The Real History of the Planet Vulcan: How a Planet's Death Birthed Relativity

The Real History of the Planet Vulcan: How a Planet's Death Birthed Relativity
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On September 23, 1846, 35-year-old French mathematician Urbain Jean Joseph Le Verrier became a celebrity in the world of science. His meteoric ascendance to fame came after months of learned toil. Earlier that year, Le Verrier found himself transfixed by Uranus' orbit -- it seemed to defy Johannes Kepler's Laws of Planetary Motion and Isaac Newton's Theory of Gravitation. Assuming those theories to be correct, he settled on an explanation for Uranus' strange movements: there must be another planet lurking nearby. Performing dazzlingly complex calculations, he determined not only the hypothetical planet's orbit, but also its size, distance from the sun, and even its location. On September 18, 1846, he mailed his predictions to astronomers at the Berlin Observatory. The letter arrived the afternoon of the 23rd. That same evening, observatory assistant Johann Galle and astronomy student Heinrich d'Arrest peered out into space and spotted the planet in almost the exact location Le Verrier predicted. Eventually dubbed Neptune, it was the first planet discovered purely by mathematical means. What's more, its existence hugely substantiated Newton's Laws of Gravitation.

Fresh off his astronomical success, Le Verrier aimed to repeat it. Mercury's orbit suffered a similar, albeit slightly smaller disturbance. So naturally, he reasoned that an undiscovered planet must be to blame. In 1859, he officially predicted the existence of a new planet inside the orbit of Mercury, which he named "Vulcan." Later that year, he visited with Edmond Modeste Lescarbault, an amateur astronomer who claimed to have observed it. Satisfied with Lescarbault's account, Le Verrier took the observations for definitive proof of Vulcan's existence, and in January of 1860, he announced the discovery to the French Academy of Sciences in Paris. Once again, Le Verrier was widely lauded for his success, and Lescarbault was even inducted into France's Legion of Honor.

But then problems started to arise. Based on Lescarbault's data, Le Verrier calculated the orbit and size of Vulcan, and instructed astronomers on when and where to watch for the new planet. But when astronomers across the world looked, most of them found nothing. So Le Verrier recalculated and advised them to try again. Again, the vast majority of astronomers saw nothing except for Mercury and the bright, shining Sun. This saga played out over and over for more than a decade, each time with the same results.

Though evidence was turning against planet Vulcan, much of the scientific community continued to support Le Verrier. His calculations, coupled with Newton's theories, had proven spectacularly correct in the past. Why would they be wrong this time?

Over time, their faith dwindled, but it persisted even as late as 1876. In that year, a volume of the engineering magazine The Manufacturer and Builder reported that, "Our text-books on astronomy will have to be revised again, as there is no longer any doubt about the existence of a planet between Mercury and the sun." The author apparently chose to focus on the rare confirmatory sightings of Vulcan and to discount all the negative results. (Even in the 19th century, there was poor science journalism apparently.)

When Le Verrier passed away in 1877 at the age of 66, efforts to confirm the existence of Vulcan mostly died with him. However, it wasn't until 1915 that the planet was dealt a final deathblow, not by astronomy, but by Albert Einstein. His theory of relativity explained that the Sun's massive gravity actually bent space locally, which perfectly accounted for the perturbations in Mercury's orbit. At the same time Vulcan vanished, the celestial mechanics of the scientific giants Newton and Kepler were shown to be incomplete. Relativity's reign began.

Today, many people likely know planet Vulcan as the home of an eponymously named species of logical, pointy-eared humanoids from Star Trek. Few know of its grander position in history: as the planetary "product of a young Frenchman's mathematics" whose death served to cement one of the greatest physical frameworks for how our universe functions: Relativity.

(Image: NASA/Johns Hopkins)

Source: Sternberg, Robert J. Why Smart People Can Be So Stupid. Yale University Press. 2003.

Source: Baum, Richard. In Search Of Planet Vulcan: The Ghost In Newton's Clockwork Universe. Basic Books. July 4, 2003

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