We Have More Evidence That Two Earth-Like Exoplanets Have Stable Climates And Seasons Just Like Us


Two exoplanets thought to be similar to Earth apparently are, at least when it comes to climate, researc†Kepler-186f is the first identified Earth-sized planet outside the solar system orbiting a star in the habitable zone. This means it’s the proper distance from its host star for liquid water to pool on the surface.


The study, which appears in the Astronomical Journal, used simulations to analyze and identify the exoplanet’s spin axis dynamics.


Researchers suggest that Kepler-186f’s axial tilt is very stable, much like the Earth, making it likely that it has regular seasons and a stable climate. Further, they think the same is true for Kepler-62f, a super-Earth-sized planet orbiting around a star about 1,200 light-years away from us.

Unstable Mars

How important is axial tilt for climate? Large variability in axial tilt could be a key reason why Mars transformed from a watery landscape billions of years ago to today’s barren desert, the researchers say.

“Mars is in the habitable zone in our solar system, but its axial tilt has been very unstable—varying from zero to 60 degrees,” says Gongjie Li, assistant professor of physics at Georgia Institute of Technology, who led the study together with graduate student Yutong Shan from the Harvard-Smithsonian Center for Astrophysics.



As a comparison, Earth’s axial tilt oscillates more mildly—between 22.1 and 24.5 degrees, going from one extreme to the other every 10,000 or so years.

The orientation angle of a planet’s orbit around its host star can be made to oscillate by gravitational interaction with other planets in the same system. If the orbit were to oscillate at the same speed as the precession of the planet’s spin axis (akin to the circular motion exhibited by the rotation axis of a top or gyroscope), the spin axis would also wobble back and forth, sometimes dramatically.


What about moons?

Fortunately, the moon keeps Earth’s variations in check. The moon increases our planet’s spin axis precession rate and makes it differ from the orbital oscillation rate. Mars, on the other hand, doesn’t have a large enough satellite to stabilize its axial tilt.

“It appears that both exoplanets are very different from Mars and the Earth because they have a weaker connection with their sibling planets,” Li says.






Kepler-62f was the most Earth-like exoplanet until scientists noticed 186f in 2014. It’s about 40 percent larger than our planet and is likely a terrestrial or ocean-covered world.



“Our study is among the first to investigate climate stability of exoplanets and adds to the growing understanding of these potentially habitable nearby worlds,” Li says.


“I don’t think we understand enough about the origin of life to rule out the possibility of their presence on planets with irregular seasons,” Shan says. “Even on Earth, life is remarkably diverse and has shown incredible resilience in extraordinarily hostile environments.

“But a climatically stable planet might be a more comfortable place to start.”

The research has been published in the Astronomical Journal

Source: Georgia Tech 



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