A group of astronomers want to change the definition of a planet. Their new proposed definition wouldn’t bring Pluto back into the planetary fold, but it could reclassify thousands of celestial bodies across the universe. From a report:
The International Astronomical Union’s (IAU) current definition of a planet, established in 2006, includes only celestial bodies that are nearly round, are gravitationally dominant and orbit our Sun. This Sun-centric definition excludes all of the bodies we’ve discovered outside our solar system, even if they may fit all other parameters. They are instead considered exoplanets. Those behind the new proposal critiqued the IAU’s definition in an upcoming paper in the Planetary Science Journal, arguing it’s vague, not quantitative and unnecessarily exclusionary.
Their new proposal would instead classify planets based on their mass, considering a planet to be any celestial body that:
- orbits one or more stars, brown dwarfs or stellar remnants and,
- is more massive than 10ÂÂ kilograms (kg) and,
- is less massive than 13 Jupiter masses (2.5 X 10^28Âkg).
Better definition: big enough to be round, too small to fuse hydrogen.
Wouldn’t that get rid of moons?
Planets orbit stars
Moons orbit planets
One day we’re gonna find something orbiting a moon and then you’re gonna feel really silly.
A subsatellite, also known as a submoon or a moonmoon, is a “moon of a moon” or a hypothetical natural satellite that orbits the moon of a planet.
https://en.wikipedia.org/wiki/Subsatellite
While that may be possible, I highly doubt such a system can be stable? Maybe it can be stable for a while though (which could still be thousands of years).
It’s theoretically possible for more massive planets. The subsatellite has to be in the Hill sphere of the moon. There’s a depiction in the linked article.
What about Pluto and Charon? Their barycenter is outside Pluto.
I propose binary (and more generally n-ary) planets.
Both orbit stars. Both are planets in my book. Planets and moons are codependent. In fact, Earth and it’s moon are binary planets.
Saying otherwise is useless stella bigotry.
And Ceres, you want it to be a planet?
Yes, it’s already a planet. Just like dwarf stars are already stars, dwarf planets are already planets. It’s right there in the name.
Ok, then, Pluto is also a (dwarf) planet, what is the big fuss?
PS: sorry, I thought you were the
OPdude at the top of this thread, we are in agreement, then.Moons are planets
That’s the definition of a planemo or planetary mass object