A possible "Planet Nine" in Earth's solar system would orbit far beyond Neptune
space.com
space.com
Here's an article (citing Caltech): http://www.science20.com/news_articles/planet_nine_not_pluto...
> 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"
- that planet nine theory still seems to be holding up;
- Batygin and Brown have just spent a week at Mauna Kea looking for it.
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...
[1] https://www.universetoday.com/118252/astronomers-are-predict...
[2] https://www.washingtonpost.com/news/speaking-of-science/wp/2...
[3] https://www.nytimes.com/2016/01/21/science/space/ninth-plane...
This new one, if it's there, will be much bigger.
is likely what the 2005 article is about.
A 10th or 11th planet might also explain it, but not as well, and it's a more complicated answer to have 2 or 3 new planets instead of one. Occam's razor: the simplest explanation is the most likely.
https://en.m.wikipedia.org/wiki/Ice_giant
More like a giant lump of ice and rock with a frozen atmosphere, a so-called “Ice Giant” like Neptune or Uranus.
Rocky planets are suposed to be formed near the star, and the stellar winds "blow" the gaseous elements away from them. The gas giants, like Jupiter and Saturn, form farther away and hence get to hold the more "volatile" elements. Hot jupiters, a class of giants that orbit very close to their stars, are weird and there a two competing hypothsies about their formation[1] so we could say that the precise mechanisms aren't fully understood (but we do have a pretty good idea).
As for ice giants, the precise mechanisms for their formation are not completely understood[2]. But what we do know, and it gives a strong(er) foundation for Planet Nine, is that super-earths (or Uranus/Neptune sized planets) are actually the most common type of (exo)planet we've observed so far, and it's a class that's surprisingly missing from our solar system[3] and a "slot" that Planet Nine would fill[4].
[0] https://en.wikipedia.org/wiki/Nebular_hypothesis#Formation_o...
[1] https://en.wikipedia.org/wiki/Hot_Jupiter#Formation_and_evol...
[2] https://en.wikipedia.org/wiki/Ice_giant#Formation
[3] https://en.wikipedia.org/wiki/Super-Earth
[4] https://en.wikipedia.org/wiki/Super-Earth#Planet_Nine
[5] I'm a sort of an astronomy geek though, and I pretty much enjoy reading this stuff up until the point I don't understand any more. Which over the years has luckily been moving forward. If you're interested in the subject, follow @plutokiller and @kbatygin on twitter, they're active and link to a lot of articles and their scientific papers.
Now, perhaps planetary formation models predict many closely orbiting Neptune class planets, and independently observations are demonstrating that this is true. That would be a stronger statement, although still perhaps somewhat driven by observational data, since any model which doesn’t predict this might be kicked to the curb by now.
However, I remember a talk held sometime last year (or maybe this year) where the mission team talked about the Kepler results and they specifically said that super-earths were now the most common planet type found. But I can't find it, and can't back that up with a strong source. What's more, looking at the published results[1], gas giants are far more frequent (and that would line up with the selection bias you noted).
The only thing I can think that would back the claim about super-earths, would be considering them on radius alone, in which case yes, the 2 < R ≤ 6 R_Earth class is the most common class[1].
Edit: I was looking mainly at the mass results (in which case a SE is any planet between 2-10x Earths mass), not the radius results. But then, the definition is still a bit shaky, with different criteria[2].
[0] https://en.wikipedia.org/wiki/Kepler_(spacecraft)#2011
[1] https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail...
The increased radius alone will reduce the surface gravity by a factor of 2 at least. But Planet 9 is also likely to be much less dense than Earth. Earth is the densest object in the solar system. You can't match our iron core with materials available in the outer reaches, so the surface will be even further away from the center.
Surface gravity on Saturn is just around 1g (for a suitable definition of "surface"). Uranus is 0.9g. Neptune is 1.1g. Planet 9 is likely to be in the same ballpark if it's an ice giant.
Gravitational force is proportional to mass and inversely proportional to the square of distance. Radius is the distance between the center of a planet and its surface.
If this sounds wrong, please see the Wikipedia page for Saturn and explain how a planet with 95 times the mass of Earth is listed as having a surface gravity of only 1.065 g.
(Actually, I was wrong above: the increased radius alone would reduce the surface gravity of this hypothetical planet by a factor of 4.6, not just 2, assuming Earth-like density.)
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!
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.
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
[2] https://en.wikipedia.org/wiki/Dwarf_planet#Dwarf_planets_and...
[3] https://en.wikipedia.org/wiki/Ceres_(dwarf_planet)#Classific...
They found 4 more Plutos.
I believe you mean Planet Ten.
There are many reasons to not want to name a planet "Goofy" that have nothing to do with their relationship to the Disney corporation.