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Planets orbiting double-star systems could support life, study suggests

This artist's illustration shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B. A new study suggests planets orbiting double-star systems could support life if located at the right distance from its host stars. Image Credit: NASA / JPL-Caltech

This artist’s illustration shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B. A new study suggests planets orbiting double-star systems could support life if located at the right distance from its host stars. Image Credit: NASA / JPL-Caltech

When NASA’s Kepler spacecraft first discovered a planet that orbited two stars, comparisons were made to Luke Skywalker’s desert home planet Tatooine in the Star Wars movies.

A NASA "travel poster" for Kepler-16b, an exoplanet that orbits two stars. Image Credit: NASA

A NASA “travel poster” for Kepler-16b, an exoplanet that orbits two stars. Image Credit: NASA

So far, the only planets discovered in two-star systems have been Saturn-sized gas giants which are unlikely to be capable of supporting life. However, scientists wondered if a planet the size of Earth could be habitable if it orbited two suns. According to a new study published in the journal Nature Communications, such a planet could potentially support life if located at the right distance from its two stars.

“This means that double-star systems of the type studied here are excellent candidates to host habitable planets, despite the large variations in the amount of starlight hypothetical planets in such a system would receive,” said Max Popp, associate research scholar at Princeton University in New Jersey, and the Max Planck Institute of Meteorology in Hamburg, Germany.

Popp and Siegfried Eggl, a Caltech postdoctoral scholar at NASA’s Jet Propulsion Laboratory (JPL), created a model for a planet in the Kepler 35 system. In reality, the system’s twin stars Kepler 35A and B host a giant planet about eight times larger than Earth, called Kepler 35b.

For their study, the team removed the gravitational influence of this giant world and added a hypothetical water-covered, Earth-size planet orbiting around the two stars. They studied how the climate of this planet might behave as it orbited the host stars with periods between 341 and 380 days.

“Our research is motivated by the fact that searching for potentially habitable planets requires a lot of effort, so it is good to know in advance where to look,” Eggl said. “We show that it’s worth targeting double-star systems.”

Whether an exoplanet orbits its home star within the “habitable zone” – the range of distances where a rocky planet is likely to have liquid water on its surface – is a key factor in determining its potential to support life. In the case of a binary system like Kepler 35, where the two stars orbit each other, the habitable zone is determined by the distance from the center of mass that both stars are orbiting.

To make matters even more complicated, a planet orbiting two stars would not travel in a circle. Rather, its orbit would wobble due to the gravitational interaction of the two stars.

The researchers found that on the far edge of the habitable zone in the Kepler 35 system, a hypothetical water-covered planet would have a lot of variation in its surface temperatures. Because such a cold planet would have a small amount of water vapor in its atmosphere, global average surface temperatures would vary over the course of a year by as much as 3.6 degrees Fahrenheit (2 degrees Celsius).

“This is analogous to how, on Earth, in arid climates like deserts, we experience huge temperature variations from day to night,” Eggl said. “The amount of water in the air makes a big difference.”

On the inner edge of the habitable zone, the global average temperatures on the planet would stay almost constant. This is because more water vapor would stay in the hypothetical planet’s atmosphere to act as a buffer.

Another feature of the study’s results is, compared to Earth, a planet orbiting two stars would have less cloud coverage. This would cause clearer skies for viewing double sunsets on these exotic worlds.

Video courtesy of NASA

 

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Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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