In 1859ĦA Le Verrier received a letter from the amateur astronomer LescarbaultĦA who reported having seen a round black spot on the Sun on March 26 1859ĦA looking like a planet transiting the Sun. He had seen the spot one hour and a quarterĦA when it moved a quarter of the solar diameter. Lescarbault estimated the orbital inclination to between 5.3 and 7.3 degreesĦA its longitude of node about 183 degĦA its eccentricity "enormous"ĦA and its transit time across the solar disk 4 hours 30 minutes. Le Verrier investigated this observationĦA and computed an orbit from it: period 19 days 7 hoursĦA mean distance from Sun 0.1427 a.u.ĦA inclination 12# 10'ĦA ascending node at 12# 59' The diameter was considerably smaller than Mercury's and its mass was estimated at 1/17 of Mercury's mass. This was too small to account for the deviations of Mercury's orbitĦA but perhaps this was the largest member of that intra-Mercurial asteroid belt? Le Verrier fell in love with the planetĦA and named it Vulcan.
In 1860 there was a total eclipse of the Sun. Le Verrier mobilized all French and some other astronomers to find Vulcan - nobody did. Wolf's suspicious 'sunspots' now revived Le Verrier's interestĦA and just before Le Verrier's death in 1877 some more 'evidence' found its way into print. On April 4 1875ĦA a German astronomerĦA H. WeberĦA saw a round spot on the Sun. Le Verrier's orbit indicated a possible transit at April 3 that yearĦA and Wolf noticed that his 38-day orbit also could have performed a transit at about that time. That 'round dot' was also photographed at Greenwich and in Madrid.
There was one more flurry after the total solar eclipse at July 29 1878ĦA where two observers claimed to have seen in the vicinity of the Sun small illuminated disks which could only be small planets inside Mercury's orbit: J.C Watson (professor of astronomy at the Univ. of Michigan) believed he'd found TWO intra-Mercurial planets! Lewis Swift (co-discoverer of Comet Swift-TuttleĦA which returned 1992)ĦA also saw a 'star' he believed to be Vulcan -- but at a different position than either of Watson's two 'intra-Mercurials'. In additionĦA neither Watson's nor Swift's Vulcans could be reconciled with Le Verrier's or Lescarbault's Vulcan.
After thisĦA nobody ever saw Vulcan againĦA in spite of several searches at different total solar eclipses. And in 1916ĦA Albert Einstein published his General Theory of RelativityĦA which explained the deviations in the motions of Mercury without the need to invoke an unknown intra-Mercurial planet. In May 1929 Erwin FreundlichĦA PotsdamĦA photographed the total solar eclipse in SumatraĦA and later carefully examined the plates which showed a profusion of star images. Comparison plates were taken six months later. No unknown object brighter than 9th magnitude was found near the Sun.
But what did these people really see? Lescarbault had no reason to tell a fairy taleĦA and even Le Verrier believed him. It is possible that Lescarbault happened to see a small asteroid passing very close to the EarthĦA just inside Earth's orbit. Such asteroids were unknown at that timeĦA so Lescarbault's only idea was that he saw an intra-Mercurial planet. Swift and Watson couldĦA during the hurry to obtain observations during totalityĦA have misidentified some starsĦA believing they had seen Vulcan.
"Vulcan" was briefly revived around 1970-1971ĦA when a few researchers thought they had detected several faint objects close to the Sun during a total solar eclipse. These objects might have been faint cometsĦA and later comets have been observed that later did pass close enough to the Sun to collide with it.
After a hectic FridayĦA when the "object" had been computed to move at 4 km/sĦA a speed consistent with that of a moonĦA JPL managers were called in. They turned the then-dying spacecraft over full time to the UV teamĦA and everyone started worrying about a press conference scheduled for later that Saturday. Should the suspected moon be announced? But the press already knew. Some papers -- the biggerĦA more respectable ones -- played it straight; many others ran excited stories about Mercury's new moon.
And the "moon" itself? It headed straight on out from MercuryĦA and was eventually identified as a hot starĦA 31 Crateris. What the original emissions came fromĦA the ones spotted on the approach to the planetĦA remains a mystery. So ends the story of Mercury's moon but at the same time a new chapter in astronomy began: extreme UV turned out not to be so completely absorbed by the interstellar medium as formerly believed. Already the Gum nebula has turned out to be a quite strong emitter in the extreme UVĦA and spreads across 140 degrees of the night sky at 540 angstroms. Astronomers had discovered a new window through which to observe the heavens.
Now the astronomical world was faced with a controversy: several observers had reported seeing the satellite while several others had failed to find it in spite of determined efforts. In 1766ĦA the director of the Vienna observatoryĦA Father Hell (!)ĦA published a treatise where he declared that all observations of the satellite were optical illusions -- the image of Venus is so bright that it is reflected in the eyeĦA back into the telescopeĦA creating a secondary image at a smaller scale. Others published treatises declaring that the observations were real. J. H. Lambert of Germany published orbital elements of the satellite in Berliner Astronomischer Jahrbuch 1777: mean distance 66.5 Venus radiiĦA orbital period 11 days 3 hoursĦA inclination to ecliptic 64 degrees. It was hoped that the satellite could be seen during the transit of Venus in front of the Sun June 1 1777 (it is self evident that Lambert made a mistake in calculating these orbital elements: at 66.5 Venus radiiĦA the distance from Venus is about the same as our Moon's distance from the Earth. This fits very badly with the orbital period of 11 days or only somewhat more than 1/3 of the orbital period of our Moon. The mass of Venus is a little smaller than the mass of the Earth).
In 1768 there was one more observation of the satelliteĦA by Christian Horrebow in Copenhagen. There were also three searchesĦA one made by one of the greatest astronomers of all timeĦA William Herschel -- all three of them failed to find any satellite. Quite late in the gameĦA F. Schorr from Germany tried to make a case for the satellite in a book published in 1875.
In 1884ĦA M. HozeauĦA former director of the Royal Observatory of BrusselsĦA suggested a different hypothesis. By analysing available observations Hozeau concluded that the Venus moon appeared close to Venus approximately every 2.96 years or 1080 days. Hozeau suggested that it wasn't a moon of VenusĦA but a planet of its ownĦA orbiting the sun once every 283 days and thus being in conjunction with Venus once every 1080 days. Hozeau also named it NeithĦA after the mysterious goddess of SaisĦA whose veil no mortal raised.
