Solar System might be 9 planets after all

[HappyDayRiot]

^In Greek mythology Tyche is linked with the goddess Nemesis. Nemesis of course being the name given to Sol's theorised companion dwarf star, hence the connection with this alternate theory.

According to the OP's article, Nemesis and Tyche are sisters.

 

[Reverend]

I agree that the demotion of Pluto is arbitrary. Frankly, it's not apparent to me why the term planet should categorize both small rocky worlds and giant gaseous ones, which have little more in common with each other than they do with miniature icy bodies in the Oort cloud.

The problem Pluto defenders have, and I have some sympathy with this view, is that basically a definitional issue revolving around semantics has been endowed with greater scientific value by the media and by media savvy astronomers than it deserves. In reality, the planet concept is like the species concept, and is open to debate. Moreover, it is of much less scientific significance than the definition of species, so there's less of a reason to be dogmatic about it, yet this is precisely what the anti-Pluto crowd has been.

I tend to agree and it's a silly debate really. The only real reason for creating the term "dwarf planet" as far as I can see is an unwillingness to include Earth in a category that could potentially include hundreds if not thousands of other objects. There is it seems still a part of the human psyche that wants to believe that we're "special" somehow and in small way clearly distinguishable against the vastness of the universe.

Of course part of it is just outdated terminology from the early days of astronomy and I suppose even astrology. Before we really understood what the strange little lights that moved against the background of stars really were. Another part of it is that, well you have to draw the line somewhere. When does a mountain become a hill? (off the top of my head) when the peak is 1000m or more higher than the base. Why? Because the bloody map makers say so.
So long as you categorise anything by size there's always going to be a blurry area where there's very little real difference between one thing and another.

Just thinking out load but let's say we were to re-categorise what we now call planets based on more tangible attributes other than size, what would they be? Mass? Average density? Core temperature? Is a planet exactly like Earth still a planet if it's in orbit around a gas giant or is it then a moon? Are they even mutually exclusive labels?

What might be useful is something like Star Trek's system of classifying stellar objects based of specific combinations of characteristics.

^In Greek mythology Tyche is linked with the goddess Nemesis. Nemesis of course being the name given to Sol's theorised companion dwarf star, hence the connection with this alternate theory.

According to the OP's article, Nemesis and Tyche are sisters.

If I' remembering this right, (and I may not be) that's not always necessarily the case. Ancient mythology can get a little fuzzy at times. Honestly, sometimes I think half of it is just the ancient equivalent of badly written fan fiction.

 

[diankra]

The simple point about planet definitions and Pluto is that, in an ideal world, nobody would have started from here. You wouldn't list Earth and Jupiter in the same category.
If you started from start there would be 'round rocks', 'big gassy things' and 'little icy things' (plus comets, tiny rocks and more) for starters. You might also have different categories for Earth/Venus/Mars/lots of Jovian [etc] moons (some sort of atmosphere) and Mercury/Luna/Ceres/other Jovian [etc] moons (round, rocky, no worthwhile atmosphere); and also different categories for Jupiter/Saturn (gas giants) and Uranus/Neptune (big, but more waterey).

But however you come at it, if Pluto's actual nature had been understood in 1930, it would never have been put in the same list as the Earth-ish and Jupiter-ish solar bodies.

 

[CuttingEdge100]

How dense is the Oort cloud compared to the Asteroid field?

 

[John O.]

They had to come up with a definition because there wasn't one, and they decided the simplest, yet most common sense set of characteristics just so happened to exclude Pluto. Oh well. It excludes a hundred other trans-Neptunian objects, they just didn't happen to be discovered 100 years ago. Uproar over Pluto's demotion is an extreme case of historical myopia. If we'd had all these bodies in front of us 100 years ago we'd have started from a much more logical definition. As it stood, astronomers had to work with the mishmash of colloquialisms and pedestrian perceptions of the solar system and try to pull something scientific out of it.

I lost all patience for the Pluto gang when I read "Planets X and Pluto", written about 35 years ago about the history of the discovery of the outer planets and realized that even then the prevailing opinion was that whenever the worldwide astronomical community got around to creating a definition, Pluto was damn near guaranteed to be excluded.

