BBC: Alien oceans could be detected by telescopes.
The next generation of telescopes could reveal the presence of oceans on planets outside our Solar System.
Detecting water on Earth-like planets offers the tantalising prospect they could sustain life.
Scientists hope the reflection of light, or "glint", from mirror-like ocean surfaces could be picked up by a US space telescope set for launch in 2014.
The research by US astronomers has been published in Astrophysical Journal Letters.
Tyler Robinson at the University of Washington in Seattle is hoping this new technique could be used in the quest to find the Holy Grail for exoplanet astronomers - a possible sister to planet Earth.
"We're focussing on a class of extra-solar planets yet to be detected, so things comparable in size and composition to the Earth and similar distances from their central star as the Earth is from the Sun," he told BBC News.
The goal is to find something Earth-like in almost every sense of the world so we can even prove it has liquid oceans on its surface."
This kind of ocean could be the signature of a planet where life had developed in the same way as it did on our own planet.
Tyler Robinson hopes "glint" - the effect seen when light is reflected from an ocean's surface - may reveal the presence of Earth-like planets beyond our cosmic neighbourhood.