Fans of Star Wars might remember watching a moody Luke Skywalker gaze at a double sunset on his home planet of Tatooine. It turns out that planets with two suns probably are more common than once thought. Scientists recently discovered the tenth such planet. And they say it adds to evidence that such planets may be more common than single-sun ones like Earth.
Scientists have known for a long time that most stars come as pairs or multiples. They wondered if these multi-star systems might also host planets. After the Kepler space telescope was launched in 2009, astronomers finally had the tools to search for these among exoplanets. Those are worlds outside Earth’s solar system.
The newfound exoplanet, Kepler-453b, is 1,400 light-years from Earth. It orbits in a two-sun — or binary — system. Planets in such a system are called “circumbinary” for the fact that they circumnavigate both stars.
Astronomers discovered Kepler-453b while watching two stars that were orbiting each other. Sometimes light coming from the stars dimmed a bit.
“That decrease has to be because of something going in front of the stars,” explains Nader Haghighipour. He’s an astronomer at the University of Hawaii at Manoa. He was one of the authors of an August 5 paper about the planet’s discovery in Astrophysical Journal.
He shared detailed of this planet and star system on August 14 at the International Astronomical Union General Assembly in Honolulu, Hawaii. And something was unusual about the new circumbinary planet. Of the other nine such planets known, eight orbit on the same plane as their stars. That means they pass in front of both stars every time they make a complete orbit. But the new planet’s orbit is tilted a small bit compared to the orbit of its suns. As a result, Kepler-453b only passes in front of its stars about 9 percent of the time.
|ONE SUN, TWO SUN In the Kepler-453 system, two stars (black dots) orbit in the center, and the planet Kepler-453b (white dot) orbits both suns.UH MAGAZINE|
“We were really lucky,” says Haghighipour. If his team hadn’t been watching the stars at just the right moment, the scientists would have missed the telltale dip in light that signaled the presence of this planet.
That they found this planet at all — the second circumbinary planet with such an off-plane orbit — probably means that they’re incredibly common, the astronomers say. Indeed, Haghighipour adds, “We realized there must be many other systems that we’re missing.”
After all, if a planet’s orbit never allows it to pass between Earth and its stars, no telltale dip in starlight will ever point to the planet’s existence. The next step will be for astronomers to figure out how to detect these types of planets. Haghighipour thinks its possible. If the planet is big enough, its gravity will affect its stars’ orbits. Astronomers could search for those tiny, telltale wobbles.