Space & Astronomy

NASA proposes redefining the word 'planet'

By T.K. Randall
February 20, 2017

Image: Solar System
Credit: Harman Smith, Laura Generosa, NASA/JPL / (PD) In order for a body to be classed as a planet under the current definition of the word, it must be in orbit around its parent star, it must be massive enough for its own gravity to make it round and it must have "cleared its neighborhood" of smaller objects within its own orbit.

Now though, scientists at NASA have come up with a new definition of the word 'planet' that focuses, not on its orbital attributes, but on its physical properties.

If this were to become formally established it would mean that our own solar system would have over 100 planets including Pluto ( which was recently demoted ) and even our own moon.

"We propose the following geophysical definition of a planet for use by educators, scientists, students, and the public," the scientists wrote."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."

In other words, to be considered a planet a body simply needs to be round and smaller than a star.

This new definition makes a lot more sense, the researchers argue, as the existing definition fails to take in to account planets in orbit around other stars or those that don't have a parent star at all.

Secondly, the 'zone-clearing' requirement is flawed because the size of the zone must be defined and in many circumstances clearing this area is impossible regardless of the size and properties of the world in question. An Earth-sized object within the Kuiper Belt for instance would never be able to clear its immediate vicinity of debris even though it is otherwise clearly a planet.

The full text of the proposal can be found - here.

Source: Science Alert

Tags: Planet