Just how Earth-like can an exoplanet be? A new study provides clues as to how two known exoplanets might have a similar axial tilt to Earth and therefore might also have regular seasons and relatively stable climates just like Earth.

Kepler-186f And Kepler-62f

Kepler-186f is an exoplanet outside the solar system that, just like Earth, is at its solar system’s habitable zone. Before it was discovered in 2014, another exoplanet, Keplet-62f, was considered the most Earth-like planet. Both planets are just at the right distance from their host stars to have water on the surface, placing them at the same zone that has allowed life to flourish on Earth.

A new study adds clues as to how these two exoplanets might be more Earth-like than previously thought, as researchers surmise that their axial tilts may also be similar to the Earth’s. By running simulations to determine the exoplanets’ spin axis dynamics, researchers of the study determined that Kepler-186f’s axial tilt is quite stable just like Earth’s, and they believe the case is also the same for Kepler-62f.

Compared to Mars, which is also in the habitable zone but whose axis is rather unstable and may vary from 0 to 60 degrees, the Earth’s axial tilt moves rather mildly between 22.1 and 24.5 degrees thanks to the moon that stabilizes its axial tilt. Though researchers do not yet know if Kepler-186f or Kepler-62f have satellites just like Earth, their calculations show that even without it, both exoplanets’ spin axes remained constant for tens of millions of years.

Why Is This Important?

As shown in our own solar system, being in the habitable zone is evidently not enough for a planet to be the perfect host to life. As mentioned, Mars is also in the habitable zone just like the Earth, but its lack of a stable-enough axis tilt may have caused it to be less than habitable. In fact, researchers believe that this may even have contributed to the decay of the planet’s atmosphere and the evaporation of its surface water.

Results of the new study could mean that the exoplanets may have stable climates and regular seasons. Naturally, researchers are not saying that either planet is host to life or harbors water, but researchers surmise that they are both rather good candidates in the search for life outside the Earth.

“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,” said Yutong Shan of Harvard-Smithsonian Center for Astrophysics, coauthor of the study.

The study is published in The Astronomical Journal.