Chuck Bednar for redOrbit.com – @BednarChuck
Astronomers from the Australian National University analyzing a small red dwarf star located some 500 light years from Earth have made a startling discovery: the presence of a massive gas giant orbiting far closer to its tiny parent star than should be possible.
This unusual exoplanet, which according to Gizmodo was first indentified thanks to an observed, temporary decline in the already dim amount of light given off by the star, has approximately the same mass as Saturn (roughly 100 times that of Earth). Conversely, its star, HATS-6, is only half the size of our Sun in terms of both mass and diameter, the researchers said.
HATS-6 is one of the smallest stars astronomers have ever seen with a gas giant, and no current model can explain how this gas giant came to be so close to its host star, the website said. The authors reported their findings in a recent edition of The Astronomical Journal.
Exoplanet likely moved inward after forming
Since it is orbiting so closely, the planet known as HATS-6b has experienced so much heat that its gas has started billowing out, causing it to inflate to approximately the size of Jupiter. Also, it has an orbital period of 3.3 days, meaning that it is closer to its star than the far smaller Mercury is to the Sun. In fact, it’s orbit is just one-tenth that of Mercury’s.
“The planet has a similar mass to Saturn, but its radius is similar to Jupiter, so it’s quite a puffed up planet. Because its host star is so cool, it’s not heating the planet up so much; it’s very different from the planets we have observed so far,” explained George Zhou from the Research School of Astrophysics and Astronomy at The Australian National University (ANU)
“It must have formed further out and migrated in, but our theories can’t explain how this happened,” added Zhou, who was joined by TJ Tan of the Perth Exoplanet Survey Telescope, Dr. Daniel Bayliss from ANU and an international team of colleagues. “The atmosphere of this planet will be an interesting target for future study.”
Typically, gas giants form in the outer regions of the solar system, where gas and ice are more abundant. However, they don’t always stay there; they sometimes wind up moving inward due to the gravity of other objects. Zhou believes that HATS-6b first formed further out before migrating, but said that “our theories can’t explain how this happened.”
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