New Exoplanets found to orbit backwards

Transiting Exoplanet
Artist's impression of a
transiting Exoplanet
Credit: STSci/NASA

The conventional view that planets orbit in the same direction as their host star rotates has been turned upside-down with the discovery of several extrasolar planets that appear to orbit backwards.

Astronomers know that a star and its planets form from the collapse of a swirling cloud of gas and dust. Until now it was believed that the clouds rotation meant that the spin of the host star, and the orbit of any planets around it, would have to be in the same direction due to a law of physics called the 'conservation of momentum'.

However, a team of European astronomers found that 6 of the 27 transiting planets they sampled, i.e. ones that pass in front of their parent stars, did the opposite.

All the discoveries are Jupiter-like planets that are orbiting very close to their host stars. In fact, they are more than five times closer to their own stars than the planet Mercury is to our Sun.

The discovery has serious consequences for other planets that may have formed in the system, because calculations suggest that having a large rogue planet can disturb the orbits of other planets and lead to them being spat out into space or consumed by the parent star.

These newly discovered planets bring the total number of exoplanets found since 1992 to 452.