Which planet has an electrical orbit

The Solar System: Neptune: The Enigma Beyond Uranus

The planet Uranus, discovered in 1781, moves strangely irregularly in the firmament. Around 1840 astronomers suspected that it was influenced by an unknown object. Two mathematicians are on the trail of the celestial body

The young mathematician knocks on the front door of the Royal Astronomer in Greenwich near London at around 4 p.m. - for the second time. As early as the early afternoon of October 21, 1845, the visitor tried unannounced to speak to George Biddell Airy. But Airy's butler explained that he was at a meeting in London and wasn't expected to come back until later.

The 26-year-old John Couch Adams from Cambridge then presented his business card and a short letter with the results of his calculations and announced that he would be back later. So now he is standing in front of the resolute butler again. But he gets rid of him: The royal court astronomer is now at home, but he is sitting at table with his wife and must not be disturbed. And: No, Dr. Airy didn't leave a message for Mr. Adams.

Adams believes he has found an unknown planet

The young mathematician is at a loss. He is an unknown scientist who comes from a simple, provincial background. Modest and shy. And so he doesn't insist on being admitted. Instead, he returns to Cambridge, deeply disappointed. Why doesn't Airy want to see him? Why doesn't the court astronomer even send him a note? In doing so, Adams, he believes, has achieved something that no human has ever done before: to prove the existence of an unknown planet purely mathematically. He even calculated where in the firmament he could be found.

Now all you have to do is point a large telescope at the relevant section of the sky in order to actually discover the object. John Couch Adams hopes that the Royal Astronomer will arrange for this to happen soon. Little does he suspect that a well-known French colleague is now dealing with the same topic. And is about to find a solution.

When John Couch Adams was born on June 5, 1819 on a farm near Laneast, Cornwall, his prospects for an academic career were slim. The parents are tenants of a farm and their options are limited. After all, there is enough to live on - despite the six siblings who still follow the firstborn. John gets his first school lesson in a farm house in Laneast, then his training is assigned to a certain R. C. Sleep - "Professor of calligraphy, shorthand, mathematics, French, Hebrew etc.", as he himself later advertises.

Sleep is working through an old algebra book with the ten-year-old, and to the teacher's astonishment, the student is soon way ahead of him in understanding math problems. At eleven, John is considered a child prodigy. In 1831 his parents sent him to a school in Devonport. The boy now spends every free minute in a library to study mathematical and astronomical books. At the age of 14 he was drawing star maps, in 1835 he was deeply impressed by the appearance of Halley's Comet and two years later he published his first scientific article on a lunar eclipse in a local newspaper.

He calculates comet orbits, solar and lunar eclipses - with mathematical knowledge that he has almost completely taught himself. Probably on the advice of a pastor who last taught John, the 20-year-old set off for Cambridge in October 1839. He passed the entrance exam at St. John's College and received a scholarship that enabled him to study mathematics, thanks in part to a small inheritance.

The young genius is primarily interested in astronomy

In the years that followed, Adams concentrated entirely on the lectures; even in his spare time, it could happen at any time that his thoughts wander to a mathematical problem and he forgets everything around him. He often spends Sunday evenings with the professor at another college - in the rooms in which the famous Isaac Newton wrote his main work, the “Principia Mathematica”.

In addition, however, he is mainly interested in astronomy. And so it happens that Adams (as he later precisely remembers) entered the bookstore "Johnson's" on June 26, 1841, rummaged through the shelves and looked at the 1832 treatise "Report on the Advances in Astronomy" by the later Royal Astronomer George Biddell comes across Airy. A passage in the book arouses the mathematician's curiosity. It concerns Uranus: something is wrong with it.

This seventh planet was discovered by William Herschel only 60 years earlier. Born in Germany and actually a musician by profession, he emigrated from Hanover to England in 1757 at the age of 18. First made his way as a music writer, leader of a military band and music teacher, also made a name for himself as a composer and conductor and finally in 1766 became a church organist in Bath, an exclusive resort in the

South West of England.

It was there that he discovered his love for astronomy and began obsessively building telescopes. He had not only taken on his position as organist and taught six to eight students a day, but also converted all the rooms in his house into workrooms in his free time, where he cast, sanded and polished mirrors, made tubes and frames, and made eyepieces.

Back to main page

Herschel explored the firmament with his telescopes, which were continually improved and which soon became outstanding, and compared it with the star maps available to him. On the evening of March 13, 1781, he noticed a celestial body whose image in the telescope was visibly larger than that of the others. Four nights later, Herschel was able to determine that the object had moved and decided to inform the professional world that he had found a new comet.

