The planet Vulcan, of “Star Trek” fame, is hot, rocky, and desolate — and a long, long way from Earth. But in the 1800s, many astronomers believed there really was a planet Vulcan. It, too, would have been hot, rocky, and desolate — but much closer to home. In fact, they suspected it was orbiting quite close to the Sun.

Astronomers got the idea that there must be another planet by plotting the orbit of Mercury, the closest planet to the Sun. Each time Mercury came closest to the Sun, it was a bit farther along in its orbit than the time before. Most of this change was caused by the tug of Venus, Earth, and other planets. But a tiny portion of it couldn’t be explained.

French astronomer Urbain Le Verrier said that an unseen planet or asteroid belt inside Mercury’s orbit was pulling at Mercury. His calculations had led to the discovery of Neptune, so astronomers took him seriously.

The planet was named Vulcan, for a Roman god of fire. It would be so small and so near the Sun that it would be visible only during a solar eclipse — when the Moon blocked the Sun from view — or when the planet passed directly in front of the Sun.

A solar eclipse in 1878 gave astronomers a chance to look for the planet. Despite their efforts, it was nowhere to be seen.

Vulcan was put to rest for good by Albert Einstein. He showed that the Sun warps the space around it — perfectly accounting for the discrepancies in Mercury’s orbit.
 

Script by Damond Benningfield