Thecolonization of Venus is the proposed process of establishing human settlements on the planetVenus. Due to the planet's extremely hostile surface environment, proposals for settling Venus focus on habitats floating in the upper-middle atmosphere[1] or on settlement of the surface contingent on firstterraforming the planet.
The colonization of Venus has been a subject of many works ofscience fiction since before the dawn ofspaceflight, and is still discussed from both a fictional and a scientific standpoint.
Space colonization is a step beyondspace exploration, and implies the permanent or long-term presence of humans in an environment outsideEarth. Colonization of space was claimed byStephen Hawking to bethe best way to ensure the survival ofhumans as a species.[2] Other reasons for colonizing space include economic interests, long-term scientific research best carried out by humans as opposed to robotic probes, and sheer curiosity. Venus is the second largestterrestrial planet and Earth's closest neighbor, which makes it a potential target.
Venus has certain similarities toEarth which, if not for the hostile conditions, might make colonization easier in many respects in comparison with other possible destinations. These similarities, and its proximity, have led Venus to be called Earth's "sister planet".
At present it has not been established whether thegravity of Mars, 0.38 times that of the Earth, would be sufficient to avoidbone decalcification and loss of muscle tone experienced by astronauts living in amicro-gravity environment. In contrast, Venus is close in size and mass to the Earth, resulting in a similar surface gravity (0.904 g) that would likely be sufficient to prevent the health problems associated withweightlessness. Most other space exploration and colonization plans face concerns about the damaging effect of long-term exposure to fractionalg orzero gravity on the humanmusculoskeletal system.
Venus's relative proximity makes transportation and communications easier than for most other locations in theSolar System. With current propulsion systems,launch windows to Venus occur every 584 days,[3] compared to the 780 days for Mars.[4] Flight time is also somewhat shorter; theVenus Express probe that arrived at Venus in April 2006 spent slightly over five months en route, compared to nearly six months forMars Express. This is because at closest approach, Venus is 40 million km (25 million mi) from Earth (approximated by perihelion of Earth minus aphelion of Venus) compared to 55 million km (34 million mi) for Mars (approximated by perihelion of Mars minus aphelion of Earth) making Venus the closest planet to Earth.
Venus's atmosphere consists mostly of carbon dioxide. Becausenitrogen andoxygen are lighter than carbon dioxide, breathable-air-filled balloons will float at a height of about 50 km (31 mi). At this height, the temperature is a manageable 75 °C (348 K; 167 °F). At 5 km (3.1 mi) higher, it is a temperate 27 °C (300 K; 81 °F) (seeAtmosphere of Venus § Troposphere).
Additionally, the upper atmosphere could provide protection from harmful solarradiation comparable to the protection provided byEarth's atmosphere. Theatmosphere of Mars, as well asthe Moon provide little such protection.[5][6][7]
Venus also presents several significant challenges to human colonization. Surface conditions on Venus are difficult to deal with: thetemperature averages around 464 °C (737 K; 867 °F),[8] higher than themelting point oflead, which is 327 °C (600 K; 621 °F). Theatmospheric pressure on the surface is also at least ninety times greater than on Earth, which is equivalent to the pressure experienced under a kilometer of water on Earth. These conditions have caused missions to the surface to be extremely brief: the SovietVenera 5 andVenera 6 probes were crushed by high pressure while still 18 km above the surface. Following landers such asVenera 7 andVenera 8 succeeded in transmitting data after reaching the surface, but these missions were brief as well, surviving no more than an hour on the surface.
Furthermore,water, in any form, is almost entirely absent from Venus. Theatmosphere is devoid of molecularoxygen and is primarilycarbon dioxide. In addition, the visible clouds are composed of corrosivesulfuric acid andsulfur dioxide vapor.
