It's been over 20 years since the first planet orbiting a Sun-like star outside our solar system was discovered, and at last count the grand total stands at 3,268. Unfortunately, only a handful of exoplanets orbit within the habitable zone around their stars. A team of astronomers has set their sights on one such exoplanet, and through computer simulations determined that it could harbor a rocky composition, oceans and, potentially, even life.
Kepler-62f was discovered in 2013 by the Kepler telescope, which was launched in 2009 and is responsible for identifying 2,325 exoplanets to date. Kepler-62f is approximately 1,200 light-years away from us, about 40 percent larger than Earth and orbits its parent star within the habitable zone, where conditions may be just right for liquid water to form.
The study, led by Aomawa Shields of the University of California, Los Angeles (UCLA) physics and astronomy department, ran computer simulations testing different combinations of orbit and atmosphere possibilities. They tested different thicknesses of the exoplanet's atmosphere, from exactly the same as Earth's up to 12 times thicker, and different concentrations of carbon dioxide in the air, up to 2,500 times more than Earth levels. In many of these scenarios, the team found that the planet could be habitable.
"We found there are multiple atmospheric compositions that allow it to be warm enough to have surface liquid water," says Shields. "This makes it a strong candidate for a habitable planet."
According to the study's lead author, in order for the exoplanet to be habitable throughout its year, Kepler-62f would need to have an atmosphere made up entirely of carbon dioxide, and for it to be three to five times thicker than our home planet's. At the distance the planet orbits its star, Shields says, it would need carbon dioxide to build up in its atmosphere at these levels in order to keep warm.
"But if it doesn't have a mechanism to generate lots of carbon dioxide in its atmosphere to keep temperatures warm, and all it had was an Earth-like amount of carbon dioxide, certain orbital configurations could allow Kepler-62f's surface temperatures to temporarily get above freezing during a portion of its year," Shields explains. "And this might help melt ice sheets formed at other times in the planet's orbit."
The orbital path possibilities were calculated using a computer model called HNBody, and its climate was simulated using the Community Climate System Model and the Laboratoire de Meteorologie Dynamique Generic model. This was the first time the results of these two types of models were combined to study an exoplanet.
The technique could be applied to other exoplanets to determine the likelihood of their habitability, where more solid data is yet to be collected by telescopes.
"It will allow us to generate a prioritized list of targets to follow up on more closely with the next generation of telescopes that can look for the atmospheric fingerprints of life on another world," says Shield.
The research was published in the journal Astrobiology.