Should Pluto be a planet again? Experts debate to reinstate the ninth world of the solar system

In 2006, Pluto lost its status as a planet when other bodies in the solar system of similar or greater size were found.

The decision to demote it to a ‘dwarf planet’ by the International Astronomical Union (IAU) at the time was highly contentious – and it now seems many still want its planet status reinstated.

In a debate where experts presented cases for and against the decision, it was found that most people in the audience still wanted Pluto to be a planet. The debate was held last week at the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts.

During the event three experts explained their own reasoning for thinking Pluto was or wasn’t a planet reports Astrobiology Magazine. And the audience members were then asked to vote on which argument they thought was best.

Dr Gareth Williams of the Minor Planet Centre defended the original IAU decision in 2006 and said Pluto should not be a planet as it had not cleared the path in its orbit – one of the prerequisites for a planet, as decided in 2006.

Science historian Dr Owen Gingerich argued that, for historical and cultural reasons, Pluto should be a planet. And Dr Dimitar Sasselov, director of the Harvard Origins of Life Initiative agreed with Dr Gingerich, but for the reason that any lump of matter large enough to form a sphere around a star should be classified as a planet.

When put to the vote, the majority of the audience – which consisted of experts and members of the general public – agreed with Dr Sasselov, who’s definition would also help classify exoplanets. The vote isn’t official, although it does highlight the continued public disapproval of Pluto being demoted.

However, if Pluto was still a planet it would cause a number of complications. Namely, several other bodies of a similar or greater size such as Ceres and Eris were found, and it is estimated there may be hundreds more Pluto-sized objects in the outer solar system.

Reinstating Pluto, therefore, could ultimately lead to our solar system not being a small family of eight easily identifiable planets, but a complicated system of dozens of obscure worlds extending far beyond the orbit of Neptune.

WHAT IS A PLANET? 

 According to the IAU, a cosmic body must satisfy three conditions before it can be classified as a planet. The first is that it must be in orbit around the sun, and not be the satellite of another planet.

Second, it must have sufficient mass to form a spherical shape under its own gravity. And finally it must have cleared the neighbourhood around its orbit.

The latter was the condition that lost Pluto its planet status.

This is because it orbits in the Kuiper Belt at the outer edge of the solar system, where many other icy rocks and worlds orbit in its vicinity.