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Venus’ cloud data prove that Venus' clouds contain a small amount of water, possibly proving that Venus once had a functioning water cycle. [7] Using image data from Magellan, scientists could fill lowlands of Venus’ surface area with water, leaving only Venusian continents visible.
The current Venusian atmosphere has only ~200 mg/kg H 2 O(g) in its atmosphere and the pressure and temperature regime makes water unstable on its surface. Nevertheless, assuming that early Venus's H 2 O had a ratio between deuterium (heavy hydrogen, 2H) and hydrogen (1H) similar to Earth's Vienna Standard Mean Ocean Water of 1.6×10 −4, [7] the current D/H ratio in the Venusian atmosphere ...
Venus' oceans may have boiled away in a runaway greenhouse effect. A runaway greenhouse effect involving carbon dioxide and water vapor likely occurred on Venus. [22] In this scenario, early Venus may have had a global ocean if the outgoing thermal radiation was below the Simpson–Nakajima limit but above the moist greenhouse limit. [2]
The surface of Venus is comparatively flat. When 93% of the topography was mapped by Pioneer Venus Orbiter, 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), about the same as the vertical distance between the Earth's ocean floor and the higher summits of the Himalayas.
Venus may have had liquid surface water early in its history with a habitable environment, [24] [25] before a runaway greenhouse effect evaporated any water and turned Venus into its present state. [26] [27] [28] The rotation of Venus has been slowed and turned against its orbital direction by the currents and drag of its atmosphere. [29]
* Gas giant likely has no surface, liquid water if present could only be on a large satellite (none known) * density implies water in atmosphere, but none found yet * Possible class II ("water cloud") or class III ("clear") atmosphere planet [12] Gliese 581 c [citation needed] Gliese 581: 5.5 700–1000 20 7–11 12.9 2007 * Not in the CHZ
Because Venus is completely covered in clouds, human knowledge of surface conditions was largely speculative until the space probe era. Until the mid-20th century, the surface environment of Venus was believed to be similar to Earth, hence it was widely believed that Venus could harbor life.
In a series of subsequent papers, Basilevsky and colleagues extensively developed a model that Guest and Stofan (1999) [22] termed the "directional history" for Venus evolution. [ 23 ] [ 24 ] [ 25 ] The general idea is that there is a global stratigraphy that progresses from heavily deformed tessera, to heavily deformed, then moderately ...