features appear on the surface of Venus. Such solutions are difficult to find in a planetary system dominated by stochastic processes. The problems of trying to account for the coronae and the search for terrestrial analogs provide yet another example of the difficulty in looking for some kind of patterns or processes that might have general applications to the other solid bodies of the Solar System. This debate is a good example of the difficulties of establishing a venusian stratigraphy. Later studies have shown that they are not restricted to any particular time. At an early stage, they were thought to have formed in a short time period after the flooding of the regional plains but earlier than the formation of the great volcanic shields. Like terrestrial mantle plumes, coronae have been the subject of controversy. NASA JPL FMIDR 59s164.Ĭoronae are probably the surface expression of hot mantle upwelling, perhaps analogous to terrestrial mantle plumes and so may be linked to the large volcanoes. A pancake dome, 35 km in diameter, occurs on the northern flank and others occur within the structure. 7.3 Aine Corona (one of the smaller examples), 200 km in diameter, centered at 59° S and 164° E. These exotic structures consist of concentric rings of grooves and ridges, typically 150 to 1000 km in diameter but with extremes ranging from 60 km to the enormous corona, Artemis that is 2500 km in diameter (Fig. 7.2.4 CoronaeĬoronae are volcano-tectonic features on Venus that again have no terrestrial analog nor appear elsewhere in the Solar System. This forms a contrast to the high volcanoes on the Earth and Mars and can be attributed to a combination of factors including high surface temperatures and pressures on Venus. However, these volcanoes are mostly low and broad and rarely exceed 2 km in elevation. There are 1500 volcanoes that are over 20 km in diameter, while another 150 are more than 100 km in diameter. Large shield volcanoes that have flows extending over a diameter of 500 km, are thought to have formed over mantle hot spots. This volcano has a large caldera, 31x28 km that contains several collapse craters up to 10 km in diameter. The summit caldera is about 30 km in diameter. 7.2 Maat Mons, 8 km high, the tallest volcano on Venus located at 0.9° N and 194.5° E. Maat Mons is the tallest volcano on Venus standing 8 km above the mean planetary radius (Fig. This structure is interpreted to be the result of volcanism and uplift over a mantle plume. Thus the edifice of Beta Regio rises nearly 10 km above the mean venusian datum. There are many larger volcanic structures on Venus. The presence of over a million small shield volcanoes that closely resemble terrestrial oceanic floor seamounts, reinforces the basaltic nature of venusian volcan-ism. This has led to the comment that on Venus, lavas flow like water, while on the outer icy planets, water ice behaves like terrestrial lavas. The only effective eroding agent that could form such a uniform lengthy channel would appear to have been low-viscosity lava, possibly carbonate-rich. But it is only about 1 km wide and 20 m deep and was cut into a surface where the temperature is around 460 ☌. The longest is Baltis Vallis that extends for a distance of 6800 km, longer than the Nile (6695 km). Some channels are compound and some deltas are present. No boulders are apparent and they are very smooth down to centimeter scales. They do not resemble lunar rilles, but meander in a form resembling that of terrestrial rivers. They do not possess tributaries and appear to be only 1 or 2 km wide. Thus there are at least 200 unique channels on the plains of Venus. One of the great lessons of comparative planetology is that caution is needed in applying terrestrial analogues when studying other planets.