|Venus is an 82% size-and-mass match to
our Earth but its proximity to the sun cooks it 100% more:
the demise of its atmosphere converted it to a 'greenhouse'
and hiked its surface temperature to double-and-a-half hotter absolute...|
But-- high-above, its 'air' is cool...
[See also planet-twinning]
At 50-58 km above the 'ground' the temperature ranges from boiling water to freezing water - and air-pressure ranges from a factor of three times Earth-normal to a third ... clouds form high in this strata, and rain continually into the reboiling depths ... ordinary nuclear-powered air-craft may ply this region, but nuclear fission fuel must first have come from other planets and moons more accessible: a necessary accessioning and transportment of Earth-stores of plutonium 239Pu by the GNSC.
Just below this habitable level, the atmosphere of Venus is a special nuclear environment pliable by small-winged heat-pump-cooled 'subplanes', deep-air-planes capable of leaping up to the tenuous 'living' heights and diving to thicker-pressured scorching depths...
At mid-level 54 km where the air is Earth-balmy, we might build clear-bubble-encased floating cities on foamed wood base: wood resource is continually growable topside in the CO2 and water vapor atmosphere, and the foam needs only be sealed against the larger gas molecules... it may float permanently charred below...
Placed poleward, beyond 60 deg North and South of the equator, the sunlight intensity for gravity-level is Earth-tropical, the atmospheric tradewinds still warm, and velocity slow enough to require minor adjustment to stay in sun-relative place: Catching a convection drift may suffice to keep such a city on the sunny-side, and all-day sun allows further poleward situation. Thermocouple lines to lower levels may extract sufficient greenhouse-heat to the sky-far-above, for electric power...
One of the primary reasons for venuforming, but not terraforming Venus, is that Venus may have had sentient inhabitants, at high altitudes where oxygen would tend above the primoridal CO2, likely including dinosaurial long before Earth had dinosaurs. The eonic interval may have been brief: as soon as Venus magmas cooled, and before the sun gained its final brightness estimated by solar astronomers to be now 40% more than during the early billion years ... so while Earth had major ice ages in the early 2 billion years, Venus may have been just very warm but liveable-- outside the 45° latitudes, even to the poles which having no significant tilt had fairly steady year-round temperatures lasting billions of years even till the final conversion of the entire atmosphere....
Because Venus is slightly smaller than Earth, it cooled slightly faster than Earth ... if the sun did not become visible too soon in the solar nebula, then Venus may have cooled to dinosaurial-supportive temperatures, just before Earth did about 300 million years ago. [If dinoaurs came to Earth from somewhere, Venus is choice] More likely though the early ocean bio-life flourishing on Venus once the surface cooled below boiling hot, about 4 billion years ago [3.5 billion for Earth], thrived until the breaking-through sun-warmth reheated the surface, and re-boiled-away the oceans - then atmospheric heat-containment by ocean-worths of water, 'hot-housed' the surface, converting all carbon-based bio-forms by the water-gas reaction to carbon-dioxide and hydrogen ... the hydrogen H2 quickly escaped the lower atmosphere, and was driven-away by sun-light and solar-winds into space, leaving Venus with its present burden of CO2 air, and its 'run-away-hot-house' temperatures, melting lead [metal] at the equator.
(The slow rotation of Venus also, contributed to the atmospheric destabilization as vegetation could not grow in the extreme equatorial 'day' heat, and night darkness could not support vegetation growth after the solar-nebula-glowing era. Also the lack of planet-core convection allowed for uranium-and-thorium natural reactors in differentiated stratas to heat the planet, extra... but in some far future this same early expenditure may allow for a cooler planet...)
