Thoreau raises a fundamental question in space exploration. Should we allow ourselves to terraform planets in an effort to make them habitable and seed objects in space with life as we know it, or should we leave nature out there to its own devices, intact and pure?

On the one hand, it would be prudent not to keep all our eggs in one basket; we might choose to spread terrestrial life to other worlds in an effort to reduce the risk of it being eliminated by catastrophes on Earth. But at the same time, one might worry that by doing so we could unleash unforeseen forces that would modify natural ecosystems in ways that could get out of hand. Moreover, artificial seeding of Earth life would muddy the waters in extraterrestrial “Walden-like” ponds. It would deprive us from the opportunity to find out if other life-forms may have existed before our arrival.

Such an impact might resemble the effect of the Spanish invasion of South and Central America, which decimated the rich culture of local populations such as the Maya. For this reason, NASA enforces tight regulations on the sterilization of space vehicles in an effort to avoid contamination of space targets with terrestrial microbes.