Comment on Sad Ganymede noises
gandalf_der_12te@discuss.tchncs.de 3 days agoThere is no objective criteria for what a planet is and isn’t.
There is, though, or rather there should be another one.
The official definition says it’s a planet if it’s big enough to be round, which IMHO is a bullshit definition because nobody cares whether your object’s round, as in, for practical settlement purposes.
What’s important though is that it’s large enough to hold an atmosphere (at least if it had one). That’s only the case if the gravitational field is strong enough, which is the case roughly for objects of mass starting at around 10^23 kg. That definition fits surprisingly well the current actual classification of what is a planet and what isn’t, though.
What’s important though is that it’s large enough to hold an atmosphere (at least if it had one).
Define an atmosphere. Because there’s multiple asteroids that technically have one, albeit extremely thin ones. And be careful about being too nitpicky, as Mercury’s atmosphere is just it’s rock being vaporized due to its proximity to the sun
Because there’s multiple asteroids that technically have one, albeit extremely thin ones.
can you please link an example?
And of course, scientists often just use the non-dimensional number characterizing this; gravitational scale height divided by the atmospheric scale height is the Gandolfi number (Gf). :-)
Gandolfi number (Gf). :-)
wait, fr?
No, and I screwed it up! Should have been the Gandalfi Number
i mean if it doesn’t exist yet, i’m glad to be the first to write a paper about it and have it be named after me or sth ;-)
Alaknar@sopuli.xyz 3 days ago
That’s the second out of the three points of the definition.
As to why it’s not bullshit - the roundness is a byproduct of the object achieving hydrostatic equilibrium (which is the actual criterion, not roundness).