
The mysterious ‘Planet Nine’ might be causing the whole solar system to wobble - daegloe
https://www.washingtonpost.com/news/speaking-of-science/wp/2016/10/20/the-mysterious-planet-nine-might-be-causing-the-whole-solar-system-to-wobble/
======
verytrivial
There seems to be an unfair amount of giggling in this thread. Brown et al
aren't, to my knowledge, simply hoping this hypothetical planet into existence
a la Nibiru. Brown discovered Eris and his handle on Twitter is @plutokiller
for a reason.

See [https://arxiv.org/abs/1603.05712](https://arxiv.org/abs/1603.05712) for
previous work.

Edit: Adding from the Conclusion

    
    
        The existence of a distant massive perturber in the
        outer solar system – Planet Nine – explains several
        hitherto unconnected observations about the outer
        solar system, including the orbital alignment of the
        most distant Kuiper belt objects, the existence and
        alignment of high perihelion objects like Sedna, and
        the presence of perpendicular high semimajor axis
        Centaurs. [...]
    

i.e. Planet nine may be Occam's razor for a number of whacky observations.

------
FuNe
" But the history of astronomy is rife with speculation that is never borne
out: The same guy who correctly predicted the existence of Neptune also
believed that a planet he called Vulcan was responsible for the wobble of
Mercury. That “discovery” caused the astronomy world to waste years looking
for something that wasn't there. (Mercury's wobble was eventually explained by
the theory of general relativity.) " Buying into the theory though and given
that there is no sight of it yet - has the possibility of a small black hole
been considered?

~~~
nickff
Depending on when exactly you think the black hole was formed, it would likely
have grown large enough to swallow the rest of the solar system. Simply
swallowing interplanetary particles would cause fairly quick growth, and the
black hole would soon be absorbing comets and asteroids; in addition, it would
obscure and distort our view of distant stars.

Apart from those issues which would make the black hole apparent, you would
have to figure out how one could form in a stable solar system. I am not aware
of any theory of black holes which would explain how one could spontaneously
form within a stable solar system.

~~~
scatters
Such a black hole would have to be primordial, and then you'd have to explain
how it came to be associated with our solar system. Far more likely that a
planetary-mass object associated with a solar system _is_ an actual planet.

I don't think it'd be likely to accrete much mass, though; a back-of-the-
envelope calculation of a 10 Earth mass black hole in the outer solar system
subject to interstellar mass flux gives an accretion rate of 0.1
nanograms/year and a radiative power of 0.1 milliwatts.

Likewise, its Schwarzschild radius would be of the order of 10cm, so
gravitational lensing events would be nigh-on unobservable.

~~~
Zardoz84
And how many Howkings radiation would have a black hole of these mass ?

~~~
scatters
I remember the rule of thumb is that a Moon-mass black hole is in equilibrium
with the microwave background (in the current era). So such a planetary-mass
black hole would be several times colder than the microwave background and
would actually absorb energy.

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cLeEOGPw
Maybe it's one of the wandering planets that got caught by Suns gravity. I'd
imagine there are plenty of those cold bodies between the stars, it would be
strange if solar system didn't encounter any of them. Also the fact that one
of them probably even hit the Earth forming Moon makes it even more likely.
Maybe Jupiter just "cleaned" our space from them.

------
mrfusion
Couldn't we get an amazing gravity boost out of this planet? How much faster
could the voyagers be going if they used it?

~~~
petewailes
Depends where it is, but probably not. Repeated gravitational assists from
things much closer would probably beat slingshotting around whatever this is,
if there's something there.

~~~
mrfusion
Why would that be? Is t there more orbital energy in things far away?

~~~
yongjik
No, the amount of speed you gain (delta-v) is, at an ideal condition, twice
the orbital velocity of the planet (or moon) you're flying by.

(Imagine throwing a ping-pong ball at a truck. If the truck is at rest, you
get the same speed back. If the truck is running at 60 mph, you may go to
jail, but assuming you don't, you get back a 120 mph ping-pong ball.)

A planet that far away from the sun must be moving at a very slow speed
(otherwise it will escape the solar system altogether), so you can't gain much
speed flying by.

~~~
mrfusion
That sounds backwards to me.

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ccozan
Isn't maybe a case for dark matter? Maybe instead of looking for hypothetical
planets, can we explain this with dark matter?

Same as we did with the unexplained galaxy rotation of outer regions.

~~~
petewailes
Short answer - no.

There is a long answer, but it requires enough knowledge of physics that you
wouldn't have asked the question. But suffice to say, there's no chance
whatsoever that this is dark matter.

~~~
stuff4ben
Wrong. Short answer - yes. There is a long answer but I too can be an Internet
scientist and offer no explanations for my reasoning except "trust me, I know
more than you do" as a certain political candidate is known to do (yes I went
there).

Also looking forward to an epic beatdown of mounds of scientific evidence that
is way above my head. But at least I will have gotten you to say more than
"trust me".

~~~
petewailes
Pithy answer - dark matter, whatever it might be (WIMPs or otherwise) is most
importantly, Weakly Interacting (the WI in WIMP). It appears to clump around
gravitational structures, acting like normal matter, but in more of a field
way, rather than a matter way (think of it like a fluid filling a container,
with uneven density - where the density is higher is where you've got matter
pulling at it).

For dark matter to be causing this, you'd need some exotic form of something
that's already exotic - it'd have to be able to interact with an intensity we
don't associate with it. It'd also be defying what we understand it to
normally do (you'd need something to make it pull into a lump from how we
think it behaves, which predisposes a physical structure like a planet).

So, is there some massive errant lump of dark matter pulling the solar system
around? From what we infer about how dark matter behaves from observation, no.

(The fluid thing is not an entirely accurate model of how dark matter works,
but it's a decent enough metaphor. However, this gets very complex and I'd
rather not spend the rest of the day getting into ever more detail about
theoretical physics.)