In 1887ĦA three years after the "moon of Venus" had been revived by HozeauĦA the Belgian Academy of Sciences published a long paper where each and every reported observation was investigated in detail. Several observations of the satellite were really stars seen in the vicinity of Venus. Roedkier's observations "checked out" especially well -- he had been fooledĦA in successionĦA by Chi OrionisĦA M TauriĦA 71 OrionisĦA and Nu Geminorum! James Short had really seen a star somewhat fainter than 8th magnitude. All observations by Le Verrier and Montaigne could be similarly explained. Lambert's orbital calculations were demolished. The very last observationĦA by Horrebow in 1768ĦA could be ascribed to Theta Librae.
After this paper was publishedĦA only one more observation was reportedĦA by a man who had earlier made a search for the satellite of Venus but failed to find it: on Aug 13 1892ĦA E. E. Barnard recorded a 7th magnitude object near Venus. There is no star in the position recorded by BarnardĦA and Barnard's eyesight was notoriously excellent. We still don't know what he saw. Was it an asteroid that hadn't been charted? Or was it a short-lived nova that nobody else happened to see?
"It is"ĦA said BarbicaneĦA "a simple meteorite but an enormous oneĦA retained as a satellite by the attraction of the Earth."Jules Verne was read by millions of peopleĦA but not until 1942 did anybody notice the discrepancies in Verne's text:"Is that possible?"ĦA exclaimed Michel ArdanĦA "the earth has two moons?"
"YesĦA my friendĦA it has two moonsĦA although it is usually believed to have only one. But this second moon is so small and its velocity is so great that the inhabitants of Earth cannot see it. It was by noticing disturbances that a French astronomerĦA Monsieur PetitĦA could determine the existence of this second moon and calculated its orbit. According to him a complete revolution around the Earth takes three hours and twenty minutes. . . . "
"Do all astronomers admit the the existence of this satellite?"ĦA asked Nicholl
"No"ĦA replied BarbicaneĦA "but ifĦA like usĦA they had met it they could no longer doubt it. . . . But this gives us a means of determining our position in space . . . its distance is known and we wereĦA thereforeĦA 7480 km above the surface of the globe where we met it."
NeverthelessĦA Jules Verne made Petit's second moon known all over the world. Amateur astronomers jumped to the conclusion that here was opportunity for fame -- anybody discovering this second moon would have his name inscribed in the annals of science. No major observatory ever checked the problem of the Earth's second moonĦA or if they did they kept quiet. German amateurs were chasing what they called Kleinchen ("little bit") -- of course they never found Kleinchen.
W. H. Pickering devoted his attention to the theory of the subject: if the satellite orbited 320 km above the surface and if its diameter was 0.3 metersĦA with the same reflecting power as the MoonĦA it should be visible in a 3-inch telescope. A 3 meter satellite would be a unaided-eye object of magnitude 5. Though Pickering did not look for the Petit objectĦA he did carry on a search for a secondary moon -- a satellite of our Moon ("On a photographic search for a satellite of the Moon"ĦA Popular AstronomyĦA 1903). The result was negative and Pickering concluded that any satellite of our Moon must be smaller than about 3 meters.
Pickering's article on the possibility of a tiny second moon of EarthĦA "A Meteoritic Satellite"ĦA appeared in Popular Astronomy in 1922 and caused another short flurry among amateur astronomersĦA since it contained a virtual request: "A 3-5-inch telescope with a low-power eyepiece would be the likeliest mean to find it. It is an opportunity for the amateur." But againĦA all searches remained fruitless.
The original idea was that the gravitational field of the second moon should account for the then inexplicable minor deviations of the motion of our big Moon. That meant an object at least several miles large -- but if such a large second moon really existedĦA it would have been seen by the Babylonians. Even if it was too small to show a diskĦA its comparative nearness would have made it move fast and therefore be conspicuousĦA as today's watchers of artificial satellites and even airplanes know. On the other handĦA nobody was much interested in moonlets too small to be seen.
There have been other proposals for additional natural satellites of the Earth. In 1898 Dr Georg Waltemath from Hamburg claimed to have discovered not only a second moon but a whole system of midget moons. Waltemath gave orbital elements for one of these moons: distance from Earth 1.03 million kmĦA diameter 700 kmĦA orbital period 119 daysĦA synodic period 177 days. "Sometimes"ĦA says WaltemathĦA "it shines at night like the Sun" and he thinks this moon was seen in Greenland on 24 October 1881 by Lieut GreelyĦA ten days after the Sun had set for the winter. Public interest was aroused when Waltemath predicted his second moon would pass in front of the Sun on the 2ndĦA 3rd or 4th of February 1898. On the 4th FebruaryĦA 12 persons at the post office of Greifswald (Herr Postdirektor ZiegelĦA members of his familyĦA and postal employees) observed the Sun with their unaided eyeĦA without protection of the glare. It is easy to imagine a faintly preposterous scene: an imposing-looking Prussian civil servant pointing skyward through his office windowĦA while he reads Waltemath's prediction aloud to a knot of respectful subordinates. On being interviewedĦA these witnesses spoke of a dark object having one fifth the Sun's apparent diameterĦA and which took from 1:10 to 2:10 Berlin time to traverse the solar disk. It was soon proven to be a mistakeĦA because during that very hour the Sun was being scrutinized by two experienced astronomersĦA W. Winkler in Jena and Baron Ivo von Benko from PolaĦA Austria. They both reported that only a few ordinary sunspots were on the disk. The failure of this and later forecasts did not discourage WaltemathĦA who continued to issue predictions and ask for verifications. Contemporary astronomers were pretty irritated over and over again having to answer questions from the public like "OhĦA by the wayĦA what about all these new moons?". But astrologers caught on -- in 1918 the astrologer Sepharial named this moon Lilith. He considered it to be black enough to be invisible most of the timeĦA being visible only close to opposition or when in transit across the solar disk. Sepharial constructed an ephemeris of LilithĦA based on several of Waltemath's claimed observations. He considered Lilith to have about the same mass as the MoonĦA apparently happily unaware that any such satellite wouldĦA even if invisibleĦA show its existence by perturbing the motion of the Earth. And even to this dayĦA "the dark moon" Lilith is used by some astrologers in their horoscopes.