Over 20 successful space missions have visited Venus since 1962. The last European probe wasESA'sVenus Express, which was in polar orbit around the planet from 2006 to 2014. A Japanese probe,Akatsuki, failed in its first attempt to orbit Venus, but successfully reinserted itself into orbit on 7 December 2015. Other low-cost missions have been proposed to further explore the planet's atmosphere, as the area 50 km (31 mi) above the surface where gas pressure is at the same level as Earth, has not yet been thoroughly explored.
At least as early as 1971[9] Soviet scientists had suggested that rather than attempting to settle Venus's hostile surface, humans might attempt to settle theVenusian atmosphere.Geoffrey A. Landis of NASA'sGlenn Research Center has summarized the perceived difficulties in colonizing Venus as being merely from the assumption that a colony would need to be based on the surface of a planet:
However, viewed in a different way, the problem with Venus is merely that the ground level is too far below the one atmosphere level. At cloud-top level, Venus is the paradise planet.
Landis has proposedaerostat habitats followed byfloating cities, based on the concept that breathable air (21:79 oxygen/nitrogen mixture) is alifting gas in the densecarbon dioxide atmosphere, with over 60% of the lifting power thathelium has on Earth.[10] In effect, aballoon full of human-breathable air would sustain itself and extra weight (such as a colony) in midair. At an altitude of 50 kilometres (31 mi) above the Venusian surface, the environment is the most Earth-like in theSolar System beyond Earth itself – a pressure of approximately 1atm or 1000 hPa and temperatures in the 0 to 50 °C (273 to 323 K; 32 to 122 °F) range. Protection againstcosmic radiation would be provided by the atmosphere above, with shielding mass equivalent to Earth's.[11]
At the top of the clouds, the wind speed on Venus reaches up to 95 m/s (340 km/h; 210 mph), circling the planet approximately every four Earth days in a phenomenon known as "super-rotation".[12] Compared to the Venusiansolar day of 118 Earth days, colonies freely floating in this region could therefore have a much shorter day-night cycle. Allowing a colony to move freely would also reduce structural stress from the wind that they would experience if tethered to the ground.
At its most extreme, the entirety of Venus could be covered in aerostats, forming an artificial planetary surface. This would be supported by the atmosphere compressed beneath it.[13]
Because there is not a significant pressure difference between the inside and the outside of the breathable-air balloon, any rips or tears would cause gases to diffuse at normal atmospheric mixing rates rather than anexplosive decompression, giving time to repair such damages.[10] In addition, humans would not requirepressurized suits when outside, merely air to breathe, protection from the acidic rain and on some occasions low level protection against heat. Alternatively, two-part domes could contain a lifting gas like hydrogen or helium (extractable from the atmosphere) to allow a higher mass density.[14] Therefore, putting on or taking off suits for working outside would be easier. Working outside the vehicle in non-pressurized suits would also be easier.[15]
Structural and industrial materials would be hard to retrieve from the surface and expensive to bring from Earth or from asteroids. The sulfuric acid poses a further challenge in that the colony would need to be constructed of or coated in materials resistant to corrosion by the acid, such asPTFE (a compound consisting wholly of carbon and fluorine).
In 2015, NASA developed theHigh Altitude Venus Operational Concept (HAVOC) for exploring the possibility of an atmospheric crewed mission.[16] They also planned a hypothetical float sky station with key supplies and communication.[17]
Venus has been the subject of a number ofterraforming proposals.[18][19] The proposals seek to remove or convert the dense carbon dioxide atmosphere, reduce Venus's 450 °C (723 K; 842 °F) surface temperature, and establish a day/night light cycle closer to that of Earth.
Many proposals involve deployment of a solar shade or a system of orbital mirrors, for the purpose of reducinginsolation and providing light to the dark side of Venus. Another common thread in most proposals involves some introduction of large quantities ofhydrogen orwater. Proposals also involve either freezing most of Venus's atmospheric CO2, or converting it tocarbonates,[20]urea[citation needed] or other forms.[citation needed]
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