[X] My Assistant

[SigurRosFan]

- BREAKING NEWS: Pluto Demoted, No Longer a Planet

- Pluto loses status as a planet

[Greg Hullender]

Uranus and Saturn are both in less eccentric orbits than Mars. I've never heard anyone suggest that they used to be in more elliptical orbits. I HAVE heard the suggestion that they both formed further in and have gradually drifted further out, but that would have happened when the Solar System was new.

[karolp]

Uranus and Saturn are both in less eccentric orbits than Mars. I've never heard anyone suggest that they used to be in more elliptical orbits. I HAVE heard the suggestion that they both formed further in and have gradually drifted further out, but that would have happened when the Solar System was new.

Well, it basically goes like this:

"Jupiter and Saturn start out at roughly 5 and 8 astronomical units; Uranus and Neptune begin much closer to the Sun than their current positions, at about 13 and 14 AU. They stay pretty comfortably in those positions for about 100,000 years. Then, quite suddenly, that 1:2 resonance is reached. Saturn and Jupiter don't change a lot initially, but the orbits of Uranus and Neptune go nuts. They get much more eccentric, so that their orbits cross; at times Uranus even gets very close to Saturn. After about a million years, the eccentricity dies down, and Uranus and Neptune are on their way out to more distant positions in the solar system, at the same time that Saturn begins to acquire its present orbit eccentricity."

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