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Vulcan (hypothetical planet)
Encyclopedia
Vulcan was a small planet
proposed to exist in an orbit
between Mercury
and the Sun
. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French
mathematician
Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan. No such planet was ever found, and Mercury's orbit has now been explained by Albert Einstein
's theory of general relativity
.
, the director of the Paris Observatory
, suggested to the French mathematician Urbain Jean Joseph Le Verrier that he work on the topic of the planet Mercury
's orbital motion around the Sun
. The goal of this study was to construct a model based on Sir Isaac Newton
's laws of motion
and gravitation
. By 1843, Le Verrier published his provisional theory on the subject, which would be tested during a transit of Mercury
across the face of the Sun in 1843. As it turned out, predictions from Le Verrier's theory failed to match the observations.
Le Verrier renewed his work and, in 1859, published a more thorough study of Mercury's motion. This was based on a series of meridian observations of the planet as well as 14 transits. The rigor of this study meant that any differences from observation would be caused by some unknown factor. Indeed, there still remained some discrepancy. During Mercury's orbit, its perihelion advances by a small amount each orbit, technically called perihelion precession. The phenomenon is predicted by classical mechanics, but the observed value differed from the predicted value by the small amount of 43 arcseconds per century.
Le Verrier postulated that the excess precession could be explained by the presence of a small planet inside the orbit of Mercury, and he proposed the name "Vulcan" for this object. In Roman mythology
, Vulcan
was the god of beneficial and hindering fire, including the fire of volcano
es, making it an apt name for a planet so close to the Sun. Le Verrier's recent success in discovering the planet Neptune
using the same techniques lent veracity to his claim, and astronomers around the world attempted to observe a new planet there, but nothing was ever found.
, who claimed to have seen a transit
of the hypothetical planet earlier in the year. Le Verrier took the train to the village of Orgères-en-Beauce
, some 70 kilometres southwest of Paris
, where Lescarbault had built himself a small observatory. Le Verrier arrived unannounced and proceeded to interrogate the man.
Lescarbault described in detail how, on 26 March 1859, he noticed a small black dot on the face of the Sun
, which he was studying with his modest 3.75 inches (95.3 mm) refractor. Thinking it to be a sunspot, Lescarbault was not at first surprised, but after some time had passed he realized that it was moving. Having observed the transit of Mercury
in 1845, he guessed that what he was observing was another transit, but of a previously undiscovered body. He took some hasty measurements of its position and direction of motion, and using an old clock and a pendulum with which he took his patients’ pulses, he estimated the duration of the transit at 1 hour, 17 minutes and 9 seconds.
Le Verrier thought he was satisfied that Lescarbault had seen the transit of a previously unknown planet. On 2 January 1860 he announced the discovery of Vulcan to a meeting of the Académie des Sciences in Paris. Lescarbault, for his part, was awarded the Légion d'honneur
and invited to appear before numerous learned societies.
Not everyone accepted the veracity of Lescarbault's "discovery", however. An eminent French astronomer, Emmanuel Liais
, who was working for the Brazilian government in Rio de Janeiro
in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault's at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated".
Based on Lescarbault’s "transit", Le Verrier computed Vulcan’s orbit: it supposedly revolved about the Sun in a nearly circular orbit at a distance of 21 million kilometres, or 0.14 astronomical unit
s. The period of revolution was 19 days and 17 hours, and the orbit was inclined to the ecliptic
by 12 degrees and 10 minutes (an incredible degree of precision). As seen from the Earth, Vulcan’s greatest elongation from the Sun was 8 degrees.
Numerous reports — all of them unreliable — began to reach Le Verrier from other amateurs who claimed to have seen unexplained transits. Some of these reports referred to observations made many years earlier, and many could not be properly dated. Nevertheless, Le Verrier continued to tinker with Vulcan’s orbital parameters as each new reported sighting reached him. He frequently announced dates of future Vulcan transits, and when these failed to materialize, he tinkered with the parameters some more.
Among the earlier alleged observers of Vulcan, the following are the most noteworthy:
Shortly after eight o'clock on the morning of 29 January 1860, F A R Russell and three other people saw an alleged transit of an intra-Mercurial planet from London. An American observer, Richard Covington, many years later claimed to have seen a well-defined black spot progress across the Sun’s disk around 1860, when he was stationed in Washington Territory
.