From time to time other "additional moons" were reported from observers. The German astronomical magazine "Die Sterne" reported that a German amateur astronomer named W. Spill had observed a second moon cross our first moon's disc on May 24ĦA 1926.
Around 1950ĦA when artificial satellites began to be discussed in earnestĦA everybody expected them to be just burned-out upper stages of multistage rocketsĦA carrying no radio transmitters but being tracked by radar from the Earth. In such cases a bunch of small nearby natural satellites would have been most annoyingĦA reflecting radar beams meant for the artificial satellites. The method to search for such natural satellites was developed by Clyde Tombaugh: the motion of a satellite at e.g. 5000 km height is computed. Then a camera platform is constructed that scans the sky at precisely that rate. StarsĦA planets etc will then appear as lines on the photographs taken by this cameraĦA while any satellite at the correct altitude will appear as a dot. If the satellite was at a somewhat different altitudeĦA it would produce a short line.
Observations began in 1953 at the Lowell Observatory and actually invaded virgin territory: with the exception of the Germans searching for "Kleinchen" nobody had ever paid attention to the space between the Moon and the Earth! By the fall of 1954ĦA weekly journals and daily newspapers of high reputation stated that the search had brought its first results: one small natural satellite at 700 km altitudeĦA another one 1000 km out. One general is said to have asked: "Is he sure they're natural?". Nobody seems to know how these reports originated -- the searches were completely negative. When the first artificial satellites were launched in 1957 and 1958ĦA the cameras tracked those satellites instead.
But strangely enoughĦA this does not mean that the Earth only has one natural satellite. The Earth can have a very near satellite for a short time. Meteoroids passing the Earth and skimming through the upper atmosphere can lose enough velocity to go into a satellite orbit around the Earth. But since they pass the upper atmosphere at each perigeeĦA they will not last longĦA maybe only one or twoĦA possibly a hundred revolutions (about 150 hours). There are some indications that such "ephemeral satellites" have been seen; it is even possible that Petit's observers did see one. (see also)
In addition to ephemeral satellites there are two more possibilities. One is that the Moon had a satellite of its own -- but despite several searches none has been found (in addition it's now known that the gravity field of the Moon is uneven or "lumpy" enough for any lunar satellite orbit to be unstable -- any lunar satellite will therefore crash into the Moon after a fairly short timeĦA a few years or possibly a decade). The other possibility is that there might be Trojan satellitesĦA i.e. secondary satellites in the lunar orbitĦA travelling 60 degrees ahead of or behind the Moon.
Such "Trojan satellites" were first reported by the Polish astronomer Kordylewski of Krakow observatory. He started his search in 1951ĦA visually with a good telescope. He was hoping for reasonably large bodies in the lunar orbitĦA 60 degrees away from the Moon. The search was negativeĦA but in 1956 his compatriot and colleagueĦA WilkowskiĦA suggested that there may be many tiny bodiesĦA too small to be seen individually but many enough to appear as a cloud of dust particles. In such a caseĦA they would be best visible without a telescope i.e. with the unaided eye! Using a telescope would "magnify it out of existence". Dr Kordylewski was willing to try. A dark night with clear skiesĦA and the Moon being below the horizonĦA was required.
In October 1956ĦA Kordylewski sawĦA for the first timeĦA a fairly bright patch in one of the two positions. It was not smallĦA subtending an angle of 2 degrees (i.e. about 4 times larger than the Moon itself)ĦA and was very faintĦA only about half as bright as the notoriously difficult Gegenschein (counterglow -- a bright patch in the zodiacal lightĦA directly opposite to the Sun). In March and April 1961ĦA Kordylewski succeeded in photographing two clouds near the expected positions. They seem to vary in extentĦA but that may be due to changing illumination. J. Roach detected these cloud satellites in 1975 with the OSO (Orbiting Solar Observatory) 6 spacecraft. In 1990 they were again photographedĦA this time by the Polish astronomer WiniarskiĦA who found that they were a few degrees in apparent diameterĦA that they "wandered" up to ten degrees away from the "trojan" pointĦA and that they were somewhat redder than the zodiacal light.
So the century-long search for a second moon of the Earth seems to have succeededĦA after allĦA even though this 'second moon' turned out to be entirely different from anything anybody had ever expected. They are very hard to detect and to distinguish from the zodiacal lightĦA in particular the Gegenschein.
But people are still proposing additional natural satellites of the Earth. Between 1966 and 1969 John BargbyĦA an American scientistĦA claimed to have observed at least ten small natural satellites of the EarthĦA visible only in a telescope. Bargby found elliptical orbits for all the objects: eccentricity 0.498ĦA semimajor axis 14065 kmĦA which yields perigee and apogee heights of 680 and 14700 km. Bargby considered them to be fragments of a larger body which broke up in December 1955. He based much of his suggested satellites on supposed perturbations of artificial satellites. Bargby used artificial satellite data from Goddard Satellite Situation ReportĦA unaware that the values in this publication are only approximate and sometimes grossly in error and can therefore not be used for any precise scientific analysis. In additionĦA from Bargby's own claimed observations it can be deduced that when at perigee Bargby's satellites ought to be visible at first magnitude and thus be easily visible to the unaided eyeĦA yet no-one has seen them as such.
In 1997ĦA Paul Wiegert (et al) discovered that Asteroid 3753 has a very strange orbit and can be considered a companion to EarthĦA though it certainly does not orbit the Earth directly.
In 1643ĦA the Capuchin monk Anton Maria Shyrl claimed to really have seen the moons of Mars. We now know that would be impossible with the telescopes of that time -- probably Shyrl got deceived by a star nearby Mars.
In 1727ĦA Jonathan Swift in "Gulliver's Travels" wrote about two small moons orbiting MarsĦA known to the Laputian astronomers. Their periods of revolution were 10 and 21.5 hours. These 'moons' were in 1750 adopted by Voltaire in his novel "Micromegas"ĦA the story of a giant from Sirius visiting our solar system.
