6 small planets orbiting sun-like star discovered
Astronomers have discovered what they say is an amazing planetary system in which six planets are orbiting around a sun-like star some 2,000 light-years away.
The University of California researchers, who used Nasa’s Kepler mission to spot the planet system, said five of the six planets are in tightly packed orbits and range in size from 2.3 to 13.5 times the mass of the earth.
They orbit the star, named Kepler-11, in less than 50 days within a region that would fit inside the orbit of Mercury in our solar system. With an orbital period of 118 days and an undetermined mass, the sixth planet is larger and farther out, the team reported in the journal Nature.
“Not only is this an amazing planetary system, it also validates a powerful new method to measure the masses of planets,” said Daniel Fabrycky, a Hubble postdoctoral fellow who led the orbital dynamics analysis. “Of the six planets, the most massive are potentially like Neptune and Uranus, but the three lowest mass planets are unlike anything we have in our solar system,” said Jonathan Fortney, who led the work on understanding the structure and composition of the planets.
The Kepler space telescope detects planets that “transit” or pass in front of their host star, causing periodic dips in the brightness of the star as measured by the telescope’s sensitive photometer. The amount of the brightness reduction tells scientists how big the planet is in terms of its radius, while the time between transits tells them its orbital period. To determine the planets’ masses, Fabrycky analysed slight variations in the orbital periods caused by gravitational interactions among the planets.
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