> 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)
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.
There's a list of 'weird' things that need to be explained. A big 9th planet orbiting within a fairly tight range of parameters would explain many things on that list.
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.
As with any system with an unknown, the unknown factor might actually be more than just one factor. Wether Planet 10 is a factor can only be determined once planet 9 is observed proper (so far we only know it has be to "there" but haven't seen it) and measured sufficiently enough to be added to the models of solar system.
That’s going to be one very rocky, veeeery frozen planet. Still, if it has moons, one of them could be geologically active if the orbit is right. Imagine a cryovolcano erupting, with Sol as a pinprick in the background.
I'm not an astronomer, much less planetary scientist[5], but it's got something to do with the size, and location[0].
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].
[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.
I’m suspicious about one statement you’ve made here. Either you haven’t made it precisely, or it may not logically follow. We’ve observed many super earths because that is what we can observe. The sensitivity of our instruments make it hard to observe Earth-like planets unless they are at Mercury-type orbital distance or even closer. There are some recent counter-examples, but to say that these are the most common because that’s what we’ve been able to observe is a selection bias of the first order.
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.
Yes, I see your point. Basically I mentioned the Kepler mission results, without providing the relevant link[0]. Right there you can see that super-earths are quite high in frequency.
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].
You can’t really have a nice atmosphere with so little incoming solar radiation, and at 10g you’d be talking about a truly THICK atmosphere. Moons though, could be “squeezed and stretched” from the gravitational interaction with the planet, but again they’d be coooooold. You’d have activity, but probably cryogenic volcanoes and the like.
Surface gravity on a planet with 10 times the mass of Earth will not be 10g.
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.
You’ve confused radius and mass. 10x mass = 10x gravity, and then radius is a totally separate issue. Mass and surface gravity are proportional, while radius depends on issues of composition.
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.)
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!
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.
FYI, Kepler's 3rd law (the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit) means it'll orbit very slowly (a planet just 100 au out would have nearly a 1000 Earth-year orbit).
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?
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.
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.
We'd also have to put Ceres back as a planet. And probably everything else that's currently classified as a "dwarf planet". And Pluto would be a double-planet with Charon, so still a different category from the rest.
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.
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.
I'm with you, but we wasted an awful lot of good mythological names on silly little moons and dwarf planets, so Planet X might have to settle for Planet McPlanetface.
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"