Official planet definition may change again
Astronomers have always debated the definition of a planet. The last time that this was changed saw Pluto (pictured) reclassified and removed from the category. But now, the proposed definition may become a little more inclusive.
In 2006, the International Astronomical Union (IAU) which officially names objects in space, firmly established a definition, one that was designed the exclude Pluto and to prevent the solar system from potentially having dozens or even hundreds of planets. For an object to qualify, it must orbit the sun, must have enough mass to become round, and must have cleared the neighbourhood around its orbit. Pluto failed at the last hurdle.
The current definition is seen as very solar-system-centric, especially the first criteria. In recent years, thousands of exoplanets have been discovered orbiting other stars. Scientists therefore needed a new definition that accounts for this.
According to the new criteria, a planet is any celestial body which orbits one or more star, brown dwarf, or stellar remnant, is more massive than 1023 kg, and finally, is less massive than 13 Jupiter masses.
This expands on, clarifies, and simplifies the existing definition. It both covers our own solar system and also includes those which orbit other stars including those that orbit brown dwarfs or neutron stars. Having a lower limit ensures that for distant objects, we can easily classify them. This is because while it may be difficult to see their exact shape, their mass can be measured.
Sadly, even this new definition excludes Pluto with Mercury just barely scraping through.
NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
