A large “shell” can be used to encase an alien world (asteroid or moon), keeping its atmosphere contained long enough for long-term changes to take root.
There is also the concepts where a usable part of a planet is enclosed in an dome in order to transform its environment, which is known as “paraterraforming”.
Paraterraforming - The worldhouse concept
The 'worldhouse' concept of paraterraforming can be formulated within the existing boundaries of technological knowledge and can provide a quasi-unconstrained global habitable environment at significantly lower levels of materials requirement and economic cost. Construction can proceed on a modular basis. A coarse-grained assessment of the possibilities of paraterraforming Mars is presented. It is suggested that the establishment of a fully habitable worldhouse environment on the planet Mercury would be a much less difficult undertaking than taerraforming Venus and could be economically important for the human exploitation of the solar system.
Shell Worlds - An Approach To Terraforming Moons, Small Planets and Plutoids
One big problem with the traditional terraforming approach is finding planets with workable initial parameters: large enough, temperate enough, wet enough, axial spin not too fast or too slow, a magnetic field, etc. A novel method to creating habitable environments for humanity by enclosing airless and otherwise useless sterile planets, moons, and even large asteroids within engineered shells is proposed. These shells are subjected to two primary opposing internal forces: compression caused by gravity and tension caused by atmospheric pressure. By careful design, these two forces can cancel each other out resulting in a net stress on the shell of zero. Beneath the shell an earthlike environment could be created similar in almost all respects to that of Earth except for gravity, regardless of the distance to the sun or other star. These would be small worlds, not merely large habitats, possibly stable across historic timescales. Each would contain a full, self-sustaining ecology, which might evolve in interesting directions over time.
Working the math on spherical shells, they ponder the fact that if the objective is to contain a 14.7 psi Earth-normal atmosphere, such a shell would experience the same kind of pressure-induced tension found in a balloon. Assume one atmosphere of pressure at the underside of the shell and vacuum above it, and it is possible to choose a shell thickness so that the compressive stress of gravity cancels out the atmosphere-induced tensile stress in the shell. A shell made completely of steel, for example, built to enclose a world 20 kilometers above its surface, would need to be 1.31 meters thick if enclosing the Earth, and 8.05 meters thick if enclosing the Moon.
Moreover, the shell mass used is there simply to create compressive force — opposing the pressure of the atmosphere within the shell — and can be no more than dead weight. Enclosing the Earth’s Moon could be done with no more than a 1-meter thick layer of steel if it incorporated 62 meters of regolith on top of it, with open-ended combinations of steel, ice, dirt and rock possible for the job.