Several billion years from now, our Sun will exhaust the supply of hydrogen fuel at its core and will become a giant star. Detailed models indicate that the Sun will expand, engulfing Mercury - then contract temporarily - and then expand once again after the supply of helium is exhausted at its center. The Sun's diameter will ultimately increase two hundred fold, and its luminosity will increase five thousand fold. As the Sun starts to gets brighter, a wave of water vaporization will spread outwards through the solar system, starting with the Earth's oceans and Saturn's rings and extending far beyond the orbit of Neptune. Even icy bodies as large as Pluto will be largely vaporized, leaving just a cinder of hot rock. So in very real sense, the observations of water vapor reported today are painting a picture of the future of our own Solar System.

Courtesy of NASA