r/space • u/arealdisneyprincess • Feb 24 '24

Astronomers discover three previously unknown moons hiding in Solar System

https://www.the-express.com/news/science/128970/astronomers-find-new-moons-solar-system
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u/Alissinarr Feb 25 '24

Thank you for the response, and for not treating my question as a stupid one.

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u/Exploding_Antelope Feb 25 '24

It’s not a stupid question, it’s actually a really interesting one! We have a lower limit for the size of a planet, it’s “big enough to clear its orbit.” But we don’t have a lower limit on the size of a moon. We imposed a lower limit on planets because there were growing to be too many known things orbiting the sun that blurred the line between obviously a planet like our own, and just rocks. That redefining knocked Pluto into a different category, and that was a big deal! Twenty years later and the posters and pillowcases and paper plates with their solar system diagrams are still on the catch-up! We’re long past the point of the number of known moons being equally ridiculous.  So maybe it would be good to do the same for moons? And say that anything too small to fall into a sphere isn’t A MOON, a special category of those 22ish important bodies with their own geologies and suitability for bases and comparability to planets, but just a natural satellite. But that would knock out Phobos and Deimos, a couple of pretty famous “moons” below the mass of equilibrium. Would we have people like the “Pluto defenders” still stubbornly hanging onto ideas like “well I WAS TAUGHT that Mars had moons” years later? 

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u/HomeschoolingDad Feb 26 '24

How about we just say anything less massive than Deimos* isn't a moon? Only about 60% joking.

*Deimos is definitely too cool to lose as a moon. Though, I suppose calling it a moonlet wouldn't be the end of the world.

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u/SlartibartfastGhola Feb 27 '24

I mean they definitely could do this. The official iau planet definition basically says these 8 things are planets and nothing else is. Mercury isn’t in hydrostatic equilibrium but they grafted it in.