Discovery! 3rd planet found in the star system & # 39; Tatooine & # 39; two stars

The only known "Tatooine" multiplanet system is even more interesting.

A third world is hiding in the two stars Kepler system-47, and he is taller than his two siblings previously discovered, reports a new study.

"We certainly did not expect it to be the planet's largest planet," said study co-author William Welsh, an astronomer at San Diego State University (SDSU) in a statement. "It was almost shocking."

Related: Gallery: The Strange Foreign Planets

Kepler-47 is an old system of about 3.5 billion years old located 3,340 light-years from Earth. One of its stars is very similar to the sun, but the other is considerably smaller and contains only one third of the mass of our sun. The two stars gravitate around their common center of mass once every 7h45 terrestrial days.

In 2012, Welsh and his colleagues, led by another SDSU astronomer, Jerome Orosz, announced the discovery of two planets circling the two stars. These worlds, Kepler-47b and Kepler-47c, both have two suns in the sky, just like the original planet of Luke Skywalker, Tatooine, in the "Star Wars" universe.

The researchers made this discovery using the most prolific planetary hunter of all time, NASA Kepler Space Telescope. Kepler, who was declared dead last fall, discovered extraterrestrial worlds by the "transit method," noting the tiny drops in brightness caused by the planets that cross the face of their host stars.

Just prior to the publication of the 2012 article, the team had detected a third transit signal in the Kepler data set, said Orosz, who also led the new study. Six months later, Kepler witnessed another transit and the researchers managed to obtain a preliminary orbit for the candidate. exoplanet.

"Knowing the preliminary orbit, we went back in time and looked at Kepler's existing data and found very small transit events," Orosz told Space.com. "In themselves, you would not think that they were a lot, but since they fit the pattern, it became obvious that these were probably from the same planet."

This planet is the new Kepler-47d, which is about 7 times larger than the Earth. This is considerably larger than Kepler-47b and c, which are respectively 3.1 and 4.7 times wider than our planet.

Kepler-47b and c perform a complete round of the circumbinary system every 49 and 303 terrestrial days, respectively. The orbital period of Kepler-47d is 87 Earth days, which means that it is the middle planet. And that was a surprise. the team thought that any additional planet in the system would likely be external to Kepler-47c.

These three extraterrestrial worlds look like nothing in our own backyard, said Orosz: They are much less dense than Saturn, the most bloated planet in our solar system.

Such extreme puffiness is common in the "hot Jupiter" extraterrestrial worlds, which surround their host stars very closely, said the researchers. But this is unusual for relatively temperate planets such as the Kepler-47 trio, whose mean temperature is estimated at minus 26 degrees Fahrenheit (minus 32 degrees Celsius; Kepler-47c), 50 degrees F (Kepler-47d) and 336 F (150 ° C, Kepler-47b).

Two-star systems are often very dynamic, the orbital trajectories of planets moving with time as they are driven back and forth by their two host stars. Indeed, the discovery of Kepler-47d has been facilitated by such a change; the orbital plane of the planet became increasingly aligned with Kepler's field of view, thus increasing the strength of the transit signal.

But such dynamism does not mean that the three Kepler-47 worlds will soon be scattered in the dark depths of interstellar space. After all, they have survived for about 3.5 billion years (assuming all three are native to the system).

And, said Orosz, "based on numerical simulations, it seems like it's a pretty robust system."

The new study, published online today (April 16) in The Astronomical Journal, reinforces two messages to remember from Kepler's pioneering work: that the diversity of exoplanets is incredible and that our solar system is far from typical. (Most of the stars in our Milky Way galaxy are part of the binary systems, after all.)

The document "also supports one of Kepler's most interesting discoveries: compact and compact planet systems are extremely prevalent in our galaxy," said Jonathan Fortney, an astronomer in Santa Cruz, who was not part of the research team. said in the same statement.

"Kepler-47 shows that any process that forms these planets – a result that has not occurred in our solar system – is common to both single-star and circumbinary planetary systems," Fortney added.

Mike Wall's book on the search for extraterrestrial life, "Over there"(Grand Central Publishing, 2018, illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on twitter @Spacedotcom or Facebook.