In 1747 a German captainĦA KindermannĦA had claimed to have seen the moon (just one!) of MarsĦA on 10 July 1744. Kindermann reported the orbital period of this martian moon as 59 hours 50 minutes and 6 seconds (!)
In 1877ĦA Asaph Hall finally discovered Phobos and DeimosĦA the two small moons of Mars. Their orbital periods are 7 hours 39 minutes and 30 hours 18 minutesĦA quite close to the periods guessed by Jonathan Swift 150 years earlier!
In 1905ĦA Pickering though he had discovered a tenth moonĦA which he named Themis. According to PickeringĦA it orbited Saturn between the orbits of Titan and Hyperion in a highly inclined orbit: mean distance from Saturn 1ĦA460ĦA000 kmĦA orbital period 20.85 daysĦA eccentricity 0.23ĦA inclination 39 degrees. Themis was never seen againĦA but nevertheless appeared in almanacs and astronomy books well into the 1950's and 1960's.
In 1966ĦA A. Dollfus discovered another new moon of Saturn. It was named JanusĦA and orbited Saturn just outside its rings. It was so faint and close to the rings that the only chance to see it was when the rings of Saturn were seen from the edgeĦA as happened in 1966. Now Janus was Saturn's tenth moon.
In 1980ĦA when Saturns rings again were seen edgewiseĦA a flurry of observations discovered a lot of new satellites close to the rings of Saturn. Close to Janus another satellite was discoveredĦA named Epimetheus. Their orbits are very close to each otherĦA and the most interesting aspect of this satellite pair is that they regularly switch orbits with each other! It turned out that the "Janus" discovered in 1966 really were observations of both of these co-orbital satellites. Thus the 'tenth moon of Saturn' discovered in 1966 really turned out to be two different moons! The spacecraft Voyager 1 and Voyager 2ĦA which travelled past Saturn shortly afterwardsĦA confirmed this.
(Inspired by this successĦA Le Verrier attacked the problem of the deviations of Mercury's orbitĦA and suggested the existence of an intra-mercurial planetĦA VulcanĦA which later turned out to be non-existent.)
On 30 Sept 1846ĦA one week after the discovery of NeptuneĦA Le Verrier declared that there may be still another unknown planet out there. On October 10ĦA Neptune's large moon Triton was discoveredĦA which yielded an easy way to determine accurately the mass of NeptuneĦA which turned out to be 2% larger than expected from the perturbations upon Uranus. It seemed as if the deviations in Uranus' motion really was caused by two planets -- in addition the real orbit of Neptune turned out to be significantly different from the orbits predicted by both Adams and Le Verrier.
In 1850 Ferguson was observing the motion of the minor planet Hygeia. One reader of Ferguson's report was HindĦA who checked the reference stars used by Ferguson. Hind was unable to find one of Ferguson's reference stars. MauryĦA at the Naval ObservatoryĦA was also unable to find that star. During a few years it was believed that this was an observation of yet another planetĦA but in 1879 another explanation was offered: Ferguson had made a mistake when recording his observation -- when that mistake was correctedĦA another star nicely fit his 'missing reference star'.
The first serious attempt to find a trans-Neptunian planet was done in 1877 by David Todd. He used a "graphical method"ĦA and despite the inconclusivenesses of the residuals of UranusĦA he derived elements for a trans-Neptunian planet: mean distance 52 a.u.ĦA period 375 yearsĦA magnitude fainter than 13. Its longitude for 1877.84 was given 170 degrees with an uncertainty of 10 degrees. The inclination was 1.40 degrees and the longitude of the ascending node 103 degrees.
In 1879ĦA Camille Flammarion added another hint as to the existence of a planet beyond Neptune: the aphelia of periodic comets tend to cluster around the orbits of major planets. Jupiter has the greatest share of such cometsĦA and SaturnĦA Uranus and Neptune also have a few each. Flammarion found two cometsĦA 1862 III with a period of 120 years and aphelion at 47.6 a.u.ĦA and 1889 IIĦA with a somewhat longer period and aphelion at 49.8 a.u. Flammarion suggested that the hypothetical planet probably moved at 45 a.u.
One year laterĦA in 1880ĦA professor Forbes published a memoir concerning the aphelia of comets and their association with planetary orbits. By about 1900 five comets were known with aphelia outside Neptune's orbitĦA and then Forbes suggested one trans-Neptunian moved at a distance of about 100 a.u.ĦA and another one at 300 a.u.ĦA with periods of 1000 and 5000 years.
During the next five yearsĦA several astronomers/mathematicians published their own ideas of what might be found in the outer parts of the solar system. Gaillot at Paris Observatory assumed two trans-Neptunian planets at 45 and 60 a.u. Thomas Jefferson Jackson See predicted three trans-Neptunian planets: "Oceanus" at 41.25 a.u. and period 272 yearsĦA "trans-Oceanus" at 56 a.u. and period 420 yearsĦA and finally another one at 72 a.u. and period 610 years. Dr Theodor Grigull of MunsterĦA GermanyĦA assumed in 1902 a Uranus-sized planet at 50 a.u. and period 360 yearsĦA which he called "Hades". Grigull based his work mainly on the orbits of comets with aphelia beyond Neptune's orbitĦA with a cross check whether the gravitational pull of such a body would produce the observed deviations in Uranus motion. In 1921 Grigull revised the orbital period of "Hades" to 310-330 yearsĦA to better fit the observed deviations.
In 1900 Hans-Emil LauĦA CopenhagenĦA published elements of two trans-Neptunian planets at 46.6 and 70.7 a.u. distanceĦA with masses of 9 and 47.2 times the EarthĦA and a magnitude for the nearer planet around 10-11. The 1900 longitudes of those hypothetical bodies were 274 and 343 degreesĦA both with the very large uncertainty of 180 degrees.
In 1901ĦA Gabriel Dallet deduced a hypothetical planet at 47 a.u. with a magnitude of 9.5-10.5 and a 1900 longitude of 358 degrees. The same year Theodor Grigull derived a longitude of a trans-Neptunian planet less than 6 degrees away from Dallet's planetĦA and later brought the difference down to 2.5 degrees. This planet was supposed to be 50.6 a.u. distant.
