For the first time astronomers have detected a planet orbiting a binary star. Since most Sun-like stars form in binary systems, this discovery could possibly increase the number of potentially earthlike planets that might exist in our galaxy. However, though there are more planets in the galaxy than originally thought, Earth’s extensive fine-tuned development requirements indicate that few, if any, exoplanets will support life.
Star Wars fans will remember the remarkable Tatooine sunset scene from A New Hope. After being told he can’t apply for an off-planet academy, Luke Skywalker heads out of the house to ponder his future under the sky. He watches as one Sun-like star follows a much redder star into the horizon. Now scientists have discovered something that makes this science-fiction scenario more believable.
Since its launch in March 2009, the Kepler Mission has used the transit method to detect over 1,000 planetary candidates. Recent analysis of Kepler’s data reveals a planet orbiting around a binary star.1 This discovery confirms a long-standing theory and impacts the search for life in the universe.
Most of the Milky Way Galaxy’s (MWG) Sun-like stars reside in binary systems. Yet, it seemed as though binary stars would not form planets or that the gravitational changes introduced by the binary orbit would destabilize any planets that did form. Either way, one could reasonably conclude that only single stars would host planets. This recent discovery demonstrates that binary systems can host planets and, thus, have the potential to increase the number of earthlike planets in the galaxy. But, a couple of points bear mentioning.
First, this planet is a gas giant with one third the mass of Jupiter, and it orbits two low mass stars with a combined mass less than the Sun. It remains to be seen whether Earth-mass planets can form in such a binary system. But even if an Earth-like planet does exist in a binary system, other issues surface. Low mass stars emit less light so a planet must orbit close to the star to receive enough heat to maintain liquid water. However, the harmful ultraviolet and x-ray radiation from such stars would seriously undermine a planet’s capacity to host life. Similarly, tidal locking would mean the planet would possess no (or a minimal) magnetic field. Thus, the radiation from the star(s) would quickly remove any water from the planet.
Second, assuming an earthlike planet in a binary system does form with liquid water, it seems unlikely to withstand all the changes in star output while maintaining habitability, like Earth did. On Earth, precise changes in the types of life and the types of landforms, as well as the location and amount of land, balanced the Sun’s fluctuating luminosity. Without this exquisite balance, Earth would have ended up like its barren neighbors, Mars and Venus. Unfortunately, the technology to detect the pertinent signatures of balance or imbalance on distant planets lays far in the future.
Although scientists found a planet that experiences two setting suns, the environment in this system ensures that no life witnesses the event. To hear the Science News Flash podcast on this topic, click here.
1. Laurance R. Doyle et al., “Kepler-16: A Transiting Circumbinary Planet,” Science 333 (September 16, 2011): 1602–6.