Atmosphere and climateEdit
- Main article: Atmosphere of Venus
Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The atmospheric mass is 93 times that of Earth's atmosphere while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. The density at the surface is 65 kg/m³ (6.5% that of water). The CO2-rich atmosphere, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the solar system, creating surface temperatures of over /</span> . This makes Venus's surface hotter than Mercury's which has a minimum surface temperature of -220 °C and maximum surface temperature of 420 °C, even though Venus is nearly twice Mercury's distance from the Sun and receives only 25% of Mercury's solar irradiance.
Studies have suggested that several billion years ago Venus's atmosphere was much more like Earth's than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the night and day sides, despite the planet's extremely slow rotation. Winds at the surface are slow, moving at a few kilometers per hour, but because of the high density of the atmosphere at Venus's surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even if the heat were not a problem. Above the dense CO2 layer are thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets. These clouds reflect about 60% of the sunlight that falls on them back into space, and prevent the direct observation of Venus's surface in visible light. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well lit. In the absence of the greenhouse effect caused by the carbon dioxide in the atmosphere, the temperature at the surface of Venus would be quite similar to that on Earth. Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days.
The surface of Venus is effectively isothermal; it retains a constant temperature between day and night and between the equator and the poles. The planet's minute axial tilt (less than three degrees, compared with 23 degrees for Earth), also minimizes seasonal temperature variation. The only appreciable variation in temperature occurs with altitude. In 1995, the Magellan probe imaged a highly reflective substance at the tops of Venus's highest mountain peaks which bore a strong resemblance to terrestrial snow. This substance arguably formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gas form to cooler higher elevations, where it then fell as precipitation. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).
The clouds of Venus are capable of producing lightning much like the clouds on Earth. The existence of lightning had been controversial since the first suspected bursts were detected by the Soviet Venera probes. However, in 2006–2007 Venus Express clearly detected whistler mode waves, the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. The lightning rate is at least half of that on Earth. In 2007 the Venus Express probe discovered that a huge double atmospheric vortex exists at the south pole of the planet.
- ↑ "Venus". Case Western Reserve University (September 14, 2006). Retrieved on 2007-07-16.
- ↑ Kasting J.F. (1988). "Runaway and moist greenhouse atmospheres and the evolution of earth and Venus". Icarus 74 (3): 472–494. doi:10.1016/0019-1035(88)90116-9.
- ↑ Moshkin B.E., Ekonomov A.P., Golovin Iu. M. (1979). "Dust on the surface of Venus". Kosmicheskie Issledovaniia (Cosmic Research) 17: 280–285. Bibcode: 1979CoRe...17..232M.
- ↑ Krasnopolsky V.A., Parshev V.A. (1981). "Chemical composition of the atmosphere of Venus". Nature 292: 610–613. doi:10.1038/292610a0.
- ↑ Vladimir A. Krasnopolsky (2006). "Chemical composition of Venus atmosphere and clouds: Some unsolved problems". Planetary and Space Science 54 (13–14): 1352–1359. doi:10.1016/j.pss.2006.04.019.
- ↑ Rossow W.B., del Genio A.D., Eichler T. (1990). "Cloud-tracked winds from Pioneer Venus OCPP images" (PDF). Journal of the Atmospheric Sciences 47 (17): 2053–2084. doi:10.1175/1520-0469(1990)047<2053:CTWFVO>2.0.CO;2, http://ams.allenpress.com/archive/1520-0469/47/17/pdf/i1520-0469-47-17-2053.pdf.
- ↑ Williams, Dr. David R. (April 15, 2005). "Venus Fact Sheet". NASA. Retrieved on 2007-10-12.
- ↑ Ralph D Lorenz, Jonathan I Lunine, Paul G Withers, Christopher P. McKay (2001). "Titan, Mars and Earth: Entropy Production by Latitudinal Heat Transport" (PDF). Ames Research Center, University of Arizona Lunar and Planetary Laboratory. Retrieved on 2007-08-21.
- ↑ "Interplanetary Seasons". NASA. Retrieved on 2007-08-21.
- ↑ Carolyn Jones Otten (2004). "'Heavy metal' snow on Venus is lead sulfide". Washington University in St Louis. Retrieved on 2007-08-21.
- ↑ 11.0 11.1 Russell, S.T.; Zhang, T.L.; Delva, M.; et al. (2007). "Lightning on Venus inferred from whistler-mode waves in the ionosphere". Nature 450: 661–662. doi:10.1038/nature05930.
- ↑ Various authors (November 2007). "European mission reports from Venus". Nature (450): 633–660. doi:10.1038/news.2007.297.
- ↑ "Venus offers Earth climate clues". BBC News. Retrieved on 2007-11-29.