Although Pluto's status as a planet may have been recently downgraded by astronomers, it's still considered an important factor in astrology. It's such an enigmatic and important body that failing to explore its secrets could be a grave mistake, especially regarding relationships.
If one learns a little about this small and distant object, it is hard to deny its value.
It's often said that Percival Lowell discovered Pluto, but the observatory he built was where Pluto was discovered, after his death. He had searched for it, but never was successful. It was finally located by Clyde Tombaugh, and a search went out for a name for the new body. It's an urban myth that it was named after Mickey Mouse's dog; it was named by an 11 year old English girl who was fascinated with both astronomy and mythology; she named it after the Roman lord of the underworld, because it was a cold, dark planet. Walt Disney gave Mickey Mouse his canine companion in the same year, and some say the dog was called Pluto to honor the discovery.
Pluto has a Moon, Charon, which is almost as large as it is. They rotate around a common gravitational center; this is part of the reason that astronomers "demoted" it from planetary status. Many objects have been discovered (both beyond Pluto and within the Solar System) that have enough mass to be considered "minor planets." Astronomers felt justified in classing Pluto with them, rather than the giant planets, Jupiter, Saturn, Uranus and Neptune, that precede it.
Pluto takes 248 years to transit the Zodiac, but its orbit is so skewed that it spends differing amounts of time in each sign; it spent 25 years in Cancer, where it was discovered, and only 12 years in Scorpio.
Not long after its discovery, Pluto was assigned the rulership of Scorpio, probably because the astrologers of the 18th and 19th centuries equated the Zodiac signs with the houses of the horoscope - they considered the 8th house the house of death, and associated the 8th sign, Scorpio with it as well.
If we carefully examine the movements of Pluto in the light of social and personal histories, we can see that it is associated with mining, uncovering secrets, personal transformation, power struggles, mass movements and other phenomena, some of which can be linked to Scorpio, and some of which cannot. There's no justification for saying that Pluto is debilitated in Taurus, because Taurus is an Earth Sign, and Pluto is associated with wealth that comes from the Earth. The same is true of exaltation; Pluto is said to be exalted in Cancer, simply because it is the sign in which it was discovered. Again, there really is no need or reason to force fit the newly discovered bodies into a system that is already airtight.
Pluto is also a remover of obstacles; when Pluto is well situated, and especially when it combines with Jupiter, it has the power to remove anything that stands in the way of success. It also rules nuclear power (plutonium, anyone?), and the need to work with another in order to prevent mutual difficulties.
Pluto is said to rule over the concentration of wealth and power; in modern times, the greatest amount of wealth has gradually moved into the hands of a smaller percentage of the population. This phenomenon is often described as Plutocracy.
But the world economy changes with Pluto's movement through the signs. Because it's also the planet of personal transformation, everything from cosmetic surgery to Yoga to Neuro-Linguistic Programming, all fall within Pluto's domain.
When combined with the other planets that define a relationship, Pluto can make things happen fast. It's usually Pluto that can turn friends into "something more than friends" or can take a casual relationship and "kick it up a notch." But it is also a separative planet, and can be seen as being prominent in many divorces and break-ups. It is also very active in liberating individuals from abusive relationships.
Often it is associated with intimacy, but intimacy itself is really the domain of Mars and Venus. Pluto's role has more to do with the effects of the physical intimacy on one's psychological make-up. One could say that the psychological theories of Sigmund Freud and Carl Jung are Plutonian in nature, because they seek to uncover what lies in the depths of the unconscious, and transform the relationship with the self. The underlying motives and complexes that drive intimate behavior have a lot to do with Pluto's role in astrology.
This tiny planet can also drive obsessions and compulsions, yet it's involved in "firsts" and unique events in the love-life. Studying the role of Pluto in relationships is a fascinating subject, and another reason to delve more deeply into astrology.