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Beyond Earthly Skies

Five Small Rocky Planets Circling an Ancient Star

2 Jan 2016, 22:00 UTC
Five Small Rocky Planets Circling an Ancient Star
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Figure 2: Artist’s impression of a rocky exoplanet.Over the years, observations have shown that small planets are common around stars, regardless of whether the star is metal-poor or metal-rich. In contrast, gas giant planets tend to be more abundant only around metal-rich stars. Kepler-444 is a planetary system that is home to five small rocky planets that orbit around a metal-poor Sun-like star. The host star of this planetary system is estimated to have formed 11.2 ± 1.0 billion years ago, when the Universe was less than 20 percent its current age. This makes Kepler-444 the oldest known planetary system hosting rocky planets and it is a good indication that planets, especially small rocky planets, can readily form throughout most of the Universe’s 13.8 billion year history. Interestingly, at the time when Earth formed, Kepler-444 and its system of rocky planets were already older than Earth is today.Kepler-444 is located at a distance of approximately 115 light years away and it is a highly compact planetary system consisting of five transiting, sub-Earth-size planets. The orbit of the outermost planet is only one-fifth the size of Mercury’s orbit around the Sun. All five rocky planets orbit their host star in less ...

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