But after several months of the exam, the professional astronomers gradually realized what Herschel had actually discovered: a planet. The first wandering star that cannot be seen with the naked eye and therefore has not been known since time immemorial. In the following decades, several astronomers tried to calculate the orbit around the sun as precisely as possible from the positions observed on the new planet - for which the name "Uranus" gradually became established, after the Greek god of the sky.

The orbit of Uranus is a mystery to scholars

But the orbit of Uranus simply did not match what scientists had predicted. For decades he was always faster than expected; then, in the 1820s, the whole thing was reversed: now it was too slow. The planet's orbit was so inexplicable that some researchers even doubted whether Newton's law of gravity is still valid at such a great distance from the sun. When John Couch Adams leafed through Airy's notes on the riddle of Uranus in Airy's notes on June 26, 1841, he spontaneously decided - and quite confidently - to solve this riddle.

A few days later he notes: “I devised a plan earlier this week to investigate the as yet inexplicable irregularities in the movement of Uranus; with the aim of finding out whether they can be ascribed to the influence of an as yet undiscovered planet. ”Others have already suspected that an unknown celestial body orbits beyond Uranus, pulls on it with its gravity and thus causes the irregularities in its orbit.

But Adams ’plan to track down the unknown with the help of mathematical calculations alone seems presumptuous. Most researchers consider this to be impossible. For Adams this would be a triumph: for the first time, a celestial body would not be discovered with the eye, but rather through complex equations. Only two years later, after graduating, the young mathematician can seriously begin his calculations. In October 1843 he finally came up with a first solution to the problem - and is now certain: The orbital disturbances of Uranus can actually be explained by a large celestial body that orbits further out in space around the sun.

But he needs more precise information about the orbit of Uranus. And so Adams turns to James Challis, director of the Cambridge Observatory, and asks him to send a letter to George Biddell Airy - the author of the same "Advances in Astronomy" pamphlet that Adams had on his undertaking two years earlier inspired.

George Biddell Airy, Royal Astronomer since 1835, has the most extensive data on Uranus at the Royal Observatory in Greenwich. And indeed: Challis writes the requested letter. "A young friend of mine, Mr. Adams from St. John's College, is working on a theory of Uranus," he wrote to Airy in February 1844, asking for information. The court astronomer, known for his care and accuracy, immediately delivers the required material. But Adams takes his time with his calculations. Much time. His teaching duties at Cambridge College leave little room for him. In addition, in the fall of 1844 he was busy calculating the orbit of a newly discovered comet. He has no way of knowing that another researcher is about to forestall him.

A competitor publishes its results faster than Adams

The calculation of the comet's orbit by Adams was inspired by James Challis, who observed the tail star and passed his data on to the mathematician. Adams published his results in October 1844 in the London Times. But to his annoyance, he has to discover that a Frenchman has been faster and published almost the same results shortly before in France.

His name: Urbain-Jean-Joseph Le Verrier. Le Verrier, eight years older than Adams, is also an exceptionally gifted mathematician and also an extremely versatile scientist. The former scholarship holder of the prestigious École Polytechnique in Paris began his career as a chemist, then received a lectureship in astronomy at the École Polytechnique. In this subject he has already distinguished himself through excellent studies on the long-term stability of the solar system and on the calculation of cometary orbits.

Le Verrier is ambitious and bursting with confidence. The aspiring researcher from Normandy is said to be "difficult" in character. Later employees will describe him as haughty, selfish, authoritarian, even despotic. In the summer of 1845, the director of the Paris Observatory suggested that he study the Uranus problem. Le Verrier immediately throws himself vehemently into the mystery of the inexplicable behavior of the seventh planet.

John Couch Adams has no idea of ​​this competition, who has already come a long way with his calculation of the orbit data for the unknown celestial body. And so, in the summer of 1845, a race begins between two opponents who are pursuing the same utterly unheard-of goal but are unaware of their competition with one another - a race that is unique in the history of astronomy.

Back to main page

Adams now assumes that the unknown planet does not move on a circular orbit, but rather an ellipse, and that its mean distance from the sun is about twice that of Uranus. The basic idea of ​​his thesis: The distance between the two planets is constantly changing, because both move on their respective orbits around the sun - but Uranus needs significantly less time for this than the unknown celestial body.

