Thirty years ago, three astronomers and Gene Roddenberry, of Star Trek fame, made the case to Sky & Telescope readers that the orange-hued star 40 Eridani A ought to host Vulcan, Spock's home. Now, a robotic survey has discovered a planet around that very star.

Art: A super-Earth we could call Vulcan
An artist's illustration of the super-Earth orbiting 40 Eridani A, the host star of the fictional Vulcan.
Don Davis

Almost three decades ago, Gene Roddenberry (producer of the Star Trek universe) wrote a letter to Sky & Telescope, along with Harvard-Smithsonian Center for Astrophysics astronomers Sallie Baliunas, Robert Donahue, and George Nassiopoulos. In their Letter to the Editor, they argued that 40 Eridani A — an orange-ish star 16 light-years away — would make the ideal home for Vulcan, the home planet of Science Officer Mr. Spock.

Now, a new discovery puts a little more science into that science fiction assertion.

A Long-ago Letter

In the July 1991 issue, the three astronomers and one movie-maker made the case for what star should be considered Vulcan's home:

The star around which Vulcan orbits was never identified in the original series or in any of the feature films based on it and so has never been officially established. But two candidates have been suggested in related literature.

Two Star Trek books named the star 40 Eridani A as Vulcan's sun, while another publication named Epsilon Eridani instead. However, Roddenberry and the astronomers made an argument for 40 Eridani A:

We prefer the identification of 40 Eridani as Vulcan's Sun because of what we have learned about both stars at Mount Wilson. . . . The HK [Project] observations suggest that 40 Eridani is 4 billion years old, about the same age as the Sun. In contrast Epsilon Eridani is barely 1 billion years old.

Based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria. On the other hand, an intelligent civilization could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun. . . . Presumably Vulcan orbits the primary star, an orange main-sequence dwarf of spectral type K1. . . . Two companion stars — a 9th magnitude white dwarf and an 11th magnitude red dwarf — orbit each other about 400 astronomical units from the primary. They would gleam brilliantly in the Vulcan sky.

Dharma Discovery

It turns out the letter authors' prediction was right — a world really does orbit the primary star of the three-star 40 Eridani system. (Whether it's home to a logic-based alien society, though, is anyone's guess!)

The world is a super-Earth, the most common type of planet in the galaxy (though a type that's missing from our solar system). At twice Earth's radius and eight to nine times its mass, 40 Eridani b sits on the line that divides rocky super-Earths from gaseous ones. The planet orbits its star every 42 days, putting just inside the system's habitable zone — in other words, where it's nice and hot. At 16 light-years away, it's the closest super-Earth known and therefore a good potential target for followup observations.

The discovery comes courtesy of the Dharma Planet Survey, designed to detect and characterize low-mass planets around bright, nearby stars. Started in 2016 and continuing until 2020, this survey uses a robotic 50-inch telescope on Mount Lemmon to look for planet-induced wobbles in 150 bright stars within 160 light-years of Earth. The spectrograph attached to the scope can measure radial velocities down to 1 meter per second, which enables it to find low-mass planets around these nearby stars.

The discovery will appear in the Monthly Notices of the Royal Astronomical Society. Read the preprint here.


Image of Anthony Barreiro

Anthony Barreiro

September 17, 2018 at 2:34 pm

"Fascinating." If Vulcan is a super-Earth, the high surface gravity of Mr. Spock's home planet could explain his superhuman strength when he goes amok. But I feel sorry for his poor human mother!

Who found the connection between this newly discovered exoplanet and a 27-year-old letter to the editor? That's a great hook for a story.

Leaving the Star Trek universe and coming back to ours for a minute, I hope this nearby super-Earth will help planetary scientists better characterize this class of planets. Are they really just bigger versions of Earth, or something different?

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Monica Young

September 17, 2018 at 4:35 pm

Anthony, I have to give the University of Florida's press office credit for the hook, I might not have known about Gene Roddenberry's letter to the editor otherwise! Hopefully having a super-Earth so nearby will make it easier to answer the interesting questions these planets raise!

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Anthony Barreiro

September 17, 2018 at 7:39 pm

Thanks! Well done, University of Florida publicist.

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Howard Ritter

September 21, 2018 at 4:38 pm

When I was just a mere lad in the Star Fleet Academy Junior ROTC (i.e., the late 1950s and early '60s), Tau Ceti and Epsilon Eridani were the go-to staples for SF writers looking for a likely home for aliens. Evidently a better understanding of astrophysics and better measurements or more extensive surveys have pegged Epsilon Eridani's age at a youthful 1 billion years, in all likelihood inadequate for intelligent life to have evolved. But how was its age estimated? It's a main-sequence K2 star of luminosity class V, a dwarf like the Sun, of about 0.7 solar mass. This means it will eventually spend about 30 billion years on the main sequence. I understand how the age of a cluster of contemporaneous stars can be estimated from the cluster's H-R diagram, but how is the age of an individual main-sequence star determined? Estimated from its rotation rate?

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September 26, 2018 at 12:43 pm

I did some digging and found a paper published in Astronomy and Astrophysics that examines the Epsilon Eridani system, and mentions within it different methods they have found in the literature of age determination. Not sure this will work, but a link I used was:

The title of the paper is "A comprehensive examination of the Eps Eri system -- Verification of a 4 micron narrow-band high-contrast imaging approach for planet searches", by Markus Janson, Sabine Reffert, Wolfgang Brandner, Thomas Henning, Rainer Lenzen, Stefan Hippler, submitted July 2, 2008. They conclude an age of less than a billion years and give reasons why in section 5.3 of the paper.

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