New planet-hunting technique may reveal 100 billion alien Earths

Astronomers from the University of Auckland, New Zealand, have come up with a new strategy that may help them to find up to 100 billion Earth-sized planets orbiting around other stars.

Although the Kepler telescope 'transit' method of finding planets has been the one talked about most here (because so far it's been the most successful), it's not the only method that astronomers use to detect planets. Another that has been used for years is the 'gravitational microlensing' technique. Astronomers have only found 15 planets so far with this method, compared to over 2,300 planets and candidates discovered so far with the transit method, but University of Auckland astrophysicist Philip Yock believes that he has a new strategy for the gravitational microlensing technique that may yield far better results.

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"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," Yock said, according to a University of Auckland press release. "These planets are generally hotter than Earth, although some could be of a similar temperature (and therefore habitable) if they're orbiting a cool star called a red dwarf."

"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 the 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."

MOA stands for Microlensing Observations in Astrophysics, a telescope at the Mt. John Observatory, in New Zealand.

Gravitational microlensing works by taking advantage of one of the fundamental principles of the universe — large objects warp spacetime. Massive objects, like stars, warp spacetime to create a 'gravity well' around them. Planets do this too, but on a smaller scale. When light interacts with a star's gravity well, the well changes the path the photons of light are traveling on. If you're on one side of the star's gravity well and there is a bright object on the other side of it, the light from that bright object will appear distorted to you — warped by the 'lens' that the gravity well creates in spacetime.

If there's a planet orbiting the star, the smaller gravity well from the planet will also distort any light from objects that are on the other side of the star-planet system from us, and the distortion will change with time as the planet goes around the star.

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Existing microlensing techniques have so far found planets that are between three times the size of Earth to over three times the size of Jupiter. Yock and his colleagues believe that the new technique they've developed will help them find smaller worlds, between one and three times the size of Earth. They believe that using an existing network of small, 'robotic' telescopes, supplemented by larger telescopes such as MOA, will reveal the abundance of Earth-like planets they predict are out there.

"Of course, it will be a long way from measuring this number to actually finding inhabited planets," said Yock in the UofA statement, "but it will be a step along the way."

(Images courtesy: D. Aguilar/Harvard-Smithsonian Center for Astrophysics and WFIRST/Goddard/NASA)

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