This puzzle planet accelerates Uranus with its gravity or slows it down a little - depending on whether it is in its orbit in front of or behind the planet discovered by Herschel. Adams therefore determines the discrepancy between the 21 positions of Uranus, which have been observed in the firmament in the previous decades, and the theoretically expected position (i.e. without the disturbance from the unknown planet). From this, conclusions can be drawn about the cause of these disturbances.

An extremely time-consuming and complex calculation with many unknowns begins. Mighty piles of paper pile up around the mathematician. In mid-September 1845 the Briton reached an interim result. This calculation enables him to narrow down a relatively narrow section of the firmament in which, according to his considerations, the unknown celestial body should be found.

Only an astronomer can check the calculations

Adams now needs the help of an astronomer who is systematically looking for the mysterious planet with a telescope in the calculated area. He presented his results to James Challis. But the director of the Cambridge Observatory shrinks back. To him, the attempt to track down a celestial body by purely mathematical means seems too adventurous. But at least he suggests that Adams contact the Royal Astronomer and writes a letter of recommendation to George Biddell Airy.

Adams knocked on Airy's doorstep in Greenwich for the first time in late September. He is on his way to see his family in Cornwall and is too humble to announce the visit to the famous man beforehand. And so Adam has bad luck: The court astronomer is currently at a conference in Paris; the mathematician can only leave his letter of recommendation. Then on October 21st the second attempt, which also remained unsuccessful and so disappointed Adams.

What the unfortunate mathematician does not know, however, is that George Biddell Airy had not left him a message because he knew nothing about his visit. Presumably the heavily pregnant wife of the court astronomer had simply forgotten to inform her husband about the visitor - and also not passed on his business card. 15 days later: In the meantime, Airy has received a piece of paper that Adams left behind with the interim results of his calculations and answers the mathematician in a letter on November 5, 1845.

The astronomer is skeptical. After all, he only saw the brief results on a piece of paper and hardly trusts the young mathematician to carry out such a complicated, in his eyes completely impossible calculation: What Adams presented him as the results of elaborate calculations, Airy considers hypothetical assumptions. So he wrote a few questions to Adams asking for more details.

November 10, 1845. In the meantime, Le Verrier has also made enormous progress. Now he is presenting the first results to the Paris Academy of Sciences. According to them, he can rule out that the planets Jupiter or Saturn cause the orbital disturbances of Uranus. Airy found out about these calculations in December and was impressed - probably also because the Frenchman is already a renowned mathematician. He is already holding the much more far-reaching solution calculated by Adams in his hands. But that escapes the court astronomer because he does not take the young Briton's results seriously.

Unfortunate circumstances set Adams further back

In addition, Airy has not yet received a reply to his letter - apparently this Adams is not sure of his cause after all. In truth, the mathematician simply did not understand how the court astronomer can ask questions that are self-explanatory from the existence of the unknown planet. It is just one more complication in a chain of unfortunate circumstances that make it extremely difficult for the young Cambridge man to bring his groundbreaking insight to the world. In the months that followed, both mathematicians worked feverishly on improved versions of their calculations. And they still don't know about each other.

June 1, 1846. Le Verrier publishes the second part of his investigation of the Uranus problem: he too has come to the conclusion that only a previously unknown planet can explain its strange movement. It also supplies the expected position of this new celestial body. Airy finds out about it; he is the only one who knows that Le Verrier's prediction comes very close to that of Adams.

Now he has no more doubts about the young Brit's results. He writes Le Verrier - without mentioning Adams - and asks the French the same questions as his compatriot seven months earlier. But unlike Adams, Le Verrier answers promptly and points out to the court astronomer that his questions are irrelevant. After all: Now Airy also thinks the time is ripe to search for the planet.

June 29, 1846. At a meeting of the Royal Observatory, Airy announced that if an observatory took on the task, there would be “a high probability” of discovering a planet soon. And in addition to Le Verrier's well-known calculations, for the first time he publicly mentions the almost identical result by Adams, which he has now had for eight months.

Back to main page

The present John Herschel, the son of the Uranus discoverer and himself a well-known astronomer, said a few weeks later about the still unknown celestial body: “We see it as Columbus saw America from the Spanish coast.Its orbit was tracked with the far-reaching means of mathematics, and with a certainty that is hardly inferior to the evidence of actual observation. ”But this evidence is still missing.

