What if the planet didn't escape at all, but was merely thrown into a very highly elliptical orbit, with a period of perhaps 1 million years or so. I have hypothesized such objects on this list before, but hadn't considered the possibility that they might be as massive as Neptune/Uranus/Saturn. Given the period of such a orbit, we wouldn't see any wobble in the Sun until the planet returned pretty close to the current solar system, so I'm not sure how we could detect such a planet. I could imagine that a planet of this size would wreak havoc during its passage near the Sun, even if it didn't actually hit anything. For example, current theories posit that the Earth's Moon has kept the Earth's inclination from changing very much since the Earth-Moon system was formed, whereas the inclination of some of the other planets seems to have changed dramatically over their lifetime. But a close encounter with a very massive object could revise that theory. I'm still wondering where the "rest" of the Earth's atmosphere went. Venus is approx the same size as Earth, but has a very dense atmosphere made mostly of CO2. Current theories say that the Earth may have had similar amounts of CO2, which is now locked up in rocks. But even if all the CO2 is accounted for, the Earth's atmosphere still has only about 25% of the mass of nitrogen of the atmosphere of Venus. So what happened to the rest of the Earth's nitrogen? It may be time to start looking for highly periodic events of very long time scales in the Earth's history. But such periodicities might be affected by the fact that a body as massive as Neptune/Uranus/Saturn might change course _on every approach_, depending upon the particular positions of the other massive planets during the approach, so the period could change somewhat on every approach. At 09:48 PM 11/12/2011, Mike Speciner wrote:

Remember that escape velocity is the velocity needed, at a particular distance from the object (the sun in this case) to just make it to "infinity" with zero velocity. The escapee slows down as it escapes.

And that's "affecting", not "effecting".

--ms

On 11/13/2011 12:38 AM, Steve Witham wrote:

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From: Henry Baker <hbaker1@pipeline.com>

http://swri.org/9what/releases/2011/giant-planet.htm

Wikipedia says escape velocity from the Sun's gravity starting at Jupiter's (current) orbit is 18.5 km/s. That's about one light year every sixteen thousand years.

Wikipedia also says the Solar System is 4.6 billion years old. Starting when the Solar System was 600 million years old, and traveling at 18.5 km/s, an object would travel about 244 thousand light years (if the Milky Way weren't effecting its path).

That's about twice the diameter of the Milky Way, or ten times the distance from the Sun to the center of the galaxy. In that same period, the Sun has orbited the center of the Galaxy 16 times.

So I guess this means the ejected planet won't be found loitering between the nearby stars. It's truckin'.

--Steve