DLC Blog

Pluto's Debated Planetary Status

Recent discoveries of other large objects orbiting the sun in our solar system have led to heated debates on whether or not these objects may be considered planets. Originally, a planet was a wandering star – then it was something that revolved around the sun. But many distant objects, asteroids, and comets revolve around our sun, and yet we do not call them planets. So the real question is, what should the definition of a planet be?

The debate began as technological advances made it possible to find more minor asteroids, comets, stars and possible planets in our solar system.

At around 3000km across, 2003 UB313 is the largest object to have been discovered in our solar system since the discovery of Neptune in 1846. This “planet” is a world of rock and ice somewhat larger than Pluto, though it’s about three times as far from the sun. Other recent discoveries include Quaoar (found in 2002) and Sedna (detected in 2004), both comparable in size to Pluto as well.

Most of these objects are associated with the Kuiper belt – a large asteroid belt surrounding our solar system. Scientists estimate there may be tens of thousands of objects revolving around our sun in the Kuiper belt, some larger than Pluto.

At only 2300km across, Pluto’s size is significantly smaller than the original estimations at its discovery in 1930. At that time, it was thought to be of a size comparable with Earth. Recent evidence indicates it’s smaller than our moon, with only about a fifth of its mass.

But some argue that Pluto has been culturally accepted as a planet for too long for it to be discounted now. "Our culture has fully embraced the idea that Pluto is a planet and scientists have for the most part not yet realized that the term planet no longer belongs to them," says Michael Brown, one of the astronomers who discovered 2003 UB313.

His conclusion is simple: "From now on, everyone should ignore the distracting debates of the scientists. Planets in our solar system should be defined not by some attempt at forcing a scientific definition on a thousands-of-years-old cultural term, but by simply embracing culture. Pluto is a planet because culture says it is.”

The other side argues that Pluto should not be considered a planet, and only objects larger than Mars should be called planets in the future.

For more information on the Pluto debates, follow the links below!

Astronomers Detect ‘10th Planet’
Farewell Pluto?

Lindsey Aakre
Student Mentor - French

Posted by Lindsey at August 16, 2005 06:12 PM in Science.