Early July 1846. Airy urges Cambridge Observatory Director James Challis to begin the search. Since Airy is now convinced that the planet exists, but does not trust the accuracy of the forecasts, he suggests a huge area. 300 hours of observation are required to test it. Challis starts on July 29th. John Couch Adams is delighted; five years after his first reflections on the unknown planet, his calculations finally lead to practical consequences. Excited, he tells Challis that the planet is probably big enough to be seen as a disk in the telescope. This makes it easier to identify: You don't have to observe a region several times to expose the changing star based on its movement. But the astronomer is not interested in Adams's hint; he stubbornly sticks to his program.

The discovery of the eighth planet is imminent

August 31, 1846. Le Verrier presented a third report to the French Academy of Sciences, in which he again narrowed down the position of the suspected celestial body - and urged astronomers to go in search of it: with good telescopes it would have to be closed without any problems find his. He doesn't know that Challis is already looking for the planet in Cambridge.

September 2, 1846. John Couch Adams also made more precise calculations, which he sent Airy by letter. But once again Adams has bad luck: The court astronomer is traveling in Germany for several weeks. Meanwhile, Le Verrier tries tirelessly to win astronomers for the search, sends out his study and writes letters. Finally, he turns to the German Johann Gottfried Galle, who once sent him his dissertation. Galle works at the Berlin observatory, which is equipped with a sufficiently powerful telescope.

September 23, 1846. Galle receives the letter and begins the search that evening. It is a clear, starry night. Galle and his assistant Heinrich d’Arrest (later an important astronomer himself) pointed the telescope at the area specified by Le Verrier for hours - in vain: the planetary disk cannot be found. They are almost discouraged when they come up with a new plan: For each star he observes through the telescope, Galle will name the position, which d’Arrest then compares with a particularly good map of this region of the sky. Shortly after midnight, the assistant suddenly exclaims enthusiastically: “This star is not on the map!” The eighth planet of the solar system has finally been found.

The news spreads within a few days and all of Europe celebrates Le Verrier as the real discoverer. On October 3rd, John Herschel addressed the public: Even a young mathematician from Cambridge came to the same prediction completely independently of Le Verrier. Thereupon a month-long, bitter dispute broke out about who should now be given the honor of the discovery. Le Verrier is furious when he learns of Adam's calculations that Airy has kept from him. Especially since he now has to read in a newspaper that the scientists on the other side of the Canal are claiming part of the fame for themselves. But John Couch Adams is silent.

Adams enviously acknowledges the success of his competitors

He's certainly deeply disappointed. But humble as he is, he does not interfere in the controversy; rather he admits the discovery to Le Verrier and Galle without envy and prefers to use the observations now available to calculate the orbit of the new planet even more precisely. On November 13, 1846, Airy, Challis, and Adams describe their perspective on planet hunting at a meeting of the Royal Astronomical Society. In contrast to the young mathematician, the two established astronomers do not give a good picture.

Why did British science miss this award, you are asked? Why wasn't the search started earlier? The answers remain unsatisfactory, and James Challis even has to confess that he saw the planet twice - on July 30th and August 12th - in his telescope without identifying it. There is also controversy about the name. Janus, Oceanus, Minerva, and other names are suggested. At the beginning of 1847, however, at least outside of France, the name “Neptune” became established - after the Roman god of the sea, with whose name the series of mythological planetary names continued. Le Verrier himself had initially suggested it, but later tried in vain for a long time to gain acceptance for the designation “Le Verrier's Planet”.

Only after months of debate, dispute and slander do the prudent scientists, especially John Herschel, succeed in reconciling the competing nations. It so happened that Adams and Le Verrier first met in person during a meeting of the British Society for the Advancement of Science in June 1847. Those present are excited: How will the two competitors for the scientific honor face each other? Will there be another argument? There is no reason to worry. The two researchers greet each other warmly, shake hands and soon chat like old friends. A connection is created that will last a lifetime.

Back to main page

For a long time, however, the two outer wandering stars remain a mystery. Their orbits and speeds can be determined relatively easily from the observation data. But only with ever larger telescopes and finally with space scouts will the following generations gain a comprehensive picture of the two giant planets.

Today we know: Both are bluish gas giants, each around 50,000 kilometers in diameter and around 60 times the volume of the earth. Both have an atmosphere that consists of 80 percent hydrogen and 15 to 19 percent helium; in addition, there are some methane (which is the reason for the blue color of the planets) and a few trace gases. Storms are more frequent on Neptune - presumably because heat rises from the interior and causes turbulence.

