The source of Earth’s water is an enduring mystery that extends to exoplanets and the notion of habitability. In broad terms, Earth’s water was either part of the planet from the beginning of its formation in the solar nebula or delivered later, maybe by asteroids and comets. The source of Earth’s water is an enduring mystery that extends to exoplanets and the notion of habitability. In broad terms, Earth’s water was either part of the planet from the beginning of its formation in the solar nebula or delivered later, maybe by asteroids and comets. Planetary Sciences Phys.org – latest science and technology news stories