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One Planet, Three Suns
On the planet Earth, we have the privilege of enjoying only one sunset each day, but imagine a world where there are three sunsets each day--or maybe even four. And yet, this phenomenon may not be so uncommon: more than half of the stars in the universe belong to multiple-star systems. However, we are particularly interested in finding and studying the star systems which contain exoplanets, the planets beyond our own solar system.
In July of 2005, an astronomer discovered one of the first exoplanets located within a triple-star system, named HD 188753 Ab. This planet is similar in nature to our gas giant, Jupiter, and it has a brief orbit of 3.3 days because it is located so close to its parent star--multiple-star systems tend to be cramped for space. Regardless, in 2007, a team of scientists who had kept watch on this new planet at the Geneva Observatory of Switzerland were unable to find any conclusive evidence confirming the presence of the planet.
Perhaps this was because the trouble with hunting for exoplanets within multiple-star systems is that they are hard to detect. Astronomers use a process, called the radial-velocity method, which essentially looks at the "wobble" of a star induced by the gravitational pull of a planet. This is quite effective for a single-star system, but it is difficult to discern the wobble HD 188753 Ab induces since it is in a close-star system and the stars' light intermingles.
On October 19, 2009, a confirmed exoplanet was discovered orbiting around the red dwarf star, Gliese 667 C. This triple-star system was studied using HARPS, the High Accuracy Radial Velocity Planet Searcher. The new planet is about six times the mass of Earth and orbits .05 AU from its parent star. Its discovery brings the total number of known exoplanets to just over 400.
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