There hasn't been any reason to question this -- until now. Researchers in Europe announced yesterday that they have observed extrasolar exoplanets revolving around their stars in the opposite direction to the stars' spin. Some of these planets, according to an article in the Los Angeles Times, have highly tilted, eccentric orbits that would destroy any smaller, rocky planets that could harbor life.
Astronomer Alan Boss at Carnegie Institution for Science in Washington explained how such "close encounters between planets orbiting the star would result in some planets getting sling-shotted into highly eccentric orbits, in some cases even backward (or retrograde) ones." The cause of the change in orbit direction could be due to a variety of causes, including pull from distant massive planets.
The discovery, announced at a meeting of the Royal Astronomical Society in Glasgow, Scotland, suggests that our solar system is unique not only in the presence of Earth, but possibly in the stability of planetary orbits.
Image copyright of the Royal Astronomical Society