No "observations" of Vulcan were made in 1861. Then, on the morning of 22 March 1862, between eight and nine o’clock Greenwich Time, another amateur astronomer, a Mr Lummis of Manchester, England, saw a transit. His colleague whom he alerted also saw the event. Based on these two men's reports, two French astronomers, Benjamin Valz
and Rodolphe Radau
, independently calculated the object’s supposed orbital period, with Valz deriving a figure of 17 days and 13 hours, and Radau a figure of 19 days and 22 hours.
On 8 May 1865 another French astronomer, Aristide Coumbrary observed an unexpected transit from Constantinople
, Turkey
.
Between 1866 and 1878 no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of 29 July 1878, two experienced astronomers, Professor James Craig Watson
, the director of the Ann Arbor Observatory
in Michigan
, and Lewis Swift, an amateur from Rochester, New York
, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun, and estimated its magnitude
at 4.5. Swift, who was observing the eclipse from a location near Denver, Colorado
, saw what he took to be an intra-mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about six or seven minutes from the "planet". Theta Cancri and the planet were very nearly in line with the centre of the Sun.
Watson and Swift had the reputation as excellent observers. Watson had already discovered more than twenty asteroid
s, while Swift had several comet
s named after him. Both described the colour of their hypothetical intra-mercurial planet as "red". Watson reported that it had a definite disk – unlike stars, which appear in telescopes as mere points of light – and that its phase indicated that it was approaching superior conjunction.
These are merely the more "reliable observations" of alleged intra-Mercurial planets. For half a century or more, many other observers tried to find the hypothetical Vulcan. Many false alarms were triggered by round sunspot
s that closely resembled planets in transit. During solar eclipse
s, stars close to the Sun were mistaken for planets. At one point, to reconcile different observations, at least two intra-mercurial planets were postulated.
In 1915 Einstein
's theory of relativity
, an entirely different approach to understanding gravity than classical mechanics
, solved the problem. His equations predicted exactly the observed amount of advance of Mercury's perihelion without any recourse to the existence of a hypothetical Vulcan. The new theory modified the predicted orbits of all planets, but the magnitude of the differences from Newtonian theory diminishes rapidly as one gets farther from the Sun. Also, Mercury's fairly eccentric orbit makes it much easier to detect the perihelion shift than is the case for the nearly circular orbits of Venus
and Earth
.
must be pointed very close to the Sun, where the sky is never black. Also, an error in pointing the telescope can result in damage for the optics, and injury to the observer. The huge amount of light present even quite far away from the Sun can produce false reflections inside the optics, thus fooling the observer into seeing things that do not exist.
The best strategy for observations might be to wait for the planet's transit
of the Sun's disk, and then observe through a strong optical filter
. A small, round dark spot might be seen moving, as happens regularly with transits of Mercury and Venus
.
In 1915, when Einstein successfully explained the apparent anomaly in Mercury's orbit, most astronomers abandoned the search for Vulcan. A few, however, remained convinced that not all the alleged observations of Vulcan were unfounded. Among these was Henry C Courten, of Dowling College, New York. Studying photographic plates of the 1970 eclipse of the Sun, he and his associates detected several objects which appeared to be in orbits close to the Sun. Even accounting for artifacts, Courten felt that at least seven of the objects were real. The appearance of some of these objects was confirmed by another observer in North Carolina
, while a third observer in Virginia
saw one of them.
Courten believed that an intra-Mercurial planetoid between 130 and 800 kilometres in diameter was orbiting the Sun at a distance of about 0.1 astronomical unit
. Other images on his eclipse plates led him to postulate the existence of an asteroid belt between Mercury and the Sun.
None of these claims has ever been substantiated after more than thirty years of observation. It has been surmised, however, that some of these objects - and other alleged intra-Mercurial objects - may exist, being nothing more than previously unknown comets or small asteroids. Today, the search continues for these so-called Vulcanoid asteroid
s, which are thought to exist in the region where Vulcan was once sought. None have been found yet and searches have ruled out any such asteroids larger than about 60 km . Neither SOHO
or STEREO
have detected a planet inside the orbit of Mercury.
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
proposed to exist in an orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
between Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
and the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French
French people
The French are a nation that share a common French culture and speak the French language as a mother tongue. Historically, the French population are descended from peoples of Celtic, Latin and Germanic origin, and are today a mixture of several ethnic groups...
mathematician
Mathematician
A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....
Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan. No such planet was ever found, and Mercury's orbit has now been explained by Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
's theory of general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
.
Argument for Vulcan's existence
In 1840, François AragoFrançois Arago
François Jean Dominique Arago , known simply as François Arago , was a French mathematician, physicist, astronomer and politician.-Early life and work:...
