Bathing in the Sunset of an 'Earth-Like' Alien World

Could a sunset on Kepler-186f look like this? Continue reading →

One of the most important things we can do in the wake of discovering an exoplanet with characteristics similar to that of Earth is to visualize what that world may look like up-close. Often scientists and artists need to use a little artistic license to achieve this feat, but if the visualization is based on real data, the result can be eerily beautiful.

In the above rendering, scientists at the Planetary Habitability Laboratory (PHL) at the University of Puerto Rico at Arecibo have rendered a very familiar scene here on Earth but used real data from the recently identified "habitable" exoplanet Kepler-186f.

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As described by Abel Mendez Torres, planetary scientist and PHL director, Kepler-186f orbits an M-dwarf, a star that is smaller and cooler than our sun. As a result, the habitable zone - the region surrounding a star where the temperature is "just right" for liquid water to persist on a planetary surface - is much closer to the star than our sun's habitable zone.

In fact, Kepler-186f receives only 32 percent of the stellar flux (i.e. sunlight) that we receive on Earth. As a comparison, Mars receives 43 percent of the stellar flux that Earth receives. This means Kepler-186f will be dimmer than Mars. As we all know, Mars is a freezing place with little atmosphere, but if Kepler-186f has a thicker atmosphere than Earth, then perhaps it can incubate liquid water on its surface.

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This "Earth-like"* world is 10 percent larger than Earth, so depending on its mass Kepler-186f could indeed support an atmosphere that is many times the density of Mars' (and indeed Earth's) modern day atmosphere.

With this in mind, the sunsets on Kepler-186f could be breathtaking. As the planet orbits its star in a very compact orbit (completing one "year" in 130 Earth days) and the M-dwarf generates less energy than our sun, the planet's star Kepler-186 will appear bigger in the evening sky. Starlight will already be shifted toward the red end of the visual light spectrum and, depending on atmospheric composition, would produce a blood-red sunset.

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It's worth keeping in mind that many assumptions are made in this rendering; we don't know if Kepler-186f even has an atmosphere, let alone if it can support liquid water oceans (or even if water exists on its surface). But should the conditions be right, this could be the first bona fide "Earth-like" exoplanet, a world that will no doubt be the focus of extensive follow-up studies in the hope of revealing more of its planetary characteristics.

*Note: "Earth-like" is a misnomer. Although Kepler-186f is of the approximate size of Earth and is located within its star's habitable zone, nothing is so far known about it's atmospheric composition (if it even has an atmosphere), whether or not it's even a rocky world (although scientists are fairly positive that it is), or if it even hosts water. This world is just as likely a frozen and barren planet like Mars or a hellish pressure cooker planet like Venus.

Source: University of Puerto Rico at Arecibo / PHL

A simulated comparison of sunset on Earth (left) and Kepler-186f using real planetary data.