Terrestrial Planet Finder will one day help us detect Earth-like worlds around other stars, no matter which technologies are deployed (Centauri Dreams remains an advocate of Webster Cash’s New Worlds Imager). But once we start finding such worlds, what sort of data signatures should we look for to help us identify habitable surface environments?

That question has been addressed in a new way by Penn State Erie assistant professor of physics and astronomy Darren M. Williams. Working with the University of Hawaii’s Eric Gaidos, Williams outlined a theory that planets with abundant water should show strong scattering of starlight from ocean surfaces and discussed ways of examining such data.

From a summary of the presentation:

“Here we simulate the specular reflection of starlight off the surface of Earth-like planets to calculate visible light curves for different viewing geometries, obliquities, and land-sea fractions. The amplitude and polarization of the reflected signal is found to be strongly dependent on the waviness and expanse of the ocean. Planets are naturally brightest in crescent phase when the oceans most-effectively scatter starlight in the direction of Earth.”

Centauri Dreams‘ take: It seems remarkable to be considering life signatures on Earth-like worlds, when at present the smallest planets we can detect (and non-visually at that) are at least the size of Neptune. But Kepler (proposed launch: 2007), the Space Interferometry Mission (launch: 2009) and the Terrestrial Planet Finder to follow could lead us to such worlds within a decade. If we continue to push the technology hard, we may one day see reflections off an alien ocean directly rather than just inferring them from raw data.

“Specular Reflection of Starlight off Distant Planetary Oceans” was presented on Friday at the AAS Division for Planetary Sciences meeting in Louisville. On other forms of biosignatures, see “Biosignatures and Planetary Properties to be Investigated by the TPF Mission,” (JPL Publication 01-008), available online.