The colonization of Venus has been a subject of many works of science fiction since before
the dawn of spaceflight, and is still discussed from both a fictional and a scientific standpoint.
However, with the discovery of Venus's extremely hostile surface environment, attention has
largely shifted towards the colonization of the Moon and Mars instead.
Reasons for colonization
Space colonization is a step beyond space exploration, and implies the permanent or
long-term presence of humans in an environment outside Earth. Colonization of space is claimed
to be the best way to ensure the survival of humans as a species. 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 largest
terrestrial planet and Earth's closest neighbour, which makes it a potential target.
Advantages
Venus has certain similarities to Earth 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 the gravity of Mars, 0.38 times that of the
Earth, would be sufficient to avoid bone decalcification and loss of muscle tone experienced by astronauts
living in an environment of microgravity. In contrast, Venus is close in size and mass
to the Earth, resulting in a similar surface gravity which would likely be sufficient to
prevent the health problems associated with weightlessness. Most other space exploration
and colonization plans face concerns about the damaging effect of long-term exposure
to fractional g or zero gravity on the human musculoskeletal system.
Venus's relative proximity makes transportation and communications easier than for most other
locations in the solar system. With current propulsion systems, launch windows to Venus
occur every 584 days, compared to the 780 days for Mars. Flight time is also somewhat
shorter; the Venus Express probe that arrived at Venus in April 2006 spent slightly over
five months en route, compared to nearly six months for Mars Express. This is because at
closest approach, Venus is 40 million km from Earth compared to 55 million km for
Mars making Venus the closest planet to Earth. Difficulties
Venus also presents several significant challenges to human colonization. Surface conditions
on Venus are difficult to deal with: the temperature at the equator averages around 450 °C, higher
than the melting point of lead. The atmospheric 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. These conditions have caused missions to the surface to be extremely brief: the
Soviet Venera 5 and Venera 6 probes were crushed by high pressure while still 18 km
above the surface. Following landers such as Venera 7 and Venera 8 succeeded in transmitting
data after reaching the surface, but these missions were brief as well, surviving no
more than a single hour on the surface. Furthermore, water, in any form, is almost
entirely absent from Venus. The atmosphere is devoid of molecular oxygen and is primarily
carbon dioxide. In addition, the visible clouds are composed of corrosive sulfuric acid and
sulfur dioxide vapor. Exploration and research
Due to the planet's hostile environment, Venus has not been studied as much as objects such
as the Moon and Mars, and it is extremely unlikely that research would be conducted
with a view to a human mission to the planet. The probe Venus Express has been in polar
orbit around the planet since 2006, but other low-cost missions have been proposed to further
explore the planet's atmosphere, as the area 50 kilometres above the surface where gas
pressure is at the same level as Earth has not yet been explored.
Aerostat habitats and floating cities
Others suggest different approachs, however, claiming that rather than attempting to colonize
Venus' hostile surface, humans might attempt to colonize the Venerian atmosphere. Geoffrey
A. Landis of NASA's Glenn 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 proposed aerostat habitats followed by floating cities, based on the concept that
breathable air is a lifting gas in the dense carbon dioxide atmosphere, with over 60% of
the lifting power that helium has on Earth. In effect, a balloon full of human-breathable
air would sustain itself and extra weight in midair. At an altitude of 50 kilometres
above Venerian surface, the environment is the most Earth-like in the solar system – a
pressure of approximately 1 bar and temperatures in the 0°C–50°C range. 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 an explosive decompression, giving time to repair any such damages. In addition,
humans would not require pressurized 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 to allow a higher
mass density. Therefore putting on or taking off suits for working outside would be easier.
Also working outside the vehicle in non pressurized suits would be easier.
At the top of the clouds the wind speed on Venus reaches up to 95 m/s, circling the
planet approximately every four Earth days in a phenomenon known as "super-rotation".
Colonies floating in this region could therefore have a much shorter day length by remaining
untethered to the ground and moving with the atmosphere. Allowing a colony to move freely
would also reduce structural stress from the wind.
Terraforming
Terraforming is the theoretical process of modifying a planet, moon, or other body to
a more human-habitable atmosphere, temperature, or ecology. Venus has been the subject of
a number of terraforming proposals. The proposals seek to remove or convert the dense carbon
dioxide atmosphere, reduce Venus's 450 °C surface temperature, and establish a day/night
light cycle closer to that of Earth. Many proposals involve deployment of a solar
shade and/or a system of orbital mirrors, for the purpose of reducing insolation and
providing light to the dark side of Venus. Another common thread in most proposals involves
some introduction of large quantities of hydrogen or water. Proposals also involve either freezing
most of Venus's atmospheric CO2, or converting it to carbonates, urea or other forms.
References
External links A Floating City on Venus - article from The
Space Monitor