, the director of the Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...
, suggested to the French mathematician Urbain Jean Joseph Le Verrier that he work on the topic of the planet Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
's orbital motion around the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The goal of this study was to construct a model based on Sir Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
's laws of motion
Newton's laws of motion
Newton's laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces...
and gravitation
Newton's law of universal gravitation
Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them...
. By 1843, Le Verrier published his provisional theory on the subject, which would be tested during a transit of Mercury
Transit of Mercury
A transit of Mercury across the Sun takes place when the planet Mercury comes between the Sun and the Earth, and Mercury is seen as a small black dot moving across the face of the Sun....
across the face of the Sun in 1843. As it turned out, predictions from Le Verrier's theory failed to match the observations.
Le Verrier renewed his work and, in 1859, published a more thorough study of Mercury's motion. This was based on a series of meridian observations of the planet as well as 14 transits. The rigor of this study meant that any differences from observation would be caused by some unknown factor. Indeed, there still remained some discrepancy. During Mercury's orbit, its perihelion advances by a small amount each orbit, technically called perihelion precession. The phenomenon is predicted by classical mechanics, but the observed value differed from the predicted value by the small amount of 43 arcseconds per century.
Le Verrier postulated that the excess precession could be explained by the presence of a small planet inside the orbit of Mercury, and he proposed the name "Vulcan" for this object. In Roman mythology
Roman mythology
Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...
, Vulcan
Vulcan (mythology)
Vulcan , aka Mulciber, is the god of beneficial and hindering fire, including the fire of volcanoes in ancient Roman religion and Roman Neopaganism. Vulcan is usually depicted with a thunderbolt. He is known as Sethlans in Etruscan mythology...
was the god of beneficial and hindering fire, including the fire of volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es, making it an apt name for a planet so close to the Sun. Le Verrier's recent success in discovering the planet Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
using the same techniques lent veracity to his claim, and astronomers around the world attempted to observe a new planet there, but nothing was ever found.
The search for Vulcan
In December 1859, Le Verrier received a letter from a French physician and amateur astronomer called Edmond Modeste LescarbaultEdmond Modeste Lescarbault
Edmond Modeste Lescarbault , was a French doctor and an amateur astronomer, best remembered for his 1859 observation of Vulcan....
, who claimed to have seen a transit
Astronomical transit
The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...
of the hypothetical planet earlier in the year. Le Verrier took the train to the village of Orgères-en-Beauce
Orgères-en-Beauce
Orgères-en-Beauce is a commune in the Eure-et-Loir department in northern France.-Population:-References:*...
, some 70 kilometres southwest of Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
, where Lescarbault had built himself a small observatory. Le Verrier arrived unannounced and proceeded to interrogate the man.
Lescarbault described in detail how, on 26 March 1859, he noticed a small black dot on the face of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, which he was studying with his modest 3.75 inches (95.3 mm) refractor. Thinking it to be a sunspot, Lescarbault was not at first surprised, but after some time had passed he realized that it was moving. Having observed the transit of Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
in 1845, he guessed that what he was observing was another transit, but of a previously undiscovered body. He took some hasty measurements of its position and direction of motion, and using an old clock and a pendulum with which he took his patients’ pulses, he estimated the duration of the transit at 1 hour, 17 minutes and 9 seconds.
Le Verrier thought he was satisfied that Lescarbault had seen the transit of a previously unknown planet. On 2 January 1860 he announced the discovery of Vulcan to a meeting of the Académie des Sciences in Paris. Lescarbault, for his part, was awarded the Légion d'honneur
Légion d'honneur
The Legion of Honour, or in full the National Order of the Legion of Honour is a French order established by Napoleon Bonaparte, First Consul of the Consulat which succeeded to the First Republic, on 19 May 1802...
and invited to appear before numerous learned societies.
Not everyone accepted the veracity of Lescarbault's "discovery", however. An eminent French astronomer, Emmanuel Liais
Emmanuel Liais
Emmanuel Liais was a French astronomer, botanist and explorer who spent many years in Brazil.He was born in Cherbourg, the son of a wealthy family in the shipbuilding industry....
, who was working for the Brazilian government in Rio de Janeiro
Rio de Janeiro
Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...
in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault's at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated".
