We're no longer biggest star system!

DaveC426913
Gold Member
18,328
1,940

Main Question or Discussion Point

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

A star about 127 light-years from Earth may have even more planets than the sun, which would make the planetary system the most populated yet found.

According to a new study, HD 10180—a sunlike star in the southern constellation Hydrus—may have as many as nine orbiting planets, besting the eight official planets in our solar system.
The two latest are (nearly) super Earths. (well, 12x and 32x Earth's mass...), probably rocky.

http://news.nationalgeographic.com/news/2012/04/120410-star-system-more-planets-sun-hd10180-space-science/

http://exoplanet.eu/star.php?st=HD+10180
 

Answers and Replies

136
1
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.
 
HallsofIvy
Science Advisor
Homework Helper
41,732
893
Dang! I want Pluto back!
 
317
0
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.
 
646
3
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.
Why? Why should our Solar System need to be the biggest?
 
537
1
Why? Why should our Solar System need to be the biggest?
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!
 
969
3

Stars with larger accretion discs produce more planets?

What would the planet number theoretical limit be for stars with large accretion discs?
 
1
0
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?
 
646
3
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.
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?

If your orbit is always concave toward the sun YOU ARE ORBITING THE SUN.
True, but you're also orbiting the Earth.

The idea of de-planeting Pluto without admitting that we have been miscategorizing the moon as a mere satellite makes me laugh.
I don't understand. Are you saying we had it wrong before, or that we still have it wrong?

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

Seriously--who lets these guys make this stuff up?
\Ignores that question
 
418
0
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.

http://news.nationalgeographic.com/news/2012/04/120410-star-system-more-planets-sun-hd10180-space-science/

http://exoplanet.eu/star.php?st=HD+10180
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 :
http://www.eso.org/public/archives/releases/sciencepapers/eso1035/eso1035.pdf)
 
537
1
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?
moon = planet?

I feel like you're saying this just to be contrary >.>
 
DaveC426913
Gold Member
18,328
1,940
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.

Seriously--who lets these guys make this stuff up?
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?
 
33,552
9,284
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.

If your orbit is always concave toward the sun YOU ARE ORBITING THE SUN.
So we have trillions of planets? Cool.
 
136
1
"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.
 
DaveC426913
Gold Member
18,328
1,940
"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.
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.
 
136
1
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.
 
DaveC426913
Gold Member
18,328
1,940
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.
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.
 
201
8

Stars with larger accretion discs produce more planets?

What would the planet number theoretical limit be for stars with large accretion discs?
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.
 
136
1
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.
 
33,552
9,284
"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.
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.
 
136
1
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.
 
DaveC426913
Gold Member
18,328
1,940
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.
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.
 
136
1
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.
 
476
2
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?

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.
 

Related Threads for: We're no longer biggest star system!

  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
14
Views
3K
  • Last Post
Replies
3
Views
5K
Replies
2
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
2
Views
2K
Replies
7
Views
2K
Top