How dense is the Oort cloud compared to the Asteroid field?

I think that's a topic of current research.

But however you come at it, if Pluto's actual nature had been understood in 1930, it would never have been put in the same list as the Earth-ish and Jupiter-ish solar bodies.

I agree completely. Astronomy is an evolving field, where categories and classifications will change. Hell, for 30 or 40 years, the prevailing opinion (particularly of its discoverer) was that Uranus was a star.

I mean does anyone really think that say, 150 years from now, if/when humanity is a spacefaring race that is capable of actually sending probes and/or manned research craft to other star systems - that our classes of stars, categories of luminosity, the Hertzsprung-Russel Diagram, for instance, will really stay exactly the way it is? Can't you imagine a torrent of uproar when Beteguese is demoted from a red supergiant to just a red giant?

 

[YellowSubmarine]

It seems people have a problem with the definition of "Clearing the Neighborhood". I hate to use Wiki as a source, but here it goes:

In the end stages of planet formation, a planet will have "cleared the neighbourhood" of its own orbital zone, meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence.

If this is the definition, it still fails for planets outside of our solar system. In particular, it fails for double planets, it fails for captured planets, it fails for planets sharing an orbit. While the last configuration is unstable, they could remain in one orbit for millions of years - are they not planets during that time? Do we call Earth and Theia in the giant impact hypothesis “planets”, “dwarf planets” or “proto planets”? What if there are planetary configurations where two planets share an orbit that is stable somehow?

The definition was made with the sole purpose to exclude Pluto and Eris, and it doesn't work very well. While you can say that Pluto and Mars are obviously different class of celestial objects, and if Mars is a planet, Pluto is not, you can say the same for Neptune and Earth. It's not clear how it's better than “the Solar System has a few hundred planets, 8 of them main planets - 4 small, 4 giant and a few hundred dwarf”. Not to mention that the distinction between “planet” and “dwarf planet” is broken linguistically.

I personally think that satellites like Phobos and Deimos shouldn't be moons, because they are not round and because their escape velocity is so small that you can jump in space with 18th century technology. What makes planets special that any rock can be a moon, but it can't be a planet?

 

[Allyn Gibson]

Also, I don't suppose there's any chance either of the Voyagers will be able to see it one day? Or would that just be too convenient?

Both Voyagers are now well beyond the orbit of Pluto, which, IIRC, was never in the right position for either to intercept anyway.

Voyager 2 could have gone to Pluto, and there were two options for doing so. One was a New Horizons-like mission profile -- Jupiter to Pluto -- and they discovered a possible Jupiter-Saturn-Pluto flightplan. But because Voyager 2 was a back-up to Voyager 1, the Jupiter-Saturn mission was always going to be the priority in case Voyager 1 failed, which scratched the Jupiter-Pluto mission. And JPL was more interested in the Grand Tour (Jupiter-Saturn-Uranus-Neptune) mission profile than the Jupiter-Saturn-Pluto profile; the Grand Tour was more bang for the buck.

 

[Allyn Gibson]

Thread necromancy!

I think this so cool!

http://www.space.com/9612-giant-stealth-planet-explain-rain-comets-solar-system-edge.html

Alas, not. The WISE mission has ruled out any large planets in the outer reaches of the solar system:

What it didn't discover, though, was another giant planet in our solar system. And it's pretty definitive: it would've seen a planet the size of Saturn out to a distance of 1.5 trillion kilometers, over a tenth of a light year! A planet the size of Jupiter would've been seen out to twice that far.

Plait is understanding WISE's sensitivity; it would have seen a Jupiter-massed planet at a distance of 1 light-year, and Tyche (which was hypothesized to be up to 4 Jupiter masses) would have been visible to about 2 light-years.

Alas, poor Tyche. We hardly knew ye.

WISE also didn't discover a brown dwarf companion to our sun, though Phil Plait's article doesn't state that. It found a brown dwarf pair six light years distant (the closest stars to the Alpha Centauri system, no less), but no brown dwarfs closer.

