Today, the International Astronomical Union (IAU) officially defined the word “planet” and, in doing so, redefined our solar system by downgrading Pluto’s status from “planet” to “dwarf planet”. In response, Louis Friedman, Executive Director of The Planetary Society commented:

“The classification doesn’t matter. Pluto — and all solar system objects — are mysterious and exciting new worlds that need to be explored and better understood. Anytime we visit a new world — planet, moon, asteroid, comet, whatever — we make exciting and surprising new discoveries about the evolution of our solar system and about our own planet.”

Friedman added, “Being The Planetary’ Society, we appreciate the intense interest in the question “what is a planet” by both professionals and the general public, and we want to hear from them.” To do this, the Society is conducting a public poll on the web at The Society is also inviting people around the world to submit photos for a time capsule to be opened when the New Horizons spacecraft reaches Pluto in 2015 as a way of connecting the long term pursuit of space exploration with the rapid pace of change here on Earth.

The IAU debate has generated a lot of attention and strong opinions on all sides of the planet definition issue, but the hot topic has been Pluto. There are fervent proponents of changing Pluto’s status as our 9th planet, suggesting instead that it is part of a new class of objects that are smaller than planets but still large enough to be spherical due to self gravity. There is also a strong outcry for Pluto’s inclusion in the exclusive list of planets.

The planetary status of three other solar system objects — Ceres, the largest asteroid that is spherical in shape; Pluto’s large moon Charon; and the larger-than-Pluto 2003 UB313 (unofficially nicknamed Xena) — have also been debated, after the IAU-appointed Planet Definition Committee recommended a definition that would include these smaller objects. With today’s IAU decision, Charon, Ceres, and 2003 UB313 will join Pluto as dwarf planets.

The Planetary Society led the public fight for a mission to explore Pluto when NASA was opposed to the mission. Through numerous grassroots letter-writing campaigns, the Society proved again and again that the public supported Pluto exploration. Today, there is a mission headed to Pluto with New Horizons, but NASA is abandoning a mission to Europa, the large moon of Jupiter with an underground ocean that could be an abode for life, commented Friedman. “We were prescient in pushing for the Pluto mission — not just an interesting new world, but an interesting whole new type of solar system object; and Europa will similarly surprise us. New worlds mean new discoveries.”



For more information, contact Jennifer Vaughn by phone: (626) 793-5100 ext. 219, e-mail:


The Planetary Society has inspired millions of people to explore other worlds and seek other life. Today, its international membership makes the non-governmental Planetary Society the largest space interest group in the world. Carl Sagan, Bruce Murray, and Louis Friedman founded The Planetary Society in 1980.


The Planetary Society

How Many Planets? Poll

More information about the IAU decision

New Horizons Time Capsule