Nevertheless, the temperatures on the top of the clouds are icy with around minus 220 degrees Celsius. Because the pressure rises with increasing depth, more and more of the gaseous components precipitate as solid ice particles. The gas envelope of the planets gradually changes into a mantle of water ice, methane and ammonia - without there being a clear, solid surface. The core in its interior probably consists of ice and rock.

Uranus is like an egg rolling around on the table

Uranus has 27 known moons, Neptune 13. Both planets are also surrounded by thin ring systems. Uranus is around 19 times farther from the Sun than Earth and takes 84 years to complete one orbit. Neptune orbits about 30 times the distance from the earth and travels around the central star once in 165 years. Uranus needs around 17 hours to turn around itself, Neptune 16. Curious is the axis of rotation of Uranus. For most planets it is perpendicular to the plane of the orbit - just like the axis of rotation of a top rotating on a table to the table surface. In Uranus, on the other hand, it is roughly in the same plane as the orbit - like an egg rolling around on the table.

The result is strange annual courses: There is a season in which the light of the sun, which is only pale here, is almost exactly over the North Pole (while the South Pole is completely in the dark). From there, its rays move to the equator and beyond, until it glows over the South Pole half a Uranus year later. Both outer planets have a magnetic field which, astonishingly, is rotated by 47 degrees for Neptune and 59 degrees for Uranus against the axis of rotation. Accordingly, the magnetic and geographic poles of these planets are much further apart than on Earth.

The magnetic fields must come about differently than on our home planet, because Uranus and Neptune do not contain an outer core of liquid iron that could generate electrical currents. Their masses (15 and 17 times more than that of the earth) are also not large enough to generate the pressure inside that converts hydrogen into a metallic and thus into an electrically conductive form (as is the case with Jupiter, 318 earth masses , and Saturn, 95 Earth masses, is the case; their magnetic fields are presumably created by electrical currents in metallic hydrogen).

With Uranus and Neptune a different mechanism must work. Researchers suspect that the pressure inside these planets causes molecules like ammonia to break down into electrically charged components. These ions are dissolved in water, can move inside the celestial bodies and thus generate a current flow that builds up the magnetic field.

The rings of Uranus were discovered in 1977, those of Neptune in 1984. Most of the information, however, was provided by the American probe "Voyager 2", which flew past Uranus in 1986 and Neptune in 1989 - the only visit to the outer planets to date (no further visits are currently planned). Of course, none of this was known about 160 years ago when Neptune first appeared in the telescope. Nobody could have guessed what kind of world had been discovered.

Both mathematicians became famous - and soon promoted

Adams and Le Verrier, the two discoverers of the eighth planet, became recognized figures in astronomy thanks to their mathematical masterpieces. And the offices soon follow the honor. Cambridge University appoints John Couch Adams Professor of Astronomy and Geometry in 1859 and Challis' successor as director of the observatory in 1861. Two years later, the now 43-year-old rediscovered unknown spheres: "I already feel completely in a new world and look back with regret on the ice age of my previous existence, which seems to have been millions of years back to me" - he has Elizabeth Bruce from Dublin Proposed marriage and received her yes.

Until his death in January 1892, Adams led the quiet life of a scholar on the grounds of the Cambridge Observatory, occupied himself with botany, geology, and history in addition to astronomy, and enjoyed playing croquet, bocce and whist. And for diversion, it calculates mathematical constants to more than 200 places after the decimal point.

Urbain-Jean-Joseph Le Verrier is still fascinated by the orbits of the heavenly bodies and plans to depict the planetary system in a single work. In January 1854 he became director of the Paris Observatory. With a hard hand he modernized this institution, where he made meteorology as well as astronomy a field of competence. His administration is considered gruff and haughty. He is authoritarian towards the employees. In 1870 he was released because of his despotic behavior and because he invested too little money from the observatory in observing the stars. But when his successor drowns in an accident, he took office again in 1873.

Four years later, Le Verrier dies of liver disease. A few weeks earlier he had seen the printing of his planet tables, for which he had compiled and revised all known knowledge about the orbits of the wandering stars over decades of work. Last year he was awarded the gold medal by the British Royal Astronomical Society for this mammoth work. The eulogy was given by the President of the Society: John Couch Adams.

Until the end of his life, Le Verrier rarely looked personally through a telescope. He was more concerned with mathematics and theory than looking into the depths of space. One contemporary even goes so far as to claim that Le Verrier himself was only interested in Neptune in theory: "I almost think he never saw it."

Back to main page