Pluto's theme is transformation and power. Destructing old patterns and transform with self-empowerment. He's intense, powerful and represents everything "deep" - also death but in the meaning of rebirth (The Phoenix rising from the ashes). As Pluto is of the deep, it's about the inner self - the inner power - the more aware and conscious we become about our own abilities (power) the more we transform and become that Phoenix. 

I persieve him as the "gate" to the universal outer worlds, which is reached through the path through his realm - the inner world - to find all the wonderous, the fantastic and with it ourselves!! Once we discover our own beauty and treasure, we transform and walk freely through the realms of life....   

Greek Mythology:  Pluto (Roman) - Hades in Greek - Both the ruler of the "underworld". He's the eldest of Cronus and Rhea's sons - the elder Brother of Zeus and Poseidon. He abducted Persephone (Demeter/Ceres daughter) as he wanted and did marry her. She stayed with him for a third or half of the year. As the ruler of the underworld he wasn't liked to be seen - neither the Humans nor the Gods, so he mostly stayed in his "kingdom". He was thought to be very rich as he ruled over all the hidden metals of the Earth. 

Some Astronomy:  A few years ago Pluto was re-classified as dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. After Pluto was discovered in 1930 it was declared to be the ninth planet from the Sun. Beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt, including the dwarf planet Eris. This led the International Astronomical Union (IAU) in 2006 to formally define the term "planet" — excluding Pluto and reclassifying it as a dwarf planet. Pluto is the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—one-sixth the mass of the Moon and one-third its volume. It has a moderately eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU (4.4–7.4 billion km) from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding. Light from the Sun takes 5.5 hours to reach Pluto at its average distance (39.5 AU). Pluto has five known moonsCharon (the largest, with a diameter just over half that of Pluto), StyxNixKerberos, and Hydra

Pluto's orbital period is currently about 248 years. Its orbital characteristics are substantially different from those of the planets, which follow nearly circular orbits around the Sun close to a flat reference plane called the ecliptic. In contrast, Pluto's orbit is moderately inclined relative to the ecliptic (over 17°) and moderately eccentric (elliptical). This eccentricity means a small region of Pluto's orbit lies closer to the Sun than Neptune's. The Pluto–Charon barycenter came to perihelion on September 5, 1989, and was last closer to the Sun than Neptune between February 7, 1979, and February 11, 1999.   (Ref. Wikipedia)   


from Nasa-Site:

This animation combines various observations of Pluto over the course of several decades. The first frame is a digital zoom-in on Pluto as it appeared upon its discovery by Clyde Tombaugh in 1930 (image courtesy Lowell Observatory Archives). The other images show various views of Pluto as seen by NASA's Hubble Space Telescope beginning in the 1990s and NASA's New Horizons spacecraft in 2015. The final sequence zooms in to a close-up frame of Pluto released on July 15, 2015.