Following the discovery of Neptune it was calculated that perturbations in the movements of the giant outer planets indicated the presence of another planet, Planet X, beyond them. Percival Lowell (b. 13 March 1855, 0745 hr LMT, Boston MA; d. 12 November 1916, Flagstaff AZ) made preliminary calculations into its position and devoted many years star-watching in search of it. He actually did photograph Pluto but the image stayed undiscovered, as he never analysed the plates. An astronomer at Mount Wilson Observatory CA, also photographed Pluto on four plates in December 1919, but nobody noticed it.
In 1920 astronomers under the direction of Vesto Slipher at the Lowell Observatory, Flagstaff AZ (the private observatory founded by Lowell on 1 June 1894), began the search again, using a new 35 cm refractor, time-lapse photography and a blink-comparator, and ten years later, found what they were looking for.
Pluto was first detected by the project leader, Clyde Tombaugh (b. 4 February 1906, Streator IL; d. 17 January 1997, Las Cruces
NM). He had been asked by Slipher to look for "what else is out there beyond
Neptune", and on 18 February 1930 at 1600 hr MST (give or take 3
minutes), he found Pluto. It was discovered from a comparison of photographs of a star-field in the constellation
Gemini that had been taken 23 and 29 January 1930.
Tombaugh had joined the team on 15 January 1929, and began searching for Pluto in April 1929. He had actually photographed Pluto twice within the first month, but the discovery went unnoticed due to a glass plate cracking during the comparison session.
Pluto was found while retrograde between 18° 18' and 18° 6' of the sign Cancer, close to the star Delta Geminorum. Tombaugh announced the find on 13 March, the anniversary of Lowell's birth.
A competition was set to name the new planet, and an 11-year old Oxford schoolgirl won by choosing the name of her favourite Walt Disney character, Mickey Mouse's dog, Pluto, who had made his debut in the cartoon film Chain Gang on 18 August 1930. One of the objections to the name was a possible connection with Pluto Water, a popular laxative of the time. The Tombaugh family cat was named Pluto, too, but that came later.
It was immediately realised that Pluto was too small to be the cause of the apparent irregularities in the orbits of Uranus and Neptune, despite being found so close to its predicted position. Tombaugh therefore continued his search, examining images including about 90 million stars for other planets beyond both Neptune and Pluto. In 1947, he concluded that there was no other planet as bright as 16th magnitude to be found.
Ironically, when Voyager flew past Neptune in 1989, Neptune was found to be in the "right" place after all. Any pre-1910 data has to be suspect since micrometers were not then in use.
Pluto is five hundred times smaller than Earth and is now known to have a diameter of only 1,419 miles (0.18 that of Earth), though it was originally thought to be considerably larger. It is therefore the smallest planet in the Solar System, smaller than our Moon, and only three times the size and ten times the mass of the largest known asteroid, Ceres.
Astronomers now realize that Pluto is actually the largest known member of an entire class
known as Kuiper Belt Objects. Astronomers in 1999 were for a time considering whether to reclassify Pluto as a minor
planet. "Pluto was lucky," said Gareth Williams, of the Harvard-Smithsonian Institute of Astrophysics in Massachusetts, "If it was discovered today, astronomers would certainly not give it the status of a planet." The controversy was revived in 2001 when the American Museum of Natural History in New York introduced a set of exhibits that reclassified Pluto as a member of the Kuiper Belt.
By this time, a newly discovered class of bodies known as Centaurs were being found beyond Neptune, Chiron being the first of these to be so identified, and Pluto could be classed as one of these. "Pluto does not have a family except for the icy bodies in the outer solar system. So we simply group it with the Kuiper Belt. In a sense we're completely side-stepping the definitional problem altogether," said Neil deGrasse Tyson, director of the museum's Hayden Planetarium.
"Pluto started out as the ninth planet, a supported fulfillment of Percival Lowell's prediction of Planet X. Let's simply retain Pluto as the
ninth major planet. After all, there is no Planet X. For 14 years, I combed two-thirds of the entire sky down to 17th magnitude, and no more
planets showed up. I did the job thoroughly and correctly", said Clyde
Tombaugh, in a letter to Sky And Telescope published in December 1994, "Pluto was
your last chance for a major planet."
Pluto probably originated in the Kuiper Belt, sucked by the Sun's immense gravity into our Solar System, and pulled into its distorted elliptical orbit by Neptune. Alternatively, it could have once been a
captured moon of Neptune. It is smaller even than Europa, Jupiter's smallest Galilean moon.
Pluto has a high orbital inclination of 17.12° so the imaginary Zodiac Belt had to be broadened to include it. Its mean distance from the Sun is 3,666,874,000 miles (39.44 AU) though this can vary from 2,750,156,000 to 4,583,592,000 miles. It orbits the Sun every 248.54 years, with an equatorial rotation of 6.3871 days. It is the faintest known planet, with a magnitude of 15. Light from Pluto at mean distance takes 5 hours 20 min to reach Earth, so when we see Pluto overhead it is actually about to set. Its high orbital eccentricity of 0.248 (due to being geared to the orbit of Neptune) means that it was within the orbit of Neptune from 21 January 1979 at 2157 hr 57" GMT, and came to perihelion during 1989, at 14° Scorpio. It re-crossed Neptune's orbit on 11 February 1999 to become again the outermost planet.
