In traditional terraforming, humans alter an uninhabitable world until higher plants and animals adapted to Earth conditions can survive unprotected on its surface. In an August 1992 paper in the Journal of the British Interplanetary Society, Richard L. S. Taylor argued that terraforming would require labor over many millennia to reach its goal. He proposed instead a technique he dubbed "paraterraforming," which would see relatively rapid construction of a "worldhouse" that would cover most of a world's surface with an air-tight "roof" between one and three kilometers high (image above).
Paraterraforming would offer other important advantages over traditional terraforming besides speed. A worldhouse could be constructed using technologies known since the 1960s, Lewis estimated. Terraforming, on the other hand, would demand technological breakthroughs. Initial investors in the paraterraforming project could live to see at least a small part of the uninhabitable world's surface roofed over and made to resemble Earth. The long timescale inherent in most traditional terraforming proposals, on the other hand, would mean that initial investors could expect to receive no gratification in return for their investment. Finally, paraterraforming's modular approach would allow "staged pay-as-you-go funding," so could proceed in fits and starts. Terraforming would require sustained high funding levels.
In his paper, Taylor emphasized Mars paraterraforming. He pointed out that Mars's gravity is only one-third as strong as Earth gravity, so terraformers would need to pile on an atmosphere 75% as massive as Earth's to give it an earthlike surface pressure. With only 28% of Earth's surface area, Mars might not contain enough gas in its crust and polar ice caps to create such an atmosphere, and importing gas from elsewhere in the Solar System might prove to be impractical. Taylor estimated that providing an earthlike surface pressure inside a two-kilometer-tall Martian Worldhouse (MWH) would require less than one-tenth as much gas as a terraformed Mars atmosphere.
Taylor proposed that MWH construction begin in a seismically stable area with little subsurface ice. The MWH roof would comprise inner and outer layers held in place by cables. Atmospheric pressure within the MWH would push its roof upwards, so supports within it would serve primarily to hold it down.
Taylor envisioned three types of MWH support towers. Inhabited Mars Support Towers (IMASTs) would resemble the 3.25-kilometer-high "vertical super-city" designed by the British architect W. W. Frischmann in 1965. Each would measure 110 meters across its foundation and consist of six load-bearing masts clustered around a hollow core outfitted to house 500,000 settlers. Mars Support Towers (MASTs), uninhabited IMASTs, could be converted into full-fledged IMASTs as martian population grew. IMASTs and MASTs would be spaced equidistantly six kilometers apart. Compression-Tension Towers (CTTs), uninhabited 30-meter-diameter tubes with tension cables running through their cores, would be spaced equidistantly two kilometers apart.
The first IMAST would provide a manufacturing and construction facility for MWH components. Six MASTs and 30 CTTs would be erected around it, yielding a habitable MWH "cell" 30 kilometers wide. Taylor envisioned adding MWH cells until eventually about 84% of Mars was roofed over.
The unroofed 16% of the planet would include Valles Marineris, a tectonic rift system with crustal layers. Taylor wrote that the abundance of mineral deposits found in Earth's rift zones suggested that Valles Marineris might provide materials for manufacturing MWH structures. Other unroofed areas would include the poles, which would provide ices and gases and serve as "dumping zones," and volcanoes taller than seven kilometers. The calderas of such volcanoes rise above most of the thin martian atmosphere; Taylor maintained that this would make them ideal locations for solar power generators.
He wrote that settlers might choose to flood with water areas of low elevation within the MWH to create lakes and seas. The towers standing in them would, he noted, need to be specially braced to stand against currents and waves.
Taylor then threw cold water on his paraterraforming concept and on the concept of planetary settlement in general, arguing that