In a UH news release issued today, the paper's lead author Eric Gaidos, an associate professor in the Department of Geology & Geophysics and the NASA Astrobiology Institute at UH Manoa, said: "The most successful technique for discovering planets to date spreads light from the host star into its constitutive wavelengths (colors)."

Gaidos continued, "A shift in wavelength, analogous to the change in pitch of the horn of a passing automobile, reveals any motion of the star along the line of sight. Monitoring of a star can detect periodic motion caused by the gravitational pull of any unseen, orbiting planet."

Astronomers reported the first planet around another sun-like star in 1995 and since then have found more than 200 such planets, all thought to be "gas giants" made mostly of hydrogen and helium like Jupiter and Saturn in our solar system.

Improved techniques and the ability to monitor fainter stars now enable astronomers to discover smaller planets, particularly planets orbiting much closer to their host star than the Earth is to the sun.

Computational simulations by co-author Nader Haghighipour, a planetary dynamicist at the Institute for Astronomy and the Astrobiology Institute at UH-Manoa, have shown that smaller Earth-sized planets can indeed exist in such tight planetary environments.

According to the paper, planets orbiting much closer to a star like the sun will be much hotter and, like Mercury and Venus in our solar system, inhospitable to life. However, many stars are much less bright than the sun, and planets close to them could still orbit within a "habitable zone" where surface temperatures could permit stable liquid water.

"Explaining the formation of habitable planets in such environments is a challenging task. However, our simulations have been successful in determining condition under which planets similar to Earth can form in the habitable zones of less bright stars," said Haghighipour.

Future space observatories beginning with NASA's James Webb Space Telescope have the potential to study such planets and determine whether they have atmospheres or oceans.

Added Gaidos, "The discovery of another life-bearing planet would be a scientific triumph for humanity, but the study of many lifeless, un-Earthly worlds would nevertheless tell us about how planets form, and help us appreciate the Earth all that much more".