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Search for earth-like planets expands.

A newly discovered planet in a binary star system located 3,000 light-years from Earth is expanding astronomers' notions of where Earthlike--and even potentially habitable --planets can form, and how to find them. At twice the mass of Earth, the planet orbits one of the stars in the binary system at almost exactly the same distance from which Earth orbits the sun. However, because the planet's host star is much dimmer than the sun, it is much colder than Earth--a little colder, in fact, than Jupiter's icy moon Europa.

Four international research teams, led by Ohio State astronomer Andrew Gould, published their discovery in the journal Science. The study provides the first evidence that terrestrial planets can form in orbits similar to Earth's, even in a binary star system where the stars are not very far apart. Although this planet itself is too cold to be habitable, the same planet orbiting a sun-like star in such a binary system would be in the so-called "habitable zone," the region where conditions might be right for life.

'This greatly expands the potential locations to discover habitable planets in the future," says American astronomer Scott Gaudi of Ohio State University, Columbus. "Half the stars in the galaxy are in binary systems. We had no idea if Earth-like planets in Earth-like orbits could even form in these systems."

Very rarely, the gravity of a star focuses the light from a more distant star and magnifies it like a lens. Even more rarely, the signature of a planet appears within that magnified light signal. The technique astronomers use to find such planets is called gravitational microiensing, and computer modeling of these events is complicated enough when only one star and its planet are acting as the lens, much less two stars.

Searching for planets within binary systems is tricky for most techniques, because the light from the second star complicates the interpretation of the data, "but in gravitational microlensing," Gould explains, "we don't even look at the light from the star-planet system. We just observe how its gravity affects light from a more distant, unrelated, star. This gives us a new tool to search for planets in binary star systems."

Gaudi adds, "Now, we know that with gravitational microlensing, it's actually possible to infer the existence of a planet--and to know its mass, and its distance from a star-without directly detecting the dimming due to the planet. We thought we could do that in principle but, now that we have empirical evidence, we can use this method to find planets in the future."

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Title Annotation:Astronomy
Publication:USA Today (Magazine)
Date:Jun 1, 2015
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