Mr. Spock and Dr. Einstein
By S. K. Smith
Long before Star Trek, astronomers were looking for the planet Vulcan. It literally took an Einstein to solve this mystery.
At the turn of the century (19th to 20th), scientists had thought they had the universe pretty well figured out. Newtonian physics was strongly entrenched, describing the motion of objects in the heavens and on earth like clockwork. A bolster to this Newtonian worldview was the discovery of the 8th planet in our solar system - Neptune.
In the mid 19th century, Uranus, then the farthest known planet from the Sun, displayed unexpected changes in its orbit. In 1845 – 46, French astronomer, Urbain Le Verrier, deduced that these perturbations were due to the gravitational pull of a more distant, yet unknown, planet. Le Verrier transmitted his calculations to a German astronomer, Johann Galle, who, when observing, located this new planet in a matter of hours. Score another one for Newtonian physics!
Flush from the victory of discovering the 8th planet, Le Verrier tackled another mystery – the unexplained anomalies of Mercury’s orbit. If Newton’s law of gravitation was correct (and predicting the existence of Neptune seemed to be concrete proof that it was), Le Verrier postulated that some planet inside Mercury’s orbit disturbed it. Le Verrier suggested the name of this hidden planet as Vulcan, after the Roman god of fire.
As Vulcan would, in theory, be closer to the Sun than Mercury, it would be very difficult to see from the Earth. Viewing would be possible during a total solar eclipse, when any sizable object near the Sun could be more easily seen whereas it wouldn’t be detected otherwise. But total eclipses were infrequent and only lasted for a few minutes.
Another opportunity would be a transit, when Vulcan would pass directly between the Earth and Sun, appearing as a dark circle on the Sun’s surface, moving rapidly from west to east in a straight line. Since the time of transit for a planet could not be predicted until its orbit was accurately known, the first sighting must be by luck.
In 1845, French amateur astronomer, Dr. Lescarbault had observed a dark object against the Sun, which he later felt must have been Vulcan. From Lescarbault’s observation, Le Verrier estimated that Vulcan’s distance from the Sun was about a third of Mercury’s and it must have a period of revolution about 19.7 days. He estimated the diameter of Vulcan to be a little over half the diameter of our Moon and a mass of one-fourth that of our Moon. Though not large enough to explain all of Mercury’s perturbations, Vulcan might be part of an asteroid belt, similar to the one between Mars and Jupiter.
With these proposed orbital parameters, the only time Vulcan could be seen in the sky in the absence of the Sun would before sunrise or after sunset at ten-day intervals. The bright twilight would make the sightings difficult; hence that explained why Vulcan had not been detected for so long. Le Verrier calculated the times of future transits and astronomers began watching for them.
Unfortunately, astronomers did not find Vulcan where it was supposed to be. Reports came in of sightings of Vulcan from time to time. In each case, a new orbit was calculated and new transits predicted, yet nothing concrete came of it. Therefore, the existence of the planet Vulcan was being questioned – some astronomers insisted it was real, others denied it. When Le Vierrier passed away in 1877, however, he firmly believed in Vulcan’s existence.
In 1878, a solar eclipse passed over the western United States as American astronomers engaged, again, in the search for Vulcan. Most of the observers saw nothing, but two astronomers reported sightings. The deduced attributes of Vulcan, though, could not account for the perturbations of Mercury. Also, the disputed accuracy of Vulcan’s location was insufficient to calculate its orbit. Hence, without reasonable ephemeris, the observations could not be repeated.
At the turn of the century (19th to 20th), photography was coming of age, so that astronomers could take photographs and study them at their own pace. The objects observed inside Mercury’s orbit were so dim and calculated to be so small that they could not account for the perturbations of Mercury – which steadfastly flaunted Newton’s Laws. Vulcan still eluded the astronomers and the mystery of Mercury continued.
Finally, Einstein literally entered into the equation. Yet, Einstein’s resolution of the Mercury anomalies was totally unexpected.
In 1915, Albert Einstein solved the mystery in his General Theory of Relativity. In General Relativity, gravitation was an extension of Newton’s laws, which simplified to Newton’s laws under most conditions. It was only in the extreme that Newton’s laws break down and Einstein’s equations provide a better model. And Mercury’s orbit, which was so close to the Sun, was one of those extremes.
Einstein’s equation E = mc2 put forth the equivalence of a large amount of energy to a small quantity of matter. The enormous energy of the Sun’s gravitational field interacting with nearby Mercury was equivalent to the mass of a small planet. Einstein’s calculations showed that the effect of the Sun’s gravitation field accounted for the perturbations of Mercury as well as smaller perturbations of planets farther out.
Since this revelation, most astronomers have abandoned the search for Vulcan. A few, however, were convinced that not all the alleged observations of Vulcan were unfounded. Some still believe that objects inside Mercury’s orbit may exist, such as previously unknown comets or small asteroids. Today, the search continues for the so-called Vulcanoid asteroids, which may exist in the region where Vulcan was once sought.
Einstein’s theory of General Relativity seemed to have vanquished the hidden planet Vulcan from our solar system – for now. Yet, as long Star Trek is in our consciousness, the home world of Mr. Spock will live long and prosper!
© December 19, 2008, S. K. Smith