Starship Asterisk*

dougettinger wrote:Do all the Exosolar Planets observed to date (assuming the necessary information is observed) have prograde orbits with respect to their binary star orbits ?
I would think that for binaries and their planets to be created angular momentum would have to be conserved making prograde orbits a necessary condition.

hstarbuck wrote:How about a stable figure eight orbit in some kind of resonance (possibly with some negative feedback to keep it stable??)? I'm pretty sure that there are no observations of this, but are there simulations that work? Then, part of the year you would be in prograde and the other part, around the other star, you would be in retrograde.

http://en.wikipedia.org/wiki/Pallas_%28asteroid%29 wrote:
<<Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered, by astronomer Heinrich Olbers on March 28, 1802. Pallas was at first considered a planet, as were the other early asteroids 1 Ceres, 3 Juno, and 4 Vesta, until the discovery of many additional asteroids led to their re-classification. The Palladian orbit, at 34.8°, is unusually highly inclined to the plane of the main asteroid belt, and the orbital eccentricity is nearly as large as that of Pluto, making Pallas relatively inaccessible to spacecraft.

With a mass estimated to be 7% of the total mass of the asteroid belt, Pallas is one of the largest asteroids. Its diameter is some 530–565 km, comparable to or slightly larger than that of 4 Vesta, but it is 20% less massive, placing it third among the asteroids. It appears to be the largest irregularly shaped body in the Solar System, not completely rounded under its own gravity. The Palladian surface appears to be a silicate material; the surface spectrum and estimated density resemble carbonaceous chondrite meteorites. >>

neufer wrote:Our solar system used to have a planet with an inclination of almost 35° to the invariant plane.

BMAONE23 wrote:Would Solar rotational dynamics allow for a stable rotation and still allow the star to slowly tumble (rotate along 2 axis')

Chris Peterson wrote:

BMAONE23 wrote:Would Solar rotational dynamics allow for a stable rotation and still allow the star to slowly tumble (rotate along 2 axis')

Maybe. More likely than tumbling, however, would be some kind of interaction that just tipped the star's axis. It happens to planets (like Venus). It seems to me a simpler explanation for retrograde planetary orbits that the star got flipped, than that planets somehow ended up orbiting against the orbital direction of the presolar nebula.

neufer wrote:1) The main angular momentum constituent of the solar system:
Jupiter has an inclination of over 6° vis-a-vis the solar equator.

1) Earth, itself, has an inclination of over 7° vis-a-vis the solar equator.

2) Our solar system used to have a planet with an inclination of almost 35° to the invariant plane.

http://en.wikipedia.org/wiki/Pallas_%28asteroid%29 wrote:
<<Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered, by astronomer Heinrich Olbers on March 28, 1802. Pallas was at first considered a planet, as were the other early asteroids 1 Ceres, 3 Juno, and 4 Vesta, until the discovery of many additional asteroids led to their re-classification. The Palladian orbit, at 34.8°, is unusually highly inclined to the plane of the main asteroid belt, and the orbital eccentricity is nearly as large as that of Pluto, making Pallas relatively inaccessible to spacecraft.

With a mass estimated to be 7% of the total mass of the asteroid belt, Pallas is one of the largest asteroids. Its diameter is some 530–565 km, comparable to or slightly larger than that of 4 Vesta, but it is 20% less massive, placing it third among the asteroids. It appears to be the largest irregularly shaped body in the Solar System, not completely rounded under its own gravity. The Palladian surface appears to be a silicate material; the surface spectrum and estimated density resemble carbonaceous chondrite meteorites. >>

Chris Peterson wrote:

neufer wrote:Our solar system used to have a planet with an inclination of almost 35° to the invariant plane.

It is not difficult to explain orbital inclinations of a few degrees for massive planets, or even a few tens of degrees for minor planets. It is very difficult, however, to understand how planets can end up with completely retrograde orbits.

dougettinger wrote:I am not sure how a flipped star in a binary system causes retrograde orbits of neighboring planets. Flipping would cause retrograde spin of the star, but how are the orbits affected by this process?

neufer wrote:If these two young planets had had a near miss instead then the smaller one of them could easily have gone retrograde.

Chris Peterson wrote:

neufer wrote:If these two young planets had had a near miss instead then the smaller one of them could easily have gone retrograde.

I don't see that as likely. I think the energy required to reverse the orbital direction of a planet (as opposed to its rotational direction) would probably destroy the planet. I guess you could construct some sort of slingshot orbit, where the planet got close to a second star; that could certainly change the direction of an orbit. But it would be tricky without ejecting the planet from the system completely. Given that a number of these retrograde systems have been seen, I think the cause should be something simpler.

Chris Peterson wrote:

dougettinger wrote:I am not sure how a flipped star in a binary system causes retrograde orbits of neighboring planets. Flipping would cause retrograde spin of the star, but how are the orbits affected by this process?

The rotational direction of the star is what defines "prograde" and "retrograde" for that star system. Retrograde planetary orbits are those that are in an opposite direction to the rotation of their star. So all you need to do is flip the rotational axis of the star 180° and you have created a system where the planets are in retrograde orbits.

I'm not actually talking about binary systems here, just single stars. It's more complex in a binary system. I could imagine that such a system started with three stars, and they interacted in a way that resulted in one being ejected, with a transfer of angular momentum such that the remaining pair end up with retrograde orbits around each other. But while that sounds perfectly feasible, it doesn't seem like planets would survive such an event.

Chris Peterson wrote:

neufer wrote:If these two young planets had had a near miss instead then the smaller one of them could easily have gone retrograde.

I don't see that as likely. I think the energy required to reverse the orbital direction of a planet (as opposed to its rotational direction) would probably destroy the planet. I guess you could construct some sort of slingshot orbit, where the planet got close to a second star; that could certainly change the direction of an orbit. But it would be tricky without ejecting the planet from the system completely. Given that a number of these retrograde systems have been seen, I think the cause should be something simpler.

Everything in the Universe is spinning. In fact, without this rotation, life on Earth wouldn't exist. We need the conservation of angular momentum to flatten out galaxies and solar systems, to make planets possible. Let's find out about the physics involved with everything that spins, and finally figure out the difference between centripetal and centrifugal force.

bystander wrote:Podcast: Rotation
Universe Today - 23 April 2010

Everything in the Universe is spinning. In fact, without this rotation, life on Earth wouldn't exist. We need the conservation of angular momentum to flatten out galaxies and solar systems, to make planets possible. Let's find out about the physics involved with everything that spins, and finally figure out the difference between centripetal and centrifugal force.

Astronomy Cast: Ep. 181: Rotation.


xkcd: Angular Momentum

dougettinger wrote:So what things inside a giant molecular cloud (GMC) cause it to begin to spin coherently and then fragment into other coherently rotating cells like tornadoes in Oklahoma? A shock wave from a supernova would make things even more random and incoherent.

dougettinger wrote:In Oklahoma what makes clouds begin to spin into tornadoes? I know of three things and perhaps you can add others. They are the gravity field of the Earth, the surface of the Earth, and the Corolis affect.

dougettinger wrote:You did not appreciate my analogy of why horizontal disks form in the Earth's atmosphere and for the same reasons cannot form in a GMC. Other factors are needed.