Terraforming

To turn an abandoned, ruined shack into a livable home, you have to add insulation, install plumbing, and set up ventilation. Terraforming works much the same way, acting as a massive planetary renovation project.

Mars, our top candidate, is currently freezing cold—with temperatures plunging tens of degrees below zero—and its atmosphere is far too thin to breathe. The very first step would be warming the planet up. Scientists have long proposed melting the frozen carbon dioxide (dry ice) locked in Martian polar ice caps, especially at the south pole, using giant orbital mirrors or heat sources to release gas into the sky. However, a 2018 NASA-backed study concluded that even if all remaining carbon dioxide on Mars were vaporized, it still would not be enough to create a sufficiently thick atmosphere on its own.

If enough greenhouse gases could be released, they would trap solar heat. In theory, as the planet gradually warms, underground ice would melt into flowing rivers and open lakes. Rising atmospheric pressure would also keep liquid water from boiling away into space, establishing the foundational Earth-like conditions needed for life.

Sci-fi movies often make it look easy: switch on a giant atmosphere generator, and within minutes you can take off your helmet. But remodeling an entire world is vastly more complicated. Deep space relentlessly bombards planets with lethal solar wind (streams of high-energy charged particles from the Sun) and cosmic radiation.

Earth deflects these dangerous rays thanks to its powerful magnetic field, generated by molten iron churning in its core. Mars, however, lost its global magnetic shield billions of years ago. Over eons, solar wind steadily stripped away most of the Martian atmosphere. Today, this stripping occurs very slowly—virtually unnoticed across human lifetimes—and many researchers argue that surface gravity (Mars has just 38% of Earth's gravity) is a far bigger challenge for holding onto gases.

On Earth, our thick atmosphere also blocks an immense amount of radiation. Because Mars lacks both a dense air cushion and a planetary magnetic field, radiation levels at the surface remain dangerously high. Until an atmosphere grows thick enough, radiation shields are vital. Proposed solutions include deploying an artificial magnetic shield, though scientists still debate whether this is strictly necessary. Furthermore, Martian soil is saturated with toxic salts called perchlorates that must be cleansed, demanding sophisticated technological interventions over generations.

Once temperatures and atmospheric pressure stabilize somewhat, the next phase is introducing pioneer life. Humans cannot just pack their bags immediately, so extremely hardy microbes and lichens would be seeded across the Martian surface first.

Oxygen-producing microorganisms like cyanobacteria, alongside genetically modified plants, would use sunlight and carbon dioxide to drive photosynthesis. Over countless generations, their metabolic work would slowly fill the atmosphere with breathable oxygen, while decaying organic matter mixes with crushed basalt to form rich topsoil. While warming the planet might take roughly a century, researchers like Chris McKay estimate that accumulating a breathable oxygen atmosphere could take well over 100,000 years.

As plant life spreads and forests take root, they would establish a self-sustaining ecological cycle. Only then would humanity reach the ultimate milestone of terraforming: walking freely across another world, shedding heavy spacesuits, and breathing fresh air under an alien sky.