~~~
nonbel
>"(you'd need something to make it pull into a lump from how we think it
behaves, which predisposes a physical structure like a planet).

So, is there some massive errant lump of dark matter pulling the solar system
around? From what we infer about how dark matter behaves from observation,
no."

Apparently people find it plausible that dark matter consists of primordial
black holes:

"An intriguing alternative view is that dark matter is made of black holes
formed during the first second of our universe's existence, known as
primordial black holes. Now a scientist at NASA’s Goddard Space Flight Center
in Greenbelt, Maryland, suggests that this interpretation aligns with our
knowledge of cosmic infrared and X-ray background glows and may explain the
unexpectedly high masses of merging black holes detected last year."
[http://www.nasa.gov/feature/goddard/2016/nasa-scientist-
sugg...](http://www.nasa.gov/feature/goddard/2016/nasa-scientist-suggests-
possible-link-between-primordial-black-holes-and-dark-matter)

So I don't see how the "clumped/lumped" dark matter explanation can be
dismissed, black holes are basically lumps of pure mass right?

~~~
petewailes
From what we think atm, you can't get a lump of dark matter, without having
something to draw it in. It seems to gather where space-time is already
distorted. Although it doesn't seem to need much (some galaxies are "made"
mostly of dark matter - i.e., they get most of their gravity from it, rather
than from the matter we observe), it does look like dark matter only clumps
around spacetime distortions (gravity wells basically), rather than being able
to clump on its own.

So yes, you could in theory have a black hole which has dark matter around it,
which could do this, but it'd be mostly the black hole, not the dark matter
doing the pulling.

Hope that made some sense!

~~~
nonbel
>"you could in theory have a black hole which has dark matter around it"

Well, the link I provided gave me the impression it is plausible that the
black holes _are_ dark matter. This sounds like a different idea than what you
are rejecting as "possible but unlikely".

~~~
petewailes
Afraid that's not the case. Black holes are categorically not dark matter.

~~~
nonbel
Well, ok. But apparently someone at NASA thinks it is plausible. Argument from
authority heuristic tells me to listen to them rather than you in this case.
Since you are not coming with any links or specific argument against what was
said there, that is pretty much all I have to go on.

~~~
petewailes
Primordial black holes are the candidate here as you mentioned (black holes
exist, primordial black holes may exist, but we haven't found any yet).

Thanks to LIGO we think we may have the first evidence for them, but there is
still a lot of work to do to prove them.

Decent article on that: [https://www.sciencenews.org/article/ligo-black-holes-
dark-ma...](https://www.sciencenews.org/article/ligo-black-holes-dark-matter)

The interesting thing will be if we can prove they are around, which would
then give some options for showing if they're dark matter or not (looking for
gravity waves in areas where there's large dark matter concentrations would be
the most likely candidate for now).

------
runeb
Leaving Occam's razor behind for a second, could this not also be explained by
multiple objects whos mass and orbits sum up to the expected properties of a
proposed Planet 9?

~~~
muninn_
It's possible I suppose, but it seems kind of strange that a planet-size group
of rocks are floating exactly together in an orbit without colliding, or
knocking each other about. What seems simpler? That we have a group of rocks
the size of Neptune floating together, or that they actually formed together
into a planet? I'm not an astrophysicist, but I'm not sure what else it would
be. Looking forward to the proof or refutation.

~~~
runeb
I didn't necessarily mean the object were very near each other. Just wondering
if there could be some set of objects out there that would, in sum, have the
observed effect on the inclination of the solar system and orbits of far-away
objects.

~~~
muninn_
Well, in order to have that affect those groups would have to be close
together wouldn't that? (serious question)

------
RikNieu
Could this hypothetical planet be responsible for lobbing comets and other
projectiles-of-death at us every couple of thousand years?

------
gchokov
Did I hear someone screaming Nibiru? :)

~~~
jd3
This past summer, during my internship at MIT's Lincoln Lab, Dava Newman
(Deputy Administrator of NASA) came to give a talk about NASA's journey to
mars. At the end of the talk (during the Q&A), some greybeard conspiracy nut
in the back of the room asked her about the existence of Nibiru; suffice it to
say, she had no idea what he was talking about..

~~~
gchokov
Right on :) Every time when there's discovery for yet another distant object
from the sun, there's some speculation that pointing to Nibiru (where does
this name come from)?

~~~
mhurron
> Nibiru (where does this name come from)?

It's Babylonian, which was then co-opted by conspiracy theorists.

[https://en.wikipedia.org/wiki/Nibiru_(Babylonian_astronomy)](https://en.wikipedia.org/wiki/Nibiru_\(Babylonian_astronomy\))

~~~
arca_vorago
Actually it's Akkadian, here is some better reading than wikipedia.

As for your comment about conspiracists, I have a feeling thou dost protest
too much, if you catch my drift.

[http://www.michaelsheiser.com/nibirupage.htm](http://www.michaelsheiser.com/nibirupage.htm)

~~~
mhurron
Ya, I believe in the cataclysm theory and need to hid that on HN, or I'm not

[https://en.wikipedia.org/wiki/Nibiru_cataclysm](https://en.wikipedia.org/wiki/Nibiru_cataclysm)

"Although the name "Nibiru" is derived from the works of the ancient astronaut
writer Zecharia Sitchin and his interpretations of Babylonian and Sumerian
mythology, he denied any connection between his work and various claims of a
coming apocalypse."

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ImTalking
That explains my mid-section.

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mseepgood
Can we kick him out?

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asymmetric
Planet 9 from outer space!

