Astronomers have autopsied a distant, broken apart planet and revealed signs of water and a rocky surface together for the first time, delighting scientists on the hunt for alien life.
In a planetary system some 150 light years away, the right conditions for life appear to have once existed, and planets like Earth may have orbited a star known as GD 61, British astronomers reported in the journal Science.
"This planetary graveyard swirling around the embers of its parent star is a rich source of information about its former life," said co-author Boris Gansicke of the Department of Physics at the University of Warwick.
Around 200 million years ago, GD 61 lost its power and began sucking in the nearest planets with its extreme gravitational pull, devouring them to pieces.
Now that Sun is what is known as a white dwarf, or a dying star that is circled by planetary debris.
Astronomers have typically studied living stars and the planets that circle them in the search for other worlds that are a reasonable distance from their stars and therefore not too cold or too hot for life.
But a handful of promising far-away discoveries by the NASA Kepler mission have been limited to the size and density of planets in this so-called Goldilocks zone.
Their compositions, whether rocky like Earth or gassy like Jupiter, have remained a mystery because astronomers couldn't get close enough to peer at their surfaces, or inside them.
The latest analysis focused on a dead planet that has been broken to bits, allowing scientists to analyze the fragments and actually see inside the contents.
Previous research has examined 12 destroyed exoplanets, or planets outside our solar system, orbiting white dwarves in this way, but never before has the signature of water been found.
Using ultraviolet spectroscopy data, scientists have shown that the fragments contain about 26 percent water by mass, far greater than the Earth's 0.02 percent.
The team detected magnesium, silicon, iron and oxygen in the white dwarf's atmosphere, making up the main components of rocks.
The high proportion of oxygen indicates the presence of water.
"Those two ingredients -– a rocky surface and water -– are key in the hunt for habitable planets outside our solar system so it's very exciting to find them together for the first time outside our solar system," said Gansicke.
The findings are based on data from the Hubble Space Telescope and the W. M. Keck Observatory on Mauna Kea on Hawaii on planets far beyond the solar system.
Researchers believe the water came from a minor planet, at least 90 kilometers (56 miles) in diameter but probably much larger.
"The finding of water in a large asteroid means the building blocks of habitable planets existed –- and maybe still exist -– in the GD 61 system, and likely also around substantial number of similar parent stars," said lead author Jay Farihi, from Cambridge's Institute of Astronomy.
"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."
While the findings offer fresh hope of someday locating other planets where life exists, they also provides a sobering reminder of what lies ahead for Earth, perhaps six billion years from now, when alien astronomers may be studying the fragments of our solar system.