Tour of WASP-18
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A new study using data from NASA's Chandra X-ray Observatory has shown that a planet is making the star that it orbits act much older than it actually is. WASP-18b is a "hot Jupiter," that is, a giant exoplanet that orbits very close to its star. Specifically, astronomers estimate WASP-18b is about ten times more massive than Jupiter, yet it orbits its star about once every 23 hours. By comparison, it takes Jupiter about 12 years to complete one trip around the Sun from its great distance. The new Chandra data of the WASP-18 system show that this huge planet is so close to its star that it may be causing a dampening of the star's magnetic field. As stars age, their X-ray and magnetic activity decreases. Astronomers determine that WASP-18 is only between 500 million and 2 billion years old, a relatively young age for a star. Given this age, astronomers expect that WASP-18 would be giving off lots of X-rays. Surprisingly, astronomers did not see any X-rays from WASP-18b during recent long Chandra observations. The researchers think that tidal forces from the gravitational pull of the massive planet - similar to those the Moon has on Earth's tides but on a much larger scale - may be responsible for disrupting the magnetic field of the star. This, in turn, may be making this star act old be before its time.
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(Credit: NASA/CXC/A. Hobart)