Could A Two Sun System Support A Habitable Planet Or Moon?
January 11, 2012

Could A Two Sun System Support A Habitable Planet Or Moon?

A team of University of Texas at Arlington (UTA) astrophysicists are suggesting that a habitable Earth-like planet could exist in a distant solar system recently discovered by NASA´s Kepler Space Telescope.

Kepler-16b, a cold, gaseous planet orbiting two stars -- similar to the fictional Tatooine of Star Wars -- in the Kepler-16 system, was discovered by Kepler back in September. Based on the discovery, the UTA team conclude that an Earth-like planet could exist in the system´s ℠habitable zone´ -- particularly as a moon orbiting Kepler-16b.

Billy Quarles, a doctoral student at UTA, and his colleagues presented their findings this week at the annual American Astronomical Society meeting.

In the study they simulated several possible configurations for a theoretical Earth-like world in the Kepler-16 system. They 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.

The team assumed that the brighter of the two stars in the Kepler-16 system is the main source of heat and light for any orbiting worlds. Based on the size and temperature of the star, the team determined that the main habitable zone possible around the stars would extend from 34 million to 66 million miles out.

UTA Department of Physics professor Zdzislaw Musielak said in a press release: “This is an assessment of the possibilities. We´re telling them where a planet has to be in the system to be habitable. We´re hoping they will look there.”

“There is less light from the star, so the planet itself has to maintain more heat,” added Quarles.

But with a circular orbit of roughly 65 million miles from the stars, Kepler-16b is on the outer edge of the habitable zone. And while this “Tatooine-like” planet is uninhabitable, an Earth-like moon in Kepler-16b´s orbit could sustain life, the researchers said.

The group is not ready to say whether a moon could have formed alongside the planet. But their simulations suggest a moon could have arrived later in Kepler-16b´s life. The team´s model suggests a planet within the habitable zone may have been thrown out of orbit due to extreme gravitational forces at work in the system. Kepler-16b´s gravitational pull could have attracted the Earth-like planet during its journey outward, turning it 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 Earth-like atmosphere, the team said.

If astronauts were to discover an Earth-like moon orbiting Kepler-16b, it would be a major first. More than 700 alien planets have been confirmed to exist so far, and Kepler has identified more than 2,000 more potential planets. But no moons have been detected outside our own solar system as of yet.

With the new study, “we can say there are exo-moons 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 planet´s orbit that could be caused by a moon´s gravitational pull -- something Kepler is equipped to do. In fact, a new project using Kepler aims to make the first systematic search for planets with moons. The UTA team´s study suggests Kepler-16b is an ideal candidate for this new project.

In addition to considering the possibility of an Earthlike exo-moon of Kepler-16b, the team considered whether an as-yet undetected Earth-like planet could exist in what they call an extended habitable zone around the Kepler-16 stars.

The results suggest that a planet around 88 million miles from the stars -- outside the orbit of the existing planet -- could maintain a stable orbit.

That theoretical, far-flung world could retain enough heat for liquid water, Quarles said, if it has “a very drastic atmosphere” of heat-trapping gases such as carbon dioxide and methane.

Pamela Jansma, dean of the UTA College of Science, said the University is proud to have the team of researchers selected from scientists across the country to present at the American Astronomical Society meeting.

“This is the type of work that captures the imaginations of students and gets them excited about exploring a career in science. It´s certain to catch the attention of other researchers and spark even more examination,” she said.


Image Caption: NASA's Kepler mission has discovered a world where two suns set over the horizon instead of just one. The planet, called Kepler-16b, is the most "Tatooine-like" planet yet found in our galaxy. Tatooine is the name of Luke Skywalker's home world in the science fiction movie Star Wars. In this case, the planet it not thought to be habitable. It is a cold world, with a gaseous surface, but like Tatooine, it circles two stars. Image credit: NASA/JPL-Caltech/R. Hurt


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