
A possible "Planet Nine" in Earth's solar system would orbit far beyond Neptune - curtis
https://www.space.com/38431-new-evidence-planet-nine-existence.html
======
ComputerGuru
I thought the presence of a ninth planet that _wasn 't_ Pluto was already
more-or-less accepted.

Here's an article (citing Caltech):
[http://www.science20.com/news_articles/planet_nine_not_pluto...](http://www.science20.com/news_articles/planet_nine_not_pluto_a_new_planet_discovered_in_our_solar_system-163869)

> mass about 10 times that of Earth and orbits about 20 times farther from the
> sun on average than does Neptune (which orbits the sun at an average
> distance of 2.8 billion miles)

which is definitely "far beyond Neptune"

~~~
mjw1007
I think the content of the NASA press release that this article is based on
is:

\- that planet nine theory still seems to be holding up;

\- Batygin and Brown have just spent a week at Mauna Kea looking for it.

~~~
stephengillie
In 12 years, this appears to have regressed from actually seeing the planet,
to just a vague theory of its existence. What's going on here?

Article from 07/2005[0] where Brown, Trujillo, and Rabinowitz discovered the
10th planet "using the Samuel Oschin Telescope at Palomar Observatory near San
Diego. It is currently about 97 times farther from the sun than Earth, or 97
Astronomical Units (AU). For comparison, Pluto is 40 AU from the sun."

Article from 01/2015[1] where Brown (and Batygin?) proposed 2 planets might be
beyond Pluto's orbit, and cite star HL Tauri, which has a planet forming disk
more than 100 AU from the star - supporting the idea of "distant planet
formation".

Article from 09/2015[2] where Sheppard and Trujillo publish a paper in Nature
in 2014. They call it "Planet X".

Article from 01/2016[3] where Brown and Batygin proposed the planet in The
Astronomical Journal.

[0] [https://science.nasa.gov/science-news/science-at-
nasa/2005/2...](https://science.nasa.gov/science-news/science-at-
nasa/2005/29jul_planetx/)

[1] [https://www.universetoday.com/118252/astronomers-are-
predict...](https://www.universetoday.com/118252/astronomers-are-predicting-
at-least-two-more-large-planets-in-the-solar-system/)

[2] [https://www.washingtonpost.com/news/speaking-of-
science/wp/2...](https://www.washingtonpost.com/news/speaking-of-
science/wp/2015/09/03/is-there-a-planet-x-a-massive-perturber-hidden-beyond-
pluto/)

[3] [https://www.nytimes.com/2016/01/21/science/space/ninth-
plane...](https://www.nytimes.com/2016/01/21/science/space/ninth-planet-solar-
system-beyond-pluto.html)

~~~
mjw1007
They decided not to classify the 2005 "10th planet" as a planet (and to stop
classifying Pluto as one).

This new one, if it's there, will be much bigger.

~~~
simcop2387
Along with that, the last estimate of it's orbit put it at something like
100-500AU away, which is what it's been so hard to find.

------
Sniffnoy
This article doesn't seem to contain much new. If you read Batygin and Brown's
blog, though, you can read more about to what extent they've been able to pin
down Planet Nine's location: [http://www.findplanetnine.com/2017/09/planet-
nine-where-are-...](http://www.findplanetnine.com/2017/09/planet-nine-where-
are-you-part-1.html)

------
HocusPocusLocus
Could we automate the search. Look for portions of the sky where the planet
covers a background star. Plot real and false positive data to see what could
be there, flying around.

Unless it orbits faster than Earth, it's periodic data too. If it does orbit
the sun faster than Earth, outside Neptune's orbit, its really cruising!

~~~
mabbo
The problem is that it's a needle in a haystack.

Everything in the sky can be thought of in terms of how many degrees or
arcseconds wide it is. The moon and sun are nearly the same 'size' in these
terms, even though the sun is so much bigger in actual size.

This planet 9? It's ten times the size of the Earth (ish), but in terms of
arcseconds, it's abysmally tiny. There simply aren't many telescopes powerful
enough to see something that small in the sky. Worse, the smaller it is the
more places in the sky you need to look to try to find it.

It's like you've dropped a single 10nm transistor on your living room carpet.

------
louithethrid
What if planet nine is a dense cloud of neptune like moons, circling one
another?

