Changes

The [[nebular hypothesis]] would not even have allowed Uranus and its twin, [[Neptune]], to form at its tremendous distance from the [[Sun]] in the time generally allotted. As the journal ''Astronomy'' stated the problem:{{cquote|Pssst … astronomers who model the formation of the solar system have kept a dirty little secret: Uranus and Neptune don’t exist. Or at least computer simulations have never explained how planets as big as the two gas giants could form so far from the sun. Bodies orbited so slowly in the outer parts of the sun’s protoplanetary disk that the slow process of gravitational accretion would need more time than the age of the solar system to form bodies with 14.5 and 17.1 times the mass of Earth.}} <ref>R.N., Birth of Uranus and Neptune, ''Astronomy'' '28'(4):30, 2000</ref>

The [[nebular hypothesis]] would not even have allowed Uranus and its twin, [[Neptune]], to form at its tremendous distance from the [[Sun]] in the time generally allotted. As the journal ''Astronomy'' stated the problem:{{cquote|Pssst … astronomers who model the formation of the solar system have kept a dirty little secret: Uranus and Neptune don’t exist. Or at least computer simulations have never explained how planets as big as the two gas giants could form so far from the sun. Bodies orbited so slowly in the outer parts of the sun’s protoplanetary disk that the slow process of gravitational accretion would need more time than the age of the solar system to form bodies with 14.5 and 17.1 times the mass of Earth.}} <ref>R.N., Birth of Uranus and Neptune, ''Astronomy'' '28'(4):30, 2000</ref>

Of course, the time allotted for the formation of the [[solar system]] is generally taken to be the alloted age of the [[Earth]]. In theory, the solar system could be older than the earth itself, but not much older. The solar system has other bodies in it that are much "younger." Nor does the above account for the [[young solar system evidence|body of evidence]] that the solar system is in fact quite young.

Of course, the time allotted for the formation of the [[solar system]] is generally taken to be the alloted age of the [[Earth]]. THe problem is that Uranus and Neptune would require more than twice the supposed age of the earth to accrete their present masses. In theory, the solar system could be older than the earth itself, but not much older. The solar system has other bodies in it that are much "younger." Nor does the above account for the [[young solar system evidence|body of evidence]] that the solar system is in fact quite young.

 

Desch<ref name=Desch>Desch, S. J. "[http://eagle.la.asu.edu/desch/papers/2007/Desch2007.pdf Mass Distribution and Planet Formation in the Solar Nebula]." Arizona State University, September 21, 2007. Accessed April 29, 2008.</ref> recognizes the problem, and supports a radical alteration of the nebula hypothesis that calls for a ''decretion'' disk, not an accretion disk. But even his model requires that Uranus and Neptune ''exchange places'' early in the process, primarily because Neptune, though about 10 AU further out from the Sun than is Uranus, is yet more massive.

=== Orientation of the Uranian system ===

=== Orientation of the Uranian system ===