As its orbital path is so elliptical its apparent speed is quite erratic. It was at its slowest last in 1850, at the time of the Great Exhibition, and reached its greatest speed most recently in 1988 as it was on the narrow end of its ellipse. At the extreme of its orbit, Pluto travels into the Kuiper Belt, on the edge of our planetary system, a realm populated by long-period comets and newly discovered planetisimals.
Pluto has a surface temperature estimated at -220°C and consists mainly of rock with 25% ice, and unlike Neptune and Uranus is solid throughout. Frozen nitrogen and carbon monoxide have been detected on Pluto. In 1988 it was established that it has an extensive but tenuous atmosphere at least as deep as its own diameter, composed largely of methane. This is a feature of Pluto's perihelion. Like a comet or centaur, as it moves away from the Sun, towards aphelion, the methane freezes and falls to the surface as snow, freshening the bright surface and causing it to become seven times more reflective than the Moon, but leaving it temporarily without an atmosphere. This will next happen between 2010 and 2015, and its atmosphere will not then return until 2237.
The Hubble space telescope began sending back high quality images of Pluto in 1995 and confirmed that Pluto's icy surface acts like a smooth mirror. Pluto is "a knock-your-socks-off plane" according to Dr Alan Stern of the Southwest Research Institute, Boulder CO, after studying new Hubble images in 1996, which showed ragged icy polar caps and clusters of dark and bright features. The bright features were thought to be fields of frozen nitrogen; the dark features hydrocarbons and frozen methane.
Pioneer 10, launched from the Kennedy Space Centre at Cape Canaveral on 2 March 1972, achieved the Third Cosmic velocity necessary to take it beyond the Solar System, leaving Earth at 32,114 mph. It crossed the mean orbit of Pluto, becoming the remotest man-made object on 17 October 1986, when it was 3,670 million miles away. By April 1989 it had passed beyond Pluto's furthest extension of orbit, travelling at 30,450 mph. It is due to reach the star Ross 248, 10.3 light years away, in the year AD 34,593.
Pluto's glyph originally comprised the initials of Percival Lowell, H. However its second symbol J shows the circle of spirit suspended inside the half-circle of soul, linked to the cross of matter. It resembles an atom hovering inside a chalice.
In mythology Pluto, or Dis, was the terrible Roman god of the underworld, lord of the dead. He was called Hadès by the Greeks, God of Death and Rebirth, and Mantus by the Etruscans. The story of Hadès, Demeter and Persephone was re-enacted ritually between 1400 BC and 400 AD as the Eleusinian Mystery Rites.
In traditions thousands of years earlier, however, the underworld was generally ruled by a goddess. In Sumeria, for example, from around 4,000 BC, Inanna, Queen of Heaven (a precursor of Ishtar), descends into the realm of her sister, Ereshkigal, Lady Of The Great Place Below and undergoes a series of rebirth rituals. The Egyptian equivalents are Isis and Sekhmet, the lioness-headed war leader and mistress of massacre and vengeance, who is analogous to the Hindu goddess Kali. Astarte held a similar role in Canaan and Phonecia. Astarte and Inanna were both early forms of Aphrodite, or Venus.
Pluto was therefore feminine in origin, but by the 12th century BC in most mythologies a god rather than a goddess personified the Plutonic higher and lower natures recognised in man (for example Shiva, Yama, Mantus, Orcus, Satan, Osiris).
In astrology, as the outermost known planet, Pluto represents the limits of our present stage of consciousness. Pluto can reach 17° above or below the ecliptic, symbolising the great heights to which man can rise and the equally great depths he can plumb. The nineteenth-century occultist Zanoni (Thomas Burgoyne), and the astrologer Alan Leo (b. 7 August 1860; d. 1918) both made mention of Pluto and its attributes up to thirty years before it was discovered, Alan Leo even mentioning it by name.
Since its discovery in 1930, Pluto has been found to have a powerful and profound influence in our horoscope, and partially displaced Mars in its rulership of Scorpio.
Its discovery in 1930 coincided with the development of psychology; the gangster era in America; the birth of dictatorships; the first man-made nuclear reaction; the discovery of plutonium with its capacity to end the world; and the world's greatest economic depression. However, its projected but short-lived re-classification as a minor planet in 1999 led to astrologers questioning the extent of its influence. "One interesting result stems from Pluto being associated with gross materialism," said Prudence Jones,
as chair of the Association of Profession Astrologers, in The Observer (17 January 1999). "The view is that the only real things are those that you can kick and fall over. If Pluto ceases to be seen by people as a real planet, then their own materialism could dissolve. Thought would become more important than things. Dogmatic religious thought is consequently going to be a force to be reckoned with." However, Pluto remains the same size and distance as it was, in the same position, and of the same materials, so should surely have exactly the same effects however it is described or classified.
