Astronomers just announced a new planet found in a double star system located 3,000 light-years from Earth that, they say, is changing their thinking on the search for habitable worlds. Four international research teams published news of this new planet – called OGLE-2013-BLG-0341LBb – in the July 4, 2014 issue of the journal Science. This newly found world has twice the mass of Earth. It orbits one of the stars in its system at almost exactly the same distance of Earth from the sun. The planet’s host star is much dimmer than the sun. So the planet is a frozen world, much colder than the Earth, a little colder in fact than Jupiter’s icy moon Europa. Earthlike life there is not likely. Still, this planet is expanding astronomers’ notions of where Earthlike – and even potentially habitable – planets can form, and how to find them.
The study provides the first evidence that terrestrial planets can form in orbits similar to Earth’s, even in a double star system where the stars are not very far apart. The same planet orbiting a sunlike star in such a binary system would be in the so-called habitable zone – the region where conditions might be right for life. Scott Gaudi, professor of astronomy at Ohio State University, said:
This greatly expands the potential locations to discover habitable planets in the future. 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.
The technique astronomers use to find such planets is called gravitational microlensing. 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. 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. Gould explained:
But in gravitational microlensing, 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.
The planet first appeared as a “dip” in the line tracing the brightness data taken by the OGLE (Optical Gravitational Lensing Experiment) telescope on April 11, 2013. The planet briefly disrupted one of the images formed by the star it orbits as the system crossed in front of a much more distant star 20,000 light-years away in the constellation Sagittarius.
Bottom line: An international team of astronomers has discovered a planet 3,000 light-years away, orbiting one of two stars in a binary system. They used the technique of gravitational microlensing to find the planet. The planet is not thought to be habitable, but it does orbit in a zone reminiscent of the habitable zone around our sun. These astronomers say their technique can be used to search other binary star systems for potentially habitable planets.
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