Scientists are trying to get Pluto back into the planet club by launching a campaign to broaden astronomical classifications which led to its demotion as a 'dwarf planet' in 2006. Six scientists belonging to different institutions across the United States argued that Pluto is a planet and so are 110 other bodies in the solar system including Earth's moon.

They were of the opinion that geological properties, such as shape and surface features, should determine what constitutes a planet. This was stated in a paper presented by the scientists at an international planetary science conference at The Woodlands, Texas.

In 2006, a new icy body was discovered beyond Pluto. The International Astronomical Union then adopted a definition for a planet based on characteristics that include clearing other objects from its orbital path.

This new definition stripped Pluto of its planet status and it was classified as a dwarf planet along with its newfound kin in the Kuiper Belt of the solar system. Ceres, the biggest object in the asteroid belt between Mars and Jupiter was also given the status of a dwarf planet. This classification left the solar system with eight planets.

The paper's lead author, Kirby Runyon, a doctoral candidate at John Hopkins University said that he and other planetary scientists are more interested in a planet's physical characteristics, such as its shape and whether it has mountains, oceans and an atmosphere to define a celestial body as a planet.

Runyon's team supports a sub-classification system, similar to biology's hierarchical method, but under this method, even the Earth's moon would be classified as a planet.