~~~
maxxxxx
I think this wouldn't be stable. Either the cloud would fall apart or collapse
into something bigger.

------
WalterBright
Pluto is good enough for me.

------
SeoxyS
We already have a ninth planet, Pluto. Why did they start calling it a rock
again? Isn't the definition of a planet a mostly spherical rock that orbits
around a star, no?

~~~
petascale
Because when Pluto was discovered, they thought it was alone out there. Then
they found that Pluto was a lot smaller than first thought (mass 1/5th of our
Moon, roughly the size of Australia), and that there were a lot of other
objects only slightly smaller in similar orbits (the Kuiper belt). And then we
found Eris which is just as big as Pluto (slightly smaller in diameter, but
more mass). So either they are all planets, potentially thousands of them in
the Kuiper belt, or we redefine 'planet' so Pluto, Eris, and similar bodies
are excluded.

So now a 'planet' is a) orbiting the Sun, b) mostly spherical, and c) mostly
alone in its orbital neighborhood[1].

Pluto, Eris et. al are still more than mere rocks, they have been reclassified
as dwarf planets[2].

It was a similar story with the asteroid belt: They found the first asteroid
(Ceres, I think) and called it a planet. Then they found another, and another,
and soon it became clear that there were a very large number of small bodies
in similar orbits. So they decided that they weren't planets after all, and
called them asteroids instead[3].

The difference with Pluto is just that it happened so recently.

[1]
[https://en.wikipedia.org/wiki/IAU_definition_of_planet](https://en.wikipedia.org/wiki/IAU_definition_of_planet)

[2]
[https://en.wikipedia.org/wiki/Dwarf_planet#Dwarf_planets_and...](https://en.wikipedia.org/wiki/Dwarf_planet#Dwarf_planets_and_possible_dwarf_planets)

[3]
[https://en.wikipedia.org/wiki/Ceres_(dwarf_planet)#Classific...](https://en.wikipedia.org/wiki/Ceres_\(dwarf_planet\)#Classification)

~~~
SeoxyS
Does a planet need to have an active hot core?

~~~
kijin
I don't think that's a requirement. We don't even know for sure what the
internal structure of other planets are like.

------
apple4ever
There is already a ninth planet- Pluto

I believe you mean Planet Ten.

~~~
curtis
I'm kind of with you on the demotion of Pluto. On the other hand, if we accept
Pluto as a planet, then we pretty much have to accept Eris [1] as well, since
Eris is more massive than Pluto, making Pluto and Eris the 9th and 10th
planets, respectively. So we'd be searching for a possible planet 11. But I
guess I'd be OK with that.

[1]
[https://en.wikipedia.org/wiki/Eris_(dwarf_planet)](https://en.wikipedia.org/wiki/Eris_\(dwarf_planet\))

~~~
gweinberg
Yes, I'd call it planet 11. But I'd also call it Goofy. Mother very easily
made a jam sandwich using no peanuts, mayonnaise, or glue -> Mercury Venus
Earth (asteroids) Mars Jupiter Saturn Uranus Neptune Pluto Mickey and Goofy.

~~~
Razengan
I _reeally_ would rather not name a major thing like a planet after an
American pop culture icon that is barely 100 years old.

~~~
freehunter
What's the difference between naming it after a fictional dog vs naming it
after a long-forgotten god from a dead religion like other planets? Either way
it's a made up pop culture icon that people may or may not understand the
reference to.

There are many reasons to not want to name a planet "Goofy" that have nothing
to do with their relationship to the Disney corporation.

~~~
zorked
Since when are Roman gods long forgotten?

~~~
freehunter
Since when was the last time anyone worshipped them? At this point they’re
just fictional characters from some old story just like Goofy.

