Researchers at The University of Auckland say the strategy would use a technique called gravitational microlensing, currently being utilized by a Japan-New Zealand collaboration called MOA, for Microlensing Observations in Astrophysics. The work will require a combination of data from microlensing and the NASA Kepler space telescope, they said.
Kepler looks for distant planets by detecting the loss of light from a star when a planet orbits in front of it, whereas microlensing measures the gravitational deflection of light from a distant star that passes through a planetary system en route to Earth -- an effect predicted by Albert Einstein in 1936.
Microlensing has been used to detect several planets as large as Neptune and Jupiter, but Auckland physicist Phil Yock and colleagues have outlined a strategy for detecting the tiny deflection caused by an Earth-sized planet.
"Kepler finds Earth-sized planets that are quite close to parent stars, and it estimates that there are 17 billion such planets in the Milky Way," he said. "Our proposal is to measure the number of Earth-mass planets orbiting stars at distances typically twice the sun-Earth distance. Our planets will therefore be cooler than Earth. By interpolating between the Kepler and MOA results, we should get a good estimate of the number of Earth-like, habitable planets in the Galaxy. We anticipate a number in the order of 100 billion."
Earth-sized planets could be detected more easily if a worldwide network of moderate-sized, robotic telescopes was available to monitor them, Yock said.
The researchers' proposal has been published in Monthly Notices of the Royal Astronomical Society.