Is it or isn’t it? That’s the question currently being posed about whether Pluto should be brought back into the planetary fold.
Growing up, many of us remember being told that Pluto was one of the nine planets in the solar system - along with Earth, Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. But then in 2006, it was determined that Pluto didn’t meet the definition for an actual planet and it was given the boot.
Now, scientists at the Harvard-Smithsonian Center for Astrophysics have opened the door for Pluto to come back as a planet by arguing that it shouldn’t have been kicked out the last time around.
According to the International Astronomical Union, a planet is described as a celestial body that: is in orbit around the sun; has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape; and has cleared the neighborhood around its orbit.
The last of these requirements has been the most controversial, since the notion of “cleared the neighborhood” is a debatable scientific point. In 2006, the IAU said Pluto was too small to knock other space rocks out of its path as it orbits the sun.
This time the IAU decided to downgrade Pluto to a “dwarf planet,” but a planet nonetheless.
The IAU’s Owen Gingerich - chairman of the organization’s Planet Definition Committee - did note, however, that “a planet is a culturally defined word that changes over time.”
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