July 4, 2014
Newly-Discovered World Gives Astronomers A New Tool To Find Planets In Binary Systems
redOrbit Staff & Wire Reports - Your Universe Online
Astronomers have located a new terrestrial planet in a binary star system located roughly 3,000 light-years from Earth, according to new research appearing in the July 4 edition of the journal Science.
Ohio State University professor Andrew Gould and four international teams of scientists used the technique of gravitational microlensing to discover the new planet, which is roughly twice the mass of Earth and orbits one of its solar system’s two stars at approximately the same distance our world orbits the sun. However, since its host star is far cooler than our sun, it actually reaches temperatures colder than those of Jupiter’s icy moon, Europa.
The discovery of this new planet, which has been dubbed OGLE-2013-BLG-0341LBb, provides the first evidence that terrestrial planets can form in orbits similar to Earth’s, even when they’re in a binary system where the two stars are fairly close to one another.
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While this new world’s sub-60 Kelvin (-352 degrees Fahrenheit or -213 Celsius) temperature is too cold for it to be habitable, it would be in the so-called “habitable zone,” with conditions suitable for life, if it happened to be orbiting a sun-like star.
“This greatly expands the potential locations to discover habitable planets in the future,” Ohio State Department of Astronomy professor Scott Gaudi explained Thursday in a statement. “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.”
Gravitational microlensing, the technique used by the study authors to discover OGLE-2013-BLG-0341LBb, uses the gravity from a star to focus and magnify the light from a more distant star in order to detect the signature of a new planet. In this instance, the astronomers detected two separate signals – the primary one usually used to locate planets, and a secondary one. Prior to this study, the second signature had only been hypothesized to exist.
Typically, searching for new worlds in binary system is difficult, since the light from the second star makes interpreting the data more difficult. However, in gravitational microlensing, Gould explained that he and his colleagues never even analyzed the star-planet system’s light. Instead, they observed how its gravity impacts light from a more distant, unrelated star. This discovery gives scientists a new tool in order to search for planets in binary systems.
The first signature was said to be a brief dimming of light, caused when the planet’s gravity disrupted one of the source star’s magnified images. However, the second was described as an overall distortion of the light signal. According to Gould, even if his team failed to detect the initial signature, the distortion alone would have made it possible for them to detect it. While it cannot be seen by the naked eye, it shows up using computer modeling.
“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,” he explained, while admitting that the nature of these distortions remains somewhat mysterious.
As for the planet itself, OGLE-2013-BLG-0341LBb first showed up as a “dip” in the line tracing the brightness data taken by the Optical Gravitational Lensing Experiment (OGLE) telescope back in April. It caused a brief disruption in one of the images formed by the star it orbits as the system crossed in front of a far more distant star located about 20,000 light-years away in the constellation Sagittarius, the university explained.
“Before the dip, this was just another microlensing event. It’s really the new OGLE-IV survey that made this discovery possible. They got a half dozen measurements of that dip and really nailed it,” Gould said. After analyzing the dip, the researchers determined that its source was headed directly toward the central star. Continued analysis eventually led to the discovery of its companion star, and ultimately detailed information about the planet itself.