Civilizations would have been literally bi-polar, crossing the equator only during the 'weeklong' evening and morning (time not days) between the 'twomonthlong' winter-night and summer-day, somewhat like Earth's polar winters and summers but much warmer in the summer for a total melt, And probably transient for that reason-- to stay on the pleasant dayside: Farming would have consisted of planting after melt in the spring-morning, tending the 'two-month-long' day, and harvesting in the fall-evening ... very similar to Earth farming.... Toward the end of the Venutian clemency era civilizations could have removed to the poles (where its last artifacts might remain) for stability, and farmed the fringes.... Eventually Venutians would have attempted Earth... possibly as early as the dinosaur era 100-million or billions of years ago, but probably also lived around the poles, making forays tropicward only for hunting.... (The Venutians could have studied Earth dayside from permanent winter observatories as Venus rotates synchronous to Earth's position.)
However, it may be possible to fairly quickly terraform Venus: one theory for its anomalously high surface temperature is the formation of bond-energetic molecules high in the atmosphere, either presently above the clouds or recently below the clouds, which [molecules] then drift down to the surface where by catalysis on the surface, or by extreme temperatures near the bottom, decompose, releasing the bond energy content, and maintain the temperature: a catalyst applied at the same height in the atmosphere might prevent such or early release the energy, allowing the clouds and surface to cool and reform to terraform capability by teams entering at the then-cooler poles.
* (Note that in the case of atoms, the increase of electron orbital radius cannot be sustained by its wavelength, and the electron drifts back in and slowly, below experimental-precision, radiates the excess energy: heating the interior of planets--an anomaly not yet detectible for Venus...)
** (N.B. if cosmic expansion is nearer critical-mass 'stop-at-infinity' as contemporary cosmology suggests, though it is probably much less after untold-or-infinite-cycles-preceding, or effectually much more if not-yet-all-collapsed before its central-hollowing Big Bang keeping it accelerating until its finality, then Vcosmos(R,T) = (R(T)/Rcosmos) · R˙cosmos = (R(T)/T(2/3)) (2/3) T(-1/3) = (2/3) R(T) / T , and twice-that for orbitals: VR = 2 Vcosmos(R,T) ⇒ ∂R(T)/∂T = (4/3) R(T) / T , which by-inspection solving a polynomial-form for its average orbital radius R(T) = Σk Rk Tk ⇒ the expansion equation Σk Rk k Tk-1 = (4/3) Σk Rk Tk-1 ⇒ k = 4/3 (i.e. Rk≠4/3 = 0), whence R = R4/3 T4/3 , cumulatively (2/3)4/3 of today's 67 million miles ~ 39 million miles (0.42 AU) : 1.72× for unit-parabolic expansion vs. 2.25× for unit-hyperbolic, today, except, cosmic-expansion, space-expansion, gravity, spacetime-relativity, are not-yet understood for large distances and velocities, especially super-lightspeed-distances... Compare also for no-gravity-decapture-boost the orbit expansion is just the cosmic expansion itself...)
*** (N.B. In the subsequent slower expansion of the cosmos, VHubble ≈ D / Tcosmos ≈ c at 13.82@9 light-years so far, over the next-2.4 Gyr, Venus will recede 38% further, to 1.00 AU, and may become a viable planet--a 'global cooling improvement'--meanwhile Earth receding likewise, halfway to Mars' present orbit, will become a 'global cooling problem'...)
(Note, As twin planets with Earth, the two started in-between 0.32 and 0.44 AU, ca 0.38 AU, probably as mini-gas-planets 'mini-Neptunes' boiling-away their proto-atmospheres just-inside today's Mercury-orbit...as suggested by the recent Kepler-11 results...meanwhile sub-mini-gas-planets Mars and its twin Astrus started in-between 0.68 and 1.24 AU, ca 0.90 AU, today's 'balmy zone'...)
Note also in any exploding-energy version of the theory all processes would be gaining potential energy, which is mass-energy, rest-mass in the case of particles, and increasing gravitational attraction and so reducing the expansion rate, possibly even shrinking orbits over eons... But it may also be a combination, especially as the ultra-density in the early moments of the Big Bang dragged the aether to expand...