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# A Quantitative Criterion for Defining Planets

## Details

**Authors** Margot, Jean-Luc

**Year** 2015

**Publisher** The Astronomical Journal

**Kind of work** article

**Discipline** Astronomy

**Secondary disciplines** Physics

**Applied** false

[Read it at the publisher](https://doi.org/10.1088/0004-6256/150/6/185) 
10.1088/0004-6256/150/6/185

## In authors' words

### What they set out to do (purpose)

To provide a simple, quantitative criterion for deciding whether a body counts as a planet, based on whether it can clear its orbital zone.

### Who or what was studied (sample)

The eight planets of the Solar System and the known exoplanet population.

### How they did it (methods)

A metric built from three quantities (star mass, planet mass, orbital period) tests whether a body can clear its orbital zone within a characteristic time such as the host star's main-sequence lifetime. It was applied to the Solar System planets and to known exoplanets.

### What they found (results)

The metric can classify 99% of known exoplanets from star mass, planet mass, and orbital period alone. All eight Solar System planets and all classifiable exoplanets satisfy the criterion.

## Commentary

### In short

A single calculation separates planets from other bodies by asking whether an object can sweep its orbital zone clear within a set time, and it sorts nearly all known exoplanets.

### Response

The paper turns a contested category boundary into a threshold (a distinction between planet and non-planet), and the threshold is defined by a relationship: the gravitational action of a body on the population sharing its orbit. Both D and R carry the result. Caveats: the boundary is drawn by a chosen time scale and is therefore conventional rather than given by nature, and the paper does not address perspectives or part-whole structure.

**Patterns it shows** D, R

Formal proof or model

**Added** 2026-10-15

**How to cite this** Margot, Jean-Luc (2015). A Quantitative Criterion for Defining Planets. The Astronomical Journal.