Topography
With the invention of the telescope, optical observations of Venus became possible, although it soon became apparent that its surface is permanently hidden by dense cloud. In 1643, Francesco Fontana was the first of several astronomers claiming to see dark markings on these clouds, while others even said that they could see part of the surface through holes in the clouds. Astronomers also claimed to have seen brilliant points in certain spots on the disk of the planet, suggesting an enormous mountain whose top was higher than the clouds. The most famous such observations were made by Johann Hieronymus Schröter, a respected observer and collaborator of William Herschel, who reported several sightings from 1789 onwards of a bright circular point of light near the southern terminator of Venus, thought to be reflected light from a very tall mountain range or peak, around 43 kilometres (27 mi) high. Herschel disputed these observations and held them to be attributable to imperfections in Schröter's telescope. Many other observers claimed to see irregularities in the terminator of Venus, and the debate continued into the 20th century until radar observations were able to penetrate the clouds and reveal that, in fact, no such giant mountains exist.
The surface of Venus is comparatively flat. When 93% of the topography was mapped by Pioneer Venus, scientists found that the total distance from the lowest point to the highest point on the entire surface was about 13 kilometres (8.1 mi), while on the Earth the distance from the basins to the Himalayas is about 20 kilometres (12 mi).
According to data from the Pioneer altimeters, nearly 51% of the surface is located within 500 metres (1640 feet) of the median radius of 6,052 km (3,761 mi); only 2% of the surface is located at elevations greater than 2 kilometres (1.2 mi) from the median radius.
The altimetry experiment of Magellan confirmed the general character of the landscape. According to the Magellan data, 80% of the topography is within 1-kilometre (0.62 mi) of the median radius. The most important elevations are in the mountain chains that surround Lakshmi Planum: Maxwell Montes (11 km, 6.8 mi), Akna Montes (7 km, 4.3 mi) and Freya Montes (7 km, 4.3 mi). Despite the relatively flat landscape of Venus, the altimetry data also found large inclined plains. Such is the case on the southwest side of Maxwell Montes, which in some parts seems to be inclined some 45°. Inclinations of 30° were registered in Danu Montes and Themis Regio.
About 75% of the surface is composed of bare rock.
Based on altimeter data from the Pioneer Venus probe, supported by 'Magellan' data, the topography of the planet is divided into three provinces: lowlands, deposition plains, and highlands.
Read more about this topic: Geology Of Venus
Famous quotes containing the word topography:
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—Walter Pater (1839–1894)