Cambridge University astronomers say they've found the shattered remains of an asteroid that contained significant amounts of water orbiting a white dwarf star at the end of its life 150 light years from Earth.
The discovery marks first time that both water and a rocky surface -- two "key ingredients" for habitable planets -- have been found together beyond our solar system, they said.
Earth is essentially a "dry" planet, with surface water accounting for only 0.02 percent its total mass, suggesting our world's oceans came long after it formed, most likely when water-rich asteroids in the solar system crashed into our planet.
The asteroid discovery at the star known as GD 61 shows the same water "delivery system" could have occurred in this distant, dying star's planetary system, lead study author Jay Farihi of Cambridge's Institute of Astronomy said.
"These water-rich building blocks, and the terrestrial planets they build, may in fact be common -- a system cannot create things as big as asteroids and avoid building planets, and GD 61 had the ingredients to deliver lots of water to their surfaces," Farihi said.
"Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system."