Planetary accretion?

I am confused since mention to star disk overspin is in the article you referenced. When the Maclaurin Spheroid overspins and fissions materials; how would this ejected material reform into planets in the observed fashion.
I had stated above that overspin would be a convenient way for planets to form, does celestial mechanics give an answer?
As in the origin of the moon and the ability to use mathematics to compute the idea of overspin ejection, can the planets be "timed" using the same premise?


Mark Vitrone

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by MarkVitrone</i>
<br />I am confused since mention to star disk overspin is in the article you referenced. When the Maclaurin Spheroid overspins and fissions materials; how would this ejected material reform into planets in the observed fashion.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The overspin breaks off an entire section of the parent body, which is the planet or moon. Fortunately, no accretion is required, because debris near an orbit is forbidden from collisions with the main body in that orbit. (It librates instead.)

So yes, overspin can form planets, but not through accretion. The planets are more or less intact at birth.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">As in the origin of the moon and the ability to use mathematics to compute the idea of overspin ejection, can the planets be "timed" using the same premise?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Unfortunately not. Tidal forces are still acting on the Moon, which allows us to work them backwards and "time" the Moon's origin from Earth. But tidal forces on the planets are now negligible, so similar timing can be done only by theory, not data.

The reason tidal forces were sufficient to get the planets into a Titius-Bode spacing, but are no longer operative, can be found in chapter six of "Dark Matter...". In brief, tidal forces depend on the ratio of diameter of the parent body to distance from the parent body. (This is raised to roughly the seventh power, depending on the rigidity of the parent.) So these forces were huge in the early solar system, when the Sun was in its formative T-Tauri phase and may have had a radius of ten or more astronomical units. But as the Sun condensed and shrank, spinning up and shedding planets by overspin many times, the tidal forces shrank too. Today, they are negligible. -|Tom|-

That makes sense.
When material is ejected from the edge of the spinning star how does it go from a nearly straight line of ejecta to a sphere? Would the tidal forces between the object and the star be enough to shape the planet? Mark

Mark Vitrone

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by MarkVitrone</i>
<br />When material is ejected from the edge of the spinning star how does it go from a nearly straight line of ejecta to a sphere? Would the tidal forces between the object and the star be enough to shape the planet?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I'm guessing you are thinking the star is oblate just before fissioning, because that's the only way I can think of that might produce a linear ejection of mass. However, that is not the case. Spinning planets first bulge at their equator, making them oblate. But with increased spin, the bulging equator starts to bulge in a preferred direction too, and the spinning planet takes on a prolate shape with only one long axis and two short ones. So when overspin finally happens, a symmetric piece of the parent star breaks off at each end of the long axis. It is then just a minor adjustment for the new planet to relax into a spherical shape.

We used to have an animation of this on the web site, but I see that it is broken. I'll try to get it fixed. -|Tom|-

A link to that animation is still active in the article <i>The Original Solar System</i> (follow tabs: Solar System / EPH)

LB

I was able to open the animation and it shows two planets forming, that is not the linear part I was talking about. I was thinking about the solar "crust" sluffing off linearly and then reorganizing as it forms into its own

Mark Vitrone