And it turns out that the spacing of the orbits of the planets around HD 10180 obey a version of Bodes law. The planets look very different from those in the Earths solar system: five of them are about the size of Neptune, and are closer to their star than Mars is to the sun. The other two planets, for which the evidence is not quite so strong, are a Saturn-like planet orbiting further out, and a planet only slightly heavier than Earth orbiting very close to the star, so that it completes an orbit every 1.18 Earth days. But never mind that. The fit with Bodes law is striking, and the astronomers show in their paper that a few other known multiplanetary systems around other stars exhibit a similar fit too, though with fewer planets .
There is, in other words, starting to be enough evidence to suggest that Bodes law might not be a complete fluke. But why might planetary orbits obey such neat patterns, at least some of the time? The researchers speculate that it could be a side-effect of the mechanism by which planetary systems form. Dr Lovis and his colleagues suggest that when many planetary systems first emerge from a disk of dust and gas around a young star, they are saturated with planets. Most of the planets are then weeded out by collisions and ejections, caused by gravitational interaction between adjacent planetary bodies. Systems with regular planetary spacings then turn out to have the greatest long-term stability, so that they can be observed today. The researchers observe that the orbital distances of successive planets with similar masses will tend to obey an approximate exponential law, much like the century-long debated and polemical Titius-Bode law in the Solar System.
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