Rocky alien planets may contain oceans

All rocky planets develop liquid-water oceans shortly after forming, suggesting that alien worlds potentially teeming with life may be common throughout the Universe, a new study has found.
Computer models and Earth's own history suggest such seas should splash around soon after these worlds' surfaces have cooled down and solidified, according to Lindy Elkins-Tanton of the Carnegie Institution for Science.
"Habitability is going to be much more common than we had previously thought," Elkins-Tanton said.
Analysis of ancient Earth rocks shows that the planet hosted an ocean of liquid water at least 4.4 billion years ago, Elkins-Tanton said.
She said this water came primarily from the planetesimals that formed Earth long ago rather than from comet impacts, as some researchers had previously believed, 'SPACE.Com' reported.

While comet-delivered water probably made a contribution later on, "it's not required," Elkins-Tanton said.

"You can make a water ocean without it," she added.
For instance, even if the pieces that built Earth contained just 0.01 per cent water by weight - an extremely conservative estimate - our planet still would have harboured an early global ocean hundreds of meters deep, she said.
Elkins-Tanton said such primitive oceans form in a multistep process. Water first boils out of the molten rock covering a newborn terrestrial planet heated up by accretionary impacts, creating a steamy atmosphere.
This atmosphere then collapses as the planet cools, returning the water to the surface and generating an ocean.

"The ramifications of this are that, in any exoplanet system anywhere in our universe, if it's made of rocky materials with similar water contents to ours, every rocky planet would be expected to start with a water ocean," Elkins-Tanton said.