I think you've confused "solar system" and "galaxy." I don't think we're yet good enough to see which way planets in other solar systems rotate.
Taking into account the factors mentioned above, as well as tidal effects from other planets, the team concluded that Venus's axis could have shifted to a variety of positions throughout the planet's evolution. Regardless of whether it flipped or not, it is bound to settle into one of four stable rotation statestwo in either direction. The researchers add that Venus would be more stable in one of the two retrograde rotational states. So in essence, it was just a question of time before Venus started spinning the wrong way.
Why Venus Spins the Wrong Way
Gravitational forcings do all sorts of things like that. This seems to be why Uranus is tilted sideways and goes the wrong way.
So why, if a solar system is formed by gravity pulling pieces together, does almost everything rotate (and revolve) the same way? Conservation of angular momentum. Even if particle movement is chaotic intially, eventually, almost everything will be rotating and revolving in the same direction.
To see this effect, go to 2:48 on the video. Or watch it all. Worth checking out.
There are many different theories of planetary and solar system formation, and they all have problems, such as the sun has 95% of the solar systems mass, but the planets have 95% of the angular momentum.
Large gas planets should be close to the sun instead of the rocky planets, which should be far from the sun.
If you think retrograde rotation is hard to explain, there are entire galaxies that rotate backwards. The arms of those galaxies instead of being swept rearward by the rotation of the galaxies, face forward.
This is God having a sense of humor and pointing out to those who will pay attention, that the universe had a creator, and did not form via nebulae coalescing, by causing some Planets and galaxies to rotate the wrong way.
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