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Scientists Find New Planet As Big As Host Star

Far out in the galaxy, astronomers at Penn State have found a planet that is just a little bit smaller than its host star, a surprising finding set to potentially change the established ideas of planet formation.

Science news is filled with headlines of discoveries that clash with established theories known only to the scientists researching them, and not to the general public. But the idea of a planet being almost as large as the star it orbits is intuitively very strange to anyone with even a vague understanding of system dynamics.

The exoplanet is twice the mass of any known body that orbits its star in less than ten days, and weighs in at about one three-hundredth the mass of its star, which may not sound like much, but just compare it to Mercury, the closest planet to the Sun which is 93 million times smaller, and you have some understanding of the magnitude of the discovery.

“This discovery really drives home the point of just how little we know about the universe,” said Suvrath Mahadevan, Professor of Astronomy and Astrophysics at Penn State and co-author on the paper describing the discovery. “We wouldn’t expect a planet this heavy around such a low-mass star to exist.”

Mahadevan and his colleagues were using the 10-meter Hobby-Eberly Telescope at McDonald Observatory in Texas to survey low-mass stars and managed to identify LHS 3154, an M-type star, which is called a ‘cold dwarf’ and is the least-massive and least-hot kind of luminescent star.

Very quickly they used the transiting method to determine there was a planet passing between the view of the telescope and the star every 3.7 days, and the apparent wobble it was causing in the position of the star indicated that it was a massive object.


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