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.