Re: Bill Nye the Science Guy to debate Creation museum founder Ken Ham[W:164]
Ken Ham points:
There are planets and moons in retrograde rotation which violates the conservation of momentum of the universe.
Rebuttal
Claim CE260:
The hypothesis that the solar system formed from the collapse of a revolving nebula is contradicted by the fact that three planets and several moons revolve backwards.
Source:
Brown, Walt, 1995. In the Beginning: Compelling evidence for creation and the Flood. Phoenix, AZ: Center for Scientific Creation, p. 19.
Response:
The "backwards" planets and moons are in no way contrary to the nebular hypothesis. Part of the hypothesis is that the nebula of gas and dust would accrete into planetessimals. Catastrophic collisions between these would be part of planet building. Such collisions and other natural processes can account for the retrograde planets and moons.
The only moons that orbit retrograde are small asteroid-sized distant satellites of giant planets such as Jupiter and Saturn, plus Triton (Neptune's large moon) and Charon (Pluto's satellite). The small retrograde satellites of Jupiter and Saturn were probably asteroids captured by the giant planets long after formation of the solar system. It is actually easier to be captured into a retrograde orbit. The Neptune system also contains one moon, Nereid, with a highly eccentric orbit. It appears that some sort of violent capture event may have taken place. The Pluto-Charon system is orbiting approximately "on its side," technically retrograde, with tidally locked rotation. As these are small bodies in the outer solar system, and binaries are likely to have been formed through collisions or gravitational capture, this does not violate the nebular hypothesis.
Uranus is rotating more or less perpendicular to the plane of the ecliptic. This may be the result of an off-center collision between two protoplanets during formation. Venus is rotating retrograde but extremely slowly, with its axis almost exactly perpendicular to the plane of its orbit. The rotation of this planet may well have started out prograde, but solar and planetary tides acting on its dense atmosphere have been shown to be a likely cause of the present state of affairs. It is probably not a coincidence that at every inferior conjunction, Venus turns the same side toward Earth, as Earth is the planet that contributes most to tidal forces on Venus.
Orbital motions account for 99.9% of the angular momentum of the solar system.
A real evidential problem would be presented if some of the planets orbited the sun in the opposite direction to others, or in very different planes. However, all the planets orbit in the same direction, confirming the nebular hypothesis, and nearly in the same plane. A further confirmation comes from the composition of the giant planets, which are similar to the sun's composition of hydrogen and helium. Giant planets could hold on to all of their light elements, but small planets like Earth and Mars could not.
my emphasis
