Just last week, the National Aeronautics and Space Administration (NASA) announced the discovery of the first Earth-sized planet we’ve found that may be habitable. Specifically, the planet is called Kepler-186f and it’s thought to be potentially habitable because it’s within the “habitable zone” of its solar system, or just the right distance from the star it orbits (like our sun) that it’s possible to have liquid water on its surface.
While planets have been previously found in the habitable zone, none have been so close to Earth in size as Kepler-186f. This newly discovered planet is only about 10% larger than Earth, while most habitable zone planets are about 40% larger than our planet. Kepler-186f is also suspected to be rocky, although its exact mass and density aren’t yet known. However, there are some clear differences between Earth and Kepler-186f that may affect whether it is indeed habitable — and has evolved life.
The biggest difference between Earth and Kepler-186f may be the star that they orbit. Kepler-186f’s star is only half the size of our sun and is much cooler. (Its star is technically a red dwarf, which is what most stars are in our galaxy, while our sun is a yellow dwarf, and is thought to be brighter than most stars in our galaxy.) Because of this and other factors, Kepler-186f only receives about one-third the amount of energy from its star that the Earth does from our sun. For example, when it’s high noon somewhere on Kepler-186f, the star’s brightness is equivalent to what we’d see an hour before sunset. But the temperature of the planet is also significantly controlled by its atmosphere, which is currently unknown.
Kepler-186f itself is in the constellation Cygnus, in the Kepler-186 star system, about 500 light-years from us. There are five planets in its system, and Kepler-186f is the one furthest from its star. (The other four planets, Kepler-186b – Kepler-186e, get too hot to be within the habitable zone.) It completes a full rotation around its star every 130 days, giving it a much shorter seasonal year. Although we won’t be visiting Kepler-186f any time soon, we can continue to learn more about it to not only better determine whether conditions truly are right for it to be habitable, but also to understand what it means to be “habitable” and just how common this feature is in our galaxy.
So while many stars can be seen in a clear night sky, this discovery is a good reminder of just how challenging it actually is to find another place like our home. Best not to take it for granted!
For further reading:
- NASA’s article “Kepler Discovers First Earth-Size Planet in the ‘Habitable Zone’ of Another Star”
- Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre
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