In 1904ĦA Thomas Jefferson Jackson See suggested three trans-Neptunian planetsĦA at 42.25ĦA 56 and 72 a.u. The inner planet had a period of 272.2 years and a longitude in 1904 of 200 degrees. A Russian general named Alexander Garnowsky suggested four hypothetical planets but failed to supply any details about them.
The two most carefully worked out predictions for the Trans-Neptune were both of American origin: Pickering's "A search for a planet beyond Neptune" (Annals Astron. Obs. Harvard CollĦA vol LXI part II 1909)ĦA and Percival Lowell's "Memoir on a trans-Neptunian planet" (LynnĦA Mass 1915). They were concerned with the same subject but used different approaches and arrived at different results.
Pickering used a graphical analysis and suggested a "Planet O" at 51.9 a.u. with a period of 373.5 yearsĦA a mass twice the Earth's and a magnitude of 11.5-14. Pickering suggested eight other trans-Neptunian planets during the forthcoming 24 years. Pickerings results caused Gaillot to revise the distances of his two trans-Neptunians to 44 and 66 a.u.ĦA and he gave them masses of 5 and 24 Earth masses.
All in allĦA from 1908 to 1932ĦA Pickering proposed seven hypothetical planets -- OĦA PĦA QĦA RĦA SĦA T and U. His final elements for O and P define completely different bodies than the original onesĦA so the total can be set at nineĦA certainly the record for planetary prognostication. Most of Pickerings predictions are only of passing interest as curiosities. In 1911 Pickering suggested that planet Q had a mass of 20ĦA000 EarthsĦA making it 63 times more massive than Jupiter or about 1/6 the Sun's massĦA close to a star of minimal mass. Pickering said planet Q had a highly elliptical orbit.
In later years only planet P seriously occupied his attention. In 1928 he reduced the distance of P from 123 to 67.7 a.u.ĦA and its period from 1400 to 556.6 years. He gave P a mass of 20 Earth masses and a magnitude of 11. In 1931ĦA after the discovery of PlutoĦA he issued another elliptical orbit for P: distance 75.5 a.u.ĦA period 656 yearsĦA mass 50 Earth massesĦA eccentricity 0.265ĦA inclination 37 degreesĦA close to the values given for the 1911 orbit. His Planet SĦA proposed in 1928 and given elements in 1931ĦA was put at 48.3 a.u. distance (close to Lowell's Planet X at 47.5 a.u.)ĦA period 336 yearsĦA mass 5 EarthsĦA magnitude 15. In 1929 Pickering proposed planet UĦA distance 5.79 a.u.ĦA period 13.93 yearsĦA i.e. barely outside Jupiter's orbit. Its mass was 0.045 Earth massesĦA eccentricity 0.26. The least of Pickering's planets is planet TĦA suggested in 1931: distance 32.8 a.u.ĦA period 188 years.
Pickering's different elements for planet O were:
Mean dist Period Mass Magnitude Node Incl Longitude 1908 51.9 373.5 y 2 earth's 11.5-13.4 105.13 1919 55.1 409 y 15 100 15 1928 35.23 209.2 y 0.5 earth's 12Percival LowellĦA most well known as a proponent for canals on MarsĦA built a private observatory in FlagstaffĦA Arizona. Lowell called his hypothetical planet Planet XĦA and performed several searches for itĦA without success. Lowell's first search for Planet X came to an end in 1909ĦA but in 1913 he started a second searchĦA with a new prediction of Planet X: epoch 1850-01-01ĦA mean long 11.67 degĦA perih. long 186ĦA eccentricity 0.228ĦA mean dist 47.5 a.u. long arc node 110.99 degĦA inclination 7.30 degĦA mass 1/21000 solar masses. Lowell and others searched in vain for this Planet X in 1913-1915. In 1915ĦA Lowell published his theoretical results of Planet X. It is ironical that this very same yearĦA 1915ĦA two faint images of Pluto was recorded at Lowell observatoryĦA although they were never recognized as such until after the discovery of Pluto (1930). Lowell's failure of finding Planet X was his greatest disappointment in life. He didn't spend much time looking for Planet X during the last two years of his life. Lowell died in 1916. On the nearly 1000 plates exposed in this second search were 515 asteroidsĦA 700 variable stars and 2 images of Pluto!
The third search for Planet X began in April 1927. No progress was made in 1927-1928. In December 1929 a young farmer's boy and amateur astronomerĦA Clyde Tombaugh from KansasĦA was hired to do the search. Tombaugh started his work in April 1929. On January 23 and 29ĦA Tombaugh exposed the pair of plates on which he found Pluto when examining them on February 18. By then Tombaugh had examined hundreds of plate pairs and millions of stars. The search for Planet X had come to an end.
Or had it? The new planetĦA later named PlutoĦA turned out to be disappointingly smallĦA perhaps only one Earth mass but probably only about 1/10 Earth masses or smaller (in 1979ĦA when Pluto's satellite Charon was discoveredĦA the mass of the Pluto-Charon pair turned out to be only about 1/400 Earth mass!). Planet X mustĦA if it was causing those perturbations in the orbit of UranusĦA be much larger than that! Tombaugh continued his search another 13 yearsĦA and examined the sky from the north celestial pole to 50 deg. south declinationĦA down to magnitude 16-17ĦA sometimes even 18. Tombaugh examined some 90 million images of some 30 million stars over more than 30ĦA000 square degrees on the sky. He found one new globular clusterĦA 5 new open star clustersĦA one new supercluster of 1800 galaxies and several new small galaxy clustersĦA one new cometĦA about 775 new asteroids -- but no new planet except Pluto. Tombaugh concluded that no unknown planet brighter than magnitude 16.5 did exist -- only a planet in an almost polar orbit and situated near the south celestial pole could have escaped his detection. He could have picked up a Neptune-sized planet at seven times the distance of PlutoĦA or a Pluto-sized planet out to 60 a.u.