Based on Lescarbault’s "transit", Le Verrier computed Vulcan’s orbit: it supposedly revolved about the Sun in a nearly circular orbit at a distance of 21 million kilometres, or 0.14 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s. The period of revolution was 19 days and 17 hours, and the orbit was inclined to the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
by 12 degrees and 10 minutes (an incredible degree of precision). As seen from the Earth, Vulcan’s greatest elongation from the Sun was 8 degrees.
Numerous reports — all of them unreliable — began to reach Le Verrier from other amateurs who claimed to have seen unexplained transits. Some of these reports referred to observations made many years earlier, and many could not be properly dated. Nevertheless, Le Verrier continued to tinker with Vulcan’s orbital parameters as each new reported sighting reached him. He frequently announced dates of future Vulcan transits, and when these failed to materialize, he tinkered with the parameters some more.
Among the earlier alleged observers of Vulcan, the following are the most noteworthy:
- GruithuisenGruithuisenGruithuisen may refer to:* Franz von Gruithuisen, a Bavarian physician and astronomer* Gruithuisen on the Moon* Mons Gruithuisen Gamma, a lunar dome...
, on 26 June 1819, reported seeing "two small spots … on the Sun, round, black and unequal in size" - Pastorff, on 23 October 1822, 24 and 25 July 1823, six times in 1834, on 18 October 1836, 1 November 1836 and on 16 February 1837, also claimed to have seen two spots; the larger was 3 arcseconds across, and the smaller 1.25 arcseconds.
Shortly after eight o'clock on the morning of 29 January 1860, F A R Russell and three other people saw an alleged transit of an intra-Mercurial planet from London. An American observer, Richard Covington, many years later claimed to have seen a well-defined black spot progress across the Sun’s disk around 1860, when he was stationed in Washington Territory
Washington Territory
The Territory of Washington was an organized incorporated territory of the United States that existed from February 8, 1853, until November 11, 1889, when the final extent of the territory was admitted to the Union as the State of Washington....
.
No "observations" of Vulcan were made in 1861. Then, on the morning of 22 March 1862, between eight and nine o’clock Greenwich Time, another amateur astronomer, a Mr Lummis of Manchester, England, saw a transit. His colleague whom he alerted also saw the event. Based on these two men's reports, two French astronomers, Benjamin Valz
Benjamin Valz
Jean Elias Benjamin Valz was a French astronomer.He was born in Nîmes and trained as an engineer. He became interested in astronomy and comets in particular, observing the return of what would later be named Comet Encke...
and Rodolphe Radau
Rodolphe Radau
Jean Charles Rodolphe Radau was an astronomer and mathematician who worked in Paris at the Revue des deux Mondes for most of his life...
, independently calculated the object’s supposed orbital period, with Valz deriving a figure of 17 days and 13 hours, and Radau a figure of 19 days and 22 hours.
On 8 May 1865 another French astronomer, Aristide Coumbrary observed an unexpected transit from Constantinople
Constantinople
Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...
, Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
.
Between 1866 and 1878 no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of 29 July 1878, two experienced astronomers, Professor James Craig Watson
James Craig Watson
James Craig Watson was a Canadian-American astronomer born in the village of Fingal, Ontario Canada. His family relocated to Ann Arbor, Michigan in 1850....
, the director of the Ann Arbor Observatory
Detroit Observatory
The Detroit Observatory sits on the corner of Observatory and Ann streets in Ann Arbor, Michigan. It was built in 1854, and was the first scientific research facility at the University of Michigan...
in Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
, and Lewis Swift, an amateur from Rochester, New York
Rochester, New York
Rochester is a city in Monroe County, New York, south of Lake Ontario in the United States. Known as The World's Image Centre, it was also once known as The Flour City, and more recently as The Flower City...
, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun, and estimated its magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
at 4.5. Swift, who was observing the eclipse from a location near Denver, Colorado
Denver, Colorado
The City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...
, saw what he took to be an intra-mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about six or seven minutes from the "planet". Theta Cancri and the planet were very nearly in line with the centre of the Sun.
Watson and Swift had the reputation as excellent observers. Watson had already discovered more than twenty asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, while Swift had several comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s named after him. Both described the colour of their hypothetical intra-mercurial planet as "red". Watson reported that it had a definite disk – unlike stars, which appear in telescopes as mere points of light – and that its phase indicated that it was approaching superior conjunction.
These are merely the more "reliable observations" of alleged intra-Mercurial planets. For half a century or more, many other observers tried to find the hypothetical Vulcan. Many false alarms were triggered by round sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
s that closely resembled planets in transit. During solar eclipse
Eclipse
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...
s, stars close to the Sun were mistaken for planets. At one point, to reconcile different observations, at least two intra-mercurial planets were postulated.