Pluto travels about 1° per year on average, but because its orbit is so eccentric the time spent in each sign varies. Its last passage through Gemini lasted 33 years, but its placing in Scorpio lasted less than 12 (1983-1995), perhaps corresponding to the increasing rate of change of our values. During this time most people perceived time to be passing far more quickly than they were used to. Pluto's orbit-crossing characteristics are associated with cosmic fecundity and the star seeding process.
Pluto is regarded as a higher octave of Mars, and in esoteric astrology it rules Pisces. The role of Hadès in the myth of Demeter (Ceres) and Persephone is highly relevant to Plutonian issues in our charts. Pluto signifies our ability to penetrate below the surface. It shows us our attitude towards enforced changes and upheavals; our sense of isolation and detachment; our capacity to endure loneliness. It exposes our anti-social tendencies; our ability to rise, phoenix-like from the ashes of destruction, and regenerate our transformed selves; our attitude towards beginnings and endings, births and deaths, actual and symbolic. It is active in our personal power struggles; obsessions; merging; sexuality; destruction; healing; intensity. Keywords include force majeure and transcendity. Pluto's message is to go where the energy is, providing a "black hole" experience and "white hole" rebirth. Some of what was ascribed to Saturn before Pluto was discovered was subsequently thought to have been the influence of Pluto.
In mundane astrology Pluto represents power to the masses, totalitarian, compulsive, collective pressures, forces of elimination, regeneration and resurgence. It relates to emerging nations, and nations in a state of renaissance and reconstruction; also to fanaticism; to an obsession with the impersonal; collective ideas and ideals. Pluto can indicate the need to purge the body politic of old deep-rooted problems. Constellated by a leader in a chart it can awaken compulsive instincts for power and dominance.
The reason for the apparent variations in the diameter of Pluto turned out to be that it has a relatively large satellite orbiting very close to its surface. James W Christy and Robert S Harrington were the first to realise that photographic images of Pluto were not symmetrical, but elongated, and from this deduced the existence of a moon. This was photographically verified and Pluto's companion planet, Charon, was announced to the world on 22 June 1978, from the US Naval Observatory, Flagstaff AZ, just as Pluto was about to cross the orbital path of Neptune. Doubt remained, however, until French astronomers at Maune Kea Observatory in Hawaii took a photograph that showed the two bodies separately.
Charon has been described as the "biggest known hailstone in the universe". Charon's surface has more blue than that of Pluto and consists of water frost and its volume of 300 million cubic miles is almost entirely of ice, its density being almost exactly the same as the density of water. It has a diameter of 737 miles and Pluto and Charon orbit each other like a pair of dumb-bells at a near-constant distance of 10,563 miles, a mere twentieth of the distance between Earth and the Moon. But whereas the Moon is only one eightieth the weight of Earth, Charon is a tenth the weight of Pluto. Starting in 1985, mutual geocentric occultations of Pluto and Charon occurred over a five-year period, during which they were in mutual eclipse every 6.4 days; Charon was periodically hidden by Pluto. If Charon hadn't been found when it was, astronomers would have had to wait for half a Plutonic year, 124 Earth years, for the next series.
During Pluto's 248 year orbit, Charon and Pluto loop around each other, showing the same face to each other, 14,000 times. Its orbit is almost exactly circular and takes 6.3871 days, which is also the rotation period of Pluto itself. Pluto and Charon therefore comprise a "fixed" pair, which is unique in the Solar System. Since Charon has a large size relative to that of Pluto they should be regarded as a double planet system. It was thought that both Pluto and Charon could be escaped moons of Neptune, but it is now thought more likely that they are probably giant comets, or centaurs, gravitationally captured from far outside the Solar System. Chiron, with which it has some similarities, may have been captured in the same way, and other smaller objects with orbits similar to that of Pluto have increasingly been discovered beyond the orbit of Neptune. These have been called Trans-Neptunian Objects, nicknamed Plutinos. Pluto and Charon are themselves the largest known members of this group of objects.
Charon is the ancient ferryman who ushers the souls of the dead across the river Styx to Hadès, Pluto's underworld. If he is not paid his coin the soul of the dead person will be left to wander eternally on the far bank. This links Pluto with Mercury since it is Hermes the Trickster (Mercury) who lures the unsuspecting souls, through deceit and intrigue, down into the depths and delivers them to Charon (Jim Christy actually named his find Charon after his wife, Charlene, but cannot have been unaware of the mythological appropriateness).
In astrology, the satellites of a planet are not generally distinguished from the planet itself, with the exception of our Moon. The vast distances involved mean that the planet's system seems to occupy a single point or second of a minute of a degree when viewed from Earth. Where we in proximity to any of the moons in our solar system, their individual qualities would presumably be as manifest as the Moon is to us now. It is a reasonable hypothesis, however, that there could be a different astrological influence when a planet's moons are all occulting the planet, for example, compared to when they are grouped to either side. When Pluto is interpreted in a horoscope we should remember that it is actually the Pluto/Charon double system that is being studied.
Last updated 21 February 2005