The naming of Pluto is a story by itself. Early suggestions of the name of the new planet were: AtlasĦA ZymalĦA ArtemisĦA PerseusĦA VulcanĦA TantalusĦA IdanaĦA Cronus. The New York Times suggested MinervaĦA reporters suggested OsirisĦA BacchusĦA ApolloĦA Erebus. Lowell's widow suggested ZeusĦA but later changed her mind to Constance. Many people suggested the planet be named Lowell. The staff of the Flagstaff observatoryĦA where Pluto was discoveredĦA suggested CronusĦA MinervaĦA and Pluto. A few months later the planet was officially named Pluto. The name Pluto was originally suggested by Venetia BurneyĦA an 11-year-old schoolgirl in OxfordĦA England.
The very first orbit computed for Pluto yielded an eccentricity of
0.909 and a period of 3000 years! This cast some doubt whether it
was a planet or not. HoweverĦA a few months laterĦA considerably
better orbital elements for Pluto were obtained. Below is a
comparison of the orbital elements of Lowell's Planet XĦA Pickering's
Planet OĦA and Pluto:
Lowell's X Pickering's O Pluto
a (mean dist) 43.0 55.1 39.5
e (eccentricity) 0.202 0.31 0.248
i (inclination) 10 15 17.1
N (long asc node) (not pred) 100 109.4
W (long perihelion) 204.9 280.1 223.4
T (perihelion date) Febr 1991 Jan 2129 Sept 1989
u (mean annual motion) 1.2411 0.880 1.451
P (periodĦA years) 282 409.1 248
T (perihel. date) 1991.2 2129.1 1989.8
E (long 1930.0) 102.7 102.6 108.5
m (massĦA Earth=1) 6.6 2.0 0.002
M (magnitude) 12-13 15 15
The mass of Pluto was very hard to determine. Several values were
given at different times -- the matter wasn't settled until James W.
Christy discovered Pluto's moon Charon in June 1978 -- Pluto was then
shown to have only 20% of the mass of our Moon! That made Pluto
hopelessly inadequate to produce measurable gravitational
perturbations on Uranus and Neptune. Pluto could not be Lowell's
Planet X -- the planet found was not the planet sought. What seemed
to be another triumph of celestial mechanics turned out to be an
accident -- or rather a result of the intelligence and thoroughness
of Clyde Tombaugh's search.
The mass of Pluto:
Crommelin 1930: 0.11 (Earth masses)
Nicholson 1931: 0.94
WylieĦA 1942: 0.91
BrouwerĦA 1949: 0.8-0.9
KuiperĦA 1950: 0.10
1965: <0.14 (occultation of faint star by Pluto)
SeidelmannĦA 1968: 0.14
SeidelmannĦA 1971: 0.11
CruikshankĦA 1976: 0.002
ChristyĦA 1978: 0.002 (Charon discovered)
Another short-lived trans-Neptunian suspect was reported on April 22
1930 by R.M. Stewart in OttawaĦA Canada -- it was reported from plates
taken in 1924. Crommelin computed an orbit (dist 39.82 a.u.ĦA asc
node 280.49 degĦA inclination 49.7 deg!). Tombaugh searched for the
"Ottawa object" without finding it. Several other searches were madeĦA
but nothing was ever found.
Meanwhile Pickering continued to predict new planets (see above).
Others also predicted new planets on theoretical grounds (Lowell
himself had already suggested a second trans-Neptunian at about 75
a.u.). In 1946ĦA Francis M. E. Sevin suggested a trans-Plutonian
planet at 78 a.u. He first derived this from a curious empirical
method where he grouped the planets and the erratic asteroid
HidalgoĦA into two groups of inner and outer bodies:
Group I: Mercury Venus Earth Mars Asteroids Jupiter Group II: ? Pluto Neptune Uranus Saturn HidalgoHe then added the logarithms of the periods of each pair of planetsĦA finding a roughly constant sum of about 7.34. Assuming this sum to be valid for Mercury and the trans-Plutonian tooĦA he arrived at a period of about 677 years for "Transpluto". Later Sevin worked out a full set of elements for "Transpluto": dist 77.8 a.u.ĦA period 685.8 yearsĦA eccentricity 0.3ĦA mass 11.6 Earth masses. His prediction stirred little interest among astronomers.
In 1950ĦA K. Schutte of Munich used data from eight periodic comets to suggest a trans-Plutonian planet at 77 a.u. Four years laterĦA H. H. Kitzinger of KarlsruheĦA using the same eight cometsĦA extended and refined the workĦA finding the supposed planet to be at 65 a.u.ĦA with a period of 523.5 yearsĦA an orbital inclination of 56 degreesĦA and an estimated magnitude of 11. In 1957ĦA Kitzinger reworked the problem and arrived at new elements: dist 75.1 a.u.ĦA period 650 yearsĦA inclination 40 degreesĦA magnitude around 10. After unsuccessful photographic searchesĦA he re-worked the problem once again in 1959ĦA arriving at a mean dist of 77 a.u.ĦA period 675.7 yearsĦA inclination 38 degreesĦA eccentricity 0.07ĦA a planet not unlike Sevin's "Transpluto" and in some ways similar to Pickering's final Planet P. No such planet has ever been foundĦA though.
Halley's Comet has also been used as a "probe" for trans-plutonian planets. In 1942 R. S. Richardson found that an Earth-sized planet at 36.2 a.u.ĦA or 1 a.u. beyond Halley's aphelionĦA would delay Halley's perihelion passage so that it agreed better with observations. A planet at 35.3 a.u. of 0.1 Earth masses would have a similar effect. In 1972ĦA Brady predicted a planet at 59.9 a.u.ĦA period 464 yearsĦA eccentricity 0.07ĦA inclination 120 degrees (i.e. being in a retrograde orbit)ĦA magnitude 13-14ĦA size about Saturn's size. Such a trans-Plutonian planet would reduce the residuals of Halley's Comet significantly back to the 1456 perihelion passage. This gigantic trans-Plutonian planet was also searched forĦA but never found.
