Update 1/12: The discovery of two more circumbinary planets (planets orbiting two stars rather than one) suggests that this may be a common phenomenon.
Fans of science fiction movies and books are familiar with planets that are warmed by more than one star. Star Wars fans will be familiar with the two-sunned planet Tatooine, whereas readers will recall that the planet in Isaac Asimov’s Nightfall had six suns. In the real world, each discovered planet has only had one sun. Until now.
NASA’s Kepler space telescope discovered a binary pair of stars that were periodically eclipsing each other from the vantage point of the telescope. More intriguingly, a third object was clearly passing in front of each of the stars at varying intervals. Measurements of the four types of eclipses within the system (star one over star two, star two over star one, the third object over star one and the third object over star two) showed that the third object was indeed a planet orbiting both of the starts.
Three Eclipsing Bodies: This artist's concept illustrates Kepler-16b, the first planet known to definitively orbit two stars -- what's called a circumbinary planet.
Credit: NASA/JPL-Caltech/T. Pyle.
The planet, Kepler-16b, is about the size of Saturn and is not expected to have a surface temperature above negative 100° Fahrenheit despite the fact that it has two suns. This is because each of the stars is considerably smaller than our sun, and the planet orbits them beyond the distance where liquid water can form.
Don’t you love it when science fiction becomes science fact?