“A new planet found last fall may be orbiting two stars, but it's far from a real-life Tatooine. Dubbed Kepler-16b, the world is a cold, Saturn-size gas giant with little chance of hosting desert farmers like the fictional Star Wars world.
But according to new computer simulations, the Kepler-16 stars may still shine on a world fit for life—a hypothetical Earthlike moon orbiting Kepler-16b.
Kepler-16b was discovered by NASA's Kepler spacecraft, which looks for dips in starlight as a planet transits—or passes in front of—a star, as seen from Earth.
For the new study, Billy Quarles, a doctoral student at the University of Texas at Arlington, and colleagues simulated several possible configurations for a theoretical Earth-mass world in the Kepler-16 system.
The team started by drawing up a "laundry list of parameters" for defining the habitable zone—the region around a star where a planet gets enough heat to host liquid water, essential for life as we know it—Quarles said Monday during ameeting of the American Astronomical Society in Austin, Texas.
The researchers assumed that the brighter of the two Kepler-16 stars is the main source of heat and light for any orbiting worlds.
Based on that star's size and temperature, the team determined that the main habitable zone possible around the Kepler-16 stars would extend from about 34 million to 66 million miles (55 to 106 million kilometers) out.
Capturing a Habitable Moon
With a roughly circular orbit about 65 million miles from the stars, the Saturn-like planet is on the outer edge of this main habitable zone. And while this "Tatooine" is uninhabitable, an Earthlike moon in Kepler-16b's orbit could sustain life, the researchers said.
The group isn't yet ready to say whether a moon could have formed alongside the planet. But their simulations suggest a moon could have arrived, fully formed, later in Kepler-16b's life.
According to the new models, a planet closer to the brighter star, squarely in the habitable zone, could have long ago been ejected from its orbit due to gravitational interactions with the other objects in the system.
Kepler-16b's gravitational pull could have attracted the Earthlike planet during its journey outward, turning the world from planet to moon.
Such a moon would technically be in the main habitable zone of the Kepler-16 system and—unlike Mars, on the outer edge of the habitable zone in our solar system—the moon would be massive enough to retain an Earthlike atmosphere, the team said.
First to Find an Alien Moon?
If astronomers were to discover an Earthlike satellite orbiting Kepler-16b—a bigif—it would be a major first.
More than 700 alien planets have been confirmed so far, and Kepler has identified more than 2,000 more potential planets.
As of yet, though, no moons have been detected outside our solar system.
With the new study, "we can say there are exomoons possible around Kepler-16b, and what's important about this is that they are detectable ... down to 0.2 Earth masses," Quarles said.
To do so would require looking for subtle irregularities in the gas giant's orbit that could be caused by a moon's gravitational pull—something Kepler is equipped to do…”