The Hypothetical Planet Vulcan

Newton’s work in both calculus and the universal Law of Gravitation in the late seventeenth century, provided a means of predicting the movement of all of the planets around the sun.  However, more refined observations and calculations in the mid-eighteenth century revealed a discrepancy between predicted and observed trajectory of Mercury around the sun.  Specifically, the perihelion (the point in the orbit of a celestial body where it is closest to the sun) of Mercury’s orbit was shifting very slightly over time, relative to what Newtonian mechanics would predict (The Planets by Dava Sobel, 2005).

Sir Isaac Newton (1643 – 1727) from

Based on this discrepancy between the observed and predicted orbit of Mercury, the astronomer Urbain J.J. Leverrier suspected that another planet or group of small bodies were the cause, being located somewhere between the sun and Mercury.  Under this proposed scenario Mercury would not longer be the planet closest to the sun.  Leverrier called this unknown planet Vulcan.

Urbain J.J. Leverrier (from

Leverrier announced in September 1859 that Vulcan would explain this discrepancy in the orbit of Mercury and that it would be about the same size as Mercury but at half the distance from the sun (The History of Astronomy: A Very Short Introduction by Michael Hoskin; 2003).  From 1859 and on the hunt was on to find Vulcan.  For over 50 years various astronomers, both professional and amateur, claimed to have identified Vulcan but such observations were never confirmed by the scientific community.  Serous attempts to identify Vulcan during solar eclipses in 1860 and 1869 were made but with no success (The Planets by Dava Sobel, 2005).

A proposed view of what the surface of the planet Vulcan would look like (by Nethskie)

HPL mentioned the search for and unlikely existence of Vulcan in a number of his astronomical articles.  In a short article, Does “Vulcan” Exist?, HPL presented both sides of the augment for the existence of Vulcan but comes to the conclusion that more than likely Mercury is still closest to the sun (Collected Essays: Science, Volume 3 by S.T. Joshi; 2005).

In another article, originally written for the Pawtuxet Valley Gleaner in October 1906, HPL mentioned that several professors from Ann Arbor, Michigan claimed to have identified Vulcan and another “intra-Mercurial body” during an eclipse in 1878.  However, as HPL points out, both bodies turned out to be well-known stars (Collected Essays: Science, Volume 3 by S.T. Joshi; 2005).

The hypothetical world of Vulcan (

What put the debate on the existence of Vulcan to an end was Albert Einstein’s General Theory of Relativity.  Essentially, Einstein stated that space itself is warped by gravity so the larger the gravitational field, the larger the warp.  Turns out, applying General Relativity to the orbit of Mercury explains the observed deviation from Newtonian mechanics.  Even Einstein was pleasantly surprised over these results.  In a letter to a colleague he wrote, “Can you imagine my joy, that the equations of the perihelion movement of Mercury prove correct?  I was speechless for several days with excitement.” (The Planets by Dava Sobel, 2005).

I am sure HPL knew of Einstein’s work and how it contributed to disproving the existence of Vulcan since he did not mention planet in his fiction or any of his scientific essays after 1906, other than a passing reference of it not existing.  Thus, around 1915, the idea of the planet Vulcan blipped out of existence much like the planet Vulcan did in J.J. Abrams’s movie Star Trek (2009) when a black hole was created inside of that world.

Next time we will be talking about a world that does exist – the planet Venus.  HPL referred to Venus quite a bit and in fact one of his stories occurs on that planet.  Thank you.  Fred.

The destruction of the planet Vulcan in J.J. Abrams’s movie Star Trek (2009;




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