Nasa scientists want Pluto to be a planet again

If their proposal for what defines a planet is accepted, there will 110 planets in the Solar System

It's been more than ten years since Pluto was cruelly stripped of its planetary status but the decision could be reversed if a group of scientists get their way.

Alan Stern, the head of Nasa's New Horizons mission to Pluto, and a host of other scientists from the space agency and universities have proposed a new definition for a planet. If it is adopted the change would make Pluto and another 109 objects in our solar system official planets.

Based on their studies, the team has created the following definition of what a planet is and published it in a short, easily digestible, paper.

"A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters," the proposed definition reads.

The team argues it is possible to make the definition simple enough for young children to understand. As part of this, the planetary scientists say it can be shortened to: "round objects in space that are smaller than stars."

"With the above definition of a planet, we count at least 110 known planets in our Solar System," Stern and colleagues write in the paper, which concludes by saying discussions with members of the public have shown there is support for a new definition.

However, for a 110 planet solar system to become official, the definition would have to be approved by the International Astronomical Union. The body, which was formed in 1919, is responsible for organising international space conferences and "the definition of fundamental astronomical and physical constants".

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In 2006, it was the IAU that changed the definition of a planet and excluded Pluto from the list of eight known planets. Resolution 5A was revealed at the IAU's conference in 2006, and gave the following definition of a planet in our Solar System.

"A 'planet' [1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit."

The current definition means Pluto is currently known as a dwarf planet. WIRED has contacted the IAU asking whether the new proposal for a definition will be looked at by its researchers.

In the new paper, which the scientists plan to put forward to the IAU, the current definition is described as "technically flawed" - it only recognises planets as objects that are orbiting our Sun and not other stars. It also says the need for zone-clearing means "no planet in our Solar System" meets the criteria for planets.

The authors argue the new definition is "geophysical" and based on the physics of the world itself.

"Understanding the natural organisation of the Solar System is much more informative than rote memorisation," they explain.

When Stern was challenged on what a 110-planet Solar System would mean for children trying to memorise the planets, he said it was an outdated approach. "So 20th century," he said on Twitter.

"Do you have mnemonics for the names of all the stars or asteroids? Rivers/ Mountains? Course not."

This article was originally published by WIRED UK