Academic anecdotes and ethical essays
A Lament for Pluto
Pluto’s discovery in 1930 granted our solar system its ninth and final planet. This tiny, lonely and misunderstood sphere—named after the god of the underworld—reaches nearly fifty astronomical units (or 7.5 billion kilometers) from our sun. Out in the cold depths of space, Pluto and its moon Charon silently trace the outermost path of our planetary system. But last year the planet club became a little more exclusive.
On August 24, 2006 the International Astronomical Union changed the criteria of 
planetary membership. To qualify, three rules must be met:
1. The object must orbit a star.
2. The object must be massive enough for its own gravity to pull it into a roughly spherical shape.
3. The object must have cleared the neighbourhood around its orbit of smaller objects.
Pluto fails number three. Just over 2300 kilometers in diameter, this diminutive outcast holds little chance of eradicating the countless celestial bullies in its orbit.
Demoted to “dwarf planet”, Pluto became a member of the far less privileged (and far more ubiquitous) Kuiper belt. This disc-shaped region—dubbed the “junkyard” of the solar system—stretches from Neptune’s orbit to roughly 500 AU (or 75 billion kilometers) out from the sun. Picture a very thin and oval donut, whose central hole contains our sun and eight planets. An estimated 200 million objects reside in the Kuiper belt, mostly comets such as Halley’s.
Pluto is one fragment leftover from the formation of our solar system. Through fate or chance, these pieces of debris in the Kuiper belt never became part of the early (or proto) planets. These forgotten fragments once held the possibility of colliding with and becoming part of a planet, but are now lowly members of the Kuiper belt junkyard.
Relegated to the trash heap, Pluto took solace in being crowned “king” of the Kuiper belt. But the discovery in 2005 of the slightly larger Xena (now officially named Eris after the goddess of chaos—those IAU people certainly keep us on our toes) dethroned the god of the underworld once more.
In the name of science, Pluto has been sacked. So Neptune regains the honour of being furthest from the sun. Perhaps the sizeable god of the sea is a superior sentinel to patrol the outer reaches of our planetary system. Yet I have always rooted for the underdog, and will lament the loss of pitiable, misunderstood Pluto.
Lee Beavington
June 26, 2007