Search conclusion
In 1877 Le Verrier died, convinced to the end of having discovered another planet. With the loss of its principal proponent, however, the search for Vulcan abated. After many years of searching, astronomers were seriously doubting the planet's existence.In 1915 Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
's theory of relativity
Theory of relativity
The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....
, an entirely different approach to understanding gravity than classical mechanics
Classical mechanics
In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces...
, solved the problem. His equations predicted exactly the observed amount of advance of Mercury's perihelion without any recourse to the existence of a hypothetical Vulcan. The new theory modified the predicted orbits of all planets, but the magnitude of the differences from Newtonian theory diminishes rapidly as one gets farther from the Sun. Also, Mercury's fairly eccentric orbit makes it much easier to detect the perihelion shift than is the case for the nearly circular orbits of Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
and Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
.
Vulcan revived
Observing a planet inside the orbit of Mercury would be extremely difficult, since the telescopeTelescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
must be pointed very close to the Sun, where the sky is never black. Also, an error in pointing the telescope can result in damage for the optics, and injury to the observer. The huge amount of light present even quite far away from the Sun can produce false reflections inside the optics, thus fooling the observer into seeing things that do not exist.
The best strategy for observations might be to wait for the planet's transit
Astronomical transit
The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...
of the Sun's disk, and then observe through a strong optical filter
Filter (optics)
Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....
. A small, round dark spot might be seen moving, as happens regularly with transits of Mercury and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
.
In 1915, when Einstein successfully explained the apparent anomaly in Mercury's orbit, most astronomers abandoned the search for Vulcan. A few, however, remained convinced that not all the alleged observations of Vulcan were unfounded. Among these was Henry C Courten, of Dowling College, New York. Studying photographic plates of the 1970 eclipse of the Sun, he and his associates detected several objects which appeared to be in orbits close to the Sun. Even accounting for artifacts, Courten felt that at least seven of the objects were real. The appearance of some of these objects was confirmed by another observer in North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
, while a third observer in Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
saw one of them.
Courten believed that an intra-Mercurial planetoid between 130 and 800 kilometres in diameter was orbiting the Sun at a distance of about 0.1 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
. Other images on his eclipse plates led him to postulate the existence of an asteroid belt between Mercury and the Sun.
None of these claims has ever been substantiated after more than thirty years of observation. It has been surmised, however, that some of these objects - and other alleged intra-Mercurial objects - may exist, being nothing more than previously unknown comets or small asteroids. Today, the search continues for these so-called Vulcanoid asteroid
Vulcanoid asteroid
The vulcanoids are a hypothetical population of asteroids that may orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, whose existence was disproven in 1915...
s, which are thought to exist in the region where Vulcan was once sought. None have been found yet and searches have ruled out any such asteroids larger than about 60 km . Neither SOHO
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
or STEREO
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
have detected a planet inside the orbit of Mercury.
See also
- Fictional planets of the Solar System
- Vulcanoid asteroidVulcanoid asteroidThe vulcanoids are a hypothetical population of asteroids that may orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, whose existence was disproven in 1915...
- Mercury's moonMercury's moonA moon orbiting Mercury was, for a short time, believed to exist.On March 27, 1974, two days before Mariner 10 made its flyby of Mercury, instruments began registering large amounts of ultraviolet radiation in the vicinity of Mercury which, according to one astronomer, "had no right to be there"...
- Planet XPlanet XFollowing the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...
- List of observations of solar and lunar transits of unknown objects
Further reading
- The subject was also featured on an episode of Arthur C. Clarke's Mysterious WorldArthur C. Clarke's Mysterious WorldArthur C. Clarke's Mysterious World is a thirteen part British television series looking at unexplained phenomena from around the world. It was produced by Yorkshire Television for the ITV network and first broadcast in September 1980....
entitled "Strange Skies", originally broadcast on November 18, 1980.
External links
- Asimov, IsaacIsaac AsimovIsaac Asimov was an American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Asimov was one of the most prolific writers of all time, having written or edited more than 500 books and an estimated 90,000...
(1975). "The Planet that Wasn't", The Magazine of Fantasy and Science Fiction - Schlyter, Paul (2006). "Vulcan, the intra-Mercurial planet, 1860-1916, 1971", The
Nine8 Planets: A Multimedia Tour of the Solar System (Appendix 7: Hypothetical Planets) converted to html by Bill Arnett.