When NASA’s Galileo probe approached Jupiter in 1995, we began to learn some of the secrets of the great giant, and one of them is as profound as Copernicus’ thought: Europa is estimated to have more water than on the entire Earth. No longer is the water of Earth considered to be unique, no longer is water scarce. The Earth is not the largest source of water in the Solar System.

Our view of the world has changed dramatically over the centuries. Columbus’ voyages proved to Europe that the Earth was not flat. Some in other parts of the world had already reached this conclusion, but for the European contemporaries of Columbus it was profound thought. Copernicus on his deathbed disclosed that the Earth was not the center of the universe. Galileo was tried and convicted because he refused to abandon Copernicus’ theory.

Our worldview has continued to evolve. Einstein’s Theory of Relativity abolished the idea that time and space are absolute and replaced it with the concept of spacetime. According to Einstein, massive objects such as the Sun bend spacetime. Gamow and Alpher of George Washington University and Herman published the Big Bang Theory, the idea that the universe began with an explosion some thirteen to fifteen billion years ago and has been expanding ever since.

The discovery and study of water on Europa is profound indeed. We know that life outside the Earth almost certainly exists. There is now a place where humans can possibly migrate, a place more likely for long-term survival than Mars, a place that unlike the Moon has abundant water or water ice. Our view of the world is changing.