The Earth is no a planet for the same reasons that Pluto is no longer considered as one

Pluto is no longer considered a planet by the International Astronomical Union (ISU), much to the dismay of planetary scientists around the world. The distant, icy world has been relegated to the category of dwarf-planets and the main reason for the demotion is that Pluto has failed to clear all the other objects in its orbit. Defining an object according to external factors is arbitrary and counter-intuitive. Michael Tanne, an angel investor has pointed out on a post on Medium, that by the same logic, the Earth no longer qualifies as a planet.

Pluto. Image: Nasa.

The Asteroid 2016 H03 discovered in the Pan-STARRS 1 survey, is a companion to the Earth in its orbit around the Sun. The Earth has not captured the asteroid and the Earth has failed to clear the orbit. That means that according to the definition of the International Astronomical Union, the Earth cannot technically be considered as a planet and that it is, in fact, a dwarf-planet.

Jupiter with its moons. It is easier for gas giants to “clear their orbits” than smaller, rocky worlds. Image Credits: NASA/JPL-Caltech

The International Astronomical Union defines a planet as: “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.” For planetary scientists, a more useful definition is one that depends on internal factors of the object being studied. If a celestial object is spherical, and is not on fire, then it is a planet irrespective of what is happening around it. Alan Stern, the lead scientist on the New Horizon mission by Nasa, has told Tech Insider that the definition of a planet currently used by the IAU is “Bull****”.

Trappist-1 system. The seven earth sized objects in the system cannot be called planets, because it has not been established that they have cleared their orbits. Image: Nasa.

The definition is not useful because of the lack of information about exoplanets. Discovering the planets in orbit around distant stars by monitoring the dips in the brightness of the host star is itself challenging. There were seven earth sized objects discovered in orbit around an ultracool dwarf star forty light years away using this method. Now, the objects in the Trappist-1 system can only be considered as planets once it has been established that they have cleared all other objects in their orbits, according to the International Astronomical Union. So to call a planet, a planet, it is necessary to discover the lack of asteroids in its orbit as well. How senseless is that?

Pluto is geologically active and exhibits all the characteristics associated with a Planet.

Planetary scientists who actually study Pluto and other celestial objects in the solar system say that Pluto is a planet irrespective of what the IAU defines it as. Pluto is a remote, icy world and exhibits all the characteristics that one would associate with a planet. Johns Hopkins University scientist Kirby Runyon has suggested a simple definition, “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 various moons of the planets, and the dwarf-planets are all planets, and there are more than 100 planets in the solar system.

The 110 spherical objects in the solar system that would be considered planets according to the proposed definition. Image: planetary.org.

Planetary scientists, including those from Nasa, want to promote Pluto back to the status of a planet. If the gas giants such as Saturn, Uranus and Jupiter are not in a category of their own, what is the need for treating smaller planets any differently? For school textbooks, the scientists have proposed the definition “round objects in space that are smaller than stars.”

The planets in our Solar System, including Pluto and other dwarf planets. Image: Nasa.

Will students have to learn the names of more than 110 planets in the solar system? Not really, there can be a focus on the more important planets, and the most important thing is communicating the different types of planets in the different zones. There are rocky planets closer to the sun, then the gas giants, and then the remote icy rocky dwarf-planets in the outer reaches of the solar system. Tanne writes, “Will scientists drop the politics, put on their scientific thinking hats, and restore the faith children everywhere have in the scientific process they are taught, and the intuition we all have that Pluto, is in fact, a planet.”

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