The Penn State and University of Hawaii researchers plan to use an optical space telescope not yet developed and a mathematical method to accomplish their goal.

Specifically, Darren Williams, associate professor of physics and astronomy at Penn Sate's Erie, Pa., campus -- the Behrend College -- said the search is for a temperate planet that contains surface water.

Williams and Associate Professor Eric Gaidos of the University of Hawaii posit large amounts of water will provide a glint of light visible in the infrared and visible spectrum if they watch a planet for a long enough time.

While there are currently no telescopes capable of identifying watery planets, the astronomers hope a terrestrial planet finder telescope will orbit the Earth within the next 10 to 20 years. In the meantime, they have arranged for the European Space Agency's Mars Express and Venus Express spacecraft to look back at Earth occasionally and observe how our watery planet appears in various phases.

The study is to be reported in an upcoming issue of the journal Icarus.