The International Astronomical Union (IAU)’s 2006 decision to no longer classify Pluto as a planet was wrong, argue David Grinspoon and Alan Stern in The Washington Post. Its reasoning was built on the strange basis that a planet must have enough of a gravitational field to clear its nearby surroundings from floating debris. This decision was controversial within the scientific community and would even mean that Earth was not a planet during its first 500 million years. Planets are often seen as lumps of matter that became spherical over time. The IAU’s flawed definition wrongly excludes bodies like Pluto from being a planet. A revision is called for.
Pluto is not a planet, writes Joseph Stromberg of Vox. It simply doesn’t meet the necessary criteria. These include orbiting the sun, being big enough to become round, and to clear the debris that floats around it. Pluto doesn’t meet the last requirement. The definition of planets has changed over time. At one point, all objects that go around the sun were deemed planets. Once we discovered that many of them were just huge asteroids, part of larger clouds, they were taken off the list. Similarly, Pluto’s surroundings weren’t seen when it was first called a planet. It is different because it is surrounded by debris that, unlike planets, it hasn’t been able to push away.