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NASA Scientists Have a Plan to Make Pluto a Planet Again

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“It’s bullshit,” Alan Stern, principal investigator of NASA’s New Horizons mission to Pluto, has said about the demotion of Pluto from the ranks of official planet status. Now Stern is heading up a team of NASA scientists who have proposed a new definition of planets that would do more than just reinstate the icy dwarf planet with the big heart to its former glory.


The proposal would redefine our definition of a planet in very simple terms. The scientists boil it all down to “round objects in space that are smaller than stars.” Yes, that would mean that Earth’s Moon, as well as many others, would be classified as a planet.

A more detailed description from the proposal breaks the method for planetary classification down as “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.”


Stern obviously has a bit of a bias in this argument considering that he led the New Horizons mission that has beamed back unbelievable images and new information about Pluto. That mission reminded people how amazing the dwarf planet is and he’s had a chip on his shoulder over its demotion for years. In 2015, he told Business Insider that astronomers shouldn’t be deciding what is or isn’t a planet. “You really should listen to planetary scientists that know something about this subject,” he said. “When we look at an object like Pluto, we don’t know what else to call it.”

Science Alert breaks down the proposal’s criticisms of our current planetary classification system:

  • “First, it recognises as planets only those objects orbiting our Sun, not those orbiting other stars or orbiting freely in the galaxy as ‘rogue planets’,” they explain.
  • Second, the fact that it requires zone-clearing means “no planet in our Solar System” can satisfy the criteria, since a number of small cosmic bodies are constantly flying through planetary orbits - including Earth’s.
  • Finally, and “most severely”, they say, this zone-clearing stipulation means the mathematics used to confirm if a cosmic body is actually a planet must be distance-dependent, because a “zone” must be clarified. This would require progressively larger objects in each successive zone, and “even an Earth-sized object in the Kuiper Belt would not clear its zone”

It might seem kind of fast to redefine planets so soon but humanity has been changing the definition forever.

If you truly love Pluto, this might be good news for you. If you’re still just having a hard time remembering that there are only eight planets instead of nine, this proposal is going to continue to make life difficult.


*Correction: Kirby Runyon, first author on the new planet definition LPSC abstract, informs us that the proposal is not being submitted to the International Astronomical Union as has been reported elsewhere. The article has been updated to correct this error.