Elon Musk, founder of SpaceX and a leading proponent of Mars colonization, has argued that humanity must become a "multi-planetary species." The idea is to prepare a "Plan B" planet in case Earth becomes uninhabitable. While such a vision may be technically feasible by fully deploying advanced technologies, and given sufficient funding and a willingness to accept certain sacrifices, should not those same resources be directed toward restoring Earth's environment? Is it ethically justifiable to prepare a "second Earth" while abandoning efforts to preserve the first?

Science and technology have undoubtedly advanced civilization. However, ethical judgments primarily rested on utilitarian principles—namely, the greatest good for the greatest number. Going forward, however, additional ethical frameworks must be considered for scientific and technological advancement.

The long-term impact of humans living in environments radically different from Earth remains unknown. Even highly trained astronauts experience bone and muscle loss, vision deterioration, and psychological stress in confined environments. While emergency return is possible from the International Space Station, orbiting 400 km above Earth, it would be virtually impossible from Mars, some 400 million km away. Even granting that Mars colonization is worthwhile, we must venture into modifying humans to adapt to the harsh environment of space. Through genome editing of embryos, we would create "post-humans" resistant to intense radiation, low gravity, and stress—and send them on a one-way ticket to Mars. By doing so, a new ethical issue is introduced: intervention in life itself. Having gained a "god's-eye view" through science and technology enabling surveying beyond the solar system, humanity ultimately comes to act as if it were divine. This is no longer an issue that can be addressed by utilitarianism alone.

Human progress has often been driven by aspiration—turning the impossible into the possible. This endeavor in itself is something noble. The successful Apollo program began with President John F. Kennedy's 1961 declaration that the United States would land a man on the Moon and return him safely within a decade. Such bold and seemingly unrealistic goals have since been referred to as "moonshots."

In 2000, President Bill Clinton proposed fitting the entire collection of the Library of Congress into a device the size of a sugar cube, spurring advances in nanotechnology. The rapid progress of AI-powered humanoid robots (physical AI) has likewise been fueled by researchers' almost childlike dream of holding a soccer world cup played by humanoid robots by 2050.

At the same time, such approaches—driven by capital and momentum—are becoming increasingly difficult for the public to accept. A relevant question appears in the Survey on the Japanese National Character, conducted every five years by the Institute of Statistical Mathematics involving a survey population of several thousand people: What kind of relationship with nature is most conducive to human happiness? Of particular note is the shift in the proportion of respondents who believe that "humans must submit to nature," which became the most common response in the latest survey (2018). This view surpassed "humans must conquer nature" in 1973, and later overtook "humans must utilize nature" in 1993. The view that nature must be conquered peaked in 1968, coinciding with the period when Japan achieved rapid economic growth through the promotion of science and technology. Other opinion surveys likewise indicate that the Japanese public's sense of the omnipotence of—and trust in—science and technology has been on the decline since then.

Many of the global challenges humanity faces today—global warming, nuclear proliferation, poverty and displacement driven by climate change, the proliferation of AI-generated misinformation and the resulting social divisions, and cyberattacks—have been brought about by rapid technological advancement and the excesses of capitalism. Humanity now finds itself struggling to manage the consequences of its own actions. It has also become increasingly clear that even with advanced technology, we are not fully capable of controlling natural disasters.

There is a growing argument that the present age in the geological time scale should be termed the "Anthropocene"—an era in which human activity leaves detectable traces in the geological record, from nuclear fallout to fossil-fuel soot and microplastics.

Humanity, which appeared only at the very end of Earth's "calendar year," has appropriated and exhausted the planet, and now contemplates expanding to and reshaping other planets as its next place of habitation. The meaning of these actions must be reconsidered from perspectives beyond mere technical feasibility.

The more we reflect, the more we recognize how our existence depends on a convergence of extraordinary contingencies—and how precious it is to sustain our Earth. Examining the grand vision of terraforming other planets holds worth precisely in that context.