More clues than telluric exoplanets look like Earth

Kepler-186f is the first planet identified on the Earth scale outside the solar system orbiting a star in the habitable zone. This means that it is the right distance from its star host for liquid water to the pool on the surface.

The Georgia Tech study used simulations to analyze and identify the dynamics of the spin axis of the exoplanet. These dynamics determine how much a planet tilts on its axis and how this angle of inclination evolves over time. The axial inclination contributes to the seasons and the climate as it affects how sunlight hits the surface of the planet.

The researchers suggest that the axial tilt of Kepler-186f is very stable, just like the Earth. . The Georgia Tech team thinks it's the same for Kepler-62f, a planet the size of a planet that revolves around a star about 1,200 light-years away. we.

What is the importance of axial inclination for climate? The great variability of the axial tilt could be one of the main reasons that Mars went from an aquatic landscape billions of years ago to the arid desert of today.

"Mars is in the habitable zone of our solar system, but its axial inclination is very unstable, ranging from zero to 60 degrees," said Gongjie Li, an assistant professor at Georgia Tech, who led the study. with graduate student Yutong Shan from the Harvard-Smithsonian Center for Astrophysics. "This instability has likely contributed to the degradation of the Martian atmosphere and the evaporation of surface waters."

For comparison, the axial tilt of the Earth oscillates more moderately between 22.1 and 24.5 degrees, rising from an extreme to

The orientation angle of the orbit of a planet around its host star may be caused to oscillate by gravitational interaction with other planets in the same system. If the orbit oscillated at the same speed as the precession of the axis of rotation of the planet (similar to the circular motion presented by the axis of rotation of a vertex or d & # 39; a gyroscope), the axis of rotation would also flicker, sometimes dramatically. 19659013] Mars and Earth strongly interact with each other, as well as with Mercury and Venus. As a result, alone, their spin axes precede with the same speed as the orbital oscillation, which can cause significant variations in their axial inclination. Fortunately, the moon keeps the Earth's variations in check. The moon increases the precession rate of the axis of rotation of our planet and differentiates it from the orbital oscillation rate. Mars, on the other hand, does not have a satellite large enough to stabilize its axial tilt. "It seems that the two exoplanets are very different from Mars and Earth because they have a weaker connection with their sister planets," said Li, a faculty member at the School of Physics. . "We do not know if they own moons, but our calculations show that even without satellites, the Kepler-186f and 62f spin axes would have remained constant over tens of millions of years."

Kepler-186f is less than 10% larger in radius than the Earth, but its mass, composition and density remain a mystery. It orbits around its star host every 130 days. According to NASA, the brightness of this star at high noon, standing on 186f, would look as bright as the sun just before sunset here on Earth. Kepler-186f is located in the constellation Cygnus as part of a star system of five planets

Kepler-62f was the most Earth-like exoplanet up to that that scientists notice 186f in 2014. It is about 40% larger than our planet. a terrestrial or oceanic world. It's in the constellation Lyra and it's the farthest planet among five exoplanets orbiting a single star.

This does not mean that the exoplanet has water, not to mention life. "Our studies are among the first to study the climate stability of exoplanets and add to the growing understanding of these potentially habitable neighbor worlds," Li said.

"I do not think we understand enough about the origin of life to exclude the possibility of their presence on planets with irregular seasons, "added Shan. "Even on Earth, life is remarkably diverse and has shown incredible resilience in extraordinarily hostile environments." But a climate-stable planet could be a more comfortable place to start. "

The article," Variations in Obliquity of the Living Zone The Kepler 62-f and Kepler 186-f planets, "is published online in The Astronomical Journal.

Learn more:
Orbital variations can trigger "snowball" states in habitable areas around sun-like stars

More information:
Yutong Shan et al. Skew Variations of Living Area Planets Kepler-62f and Kepler-186f, The Astronomical Journal (2018). DOI: 10.3847 / 1538-3881 / aabfd1