About how many Earth days does Kepler-186f take to orbit its star?

Kepler-186f takes about 129.9 Earth days to complete one orbit around its star. That relatively short year results from its orbit around Kepler-186, a cool red dwarf that is much dimmer and less massive than the Sun.

NASA’s Kepler space telescope discovered Kepler-186f by the transit method, measuring the slight dip in starlight produced when the planet crossed its star. Announced in 2014, it was the first roughly Earth-sized planet found in the habitable zone of another star. Kepler-186f is the outermost of five known planets in the system and lies about 0.43 astronomical units from its host star.

The number is easy to confuse with the planet’s distance or with the 24.7-day period associated with LHS 1140 b. Kepler-186f’s 129.9-day orbit does not prove that it is habitable: its atmosphere, surface conditions, and presence of liquid water remain unknown. Because its red-dwarf star produces only about 5% of the Sun’s luminosity, the planet can receive temperate levels of energy despite orbiting much closer than Earth does to the Sun.