Last Thursday, the folks from NASA’s Kepler Mission had a very exciting announcement. They found a planet the size of Earth in the habitable zone around its star. Are we ready to dial long distance to see who answers? Not so fast…

In the ongoing quest to find planets like Earth around other stars, we have come a long way in only about 25 years. At first we needed to develop the technology to see any planets around faraway stars at all; then came the challenge to find the small ones. Being small is not enough though, the planets need to be at the right distance from their star to have liquid water at least part of their year, which is the definition of being in the habitable zone.

Until now we’ve found Earth-sized planets, but not at the right distance. We’ve found planets in the habitable zone, but not of the right size. And we’ve even found planets with water, but not at the right temperature for said water to be liquid.

Figure 1: Kepler-186f (artist concept, Credit: NASA Ames/SETI Institute/JPL-Caltech).

Finally we have two of the conditions in one planet at the same time. Kepler-186f is the right size and at the right distance from its star to have liquid water. With Kepler’s instrumentation, they could figure out the size of this planet, but not its mass or composition. Given the size, however, it is most likely a rocky world, much like our terrestrial planets. If it has more iron it’ll be denser and therefore more massive for its size, if it has more ices it’ll be less dense and less massive.

The Kepler-186 system has five planets (that we know of so far). The first four are further inward and therefore much hotter, but the fifth one is the one in question here. The star hosting this system is much smaller and dimmer than our Sun, it is a red dwarf. It is about half the size of our Sun, and provides about a third of the energy. Therefore it is not surprising that the year of this Earth-like planet is only 130 of our days. In order to be at the right temperature, the habitable zone around a star giving off much less energy that our Sun would have to be further inward.

Figure 2: Habitable zones around stars of different sizes and temperatures (Credit: NASA Ames/SETI Institute/JPL-Caltech).

Figure 3: Comparison of Earth and Kepler-186f in their respective systems (Credit: NASA Ames/SETI Institute/JPL-Caltech).

Stars are born in interstellar clouds of gas and dust. They are born not singly but in clusters, and in such clusters you’ll have a few really massive ones (blue giants), many more mid-sized ones (like our Sun), and loads of little ones (red dwarfs). In our Milky Way Galaxy, 70% of the stars are red dwarfs. Since these stars are smaller, the transit of planets across their surfaces (from our point of view) will take much less time, so it would be much easier and faster to confirm the presence of planets. There happen to be a lot of these red dwarfs in our solar neighborhood.

Life on our Earth is most sensitive to the visual range of light (400-800 nanometers), since that’s the kind of light our Sun gives off most. If there is indeed life on this newly discovered world, this life would see things differently from us. It would see a red sun at all times. Since the peak energy output of this star would be in the infrared, these life forms would evolve to be most sensitive to infrared.

The Kepler-186 system is about 500 light-years away from Earth in the constellation of Cygnus, and, as it turns out, about as far from us as the Omega Cygni multiple star system, which in the Star Trek universe is located between the Tholian Assembly and Romulus. In 2269 Harry Mudd will try to sell the locals their own ocean (TAS: "Mudd's Passion"). Let’s try to keep Harry Mudd away from this new world, whether or not it turns out to even have any oceans.

Figure 4: Location of Omega Cygni (second cube from the left on the bottom; image from Memory Alpha).

But we are getting a bit ahead of ourselves. The next step in the investigation will be to see if it actually has any water. If it does, then we should examine a possible atmosphere for byproducts of photosynthesis. We shall see what develops. You can be sure that I will follow news of this world very closely.

Here are a few links for you if you’d like to know more about this topic.

The Kepler Mission:

The Kepler-186f discovery announcement:

NASA’s Kepler-186f discovery announcement:

NASA Ames (home of the Kepler mission):

SETI Institute:

Memory Alpha:

Inge Heyer


Inge Heyer is an avid Star Trek fan and frequent convention guest. After earning a BA in physics and astronomy, Heyer obtained a master's degree in astronomy at the University of Hawaii. As a senior data analyst at  the Space Telescope Science Institute in Baltimore, she worked on images received from the the Hubble Space Telescope's Wide-Field and Planetary Camera 2. Following this she led the outreach education efforts for the Joint Astronomy Centre in Hawaii. More recently, she has obtained her doctorate in Science Education from the University of Wyoming, and is now a visiting assistant professor in astronomy and physics at Loyola University Maryland.


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