Tom van Flandern examined the positions of Uranus and Neptune in the 1970s. The calculated orbit of Neptune fit observations only for a few yearsĦA and then started to drift away. Uranus orbit fit the observations during one revolution but not during the previous revolution. In 1976 Tom van Flandern became convinced that there was a tenth planet. After the discovery of Charon in 1978 showed the mass of Pluto to be much smaller than expectedĦA van Flandern convinced his USNO colleague Robert S. Harrington of the existence of this tenth planet. They started to collaborate by investigate the Neptunian satellite system. Soon their views diverged. van Flandern thought the tenth planet had formed beyond Neptune's orbitĦA while Harrington believed it had formed between the orbits of Uranus and Neptune. van Flandern thought more data was neededĦA such as an improved mass for Neptune furnished by Voyager 2. Harrington started to search for the planet by brute force -- he started in 1979ĦA and by 1987 he had still not found any planet. van Flandern and Harrington suggested that the tenth planet might be near aphelion in a highly elliptical orbit. If the planet is darkĦA it might be as faint as magnitude 16-17ĦA suggests van Flandern.
In 1987ĦA Whitmire and Matese suggested a tenth planet at 80 a.u. with a period of 700 years and an inclination of perhaps 45 degreesĦA as an alternative to their "Nemesis" hypothesis. HoweverĦA according to Eugene M. ShoemakerĦA this planet could not have caused those meteor showers that Whitmire and Matese suggested (see below).
In 1987ĦA John Anderson at JPL examined the motions of the spacecraft Pioneer 10 and Pioneer 11ĦA to see if any deflection due to unknown gravity forces could be found. None was found -- from this Anderson concluded that a tenth planet most likely exists! JPL had excluded observations of Uranus prior to 1910 in their ephemeridesĦA while Anderson had confidence in the earlier observations as well. Anderson concluded that the tenth planet must have a highly elliptical orbitĦA carrying it far away to be undetectable now but periodically bringing it close enough to leave its disturbing signature on the paths of the outer planets. He suggests a mass of five Earth massesĦA an orbital period of about 700-1000 yearsĦA and a highly inclined orbit. Its perturbations on the outer planets won't be detected again until 2600. Anderson hoped that the two Voyagers would help to pin down the location of this planet.
Conley PowellĦA from JPLĦA also analyzed the planetary motions. He also found that the observations of Uranus suddenly did fit the calculations much better after 1910 than before. Powell suggested a planet with 2.9 Earth masses at 60.8 a.u. from the SunĦA a period of 494 yearsĦA inclination 8.3 degrees and only a small eccentricity. Powell was intrigued that the period was approximately twice Pluto's and three times Neptune's periodĦA suggesting that the planet he thought he saw in the data had an orbit stabilized by mutual resonance with its nearest neighbours despite their vast separation. The solution called for the planet to be in GeminiĦA and also being brighter than Pluto when it was discovered. A search was performed in 1987 at Lowell Observatory for Powell's planet -- nothing was found. Powell re-examined his solution and revised the elements: 0.87 Earth massesĦA distance 39.8 a.u.ĦA period 251 yearsĦA eccentricity 0.26ĦA i.e. an orbit very similar to Pluto's! CurrentlyĦA Powell's new planet should be in LeoĦA at magnitude 12ĦA however Powell thinks it's premature to search for itĦA he needs to examine his data further.
Even if no trans-Plutonian planet ever was foundĦA the interest was focused to the outer parts of the solar system. The erratic asteroid HidalgoĦA moving in an orbit between Jupiter and SaturnĦA has already been mentioned. In 1977-1984 Charles Kowal performed a new systematic search for undiscovered bodies in the solar systemĦA using Palomar Observatory's 48-inch Schmidt telescope. In October 1987 he found the asteroid 1977 UBĦA later named ChironĦA moving at mean distance 13.7 a.u.ĦA period 50.7 yearsĦA eccentricity 0.3786ĦA inclination 6.923 degĦA diameter about 50 km. During his searchĦA Kowal also found 5 comets and 15 asteroidsĦA including ChironĦA the most distant asteroid known when it was discovered. Kowal also recovered 4 lost comets and one lost asteroid. Kowal did not find a tenth planetĦA and concluded that there was no unknown planet brighter than 20th magnitude within 3 degrees of the ecliptic.
Chiron was first announced as a "tenth planet"ĦA but was immediately designated as an asteroid. But Kowal suspected it may be very comet-likeĦA and later it has even developed a short cometary tail! In 1995 Chiron was also classified as a comet - it is certainly the largest comet we know about.
In 1992 an even more distant asteroid was found: Pholus. Later in 1992 an asteroid outside Pluto's orbit was foundĦA followed by five additional trans-Plutonian asteroids in 1993 and at least a dozen in 1994!
MeanwhileĦA the spacecraft Pioneer 10 and 11 and Voyagers 1 and 2 had
travelled outside the solar systemĦA and could also be used as
"probes" for unknown gravitational forces possibly from unknown
planets -- nothing has been found. The Voyagers also yielded more
accurate masses for the outer planets -- when these updated masses
were inserted in the numerical integrations of the solar systemĦA the
residuals in the positions of the outer planets finally disappeared.
It seems like the search for "Planet X" finally has come to an end.
There was no "Planet X" (Pluto doesn't really count)ĦA but instead an
asteroid belt outside Neptune/Pluto was found! The asteroids outside
Jupiter's orbit that were known in August 1993 are as follows:
Asteroid a e Incl Node Arg perih Mean an Per Name
a.u. deg deg deg deg yr
944 5.79853 .658236 42.5914 21.6567 56.8478 60.1911 14.0 Hidalgo
2060 13.74883 .384822 6.9275 209.3969 339.2884 342.1686 51.0 Chiron
5145 20.44311 .575008 24.6871 119.3877 354.9451 7.1792 92.4 Pholus
5335 11.89073 .866990 61.8583 314.1316 191.3015 23.3556 41.0 Damocles
1992QB1 43.82934 .087611 2.2128 359.4129 44.0135 324.1086 290
1993FW 43.9311 .04066 7.745 187.914 359.501 0.4259 291
Epoch: 1993-08-01.0 TT
In November 1994 these trans-Neptunian asteroids were known:
