Curious tilt of the sun traced to undiscovered planet | Hacker News Reader

Curious tilt of the sun traced to undiscovered planet

phys.org

77 pointsnoyesno16 comments

I don't know about you but I find it incredible that while we can see galaxies formed 13 billion years ago[0], we have completely missed the existence of a large planet in our own solar system.

I can only guess what kind of theories the Nibiru/PlanetX[1] enthusiasts will cook up based on this announcement.

[0] http://www.space.com/32150-farthest-galaxy-smashes-cosmic-di...

[1] https://en.wikipedia.org/wiki/Nibiru_cataclysm

Also, since the article says:

> It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery

Why hasn't the existence of an additional planet been hypothesized before?

It's not that it hadn't been hypothesized before, it's rather that the numbers that they attribute to this hypothesis stack up well against a lot of Solar System observations. In other words, the hypothesis is not merely that there is another large, undiscovered planet in the far reaches of the Solar System, but rather the details of its mass and orbit that make this a compelling case. Part of the reason that this hypothesis wasn't possible before is because the observational data to support these numbers was lacking. The amount of knowledge we've gained about the Kuiper Belt over the last decade or so is phenomenal and drives our understanding of what might have happened in the early Solar System. It's worth reading the original paper to get a handle on the rigour with which this hypothesis has been analyzed and the coupling with observations of the Kuiper Belt [1].

[1] https://arxiv.org/pdf/1304.5166.pdf

I think this is the same as the hypothesis for Planet X that has been around since the 90s. Seems like they've just modified it slightly. They take observations they can't explain, and then make something up out of thin air that will explain the observations.

Not saying this is a bad strategy, just that in my view it's not much different from hypotheses for additional planets which have come before.

There have been constant hypothetical planets and even companion stars theorized to explain various discrepancies.

The problem is that we have a lot of missing information about the orbital mechanics of bodies that far and the discrepancies can be sometimes so small that they can hide or be "explained" by observation and calculations errors.

Even distant galaxys send a lot of energy our way, whereas very cold, very distant and dark matter is simply very hard to detect, especially from below the earth's atmosphere. We need more space based telescopes. These things are a gold mine for science.

There must be a huge amount of brown dwarves out there (probably also closer than Alpha Centauri), but we don't have enough of the right tools to look for them. Look at https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brow... #3 and #4 were found in 2013 and 2014!

These galaxies are considerably more energetic and they are also considerably larger in arcs in the sky than most planets especially small planets in the outer solar system and beyond.

If you are just coming to the Planet Nine story, the best background information is the scientists' blog at www.findplanetnine.com.

Instead of it being a 9th Planet (formed along with others as our solar system was created), it's perhaps just an enormous object (black hole?!) whose gravitation causes the sun to tilt ?

Does the sun's tilt match it's position within the milky way galaxy ?

I'm going to assume both of these options have been considered and ruled out. Also, the article mentions that this Planet 9 explains the orbits of Kuiper belt objects as well.

Interestingly enough, the new IAU definition of "planet" makes no reference to origin:

A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Whether a black hole could be considered a planet would hinge, I believe, primarily on b: Arguably, any black hole has sufficient mass to overcome rigid body forces, but does the notion of hydrostatic equilibrium apply?

More broadly, the definition of planet would allow for bodies of extra-solar origin captured by the sun....

Is there any reason, apart from not knowing exactly where to look, that we can't find such a planet by watching for when it passes in front of stars?

I'm not an astronomer, but I imagine there are too many small untracked objects, between Mars and Jupiter for instance, that periodically occlude stars. I imagine the signal-to-noise ratio is too high to start a search every time something blocks a star. How many millions of times per day must an asteroid somewhere block a star as visible from Earth? Gravitational perturbations are a smaller signal, but the signal-to-noise ratio is better, I imagine.

Maybe although I make a 10 times the size of earth planet at 20 times the distance of Neptune equivalent to a 77km wide main belt asteroid, so maybe not all that noisy. Plus the predicted orbit tilt must help a lot. Sounds like a doable big data problem to me.

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