Rogue astronomers are demanding Pluto be reinstated as a planet.
The far-flung icy ball at the edge of the known solar system was demoted to 'dwarf planet' status in 2006.
The 2003 discovery of Eris - three times further away from the sun than Pluto and 27 percent bigger - forced the International Astronomical Union to redefine what it meant to be a planet.
To be considered a proper planet, it was decided astronomical bodies had to have cleared the orbit around the sun of other objects.
But this definition has now been challenged. Astronomers at the University of Central Florida say that particular definition had only been used once before in the scientific literature - and that was more than 200 years ago.
"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research," UCF planetary scientist Philip Metzger.
"And it would leave out the second-most complex, interesting planet in our solar system."
The first-ever close-up images of Pluto, beamed back to Earth by the New Horizons mission in 2015, revealed a world covered in mountains and nitrogen glaciers, which no one expected.
"Pluto is showing a diversity of planetary geology that is truly thrilling," John Grunsfeld, NASA associate administrator for the Science Mission Directorate, said at the time.
Dr Metzger says a planet should be defined by what it is, rather than what it does.
"Dynamics are not constant, they are constantly changing. So, they are not the fundamental description of a body, they are just the occupation of a body at a current era."
He says the definition should be if a body is large enough for its gravity to pull it into a spherical shape.
"It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body," he says.
"Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons… It's more dynamic and alive than Mars. The only planet that has more complex geology is the Earth."
If his bid fails, there is always the chance Pluto could be redefined as a strange kind of comet.
Dr Metzger's research was published in the planetary science journal Icarus.
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