Does Gravity bend Gravity?

  • #26
6,814
15
Hot jupiters are a classic example of selection bias. They are relatively common because they are easiest to find.
And there's another likely selection bias in that any solar system with a hot Jupiter isn't going to have inner planets.

The assumption before exoplanet observation was that our solar system was typical, and even with our limited data, it's pretty clear that this is not the situation.

Planetary spacing was an 18th century exercise in numerology resulting in the Titius-Bode law.
I know of no particular reason earth orbit could not be substantially different than it is and still be stable.
The planetary people that I know of strongly disagree with that. If you have Jupiter mass objects in the inner solar system then the inner solar system becomes wildly dynamically unstable. It turns out that one reason that objects in our solar system are relatively "well behaved" is that Jupiter and Saturn are in a rough resonance that circularizes both their orbits. If you didn't have that resonance then over the course of a billion years, there's really nothing to keep Jupiter from crashing into the inner solar system.

It turns out that it's very hard to keep N-bodies dynamically stable.

I know people who have at least speculated that Titus-Bode is an application of the anthropic principle. Most solar systems don't have well spaced planets, but solar systems without well spaced planets end up without astronomers.
 
  • #27
Chronos
Science Advisor
Gold Member
11,408
741
And there's another likely selection bias in that any solar system with a hot Jupiter isn't going to have inner planets.
That is not in dispute.
twofish-quant said:
The assumption before exoplanet observation was that our solar system was typical, and even with our limited data, it's pretty clear that this is not the situation.
While our solar system is not proven to be typical, neither is it proven atypical. We simply have not detected enough multi-planet systems to draw any such conclusion.
twofish-quant said:
The planetary people that I know of strongly disagree with that. If you have Jupiter mass objects in the inner solar system then the inner solar system becomes wildly dynamically unstable.
Again, that is not in dispute. There just isnt space enough for other inner planets to achieve a stable orbit with an 800 pound gorilla in the room.
twofish quant said:
It turns out that one reason that objects in our solar system are relatively "well behaved" is that Jupiter and Saturn are in a rough resonance that circularizes both their orbits. If you didn't have that resonance then over the course of a billion years, there's really nothing to keep Jupiter from crashing into the inner solar system.
References would be appreciated. I've occasionally seen similar claims on creationist sites, but, never seen it affirmed in mainstream literature
 
  • #28
516
63
That is not in dispute.
While our solar system is not proven to be typical, neither is it proven atypical. We simply have not detected enough multi-planet systems to draw any such conclusion.Again, that is not in dispute. There just isnt space enough for other inner planets to achieve a stable orbit with an 800 pound gorilla in the room. References would be appreciated. I've occasionally seen similar claims on creationist sites, but, never seen it affirmed in mainstream literature
It is part of the Nice Model, published in Nature in 2005.
http://www.nature.com/nature/journal/v435/n7041/full/nature03539.html
http://www.nature.com/nature/journal/v435/n7041/full/nature03540.html
http://www.nature.com/nature/journal/v435/n7041/full/nature03676.html
 
Last edited by a moderator:
  • #30
6,814
15
While our solar system is not proven to be typical, neither is it proven atypical. We simply have not detected enough multi-planet systems to draw any such conclusion.
That's not true. With Kepler, the number of exoplanets are in the thousands, and that's enough data to show that the solar system is not typical. Here is one paper that goes through the selection effects, and it was written with 2006 data.

Observational biases in determining extrasolar planet eccentricities in single-planet systems
http://arxiv.org/abs/1008.4152v1

Based on 2006 data, you could argue that as many as one third of large planets have circular orbits, but that's enough to make the solar system uncommon.

With the new Kepler data, the solar system also looks pretty uncommon since most of the planets have non-circular orbits....

The Exoplanet Eccentricity Distribution from Kepler Planet Candidates
http://arxiv.org/abs/1203.1631

The argument is whether the solar system is atypical-uncommon or atypical-rare....

The fact that most planets have eccentric orbits was a big shock. The belief in 1990 was that since gas and dust go into circular orbits in a disk, that they would end up with nice circular planetary orbits. This wasn't what people found....

as far as See http://en.wikipedia.org/wiki/Stabili...e_Solar_System [Broken] for a counter example.

Our solar system is pretty stable. However what people are finding is that if you just put some random planets into a solar system, it's hard to keep them from hitting each other, and doing some very complex things.

http://arxiv.org/abs/0903.4700
Planet-planet scattering leads to tightly packed planetary systems

http://arxiv.org/abs/0801.3226
Extrasolar Planet Interactions

This is all starting to form a nice picture. Solar systems go through a phase in which planets are in eccentric orbits and they hit each other. Most never leave that state, but we were lucky, and our solar system ended up in a stable system.

http://arxiv.org/abs/0706.1235

From mean-motion resonances to scattered planets: Producing the Solar System, eccentric exoplanets and Late Heavy Bombardments
 
Last edited by a moderator:

Related Threads on Does Gravity bend Gravity?

Replies
1
Views
3K
  • Poll
  • Last Post
Replies
1
Views
6K
  • Last Post
Replies
11
Views
7K
  • Last Post
Replies
9
Views
3K
  • Last Post
Replies
14
Views
4K
Replies
71
Views
5K
Replies
1
Views
2K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
3
Views
3K
Top