The Ghost Planet
The planet Vulcan? Hey, wasn't that just a made-up planet Gene Roddenberry created for Star Trek? Not at all, gentle reader. For a period of many years in the late nineteenth century, some, if not all, of the world’s astronomer’s believed in the existence of a planet Vulcan that orbited the Sun inside the orbit of Mercury. Vulcan was actually “observed” quite a few times through the telescope by both professional and amateur astronomers. But, Vulcan never really did exist. It was a theoretical construct created to solve a problem in planetary dynamics that never would be solved by the then-standard Newtonian model of planetary motion. The story, with its fascinating twists and turns, the fleeting and ambiguous sightings of Vulcan, and the lengths to which supporters of Vulcan’s existence went to explain away the lack of evidence make this story of interest to skeptics.
The story actually starts in 1781 with the discovery by William Herschel of the planet Uranus. It soon became clear to astronomers that Uranus was behaving badly — it wasn't moving along the orbit predicted for it by Newtonian physics. What could be the matter? Was Newton wrong? Impossible! If Newton wasn't wrong, then he had to be right, and something else had to be causing the odd orbit of Uranus — something doing so in obedience to Newton’s laws. The obvious answer was that there was another planet beyond Uranus, the gravitational influence of which was causing Uranus to orbit as it did.
Finding this hypothetical planet was a huge challenge. In the early 1840s, two mathematicians, John C. Adams of England and Urbain Jean Joseph LeVerrier of France (shown above on a 1958 French postage stamp — England has never so honored Adams), both started working on the problem independently. It was incredibly complex, for it required taking into account the gravitational influences of the Moon, the Sun, and the known planets on the orbit of Uranus and then using the nature of the unexplained Uranian movement to predict the orbit of the new planet. Adams and LeVerrier solved the problem almost simultaneously. On September 23, 1846, German astro-nomers in Berlin, using LeVerrier’s predictions (Adams had been somewhat shy about publishing his work) discovered Neptune.
The discovery was hailed, quite properly, as a great victory for Newtonian theory. LeVerrier and Adams went on to great fame. The discovery of Neptune was, it should be noted, a great embarrassment to astrology, which had never even hinted at the existence of such a planet. The same was true of the earlier discovery of Uranus and the later discovery of Pluto. Not to be phased, however, astrologers attributed influences to the planets following their discoveries. Linda Goodman, in her 1968 Love Signs, stated that planets have no astrological effects until discovered by astronomers!
Impressive as the discovery of Neptune was, another challenge to the Newtonian view of the solar system remained. Mercury was also orbiting in a fashion that was not predicted by Newton’s laws. It was natural to try the same approach to the problem of Mercury’s orbit as had been applied so successfully to the case of Uranus. And try LeVerrier did. He spent much time and effort throughout the rest of his productive life calculating where the planet Vulcan, interior to Mercury’s orbit, should be. He was occasionally buoyed by supposed reports of sightings of Vulcan where the calculations, sort of, said it should be.
LeVerrier died in 1877 and so never knew the solution to the mystery of Mercury’s orbit. It’s orbital deviations were shown by Einstein in 1915 to be due to relativistic effects of the Sun’s huge mass bending space-time. These effects are utterly trivial for planets further away from the Sun.
The authors trace the entire story of Vulcan from the time of Herschel to the resolution of the problem by Einstein. They cover some of the same ground as Grosser did in his wonderful 1962 Discovery of Neptune but add substantially to the post-1846 events. They include much on the personalities (often, but not always, charmingly eccentric) of the major players in the story and the difficulties of doing astronomical observation in, say, the South Seas or American Indian Territory in the late 1800s. It is an exciting and adventurous scientific mystery, very well told.
Skeptics will be especially interested to note that while Vulcan was abandoned by astronomers by the early twentieth century, astrologers, no doubt stung by being caught out when Uranus, Neptune, and Pluto were discovered, have refused to give up on Vulcan. Thus, Goodman, again in her 1968 Love Signs, assigned astrological influence to Vulcan, calling it the “true ruler of Virgo” and stating that it “will become visible through telescopes in a few years.”