Terraforming is the deliberate composition of a region, ecosystem, or entire planet to make it suitable for "Earth-like" life. Originally coined to describe hypothetical megaprojects on Mars or Luna, it is now clear that the evolutionary career of homo sapiens has had terraforming-scale effects on Earth, albeit ones that were seldom intentional or well-planned and which have made complex life here more precarious. This moment comes with the realization that for a viable planetarity to be achieved, further terraforming will be necessary, but will also demand not the improvisational emergence of past centuries, but the planetary-scale coordination of reason and care. This may resemble governance, or technology, or land-use policy, or biotechnology, but will surely incorporate them all and more into a new institutional form. Properly calibrated, the terraforming will extend the experimental impulses of cosmotechnics that link the scientific disclosures of our astronomic condition to our philosophical reflections—one feeding the other. It will cohere not from the pre-Copernican dominion of humans over their Blue Marble garden, but from a recognition of our own mediality. First, it recognizes that the human form that specifies designs for a planet in the course of terraforming is less the Vitruvian core from which technological prostheses extend than it is the result of millions of years of interfacial co-extension with technical systems. The human is plastic, and so available to further conscious revision. Second, the cognitive capacity for prospective abstraction that models the terraforming-to-come is itself an emergent faculty of the planet, not a virtual superimposition. It is an active by-product of planetary evolutionary unfoldings. The terraforming is foremost a planet thinking itself and artificially composing itself accordingly.