 

[YellowSubmarine]

At a distance of 1 light year, a Jupiter-massed thing would be a dwarf planet, not a planet, as it wouldn't have cleaned its neighbourhood. Nobody with an odd planets agenda will ever gain any gravity in the matter.

 

[rhubarbodendron]

The WISE mission has ruled out any large planets in the outer reaches of the solar system

just for the sake of the argument: isn't it theoretically possible - though of course utterly unlikely - that there is another planet hidden from our sight exactly behind the sun with the same orbit period (roughly 365.25 days) than Terra?
In that case we could only detect it by sending a probe beyond the sun and even then it would have to be pretty sharp-eyed to find a planet that far out that it'd be in orbit #10


I don't know about you all but in spite of all scientific definitions my gut feeling is telling me anything orbiting a star which isn't dust or debris is a planet.
I mean, in the end all these other definitions of planets, past and present ones, base on someone's gut feelings, too. It's all pretty subjective. The problem is that there are no strictly divided cathegories but all kinds of hybrids between them.
Is a planet something that's solid? But what about the gas planets?
Is a planet something that has an atmosphere? But what if a planet loses its atmosphere to the sun (Mercury) ?
Is a planet something that orbits a sun? But what about the recently discovered "wanderers" that just take a stroll through the galaxy?
There are so many different types that drawing a border between them must necessarily be rather arbitrary. Whatever definition one chooses, there will always be celestial bodies that won't fit into it. Therefore I think the definition doesn't really count. What counts is that we get to know more and more about our solar system. I find every newly discovered object in our backgarden exciting, no matter what it's called.

 

[PurpleBuddha]

Pluto IS the 9th planet...and the other "dwarf" planets are planets too.

I don't give a f*&k about the pathetic definition which was made due to some vendetta against the pro Pluto crowd. If its round and orbits a star it is a planet, even if there are a million of them in our solar system.

Yes, I take the demotion of Pluto VERY personally, it was my favorite planet as a child and holds a sentimental place in my heart.

Your emotional bias and childhood experiences have absolutely no bearing on the issue of whether we should call Pluto a planet or not.

If you have a better definition for a planet and can explain why we do not call every rock or ice ball in space a planet, then have at it. Otherwise you sound a bit like my six year old when I tell him to get off the computer.

 

[YellowSubmarine]

isn't it theoretically possible - though of course utterly unlikely - that there is another planet hidden from our sight exactly behind the sun with the same orbit period (roughly 365.25 days) than Terra?

https://en.wikipedia.org/wiki/Counter-Earth

In short, no, because Earth's L3 is unstable. It would also disqualify both Earth and Counter-Earth from being planets. Besides, binary Earths would have been much cooler.

That being said, two planets sharing the same orbit without being a binary have been discovered, and I think even more bizarre configurations have been discovered, but I couldn't dig up the link. I doubt that they would last long.

 

[PurpleBuddha]

isn't it theoretically possible - though of course utterly unlikely - that there is another planet hidden from our sight exactly behind the sun with the same orbit period (roughly 365.25 days) than Terra?

https://en.wikipedia.org/wiki/Counter-Earth

In short, no, because Earth's L3 is unstable. It would also disqualify both Earth and Counter-Earth from being planets. Besides, binary Earths would have been much cooler.

That being said, two planets sharing the same orbit without being a binary have been discovered, and I think even more bizarre configurations have been discovered, but I couldn't dig up the link. I doubt that they would last long.

This reminds me of a question I have always be afraid to ask others in person because it is kind of stupid.

If two bodies of the same mass shared an orbit, would their shared orbit guarantee the same orbital speed?

 

[YellowSubmarine]

If two bodies of the same mass shared an orbit, would their shared orbit guarantee the same orbital speed?

Do not quote me on this, but I suspect if the orbit is perfectly circular – yes. For varying values of "guaranteed" – the gravitational pull of other bodies in the Solar system would still speed them up and slow them down. But if the orbits are skewed, nope.

