# Planet 10?



## Brian G Turner (Jun 22, 2017)

No, not the dark giant currently being sought for - but a  Mars-sized object might possibly exist on the outskirts of our solar system:

Weird orbits hint ‘Planet Ten’ might lurk at solar system edge


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## BAYLOR (Jun 25, 2017)

So it could be awondering planet captured by our sun? Interesting possibility. Perhaps its capture might have contributed to the asteroid event that ended the  Dinosaurs?  It's just a thought.


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## J Riff (Jun 26, 2017)

No it can't be a wandering planet. It's gotta be part of something blowed up real good! in this solar system.


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## Dave (Jun 26, 2017)

Personally, I think this wandering planet and the missing gas giant have to be one and the same object. However, it must be a very unusual thing and possibly unlike anything we know about already. It must have a very dark surface. It is massive to exert such a gravitational pull, but no one can see it, so it cannot reflect much light. It seems to move around, so the orbit isn't regular, but it is also has to be very far away, even at perihelion, or else someone would have observed it. It will probably continue to be a mystery for a long time.


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## Vertigo (Jun 26, 2017)

Dave said:


> Personally, I think this wandering planet and the missing gas giant have to be one and the same object. However, it must be a very unusual thing and possibly unlike anything we know about already. It must have a very dark surface. It is massive to exert such a gravitational pull, but no one can see it, so it cannot reflect much light. It seems to move around, so the orbit isn't regular, but it is also has to be very far away, even at perihelion, or else someone would have observed it. It will probably continue to be a mystery for a long time.


Well if they are one and the same then I could come up with some easy reasons for us not finding it yet. Consider Pluto has a semi major axis of around 39AU giving it an orbital period of 248 years. However its perihelion - aphelion is 29AU - 49AU, so moderately eccentric. Now the 'missing' gas giant is reckoned to be around 700AU out so if that's its semi major axis then it will have a orbital period of over 18,500 years! If its orbit is significantly eccentric then it could have been a lot further away than 700AU for a lot longer than we humans have had telescopes, making observations of it very very hard.

I would add that if they are not one and the same, then the failure to spot a Mars sized planet at a similar distance to Pluto is much harder to explain away.


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## Ursa major (Jun 26, 2017)

Aren't we talking about an object with about the same mass as Mars, rather than about the same diameter...?


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## Vertigo (Jun 26, 2017)

Ursa major said:


> Aren't we talking about an object with about the same mass as Mars, rather than about the same diameter...?


Yes I believe so but all the rocky planets have comparable densities though Mars is lower so I guess a Mars mass planet out there might be somewhat smaller than Mars but probably not all that much smaller.


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## Ursa major (Jun 26, 2017)

I wasn't thinking necessarily of a "traditional" rocky planet, but something that either never made it to being a planet or (perhaps more likely) was a remnant of the destruction of a larger planet. (I'm going to assume that anything a _whole lot_ denser would tend to have a much greater mass because of how it was formed, so there won't be any planetary-mass brown dwarfs with a mass anywhere near as small as Mars's.)

In that mode of thinking.... if something with a density akin to the that of the Earth's inner core (or that of a gas giant) was out there, its disk would be quite a bit smaller than that of Mars.


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## Vertigo (Jun 26, 2017)

Only looking at the current models for solar system formation such planets are more likely closer to the sun. Something to do with their being more oxidising elements out there and so a highly metallic core is, apparently, less likely. Of course if it's a captured wanderer (or a closer planet that has been spat out in the past) then all bets are off on its composition!!


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## Brian G Turner (Jun 26, 2017)

Ursa major said:


> In that mode of thinking.... if something with a density akin to the that of the Earth's inner core (or that of a gas giant) was out there, its disk would be quite a bit smaller than that of Mars.



I did wonder about that, but while checking up a news item on Psyche - which fits this profile - I noticed the piece mentioned it is "very bright" and therefore always presumed to have a high metal composition:

A Metal Ball the Size of Massachusetts That NASA Wants to Explore


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## Mirannan (Jun 26, 2017)

I would like to point out that most of the already known objects in the Kuiper Belt (at least those of known composition) are iceballs. Ice is considerably less dense than rock, so a Mars-mass object in the Kuiper Belt - if it follows the pattern - would be approximately half as dense as Mars; hence, around 8500km in diameter.


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## Vertigo (Jun 26, 2017)

Mirannan said:


> I would like to point out that most of the already known objects in the Kuiper Belt (at least those of known composition) are iceballs. Ice is considerably less dense than rock, so a Mars-mass object in the Kuiper Belt - if it follows the pattern - would be approximately half as dense as Mars; hence, around 8500km in diameter.


So an awful lot bigger than Pluto and we really should have seen it already...

In fact Pluto fits that pattern very nicely being roughly half the density of Mars - 1.9 g/cm^3 versus 3.9 g/cm^3 - only, of course it's much smaller than Mars.


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## Mirannan (Jun 26, 2017)

Vertigo said:


> So an awful lot bigger than Pluto and we really should have seen it already...
> 
> In fact Pluto fits that pattern very nicely being roughly half the density of Mars - 1.9 g/cm^3 versus 3.9 g/cm^3 - only, of course it's much smaller than Mars.



Well, yes - unless it's on the outer edge of the Belt or, by coincidence, it happens to be near its apogee right now. And "right now" in this context might mean since the invention of the telescope. Pluto itself has a 248-year period; Eris (strictly not in the Kuiper belt but in the scattered disc) has one of 560 years. Sedna's period is 11,000 years; if an object like it was at its aphelion right now, it would have been hundreds of AU out for all of recorded history.


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## Vertigo (Jun 26, 2017)

Good point!


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## J Riff (Jun 26, 2017)

Wow, here we go again. It blowed up I tells ya, blowed up good. How dull would the galaxy be without that things blowed up good now and then? I expect 'it' will be deemed an enemy planet, until we can land there and establish fast food outlets.


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## thaddeus6th (Jun 27, 2017)

This is clearly Mondas.


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## Vertigo (Jun 27, 2017)

thaddeus6th said:


> This is clearly Mondas.


Hmmmm maybe we shouldn't look _too_ closely!


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## Serendipity (Jul 4, 2017)

So who is going to come up with the game of 'Hunt the Planet' (not 'Hunt the Bismarck' I hasten to add)?


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## Galactic Journey (Jul 16, 2017)

Everyone wants to find "Planet 10."  Except it won't be a planet, even if they find it, but just a large KBO...


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## Cathbad (Jul 16, 2017)

thaddeus6th said:


> This is clearly Mondas.


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