http://www.cam.ac.uk/research/news/watery-...able-exoplanetsBasically a weird overabundance of oxygen has been discovered in the atmopshere of a white dwarf 150 light years away. And since the white dwarf doesn't contain any significant amounts of carbon, the excess oxygen can't be the result of nuclear fusion or comet impact, which means it must come from a rocky planet or water-rich asteroid. By analizing the amount of silicon, aluminium and other elements it was ascertained that there is still too much oxygen to have come from a rocky planet being torn by the star's gravity, so the only explanation left is that it must have come from large Ceres-like asteroid, with more than 20% of its mass being water, that was shredded by the star's gravity.
Furthermore, in order for an asteroid of such size (90 km or more) to come so close to the white dwarf, it must have been pushed by a giant planet.
So, essentially we have a system with large water-rich asteroids in the vicinity of planets, an arrangement which ensured the bombardment of Earth, providing it with abundant water during the first half of a billion years of its existence.
It is quite possible that water-rich rocky planets are present in the system, however they must be frozen because the white dwarf has a minuscule energy output.
