Venus 2.0

I just discovered that part of this idea has been independently dreamed up by others (see terraforming article at wikipedia.com), but the other part perhaps has not. So be it.

The Law of Gravitation lets us compute a location in space where the attractive forces between two objects cancel each other out. This is usually called the First Lagrange Point, or the L-1 Point, after the mathematician who first worked it out. Currently NASA has a special satellite at the Earth/Sun L-1 Point, called SOHO, which has been on-station for several years, and is constantly observing the Sun (the Earth can never block the view!).

Venus has an L-1 point with respect to the Sun also, of course. The first part of this idea is to put a huge disc there, perhaps 15,000km in diameter. The shadow cast by this disc needs to COMPLETELY shield Venus from the Sun.

Minor details regarding the disc are that it should be a mirror, to protect itself from all that sunlight, and it should have a balance between mass and area, like a solar-sail, so that it never needs fuel to hover on-station at the Venus/Sun L-1 Point. Indeed, the outer rim of this sail should be adjustable, so that its total area can be diminished a bit, to let it fall closer to the Sun, or expanded a bit, to let it be blown by sunlight (and the Solar Wind) farther from the Sun. This would be analgous to the ballast tanks on a submarine. And, of course, the mirror needs to rotate once per Venus-year, so that it constantly keeps its full area shielding Venus from the Sun. This mirror must be built to be as permanent and reliable as possible.

OK, with NO sunlight arriving, Venus will in short order experience an Ice Age, colder than Pluto, with frozen carbon dioxide blanketing the surface, and vacuum everywhere. Then would be a good time to land nuclear-powered mass-drivers (electromagnetic catapults) in several places, along with appropriate scooping machinery. Cannisters of frozen CO2 can be launched totally away from Venus, and in fact probably should be sent to Mars, to thicken its air. After enough has been sent, the equipment is shipped out for other uses elsewhere.

From the Oort Cloud we locate some sizeable ice bodies (there are closer ones, such as might be moons of Saturn, or even the worldlet known as Chiron). The afore-mentioned mass drivers can now be used like rocket motors, expelling some ice to push the rest of these bodies until they get onto a collision course with Venus. We will be wanting plenty of water, so we need to move a number of worldlets -- even a 100-km-wide ice body will only be a drop in the Venus-bucket.

A significant goal will also be that of seeking large amounts of ammonia-ice, which will provide essential nitrogen for the future atmosphere of Venus. I think some of the outer moons have decent supplies.... This part is a bit iffy, because I don't know how much nitrogen Venus currently has in its atmosphere. Perhaps, after the excess carbon dioxide is shipped out, the existing nitrogen may prove sufficient.

Now we are ready for the second big trick, which is to put another mirror in space near Venus. This one gets put into a 24-hour orbit! It reflects sunlight to the surface. The amount that arrives will depend on the mirror's diameter, and of course we will be wanting this to equal the amount that we are comfortable with here on Earth. And it yields a perfectly Earthly day/night cycle. And as soon as the place warms up again, we can start importing Life. (We can put a smaller mirror in a month-long orbit if we want to simulate the Earth's Moon -- without the tidal effects, of course.)

Note that this day/night mirror is also going to need to be like a solar sail, because its orbit will require constant adjustment throughout each Venus-year. See, it needs to be in a technically polar orbit (with respect to Venus' rotation), because it needs to be in sunlight all the time, and that means it must circle outside and around the conical shadow cast by the big mirror at the L-1 point. Only constant orbital adjustments will meet the need for reliable sunlight, as Venus revolves about the Sun.

The preceding is a workable set of ideas, but the result is actually still going to be rather alien to Earthlings. Some background information is now essential, in order to be able to explain this clearly. First, as you may know, the planets in the Solar System mostly go around the sun in a disc-like region known as the "ecliptic". If we left the Earth from its North Pole and looked down at the ecliptic from a distance, we'd see all the planets moving counterclockwise around the Sun. And we'd also see that the planetary rotations (and the Sun's rotation) are mostly counterclockwise, also. The exceptions are Uranus, which has a sideways axial tilt, and Venus, which is almost perfectly "upside down" -- it would be seen to rotate clockwise, slowly (once per 243 Earth-days). Technically, one should consider the North Pole on Venus to be on the same side of the ecliptic as the South Poles of all the other planets (standing on the North pole of a world, you rotate counterclockwise).

On Earth, the polar regions are cold because sunlight arrives there at a shallow angle. (A simple sunbeam through the clouds, when it illuminates the ground, covers more ground surface than a similar sunbeam at the equator. And less light per unit of ground area means less warmth.) The effect of reflected light from the day/night mirror will be much the same, but actually worse, because this mirror will be so much closer to Venus than the Sun. True sunlight arrives in parallel beams, because the Sun is bigger than the planets it shines upon, while reflected light is going to have a conical spread. Some careful planning is going to be needed, to ensure that ENOUGH light is reflected, to keep Venus warm, without frying the regions directly beneath the mirror!

Now note carefully that the regions of diminished reflected light will NOT be the axial-rotation poles of Venus, because the day/night mirror has to be located in a polar orbit. Venus' axial poles will ALWAYS be directly illuminated as the day/night mirror passes overhead! So this means that the regions of Venus that receive the least amount of reflected light will be located on the equatorial belt of the planet. We can count on both of them to be wintery.

However, because Venus DOES rotate (243 Earth days), and because it DOES revolve around the Sun (225 Earth days), those two wintery regions are going to "move" around the equator of Venus. If my calculations are right, one of those wintery regions will move completely around Venus' equator in 225-(243-225) or 225-18 or 207 Earth-days (the directions of Venus' rotation and revolution work together to reduce the time). Since there will be two wintery regions, any point on the equator will be experiencing cold weather every 103-104 days (a bit more than 3 Earth-months), and hot weather equally often. Regions between the equator and the poles will be more temperate, of course, but the weather is still going to be "interesting", becoming warmer and chillier in the same cycle. I'm pretty sure that Earthly life-forms will be able to adapt in short order, as soon as bacteria have prepared enough soil for plants to produce enough oxygen.