Discovering Planet Vulcan
The story of how a country doctor thought he found a new planet in the solar system.
The following is an excerpt from Thomas Levenson’s The Hunt For Vulcan.
Edmond Modeste Lescarbault was a humble, almost diffident man. He lived a small life, confined mostly to a modest compass between the Seine and the Loire rivers, about seventy miles west and a touch south of Paris. He had studied medicine, and in 1848 opened a practice in a little country town, Orgères-en Beauce. He stayed put there for the next quarter of a century. He died in 1894, ninety years old, locally honored— the street where he kept his surgery is now named rue du Dr. Lescarbault— and generally forgotten. The country doctor had one great passion. As a boy, he had fallen in love with the night sky. Children grow up, of course, and most put away childish things. Not Lescarbault. Like many before and since, he discovered in astronomy the same consolation that would later comfort Albert Einstein: the contemplation of “this huge world, which exists independently of us,” which, he wrote, serves as “a liberation.”
For Lescarbault, liberating himself from the daily medical round led him to build a genuinely impressive amateur’s observatory: a low stone barn with a modest dome at one end. There he mounted a perfectly competent telescope, a four-foot-long refractor with an objective lens almost four inches in diameter. He would steal time there between patients, just minutes sometimes, sneaking from his office to the dome to look, perhaps to dream, just a little. The discovery of the asteroids in the belt between Mars and Jupiter led him to wonder: where else might such treasures lurk? An answer came to him on the 8th of May 1845—the day Le Verrier missed the timing of Mercury’s encounter with the sun.
Lescarbault watched Mercury’s moving dot across the solar face, untroubled by any mathematical subtleties. Instead, he thought not about the planet in transit, but whether there might be other unobserved transits to seek. If a Ceres- or a Pallas-sized asteroid lurked close to our star, its transits would likely be the only opportunity to see it—and the search for such events would be a perfect target for an enthusiastic amateur astronomer, eager for the thrill of finding something in the cosmos that not one other human in all of time had perceived.
He was slow to act on that epiphany. Ordinary life intervened. His medical practice needed nurturing, for one thing, but more important, he was a true amateur. He lacked both the knowledge and tools to achieve the precision needed to capture a phenomenon as delicate as an asteroid breaching the limb of the sun. It took him more than a decade to prepare, but by 1858, he had fitted his telescope with homemade instruments good enough to fix the position of objects within its field of view. He was, at last, ready to go hunting.
Saturday, March 26, 1859. Orgères, on the edge of spring, enjoys a sun-warmed afternoon. The flux of patients eases. As is his habit, Dr. Lescarbault takes the opportunity to retreat to his observatory. He turns his telescope toward the sun. An object leaps into view: a small, regular dot, just inside the edge, or limb of our star. He makes an estimate of its size: about one quarter the apparent diameter of Mercury. He has just missed its first appearance at the edge of the sun. Working backward from its apparent rate of motion, he estimates the time it crossed the solar limb at almost exactly four o’clock or, to be precise, at 3h 59m 46s p.m., plus or minus five seconds. He writes that down, using a piece of charcoal to scratch on a board. Another patient arrives and, likely with unrecorded frustration, he pulls his eye from his telescope. A few minutes later, he returns. The spot is still there, moving across the face of the sun. He tracks it continuously now, noting its nearest approach to the center of the solar circle, and then the instant and place it disappears over the solar limb. He records the time again: 5h 16m 55s. Total transit duration: one hour, seventeen minutes and nine seconds. If an asteroid were ever to be discovered within the innermost wards of the solar system, this is how it would reveal itself. Lescarbault meticulously transcribes his notes, and then . . .
Does nothing . . .
For nine months . . .
Until, at last, he permits himself to write a letter to be delivered—by hand—to Paris.
He “broke his silence,” Le Verrier later wrote, “solely because he had seen an article in the journal Cosmos on [my] work on Mercury.” Lescarbault described the data he had collected that Saturday in March—and added one bold claim: “I am persuaded also that [the planet’s] distance from the Sun is less than that of Mercury, and that this body is the planet, or one of the planets, whose existence in the vicinity of the Sun M. Le Verrier had made known a few months ago, by that wonderful power of calculation which enabled him to recognize the conditions of the existence of Neptune. . . .”
Lescarbault entrusted it to a M. Vallée, “Honorary Inspector General of Roads and Bridges,” for delivery to the obvious recipient, Le Verrier himself. Dated December 22, 1859, it reached Paris a few days later. Le Verrier’s first reaction—as he told it—was one of doubt. But he was prepared to hope. There was only one way to be sure if Lescarbault could possibly have made the observations he claimed to have achieved: meet the man; inspect his instruments; test him. No matter how unlikely it might be that some rural hobbyist could have plucked such a prize, even the possibility that he might made any delay intolerable. Le Verrier was promised to his father-in-law’s for a New Year’s Day celebration—but the train schedules showed that it was just possible that he could get to Orgères and back to Paris before midnight on the 31st. He commandeered Vallée to return with him as a witness, and the two men set out to see if Lescarbault’s “planet” might actually exist.
