With the discovery of a new batch of transiting exoplanets, astronomers were surprised to find that 6 out of 27 were found to be orbiting in the opposite direction to the rotation of their host star — the exact reverse of what is seen in our own Solar System. The new discoveries provide an unexpected and serious challenge to current theories of planet formation. They also suggest that systems with exoplanets of the type known as "Hot Jupiters" are unlikely to contain Earth-like planets.