♇ Pluto

Named for the Roman god Pluto (Greek: Hades, Plouton)

The underworld The earth’s hidden wealth

Which sign is Pluto in now?

Pluto by Hendrick Goltzius, after Polidoro da Caravaggio
Pluto Hendrick Goltzius, after Polidoro da Caravaggio, probably 1592 National Gallery of Art, Washington An engraving, not a painting. The print is lettered PLVTO; the figure stands in an arched niche holding a flaming torch. Public domain, via Wikimedia Commons

Ruler of the underworld and of the wealth hidden beneath the earth.

The god

Pluto comes from Ploutōn, a Greek name for Hades, ruler of the underworld. It was often linked with Ploutos, the god of wealth, because mineral wealth was found underground, and Hades was the god of the hidden wealth of the earth, from the fertile soil that nourished the seed grain to the gold, silver and other metals mined from it. He was a son of Kronos and Rhea, and when he and his brothers Zeus and Poseidon divided the world into three realms, the underworld became his. Ancient writers described him as fierce and inexorable. As Plouton he was often shown with a scepter and an overflowing horn of plenty, which set him apart from the gloomier Hades.

How the planet got its name

Clyde Tombaugh discovered Pluto at Lowell Observatory in Flagstaff, Arizona, on February 18, 1930, after nearly a year of searching. The name came from Venetia Burney, an 11-year-old in Oxford, who suggested the Roman god of the underworld over breakfast with her mother and grandfather; he passed the idea on to the observatory, and it was chosen. It helped that the first two letters of Pluto are the initials of Percival Lowell, the observatory’s founder. In 2006 the International Astronomical Union reclassified Pluto as a dwarf planet; the tracker still includes it.

Symbols

Horn of plenty Scepter Keys Throne Cerberus Cypress

The planet

A dwarf planet in the distant Kuiper Belt, about two-thirds the diameter of our Moon, probably with a rocky core inside a mantle of water ice. Ices of methane and nitrogen frost its surface, it has mountains, valleys, plains, craters and glaciers, and its thin atmosphere is mostly nitrogen, methane and carbon monoxide. NASA’s New Horizons spacecraft photographed its “heart” on July 13, 2015. Its stretched orbit sometimes brings it closer to the Sun than Neptune.

Diameter
2,376 km 0.19 × Earth
Mass
0.013 × 10²⁴ kg 0.002 × Earth
Gravity
0.7 m/s² 0.071 × Earth's
Length of day
6.4 Earth days sunrise to sunrise
Length of year
247.9 Earth years one trip around the Sun
Distance from the Sun
5,906.4 million km 39.48 AU (Earth = 1)
Average temperature
-225 °C -373 °F
Moons
5
Rings
No

Figures from NASA’s Planetary Fact Sheet; the temperature is its “mean temperature.” Comparisons with Earth are worked out from the same sheet.

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