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We're no longer biggest star system!

  1. May 17, 2012 #1


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    Yet to be confirmed, but they've discovered a star system with 9 planets! (And those are just the big detectable ones!)

    The two latest are (nearly) super Earths. (well, 12x and 32x Earth's mass...), probably rocky.


  2. jcsd
  3. May 17, 2012 #2
    Fantastic. I was waiting for that to happen... I think 6 planets was the most last time I looked at exoplanet.eu. I wasn't expecting 8 to be bettered so soon.
  4. May 18, 2012 #3


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    Dang! I want Pluto back!
  5. May 18, 2012 #4
    This just in: the IAU votes to reverse its 2006 decision, and adds Eris to the list of planets as well, citing a need for our solar system to remain on top.
  6. May 18, 2012 #5
    Why? Why should our Solar System need to be the biggest?
  7. May 18, 2012 #6
    you must be an alien spy from this HD 10180 system! Trying to trick us into thinking we are still "adequate" with our smaller number of planets!
  8. May 18, 2012 #7

    Stars with larger accretion discs produce more planets?

    What would the planet number theoretical limit be for stars with large accretion discs?
  9. May 21, 2012 #8
    We still have nine planets--Earth's moon is large enough that its orbit is always concave toward the sun. It's a planet, with an orbit highly perturbed by a larger neighbor.

    The idea of de-planeting Pluto without admitting that we have been miscategorizing the moon as a mere satellite makes me laugh.

    If your orbit is always concave toward the sun YOU ARE ORBITING THE SUN.

    That's a much more compelling, understandable, and intuitive description than something that needs to fuss about where the barycenter is. You could have an added descriptive for a double planetary system with a barycenter inside one of the planets.

    Seriously--who lets these guys make this stuff up?
  10. May 21, 2012 #9
    First of all, how does its size affect whether or not its orbit is always concave towards the sun? Second, by your arguments, pretty much everything in the Asteroid Belt should also be considered a planet?

    True, but you're also orbiting the Earth.

    I don't understand. Are you saying we had it wrong before, or that we still have it wrong?

    Okay ... but again, the Moon's also orbiting the Earth.

    \Ignores that question
  11. May 21, 2012 #10
    Thanks Dave:smile: I recall reading back in 2010 about HD10180.

    "The HD 10180 system represents an interesting example of
    the various outcomes of planet formation. No massive gas giant
    was formed, but instead a large number of still relatively massive
    objects survived, and migrated to the inner regions. Building a
    significant sample of such low-mass systems will show what are
    the relative influences of the different physical processes at play
    during planet formation and evolution." (C. Lovis et al.: The HARPS
    search for southern extra-solar planets, Astronomy & Astrophysics
    manuscript no. HD10180 ESO 2010 - August 13, 2010, p.15 :
  12. May 21, 2012 #11
    moon = planet?

    I feel like you're saying this just to be contrary >.>
  13. May 21, 2012 #12


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    OK, let's assume you're not pulling our leg.

    1] By definition, if it's orbiting a planet, it's not a planet. And yes, the Moon is orbiting Earth.

    2] Size has nothing to do with it. If did want to factor size in as part of some new msouthian definition of planets, why start with the Moon, why not start with all the objects larger than the Moon yet still not planets?
  14. May 23, 2012 #13


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    We are still in the system with the most known objects [optional: orbiting the star].
    And this won't change in the foreseeable future, unless some aliens send us terabytes of data about their own system.

    So we have trillions of planets? Cool.
  15. May 23, 2012 #14
    "We are still in the system with the most known objects. And this won't change in the foreseeable future"

    I'm not so sure. Anyway, counting numbers of objects is unhelpful when they follow a power law, since the number is effectively infinite for most star systems. Better to get a fractal measure, i.e. plot quantity against radius (or mass) on a log-log graph, and compare the height and slope for different star systems.
  16. May 23, 2012 #15


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    Well, there are currently 88 objects in the solar system larger than 200 miles in radius. It is going to be quite a while before we are able to detect objects smaller than that in extrasolar systems.
  17. May 24, 2012 #16
    True, but simulations are getting more sophisticated, I could imagine simulations being able to show beyond reasonable doubt that a system must have over a certain amount of mass in its vicinity in order to fit with various stellar observations. And given that no giant planet is found, it there must be at least 100 objects bigger than 10km in order to be stable... or whatever.

    So yeah, I don't imagine us detecting 89 individual small objects in a faraway star system anytime soon, but I could see how one could build sufficient evidence for a system requiring over a 100 such objects in order to fit with observations and simulations and accurate models of that star's formation etc.
  18. May 24, 2012 #17


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    I don't think anyone doubts that other systems are probably like our own. We are simply talking about what is currently known and factual.
  19. May 24, 2012 #18
    I remember watching something on the Science channel episode about astrophysicists who were theorizing how the solar system, and the planets inside of it, were formed.

    Apparently, an amazingly long time ago (remember, I watched this on TV about a year ago, I can't remember the numbers, sorry) we had way more planets than we do now.

    I was watching it while also surfing the web and eating, so as far as I could tell, a lot of the planets crashed into each other.

    Forgive me for this being really vague, but basically, some astrophysicists theorize that our solar system had several times more planets than we currently do, back when it was young and planets were just forming.
  20. May 24, 2012 #19
    Yeah but 'known and factual' in astronomy is statistical. We 'know' a planet exists because its sigma is greater than 4 (or whatever). It is possible to 'know' a star system to has > 100 objects in it (with sigma > 4), without there being a sigma>4 on 100 individual objects.
    To take it to the extreme, we know factually that certain systems have accretion disks made out of millions of particles, but we don't need to verify individual grains to be able to state that fact.

    Anyway, I've no idea what the theoretical planet limit is, or if there is one. The definition of planet is a bit arbitrary, so a bit hard to theorise about I would have thought.
  21. May 25, 2012 #20


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    Well, known objects can be counted. You can store the orbital parameters in a database, and predict their future positions (with an uncertainty). If you could detect meter-sized objects in the asteroid belt, you would get a really large number of them. However, this would just increase the number of known objects.

    Well, observing every dust particle is not useful, of course, but our solar system wins for every lower bound which is at most close to the moon in mass or diameter.
  22. May 25, 2012 #21
    Counting the number of objects in a star system is like counting craters on the moon, or rocks in a pile of rubble. The closer you look, the more you find, the number is effectively infinite as you find smaller and smaller ones all the way to the microscopic level.
    You could impose a lower bound, but that is artificial. Anyway here's some thoughts on that subject- http://www.fractalforums.com/mathematics/how-long-is-the-coastline-of-great-britain.
  23. May 25, 2012 #22


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    The fact remains that the number of known objects in our system exceeds the number of known objects in any other system, with or without any bound.
  24. May 25, 2012 #23
    I agree.
    The discussion being that 'most known objects' is different from 'known to have most objects'.
    Our solar system will have the most known objects for the foreseeable future. But it is quite likely that another star system will be known to have most objects.. in the next few decades.
    Anyway, enough talk from me, I'm not an astronomer.
  25. May 26, 2012 #24

    Well, what if you have two rocks that are the same size? That would be a double planet.

    I think it is OK to think of the Moon and Earth as a double planet, because the Moon is proportionally large compared to all other moons. I have seen this elsewhere as well.

    How about this: it's a double planet if the center of mass is not inside any of the objects. With the Earth/Moon system it is. So the Moon is a moon.
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