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SDSU Astronomers Discover Planets That Orbit Two Suns

This illustration shows a planetary system orbitting two sun-like stars.
Lior Taylor
This illustration shows a planetary system orbitting two sun-like stars.

Three studies released Wednesday, in the journal Nature and at the American Astronomical Society's conference in Austin, Texas, demonstrate an extrasolar real estate boom.

San Diego State University astronomers, along with a team of scientists, have discovered two more planetary systems with two suns. Before, it was believed planets could only orbit a single sun, because a double sun, also known as a double star, would make the system too chaotic.

"For me, it's interesting to think about what life would be like on these planets," said SDSU astronomer Jerome Orosz. "First of all you’d see a double sunrise and a double sun set every day and second of all, your climate would be very very odd because as the stars orbit each other, the distance from the planet to each star is changing and so the amount of sunlight you get is a very complex function of time.”


The two new planets, Kepler-34 b and Kepler-35 b, are gaseous Saturn-size planets. Kepler-34 b orbits its two sun-like stars every 289 days, and the stars themselves orbit and eclipse each other every 28 days.

Orosz said the discovery confirms it’s not a fluke of nature.

"If you look up at the sky at night, half of the stars you see are in double star systems," explained Orosz. "So the fact that nature can make planets around double stars – it increases the number of places you can look for planetary systems."

Astronomers are finding other worlds using three different techniques and peering through telescopes in space and on the ground.

Confirmed planets outside our solar system — called exoplanets — now number well over 700, still-to-be-confirmed ones are in the thousands.


NASA's new Kepler planet-hunting telescope in space is discovering exoplanets that are in a zone friendly to life and detecting planets as small as Earth or even smaller. That is moving the field of looking for some kind of life outside Earth from science fiction toward plain science.

"Nature must like to form planets because it's forming them in places that are kind of difficult to do," said San Diego State University astronomy professor William Welsh, who wrote a study about planets with two stars that's also published in the journal Nature.

The gravity of two stars makes the area near them unstable, Welsh said. So astronomers thought that if a planet formed in that area, it would be torn apart.

Late last year, Kepler telescope found one system with two stars. It was considered a freak. Then Welsh used Kepler to find two more. Now Welsh figures such planetary systems, while not common, are not rare either.

Orosz said now that they know what they’re looking for, it opens up a whole new world of astronomy.

Corrected: September 21, 2023 at 9:45 PM PDT
The Associated Press contributed to the information in this report.