Using gravitational microlensing, a team of astronomers led by Prof Andrew Gould from Ohio State University has detected a cold terrestrial exoplanet orbiting one member of the binary star system OGLE-2013-BLG-0341.
Artistic representation of the exoplanet OGLE-2013-BLG-0341LBb and its two parent stars. Image credit: Cheongho Han / Chungbuk National University.
The newly discovered alien word, labeled OGLE-2013-BLG-0341LBb, is located in the constellation Sagittarius, about 3,000 light-years away.
It is twice the mass of Earth, and orbits one of the stars in the binary system at almost exactly the same distance from which Earth orbits the Sun.
But its star is 400 times dimmer than our Sun, so the exoplanet is very cold – around minus 213 degrees Celsius.
The second star in the star system is only as far from the first star as Saturn is from our Sun. But this binary companion, too, is very dim.
OGLE-2013-BLG-0341LBb first appeared as a dip in the line tracing the brightness data taken by the Optical Gravitational Lensing Experiment (OGLE) telescope on April 11, 2013.
The exoplanet 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.
“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 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,” explained Prof Gould, who co-authored the discovery paper in the journal Science.
Although OGLE-2013-BLG-0341LBb is too cold to be habitable, the same exoplanet orbiting a Sun-like star in such a binary system would be in the so-called habitable zone.
Binary star systems composed of dim stars like in OGLE-2013-BLG-0341 are the most common type of star system in our Milky Way Galaxy. So this discovery suggests that there may be many more terrestrial exoplanets out there – some possibly warmer, and possibly harboring life.
“This greatly expands the potential locations to discover habitable planets in the future. We had no idea if Earth-like planets in Earth-like orbits could even form in these systems,” concluded co-author Prof Scott Gaudi of Ohio State University.
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A. Gould et al. 2014. A terrestrial planet in a ~1-AU orbit around one member of a ∼15-AU binary. Science, vol. 345, no. 6192, pp. 46-49; doi: 10.1126/science.1251527