In an elliptical orbit, speed is inversely proportional to the distance to the sun. Since the sun is not precisely in the centre of the ellipse, the planet that is further away from the sun at any given moment would move slower. Try imagining the counter-planet in this highly-elliptical orbit.

 

[rhubarbodendron]

isn't it theoretically possible - though of course utterly unlikely - that there is another planet hidden from our sight exactly behind the sun with the same orbit period (roughly 365.25 days) than Terra?

https://en.wikipedia.org/wiki/Counter-Earth

In short, no, because Earth's L3 is unstable. It would also disqualify both Earth and Counter-Earth from being planets. Besides, binary Earths would have been much cooler.

That being said, two planets sharing the same orbit without being a binary have been discovered, and I think even more bizarre configurations have been discovered, but I couldn't dig up the link. I doubt that they would last long.

ah, there's a misunderstanding.
I am talking not of a counter-earth, sharing our own orbit. I meant the (purely theoretical) possibility of a planet inhabiting orbit number 10 which just happens to always be on the opposite side of the sun from us.
Such an object would of course have to be incredibly fast to keep up a 365.25 day orbit with such a diameter.
I'm not that good at maths - would it be able to exist or would it get torn apart or just flung out of our solar system?
My guess is that a gas planet even if it was a gigant propably couldn't move that fast. But how about a small iron-core planet or something with an even higher density?

 

[YellowSubmarine]

I'm not that good at maths - would it be able to exist or would it get torn apart or just flung out of our solar system?

Of course it can move that fast. Objects travelling at very big speeds have been discovered. At 100 AU, your planet would have to travel at 3000 km/s. Stars known to travel 1500 km/s (at least) exist, so 3000 km/s is a possibility. But that will put it on a hyperbolic trajectory that will not only fling it out of the Solar system, it would fling it out of the galaxy. We don't know the escape velocity of the Milky Way, but it is 1000 km/s or lower.

So, save for the perpetuum mobile powering its antimatter engines that accelerate the planet towards the sun, it won't stay here very long. A technology that we need to get a hold of to avoid getting ourselves flung into intergalactic space when Andromeda comes knocking on our door.

You should read on escape velocity and what an orbit is.

 

[sojourner]

isn't it theoretically possible - though of course utterly unlikely - that there is another planet hidden from our sight exactly behind the sun with the same orbit period (roughly 365.25 days) than Terra?

https://en.wikipedia.org/wiki/Counter-Earth

In short, no, because Earth's L3 is unstable. It would also disqualify both Earth and Counter-Earth from being planets. Besides, binary Earths would have been much cooler.

That being said, two planets sharing the same orbit without being a binary have been discovered, and I think even more bizarre configurations have been discovered, but I couldn't dig up the link. I doubt that they would last long.

ah, there's a misunderstanding.
I am talking not of a counter-earth, sharing our own orbit. I meant the (purely theoretical) possibility of a planet inhabiting orbit number 10 which just happens to always be on the opposite side of the sun from us.
Such an object would of course have to be incredibly fast to keep up a 365.25 day orbit with such a diameter.
I'm not that good at maths - would it be able to exist or would it get torn apart or just flung out of our solar system?
My guess is that a gas planet even if it was a gigant propably couldn't move that fast. But how about a small iron-core planet or something with an even higher density?

Orbits don't work that way.The faster you orbit, the larger the radius of the orbit. So to have two objects directly opposed and moving at the same speed, they'd have to be sharing the same orbital radius.

 

[publiusr]

Now early on, there may have been more planets in the solar system
http://www.centauri-dreams.org/?p=20568

If things get a little busy, they can become ejected
http://en.wikipedia.org/wiki/Three-body_problem

 

[rhubarbodendron]

So to have two objects directly opposed and moving at the same speed, they'd have to be sharing the same orbital radius.

Ah now I get it: You're paraphrasing Kepler's law of planetary motion.

A good point and I hadn't thought of it. Planet #10 would get flung out of the solar system if it was that fast. (I think, having just discovered the necessary formula online, I'll yield to the temptation and make a quick calculation during lunch break. I'm curious as to how fast it'd have to be =) )