"It's bullshit," Alan Stern, principle 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.
Image: NASA/New Horizons
Since Pluto was infamously demoted to a dwarf planet in 2006, some astronomers have turned their attention to finding the true Planet 9, a hypothetical, Neptune-sized world that orbits the Sun at least a few hundred times further out than Earth. While there's no shortage of ideas about what Planet 9 could look like — or what it may have experienced throughout its life — so far, no one has been able to spot this elusive world.
The proposal that Stern's team has submitted to the IAU for approval 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 will be up to the International Astronomical Union to make a final call on whether or not this new system should be adopted. 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.