[Aswathy]

Why do some star-planet systems are so compact like Kepler11 ?

[CaptainPanic]

Because stuff gets attracted towards the stars by the gravity?
In fact, the large majority of the matter in any star system ends up inside the star.

Disclaimer: I'm no astronomy expert... and you should regard this post as an opinion rather than fact.

[Airbrush]

Aswathy, on 19 December 2011 - 07:51 AM, said:

Why do some star-planet systems are so compact like Kepler11 ?

By random chance. Kepler 11 and the other first discovered planetary systems, are compact. As the sampling period gets longer, less compact systems will probably be discovered. They need 3 transits to confirm a planet, and that would take 3 years for a system like our own.

[Aswathy]

Then, it will indicate that because of weak gravitational force acting on the planets, the systems are less compact like our solar system.Is that right? But then, as because the gravitational force is weak ,the planets will be orbiting the star at a small distance.Then, how come our solar system (less compact), has more than 8 planets orbiting the sun and the last planet being orbiting the sun at 5.9 billion km away?

[CaptainPanic]

Airbrush, on 20 December 2011 - 01:11 AM, said:

By random chance. Kepler 11 and the other first discovered planetary systems, are compact. As the sampling period gets longer, less compact systems will probably be discovered. They need 3 transits to confirm a planet, and that would take 3 years for a system like our own.

How long is Kepler's mission then? To find planets like Jupiter and further out, it would need to span multiple decades!

[Airbrush]

CaptainPanic, on 20 December 2011 - 07:41 AM, said:

How long is Kepler's mission then? To find planets like Jupiter and further out, it would need to span multiple decades!

Kepler is devoted to finding Earth-sized planets, or even smaller, if possible, with special interest in the habitable zones. Most stars in Kepler's view are smaller than our Sun, so after 3 years of gathering data, they should have confirmed most of the planets with periods of one year or less, and thus mission accomplished. A few extra years would be nice, if affordable. As Marcy said, "The best is yet to come!" How could congress refuse to extend the mission a few more years after the astonishing findings?

Trivia question: What is the closest and most distant stars in Kepler's field of view?

Aswathy, on 20 December 2011 - 07:10 AM, said:

Then, it will indicate that because of weak gravitational force acting on the planets, the systems are less compact like our solar system.Is that right? But then, as because the gravitational force is weak ,the planets will be orbiting the star at a small distance.Then, how come our solar system (less compact), has more than 8 planets orbiting the sun and the last planet being orbiting the sun at 5.9 billion km away?

Correct me if I am wrong, but I think compactness of planetary systems is random. It's just how the original accretion disk formed. Anyone know of any rules about systems around stars of various sizes?

This post has been edited by Airbrush: 20 December 2011 - 10:56 PM

[CaptainPanic]

Airbrush, on 20 December 2011 - 05:30 PM, said:

Kepler is devoted to finding Earth-sized planets, or even smaller, if possible, with special interest in the habitable zones. Most stars in Kepler's view are smaller than our Sun, so after 3 years of gathering data, they should have confirmed most of the planets with periods of one year or less, and thus mission accomplished. A few extra years would be nice, if affordable. As Marcy said, "The best is yet to come!" How could congress refuse to extend the mission a few more years after the astonishing findings?

Trivia question: What is the closest and most distant stars in Kepler's field of view?

Thanks for the answer.

As for the trivia question (in the spirit of a quiz I refused to google it): I believe that the furthest out that any measurements are done on is about 1000 lightyears? Closest I am guestimating at 20 lightyears.
But the furthest out in general is probably a lot further. Several billion lightyears, I guess. But there's no chance Kepler will find planets around those.

I think that an extension of the mission will cost only a fraction of the initial investment (the design, construction and testing of the Kepler satellite itself, and the launch system)... so if there is reason to extend the mission, it would be a waste not to give that bit of money.

[Moontanman]

Aswathy, on 20 December 2011 - 07:10 AM, said:

Then, it will indicate that because of weak gravitational force acting on the planets, the systems are less compact like our solar system.Is that right? But then, as because the gravitational force is weak ,the planets will be orbiting the star at a small distance.Then, how come our solar system (less compact), has more than 8 planets orbiting the sun and the last planet being orbiting the sun at 5.9 billion km away?

Kepler or what we see as patterns from it's data, has an observational bias, just like previous planet hunters found lots of large planets near their stars this is because those planets were easier to find, low hanging fruit if you will. We used to have many ideas around why our solar system is arranged in the way it is but like most problems in statistics one data point does not a curve make so as we see and confirm new planetary systems we are getting more data points but so far they are skewed toward the easiest data at hand as we get more data points a more reliable model can be made of planetary systems formation and structure.

[Airbrush]

Moontanman, on 21 December 2011 - 03:00 PM, said:

Kepler or what we see as patterns from it's data, has an observational bias, just like previous planet hunters found lots of large planets near their stars this is because those planets were easier to find, low hanging fruit if you will. We used to have many ideas around why our solar system is arranged in the way it is but like most problems in statistics one data point does not a curve make so as we see and confirm new planetary systems we are getting more data points but so far they are skewed toward the easiest data at hand as we get more data points a more reliable model can be made of planetary systems formation and structure.

Good answer Moontanman. We have no idea how planetary systems are structured in general. We only know about our own solar system. Kepler will give us a better idea.

So much can happen in a planetary system while it is forming. Large planets seem to form almost anywhere, and they pull on their fellow planets, throwing some out to the edge of the system in irregular orbits, and throwing others towards the star. This can rearrange a system greatly over Billions of years. When Kepler reveals this, remember where you heard it first.

This post has been edited by Airbrush: 21 December 2011 - 07:05 PM

[Moontanman]

When we discuss this subject i often think of how interesting it would be if an earth like planet was found orbiting alpha centari... Wouldn't the futurists go nuts! I wonder how hard it would be to justify a really large orbiting scope at Lagrange 2 to check it out.

This post has been edited by Moontanman: 22 December 2011 - 08:12 AM

[Aswathy]

Thank you for all of your answers.