Here Come the Earths!

These are truly exciting times, not only for astronomers, but also for Star Trek fans, especially those with an eye on the list of planets we have encountered in the over 1000 hours of Star Trek. Anyone interested in such a list should head over to Memory Alpha, where they keep a rather detailed collection. Of course, being that these planets are all places of activity in our stories, they are almost all of a nature allowing physical beings (humans and others) to move on their surfaces. They may or may not be M-class planets, i.e. able to support life requiring liquid water, but the stories would imply that most of them are in fact in that category.

Why the excitement? As little as two years ago the only planets found outside of our own Solar System were big ones, Neptune-sized gas giants and larger. A few were in systems with multiple planets, but most were singletons. With improved instrumentation astronomers are now able to look for and detect smaller worlds. First it was “super-Earths,” but now we can see Earth-sized planets in orbits around other stars.

At the American Astronomical Society meeting two weeks ago, the folks from the Kepler mission had some astounding announcements. In their catalog of planet candidates, they have added 461 planets, four of which are less than twice the size of Earth and do orbit in the habitable zone around their primary star. Altogether, they have 2740 planet candidates orbiting 2036 stars, which implies plenty of multiple planet systems. Of these candidates, 350 are Earth-sized (but not necessarily in the habitable zone). It is now believed that at least one in six stars has an Earth-like planet, and most Sun-like stars have planetary systems.

The method by which these planets are detected is called a transit. We wait until the planet crosses its star from our point of view, which slightly diminishes the light we receive from the star. Knowing the type of star, we can figure out the size of the planet and its orbit by how much the light diminishes and by the time that passes between transits. This method requires great precision, which fortunately the Kepler spacecraft can provide. Given that it takes less time to see planets orbiting closer to their star (more frequent transits), most of the Earth candidates found so far are rather close in (Mercury’s orbit or closer). As time goes on we’ll find more of those further out.

Two Earth-sized Kepler planets, unfortunately much closer to the star than the habitable zone.

Meanwhile, there are other teams also looking for Earths. Astronomers with the European Southern Observatory (ESO) have found a roughly Earth-sized planet around Alpha Centauri B. Alpha Centauri was Zefram Cochrane’s home system in the TOS episode “Metamorphosis”! The Alpha Centauri system was also mentioned in DS9’s "Field of Fire", as well as in TNG’s "Qpid" and ENT’s "Twilight." In Star Trek’s time there will be a colony with a university over there.

A planet roughly Earth-size orbits Alpha Centauri B, alas not in the habitable zone, but much closer and incredibly hot (image from ESO).

What a change! Follow-up observations of these various systems will confirm the planets, at which point they will be listed in the Extrasolar Encyclopedia, which as of a week ago has 859 confirmed planet observations. I can’t wait to see more Earths in orbits closer to ours. I think that within the next ten years we will find many Earth-sized planets in the habitable zones of other solar systems. We will need to expand our search beyond the patch of the Galaxy that Kepler is looking at, but I believe and hope that we will be able to check off many of the stars from our Star Trek chart of worlds one by one and say “Yep, here’s another one.” Who knows, maybe someone will write stories incorporating the newly found Earths into our Star Trek collection of planets. 

Until then, good hunting!

Planets found to date range from Earths to super-Jupiters.

The sizes of the planet candidates so far.


Kepler-22b is in the habitable zone of its primary, but about 2.4 times the size of Earth.

(These last three images are from the Kepler mission and NASA.)

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

The Extrasolar Planets Encyclopedia (all the details on all extrasolar planets confirmed so far):

The Kepler Mission (NASA website):

A poster of planet candidates:

Memory Alpha Star Trek Planet List:

Inge Heyer

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Inge Heyer
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