Object a e incl R Mag Diam Discovery Discoverers
a.u. deg km Date
1992 QB1 43.9 0.070 2.2 22.8 283 1992 Aug Jewitt & Luu
1993 FW 43.9 0.047 7.7 22.8 286 1993 Mar Jewitt & Luu
1993 RO 39.3 0.198 3.7 23.2 139 1993 Sep Jewitt & Luu
1993 RP 39.3 0.114 2.6 24.5 96 1993 Sep Jewitt & Luu
1993 SB 39.4 0.321 1.9 22.7 188 1993 Sep Williams et al.
1993 SC 39.5 0.185 5.2 21.7 319 1993 Sep Williams et al.
1994 ES2 45.3 0.012 1.0 24.3 159 1994 Mar Jewitt & Luu
1994 EV3 43.1 0.043 1.6 23.3 267 1994 Mar Jewitt & Luu
1994 GV9 42.2 0.000 0.1 23.1 264 1994 Apr Jewitt & Luu
1994 JQ1 43.3 0.000 3.8 22.4 382 1994 May Irwin et al.
1994 JR1 39.4 0.118 3.8 22.9 238 1994 May Irwin et al.
1994 JS 39.4 0.081 14.6 22.4 263 1994 May Luu & Jewitt
1994 JV 39.5 0.125 16.5 22.4 254 1994 May Jewitt & Luu
1994 TB 31.7 0.000 10.2 21.5 258 1994 Oct Jewitt & Chen
1994 TG 42.3 0.000 6.8 23.0 232 1994 Oct Chen et al.
1994 TG2 41.5 0.000 3.9 24.0 141 1994 Oct Hainaut
1994 TH 40.9 0.000 16.1 23.0 217 1994 Oct Jewitt et al.
1994 VK8 43.5 0.000 1.4 22.5 273 1994 Nov Fitzwilliams et al.
Diameter is in km (and is based on the magnitudes and a guess at albedoĦA
and is given to too many significant figures)
The trans-Neptunian bodies seem to form two groups. One groupĦA composed
of PlutoĦA 1993 SCĦA 1993 SB and 1993 ROĦA have eccentric orbits and a 3:2
resonance with Neptune. The second groupĦA including 1992 QB1 and 1993 FWĦA is
slightly further out and in rather low eccentricity.
This would mean that once every 30 million years that hypothetical companion star of the Sun would pass through the Oort cloud (a hypothetical cloud of proto-comets at a great distance from the Sun). During such a passageĦA the proto-comets in the Oort cloud would be stirred around. Some tens of thousands of years laterĦA here on Earth we would notice a dramatic increase in the the number of comets passing the inner solar system. If the number of comets increases dramaticallyĦA so does the risk of the Earth colliding with the nucleus of one of those comets.
When examining the Earth's geological recordĦA it appears that about once every 30 million years a mass extinction of life on Earth has occurred. The most well-known of those mass extinctions is of course the dinosaur extinction some 65 million years ago. About 15 million years from now it's time for the next mass extinctionĦA according to this hypothesis.
This hypothetical "death companion" of the Sun was suggested in 1985 by Daniel P. Whitmire and John J. MateseĦA Univ of Southern Louisiana. It has even received a name: Nemesis. One awkward fact of the Nemesis hypothesis is that there is no evidence whatever of a companion star of the Sun. It need not be very bright or very massiveĦA a star much smaller and dimmer than the Sun would sufficeĦA even a brown or a black dwarf (a planet-like body insufficiently massive to start "burning hydrogen" like a star). It is possible that this star already exists in one of the catalogues of dim stars without anyone having noted something peculiarĦA namely the enormous apparent motion of that star against the background of more distant stars (i.e. its parallax). If it should be foundĦA few will doubt that it is the primary cause of periodic mass extinctions on Earth.
But this is also a notion of mythical power. If an anthropologist of a previous generation had heard such a story from his informantsĦA the resulting scholarly tome would doubtless use words like 'primitive' or 'pre-scientific'. Consider this story:
There is another Sun in the skyĦA a Demon Sun we cannot see. Long agoĦA even before great grandmother's timeĦA the Demon Sun attacked our Sun. Comets fellĦA and a terrible winter overtook the Earth. Almost all life was destroyed. The Demon Sun has attacked many times before. It will attack again.This is why some scientists thought this Nemesis theory was a joke when they first heard of it -- an invisible Sun attacking the Earth with comets sounds like delusion or myth. It deserves an additional dollop of skepticism for that reason: we are always in danger of deceiving ourselves. But even if the theory is speculativeĦA it's serious and respectableĦA because its main idea is testable: you find the star and examine its properties.
HoweverĦA since the examination of the entire sky in the far IR by IRAS with no "Nemesis" foundĦA the existence of "Nemesis" is not very likely.
William Graves Hoyt: "Planet X and Pluto"ĦA The University of Arizona Press 1980ĦA ISBN 0-8165-0684-1ĦA 0-8165-0664-7 pbk.
Carl SaganĦA Ann Druyan: "Comet"ĦA Michael Joseph LtdĦA 1985ĦA ISBN 0-7181-2631-9
Mark Littman: "Planets Beyond - discovering the outer solar system"ĦA John Wiley 1988ĦA ISBN 0-471-61128-X
Tom van Flandern: "Dark MatterĦA Missing Planets & New Comets. Paradoxes resolvedĦA origins illuminated"ĦA North Atlantic Books 1993ĦA ISBN 1-55643-155-4
Joseph Ashbrook: "The many moons of Dr Waltemath"ĦA Sky and TelescopeĦA Vol 28ĦA Oct 1964ĦA p 218ĦA also on page 97-99 of "The Astronomical Scrapbook" by Joseph AshbrookĦA SKy Publ. Corp. 1984ĦA ISBN 0-933346-24-7
Delphine Jay: "The Lilith Ephemeris"ĦA American Federation of Astrologers 1983ĦA ISBN 0-86690-255-4
William R. Corliss: "Mysterious Universe: A handbook of astronomical anomalies"ĦA Sourcebook Project 1979ĦA ISBN 0-915554-05-4ĦA p 45-71 "The intramercurial planet"ĦA p 82-84 "Mercury's moon that wasn't"ĦA p 136-143 "NeithĦA the lost satellite of Venus"ĦA p 146-157 "Other moons of the Earth"ĦA p 423-427 "The Moons of Mars"ĦA p 464 "A ring around Jupiter?"ĦA p 500-526 "Enigmatic objects"
Richard Baum & William Sheehan: "In Search of Planet Vulcan" Plenum PressĦA New YorkĦA 1997 ISBN 0-306-45567-6 ĦA QB605.2.B38
... Appendices
... Names
... Hypotheticals
... Pictures
... 