One place Planet 9 could be hiding | Hacker News Reader

One place Planet 9 could be hiding

universetoday.com

66 pointsBrajeshwar76 comments

Would it be a bigger surprise if Planet 9 existed, or if Planet 9 doesn't exist? This isn't my field of study, but as I understand there's a good amount of indirect evidence for a Planet 9... and still no direct proof. Assuming we're searching in the right areas, if a scan of the first 80% didn't reveal it, it seems unlikely (but of course not impossible) that we'll find it in the last 20%.

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's long way down the road to the chemist's, but that's just peanuts to space.”

"Don't Panic."

I like to tell people how big space is just by describing how fast voyager 1 is moving and how long it will take to reach 1 light year of travel. Voyager 1 launched back in the 70's and is traveling around 38,210 mph. Even at that speed it will take another approximate 18,500 years for it to reach it's first light year traveled. The closest star is about 4.2 light years away so at it's current speed it would take about 75,000 years for it to reach Alpha Centauri.The more you start getting into the numbers and things like how many light years across the milky way is and how far to the next galaxy and how many galaxies their are you start to see the universe is unimaginably large. I don't think one could fully grasp it's size. Amazing

There’s a difference between completing 80% of the work, and ruling out 80% of the options.

We could rule out 80% of the options and still have 99% of the work yet to be completed.

Like if we’re looking for a bacteria on the land surface of the earth, and we rule out 80% of the options, that leaves us with searching an area the size of Africa for a microscopic life form.

Doesn't change the fact that whatever probability you previously assigned to finding Planet 9, it should be one fifth of that now. (Sort of. Not so drastic if you have strong reasons to think there is a Planet 9)

The suggestion is maybe part of the sky is easier to survey, so it was completed cheaply, even though that part wasn't the most likely part. I don't know which way it is, but it's an interesting question, and that's what OP is getting at for understanding the relevant probabilities instead of the relevant area.

Existing would be the bigger surprise. We've ruled out anything of Earth's mass out to distances of 100 AU and Jupiter's mass to 1000 AU, since those would be visible to telescopic searches and have measurable gravitational effects on known objects that we don't see from observation. It's almost certain that there's nothing that would meet the "clearing the neighborhood" definition of a planet. At most there would be more dwarf planets on the size order of Pluto and Eris and Quaoar, which are common, but those are each comparatively tiny, like 0.2% of Earth's mass.

The article says "78% of places have been searched"... but that's a really weirdly imprecise way of saying that. What are "places" here? Like, the sphere out to 100 AU is 78% of the volume out to 120 AU... but that makes no sense, the possible locations go out to 1000 AU or more.

There are indeed lots of claims of some evidence for another planet existing... but all those claims are different with no consensus, and it's largely fairly specious proposals trying to get some funding.

Eh, we ruled that out - within our observable time-frame, but we do not know about exotic, long-term orbits. Like a 50.000 year elipse out into the ort cloud and back in.

> continues to search for the elusive Planet Nine (also called Planet X)

In light of Pluto's demotion, surely we should deprecate "Planet X" in favor of "Planet Ix".

I hear there are many new machines on Ix.

Leto II is the only person to get this joke.

Ixian Ambassador Hwi Noree walks on a bridge…

I've always thought the idea of planet nine being a primordial black hole was kinda cool, but AFAIK we have no evidence to suggest this.

Unless I'm mistaken if PBHs do exist then one with 2-4 Earth masses is within the plausible range. It'd be about the size of a billiard ball. The existence of lots and lots of PBHs of various sizes is one dark matter candidate.

https://en.wikipedia.org/wiki/Primordial_black_hole

If there were such a thing out there we could send a probe to it. I can't imagine what kinds of interesting physics we could do if we could directly examine a black hole.

It'd be neat if it were actually useful in the far future too, like as a power source to generate and beam energy to interstellar spacecraft. There's even concepts like this:

https://en.wikipedia.org/wiki/Black_hole_starship

A PBH of that mass would not be useful for this but perhaps there'd be a way to leverage the extreme conditions created near the event horizon to generate smaller ones that evaporate quickly... like the extreme physics analog of sourdough starter.

The idea of a black hole starship is that you carry the black hole around, just like any other engine. If you want to beam power from it, there isn't anything at all there to gain compared to beaming power from the Sun.

And if you want to carry it with your ship, it weighting 2 Earth masses is kind of a drawback.

You don't move the blackhole+ship, that's crazy. You'd simply move the universe around your ship.

Which is already possible by shoveling dark matter into an oven, right?

I always wondered why there's no episode where the implications of more than two dark matter engines working at once were explored :)

How would you move a black hole around?

Just get out and push

AFAIK, the most popular answer is to give it an electrical charge.

I really don't know how are you supposed to maintain that change long-term. But then, it's similar to the problem of deciding whether the emissions from the black hole are particles that you can focus around, so I guess it's an open problem.

There was a scifi story decades ago about using small but heavy objects (neutronium, IIRC) as an integral part of space ships. The idea was not to use them to generate energy, but to generate a gravitational field to counteract the effects on humans of high acceleration. The object was held in front of the spacecraft, and would be moved closer when high acceleration was needed.

I guess if the ship was just drifting, you'd have the heavy object at a sufficient distance to cause ~1g gravity.

I don't remember the story's title or author(s), but it likely appeared in Analog.

It's Charles Sheffield, in particular his McAndrew series.

Thank you! With that help, I was able to find the story: "Moment of Inertial." And here's a link to the story: https://www.baen.com/Chapters/067157857X/067157857X__2.htm

If I recall, he used that invention in several stories. They're quite enjoyable. Sheffield, as a writer with a hard science background, came up with some very interesting ideas, such as The Sturm Invocation, and the entire Proteus series was very well-considered. Sometimes I get a taste for the diamond-hard sf and he scratches that itch. Hal Clement, too, if you're into that; Half Life is probably the best novel where the concept of the scientific method itself is at the forefront.

I now have Half Life on order, your fault.

I was intrigued by another Hal Clement title, Trio for Slide Rule and Typewriter. I have a slide rule sitting a few feet from me as I write this, in case of emergency. No typewriter, though.

Pay especial attention to the General Order and such right at the very start. I literally have incorporated those two ideas into the highest levels of how I solve problems. Hopefully, you will enjoy the book as much as I.

There are far more feasible alternatives to deep space propulsion that could actually work now, and all you have to do is detonate a couple of nukes.

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...