Terraforming the planet can take a whole millennium or more. All because of the titanic tasks. For most planets, it will be necessary not only to create a magnetosphere and an acceptable atmosphere, but also to deliver water, change the mass of the planet and even the speed of its rotation.
Greenhouse factories
Complexes that will modify the atmosphere in such a way that it becomes as comfortable as possible for the life of organisms. Such factories must not only change the chemical composition of the atmosphere, but also heat or cool certain parts of the planet.
Source: img0.reactor.cc
Solar screens
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Solar screens can be used not only to cool planets (Venus), reflecting "extra" sun rays, but also to heat it (Mars), directing additional energy to the planet's surface. It should be noted that the position of the orbital "umbrellas" will not be static. It will have to be changed so that the cooling or heating effect does not decrease. Scientists believe that a significant cooling of the atmosphere of Venus will contribute to a drop in pressure, since a significant part of it will fall in the form of dry ice to the surface.
Source: motto.net.ua
Asteroid bombardment
To create an acceptable hydrosphere on Venus requires at least 1,000,000,000,000,000,000 tons of water. The easiest way to deliver that much water would be to bombard the surface with icy comets or asteroids. The bombardment is even capable of spinning up or reducing the planet's rotation speed. Such a bombardment of Venus can shorten the Venusian day. Due to the slow change of day and night, the planet warms up strongly during the day and cools down at night.
Source: mirkosmosa.ru
Nuclear winter
A series of hydrogen bomb explosions can cause a nuclear winter on Venus, which will not only lower the temperature of the planet, but will bind acid with dust. By the way, an alternative has already been found to neutralize acids: asteroids such as (216) Cleopatra.
Source: lowbird.com
Electric wires
along the equator Some planets lack a magnetic field that would protect living organisms on the planet's surface from charged particles. There are several ways out, but the most realistic is to create an artificial magnetic field using a special wire stretched along the entire equator of the planet.
Source: gogetnews.info
Colonization of planets
extremophiles In April 2012, the German Center for Aviation and Astronautics published a report that in laboratory conditions simulating the atmosphere of Mars, some species of lichens and cyanobacteria, after 34 days of stay, were able to adapt and showed the possibility of photosynthesis.
Source: esa.int
Promotion of the planet using asteroids
It is allowed to launch a massive asteroid from the Main Belt into the orbit of a satellite of Mars in order to activate the effect of the planetary "dynamo" and enhance the own magnetic field of Mars.
Source: images.astronet.ru
Increase in the mass of the planets
The force of gravity on Mars is 2.63 times less than on Earth, so the weight of Mars will have to be "increased" if we do not want the future colonists of the planet to change forever. Their muscles will shrink, internal organs will be rebuilt, and descendants will no longer be able to return to Earth. You can also increase the mass of the planet by bombarding asteroids.
Source: technobuffalo.com