If it turns out that Planet Nine did exist, but was either destroyed by a collision or flung out of the solar system, then does this resolve YES or NO?

I presume NO, otherwise it becomes impossible for this to ever confidently resolve NO.

Must have existed in the solar system at some point while this market was open. 100 million years ago wouldn't count.

Pretty sure that still has the same resolution problem...

Perhaps Planet Nine existed in the solar system last year but was flung out without anyone noticing. No amount of solar system exploration can prove whether or not it was there last year.

"Resolves once it's confirmed beyond a doubt that it exists in the solar system, or..." seems like a simpler resolution criteria. I highly doubt the odds of Planet Nine both existing and being flung out of the solar system after market creation yet before being discovered are high enough to affect the practical odds of the market at all. While if Planet Nine is never discovered then someone could always argue that it might have existed and we might have missed it while this market was open, and you could never prove them wrong.

Well if it's flung out of the solar system that doesn't mean it disappeared, it's still out there and its path can be traced backwards.

But yeah I agree it's simpler (and more in keeping with the description) if I just pin the relevant time to resolution, let's do that instead.

What happens if Pluto is reclassified as a planet?

That's Pluto, not planet nine.

Yes, it's called Pluto 🤣

https://pubs.aip.org/physicstoday/article/72/3/70/916004/The-Planet-Nine-hypothesisThe-putative-planet There are too many minor planets orbiting in the same direction to be a fluke, and I think the Planet Nine hypothesis makes the most sense

https://manifold.markets/RyanGuill/will-planet-9-be-discovered-before?r=Unlhbkd1aWxs

Will planet 9 be discovered before 2030?

23% chance. Planet 9 is a hypothetical gravitational object in the outer solar system, that would explain the orbits of some trans neptunian objects. https://en.wikipedia.org/wiki/Planet_Nine If any object with mass is discovered that explains these orbits before midnight US/Eastern time on 1/1/2030, this question will resolve YES.

Does the planet need to fit within the parameters defined in the Batygin and Brown hypothesis? E.g 0.2 <= eccentricity <= 0.5 ?

@JonLamb No, it just needs to be any planet that could reasonable be considered Planet Nine. i.e. if scientists announce "we found Planet Nine!", that counts.

But did it clear its path? Is it really a planet than?

https://astrobiology.nasa.gov/news/the-case-strengthens-for-planet-9/