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Tatooine-like planets may be more common than previously thought

Two new, circumbinary planets have been discovered by an international team of researchers.  It confirms and establishes a whole new class of planets that orbit two stars.

The planets, Kepler-34b and Kepler-35b, are both low-density, gas-giants, about the same size as Saturn. They both lie on the fringe of the habitable zone, just outside where liquid water could exist – but the similarities stop there.

“Now that we have two more systems, we can see a great diversity in them – they’re not exactly the same as Kepler-16,” Bill Welsh, study co-author and researcher at San Diego State University, told “The orbital characteristics are different and the temperatures are different.”

Both systems were found in the constellation Cygnus – the swan. 

Kepler-34b is 4900 light-years from earth, orbiting its two stars every 289 days, while they orbit each other every 28 days. Kepler-35b is 5400 light-years from earth, orbiting its stars every 131 days, while they orbit each other every 21 days.  

In order to identify possible circumbinary planets, researchers looked for key changes to the entire system.

“As the stars go around each other, it should be like clockwork – they should eclipse each other exactly, periodically,” Welsh said. “If there’s another object going around the two stars, then sometimes that eclipse can be early or late.”

“We’re using the eclipses of the stars themselves to tell us there’s something interesting about the system,” he added.

That change is much harder to spot than in single star systems, like our own sun.

“There are huge eclipses as one star passes in front of the other, so the light changes dramatically, maybe by as much as 50 per cent,” Welsh said.  “On top of that we may have a one per cent change.  We’re looking for that one per cent change on top of that 50 per cent change.”

That’s on the high end.  The change they’re looking for could be as small as 0.1 per cent.

These two new planets, researchers say, show there could be many millions more like them in the galaxy

“The environment around a binary star is chaotic.  The stars are whipping around each other, there are intense gravity changes and it would seem an unlikely place to form planets,” Welsh said. “Yet, here we are finding them – and we estimate there should be at least millions of these things in our galaxy."

“It’s telling us nature likes to make planets,” he added.

The research was reported in the latest issue of the Journal, Nature

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