Le Verrier and Vallée arrived at Orgères-en-Beauce unannounced, covering the last twelve miles from the nearest railway station on foot. A few days later, he painted for the Académie a calm, almost placid picture of the encounter: “We found M. Lescarbault to be a man long devoted to the study of science. . . . He permitted us to examine his instruments closely, and he gave us the most detailed explanations of his work, and in particular of all the circumstances of the passage of a planet across the sun.” The two men from Paris made Lescarbault walk them through each phase of his observation until they were convinced that their amateur had in fact seen what he said he had—and, crucially, that his interpretation of the event was correct. “M. Lescarbault’s explanations, the simplicity with which he offered them to us gave us total conviction that the detailed observation he had completed must be admitted to science.”
Le Verrier told the story very differently in private. Released from the conventions of scientific discourse, he seems to have composed a hero’s epic. Abbé Moingo, editor of the same journal, Cosmos, in which Lescarbault had first read of the problem of the precession of Mercury, was present at one of these performances. Le Verrier told of setting out for Orgères, Moingo wrote, assuming that no mere rural medico could have both discovered a new planet and kept quiet about it for nine months. Yet he had “a secret conviction that the story might be true.” At the doctor’s house, the astronomer confronted “the lamb” who trembled before the lion from Paris: “One should have seen M. Lescarbault . . . so small, so simple, so modest and so timid.” Le Verrier roars; Lescarbault stammers—and yet, according to the Abbé, still manages to defend himself at every turn. “You will then have determined . . . the time of first and last contact?” Le Verrier demanded, noting that measuring first contact is “of such extreme delicacy that professional astronomers often fail in observing it.” Lescarbault admitted that he had missed first contact, but had estimated the timing by checking how long it took for his spot to travel the same distance again it had already passed from the limb. Not good enough, said Le Verrier, and on learning that the doctor’s chronometer lacked a second hand, stormed “What! With that old watch, showing only minutes, dare you talk of estimating seconds? My suspicions are already too well founded.”
Lescarbault rallied from even that devastating assault, though, showing his visitors the pendulum he used to count seconds, and reminding the astronomer that as a doctor “my profession is to feel pulses and count their pulsations . . . I have no difficulty in counting several successive seconds.” By this point in the remembered (and, to modern ears at least, suspiciously dramatic) account, it’s becoming clear what Moingo (and/or Le Verrier) is doing. The ebb and flow of leonine attack, each swipe seemingly fatal, and yet disarmed by a counter from the charmingly naive lamb, enlarges Lescarbault. The famous astronomer plays the part of the skeptic (never mind how much he may have hungered for one outcome over another), while the country doctor becomes more and more a competent, even an excellent man of science. The interrogation lasted an hour, enough to exhaust Le Verrier’s reservoir of doubt. At the last, he surrendered: “with a grace and dignity full of kindness, he congratulated Lescarbault on the important discovery he had made.” He would lead Lescarbault to a more tangible reward as well, securing within the month the Légion d’Honneur for “the village astronomer” who had, it seemed, discovered the first intra-Mercurian planet.
The next step was all Le Verrier. Lescarbault had none of the mathematical skill needed to transform his observation into a planetary orbit. Le Verrier did so in less than a week. By making the assumption that its orbit was nearly circular, he calculated that the new planet would complete one revolution around the sun in just under twenty days, on a path that never exceeded eight degrees distance from the sun. Such an object would be difficult if not impossible to see directly. But if Le Verrier’s analysis were even close to correct, the proposed planet would repeat its transits two to four times each year.
With that, planet fever hit the popular press—The Times of London, Popular Astronomy in the United States, The Spectator (which had some very kind words for Dr. Lescarbault). Alternative orbits were proposed: one reexamined the data on the assumption that the new planet traced a highly eccentric ellipse around the sun. Others returned to old records to see if Lescarbault’s planet had been seen and ignored previously—and just as with Uranus and Neptune, candidate objects soon turned up, reaching double figures in a series of sightings stretching back to the mid-eighteenth century.
It was clear more work needed to be done, beginning with a repeat observation of the mystery object. Nonetheless, the celebrations continued heedless of any lingering uncertainty—and for good reason. The faith in the new planet stood in equal measure on Le Verrier’s own reputation and the rock-solid logic behind the discovery. Mercury’s perihelion precession was and is real. Newtonian gravitation provides an obvious solution to such a problem. The appearance of an object exactly where necessity suggested it ought to be made perfect sense. It fit. It had a moral right to be true.
Celestial facts need labels. This time, there was no nationalistic controversy to navigate, no tussle pitting “Oceanus” vs. “Le Verrier.” The common practice held: planets major and minor took their identities from the gods of antiquity. It’s an oddity of history that there is no record of who first fixed on the ultimate choice, but the decision was easy. A body that never escaped the intense fires of the sun had only one real counterpart on Olympus: Venus’s husband, the lord of the forge. By no later than February 1860, the solar system’s newest planet knew its name:
Excerpted from The Hunt for Vulcan by Thomas Levenson. Copyright © 2015 by Thomas Levenson. Excerpted by permission of Random House, A Penguin Random House Company. All rights reserved.
Thomas Levenson is author of The Hunt for Vulcan…And How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe (Random House, 2015) and a Professor of Science Writing at the Massachusetts Institute of Technology in Cambridge, Massachusetts,