Space Telescope Science
If you go walking along the beach or take an ocean cruise, it's hard to believe that Earth is essentially a "dry" planet. Barely 0.02 percent of our home planet's mass is surface water. In fact, our oceans came along a few hundred million years after Earth formed 4.6 billion years ago. Though still debated, astronomers think that the primeval Earth was most likely irrigated when water-rich asteroids in the solar system crashed into our planet.
Now astronomers have found that the same water "delivery system" could have occurred in a dying star's planetary system. Hubble Space Telescope spectroscopic observations have found forensic evidence for the same kind of water-rich asteroids that may have once brought water to Earth. Observations made with Hubble's Cosmic Origins Spectrograph (COS) allowed the team of astronomers to do a robust chemical analysis of debris falling into the white dwarf star GD 61, located 150 light-years from Earth. They didn't detect planets but the building blocks of planets. The asteroids are plummeting deep into the gravitational field of the white dwarf, presumably due to gravitational perturbations from a surviving Jupiter-sized planet in the system. This is circumstantial evidence that potentially habitable planets once existed in this star system. However, the star burned out 200 million years ago.